Electrode active material

Abstract

To solve the problem in which an electrode active material having an O2 type structure has room for improvement in capacity at high potentials.SOLUTION: An electrode active material has at least one O2-like structure selected from an O2-type structure, a T#2-type structure, and an O6-type structure. Here, the crystal size of the O2-like structure, as measured by XRD, is 400 Å or more and 1000 Å or less.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present application discloses an electrode active material. [Background technology]

[0002] Known electrode active materials have an O2-like structure. As disclosed in Patent Document 1, an electrode active material having an O2-like structure can be obtained by ion-exchanging at least a portion of Na in a Na-containing oxide having a P2-type structure with Li. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-182420 Summary of the Invention [Problem to be solved by the invention]

[0004] Electrode active materials with an O2-like structure have room for improvement in terms of the ratio of capacity at high potential to the total capacity. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> An electrode active material, having at least one O2-like structure selected from the group consisting of an O2-type structure, a T#2-type structure, and an O6-type structure; The crystallite size of the O2-like structure measured by XRD is 400 Å or more and 1000 Å or less. Electrode active material. <Aspect 2> The electrode active material of embodiment 1, The ratio of the capacity at 3V or higher to the total capacity is 75.0% or more. Electrode active material. <Aspect 3> The electrode active material according to Embodiment 1 or 2, comprising, as constituent elements, at least one element selected from Ni, Mn, and Co, Li, and O, electrode active material. <Embodiment 4> The electrode active material according to Embodiment 3, Li [Figure 4] , , [Figure 3] , , [Figure 2] , , [Figure 1] ,

[0007] , [Figure 5] , ,

[0006] , , , , , , Na b Ni x-p Co y-q Mn z-r M p+q+r [[ID=2​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​The figure shows the relationship between the crystallite size of the O2-like structure measured by XRD and the percentage of the capacity at 3 V or higher in the total capacity. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, one embodiment of the electrode active material etc. of the present disclosure will be described, but the electrode active material etc. of the present disclosure is not limited to the embodiment described below.

[0009] 1. Electrode active material An electrode active material according to one embodiment has at least one O2-like structure selected from the group consisting of an O2-type structure, a T#2-type structure, and an O6-type structure, and the crystallite size of the O2-like structure measured by XRD is 400 Å to 1000 Å.

[0010] 1.1 Crystal structure The electrode active material according to one embodiment has at least one O2-like structure selected from the group consisting of an O2-type structure (belonging to the space group P63mc), a T#2-type structure (belonging to the space group Cmca), and an O6-type structure (belonging to the space group R-3m, with a c-axis length of 2.5 nm to 3.5 nm, typically 2.9 nm to 3.0 nm, and different from the O3-type structure also belonging to the space group R-3m). The electrode active material may have an O2-like structure as a main phase.

[0011] 1.2 Crystallite size In one embodiment of the electrode active material, the crystallite size of the O2-like structure measured by XRD is 400 Å or more and 1000 Å or less. According to the inventor's findings, when the crystallite size of the O2-like structure measured by XRD is 400 Å or more, the proportion of the capacity at high potential to the total capacity increases, and the energy density is likely to be improved. The crystallite size may be 900 Å or less, 850 Å or less, 800 Å or less, 750 Å or less, 700 Å or less, 650 Å or less, 600 Å or less, 550 Å or less, or 500 Å or less.

[0012] In the present application, the crystallite size of the O2-like structure in the electrode active material is measured by XRD as follows. That is, an X-ray diffraction pattern is obtained for the electrode active material using CuKα as a radiation source, and the crystallite size of the O2-like structure is determined based on the Scherrer equation using PDXL2 software (manufactured by Rigaku) ​​from the X-ray diffraction peaks derived from the (002) plane of the O2-type structure, the (002) plane of the T#2-type structure, and the (006) plane of the O6-type structure. If multiple X-ray diffraction peaks derived from the (002) plane of the O2-type structure, the (002) plane of the T#2-type structure, and the (006) plane of the O6-type structure are observed in the X-ray diffraction pattern, the crystallite size is determined based on the main peak (the one with the highest peak intensity) among the multiple peaks. Even if multiple peaks overlap, the crystallite size can be determined based on the overlapping peaks.

[0013] In the electrode active material according to one embodiment, a single crystallite may form a particle, or multiple crystallites may form a particle. In other words, the electrode active material according to one embodiment may be (1) an independently existing single-crystal particle, (2) an aggregate (secondary particle) of multiple single-crystal particles, (3) a polycrystalline particle including multiple crystallites, or (4) an aggregate (secondary particle) of multiple polycrystalline particles. In particular, when the electrode active material is a polycrystalline particle, particularly when the electrode active material is a spherical polycrystalline particle (described below), higher performance as an electrode active material is likely to be ensured. The electrode active material according to one embodiment can be obtained by ion-exchanging at least a portion of the Na in a Na-containing oxide having a P2 structure with Li, as described below. The P2 structure is a hexagonal crystal system with a large diffusion coefficient of Na ions, which facilitates crystal growth in a specific direction. Therefore, crystallites having a P2 structure typically have a crystal growth direction biased in a specific direction (e.g., plate-like). In this way, when Na in P2-type crystallites, whose crystal growth direction is biased in a specific direction, is ion-exchanged with Li to obtain crystallites with an O2-like structure, the ends of the crystallites with the O2-like structure (the ends in the crystal growth direction described above) tend to serve as inlet and outlet ports for intercalation. In other words, when the electrode active material is a polycrystalline particle, the effects of increasing the number of inlet and outlet ports for intercalation contained in one particle, reducing reaction resistance, shortening the migration distance of lithium ions, reducing diffusion resistance, and reducing the amount of expansion and contraction of the particle as a whole during charge and discharge can be expected.

[0014] As described above, the crystallites of a Na-containing oxide having a P2 structure tend to be plate-shaped. That is, a Na-containing oxide having a P2 structure can be formed into plate-shaped particles, or small plate-shaped crystallites can be connected to each other to form spherical particles. In other words, a single electrode active material particle may be a plate-shaped single crystal particle as a whole, or a spherical polycrystalline particle. A spherical polycrystalline particle has multiple crystallites on its surface. When the electrode active material is a spherical polycrystalline particle, spheroidization reduces the degree of curvature and reduces the lithium ion conduction resistance. This, for example, improves the rate characteristics of the battery and increases the reversible capacity. In this application, "spherical particles" refers to particles with 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 where S is the orthogonal projected area of ​​the particle, and L is the perimeter of the orthogonal projected image of the particle. The circularity of a particle can be determined by observing the appearance of the particle using a scanning electron microscope (SEM), transmission electron microscope (TEM), or optical microscope.

[0015] 1.3 Chemical composition The chemical composition of the electrode active material according to one embodiment is not particularly limited as long as it can maintain an O2-like structure. The electrode active material may contain, for example, at least one element selected from Mn, Ni, and Co, Li, and O as constituent elements. The electrode active material is particularly likely to achieve higher performance when it contains Li, Mn, Ni, Co, and O as constituent elements. The electrode active material may contain Li, Mn, Ni, Co, and O as constituent elements. a Na b Ni x-p Co y-q Mn z-r M p+q+rO2 (where 0 < a < 1.00, 0 ≤ b ≤ 0.20, 0.15 < x < 0.35, 0.15 < y < 0.45, 0.25 < z < 0.55, 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) may have a chemical composition represented thereby. When the electrode active material has such a chemical composition, the O2-like structure is likely to be maintained, and higher performance is likely to be ensured. 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, 0.60 or more, 0.70 or more, or greater than 0.70, and less than 1.00, and may be 0.90 or less, 0.80 or less, or 0.70 or less. In the above chemical composition, b is 0 or more, and may be 0.01 or more, 0.02 or more, or 0.03 or more, and 0.20 or less, and may be 0.15 or less, or 0.10 or less. In the above chemical composition, x is greater than 0.15, and may be 0.20 or more, and less than 0.35, and may be 0.30 or less, 0.25 or less, or 0.20 or less. In the above chemical composition, y is greater than 0.15, and may be 0.20 or more, 0.25 or more, 0.30 or more, 0.35 or more, or 0.40 or more, and less than 0.45, and may be 0.40 or less. z is greater than 0.25, and may be 0.30 or more, 0.35 or more, or 0.40 or more, and less than 0.55, and may be 0.50 or less, 0.45 or less, or 0.40 or less. The element M has little contribution to charge and discharge. In this regard, in the above chemical composition, p + q + r being less than 0.17 makes it easy to ensure a high charge-discharge capacity. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, the inclusion of the element M makes the O2-like structure likely to be stabilized. In the above chemical composition, p + q + r is 0 or more, and may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more.The composition of O is approximately 2, but is not necessarily exactly 2.0 and is variable.

[0016] 1.4 Other The electrode active material according to one embodiment may be, for example, solid particles, hollow particles, or particles having voids. The particle size of the electrode active material is not particularly limited, but smaller sizes are considered to be more advantageous. For example, the average particle diameter (D50) of the electrode active material 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. The average particle diameter (D50) is the particle diameter (D50, median diameter) at 50% cumulative in a volume-based particle size distribution determined by a laser diffraction / scattering method.

[0017] The electrode active material according to one embodiment may be a positive electrode active material. In the electrode active material according to one embodiment, the crystallite size of the O2-like structure measured by XRD is 400 Å or more, which increases the ratio of the capacity at high potential to the total capacity, and facilitates improvement of the energy density. For example, in one embodiment, the ratio of the capacity at 3 V or more to the total capacity is 75.0% or more. This ratio may be 85.0% or less or 82.0% or less. The method for measuring the ratio of the capacity at 3 V or more to the total capacity is as shown in the examples.

[0018] 2. Manufacturing method of electrode active material An electrode active material according to an embodiment can be produced, for example, by the following method: That is, the method for producing an electrode active material according to an embodiment includes obtaining a Na-containing oxide having a P2-type structure (S1), and bringing the Na-containing oxide into contact with an ion exchange material to ion-exchange at least a portion of the Na contained in the Na-containing oxide with Li, thereby obtaining a Li-containing oxide having an O2-like structure (S2).

[0019] 2.1 S1 In S1, the Na-containing oxide having a P2 type structure is, for example, S11: Obtaining a precursor; S12: Coating the surface of the precursor with a Na source to obtain a composite; and S13: Calcining the composite Here, the step S13 can be produced through the following steps: S13-1: Pre-baking the composite at a temperature of 300°C or higher and lower than 700°C for 2 hours or higher and 10 hours or lower; S13-2: Following the preliminary firing, the composite is subjected to main firing at a temperature of 700°C or higher and 1100°C or lower for 30 minutes or higher and 48 hours or lower; and S13-3: Following the main sintering, the composite may be rapidly cooled from a temperature T1 of 200°C or higher to a temperature T2 of 100°C or lower.

[0020] 2.1.1 Precursor preparation The precursor may contain at least one of Mn, Ni, and Co, or may contain Mn, Ni, and Co. The precursor may be a salt containing at least one element of 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, or may be spherical particles as described below. The particle size of the particles made of the precursor is not particularly limited.

[0021] In S11, the precursor precipitate may be obtained by coprecipitation using an ion source capable of forming a precipitate in an aqueous solution with transition metal ions and a transition metal compound containing at least one element selected from Mn, Ni, and Co. This facilitates the production of spherical particles as the precursor. The "ion source capable of forming a precipitate in an aqueous solution with transition metal ions" may be, for example, at least one selected from sodium salts such as sodium carbonate and sodium nitrate, sodium hydroxide, and sodium oxide. The transition metal compound may be the above salt or hydroxide containing at least one element selected from Mn, Ni, and Co. Specifically, in S11, the ion source and the transition metal compound may be prepared as separate solutions, and the respective solutions may be added dropwise and mixed to obtain the precursor precipitate. In this case, water, for example, is used as the solvent. Various sodium compounds may be used as bases, and aqueous ammonia or the like may be added to adjust the basicity. In the case of the coprecipitation method, for example, an aqueous solution of the transition metal compound and an aqueous solution of sodium carbonate are prepared, and the respective aqueous solutions are added dropwise and mixed to obtain the precursor precipitate. Alternatively, the precursor can be obtained by a sol-gel method, and in particular, by a coprecipitation method, spherical particles can be easily obtained as the precursor.

[0022] In step S11, the precursor may contain element M. The element M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. The element M has the function of stabilizing, for example, a P2-type structure or an O2-like structure. The method for obtaining a precursor containing element M is not particularly limited. When obtaining a precursor by coprecipitation in step S11, 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 the respective aqueous solutions are added dropwise and mixed to obtain a precursor containing element M together with at least one element of Mn, Ni, and Co. Alternatively, in the manufacturing method of the present disclosure, element M may not be added in step S11, and element M may be doped during the firing step described below.

[0023] 2.1.2 Preparation of the complex In S12, the surface of the precursor obtained in S11 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 S12, the amount of Na source coated on the surface of the precursor may be determined taking into account the amount of Na lost during subsequent calcination. In S12, the coverage rate of the Na source on the surface of the precursor is not particularly limited. In S12, the method for coating the surface of the precursor with the Na source is not particularly limited. For example, the precursor and the Na source may be mixed in a mortar or a mixer, or the precursor may be brought into contact with a solution containing the Na source using a tumbling fluidized coating method, a spray drying method, or the like, and then dried.

[0024] In S12, the precursor may be coated with an M source together with the Na source. For example, in S12, the precursor obtained in S11 may be mixed with a Na source and an M source containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W to obtain a composite. The M source may be, for example, a salt containing the element M, such as a carbonate or a sulfate, or a compound other than a salt, such as an oxide or a hydroxide. The amount of the M source relative to the precursor may be determined depending on the chemical composition of the Na-containing oxide after firing.

[0025] 2.1.3 Firing of the composite In S13, the composite obtained in S12 is calcined to obtain a Na-containing oxide having a P2-type structure. S13 may include the above-mentioned S13-1, S13-2, and S13-3. By adjusting the conditions in S13-1, S13-2, and S13-3 depending on the target chemical composition of the finally obtained O2-like structure, it is possible to adjust the crystallite size and shape (plate-like particles or spherical particles) of the P2-type Na-containing oxide obtained in S13, and thus the crystallite size of the finally obtained O2-like structure can be adjusted.

[0026] In S13-1, the composite is pre-fired at a temperature of 300°C or higher but lower than 700°C for 2 hours or higher but 10 hours or lower. In S13-1, the composite may be optionally shaped and then pre-fired. The pre-fired temperature is lower than that of the main firing. If the pre-fired temperature in S13-1 is insufficient, the P2 phase may not be sufficiently formed in the finally obtained Na-containing oxide. In S13-1, by setting the pre-fired temperature to 300°C or higher but lower than 700°C and the pre-fired time to 2 hours or higher but 10 hours or lower, the composite can be sufficiently pre-fired, improving heat uniformity and making it easier for the Na-containing oxide obtained via S13-2 and S13-3 described below to be suitable. The pre-firing temperature may be 400°C or higher and lower than 700°C, 450°C or higher and lower than 700°C, 500°C or higher and lower than 700°C, 550°C or higher and lower than 700°C, or 550°C or higher and lower than 650°C. The pre-firing time may be 2 hours or higher and lower than 8 hours, 3 hours or higher and lower than 8 hours, 4 hours or higher and lower than 8 hours, 5 hours or higher and lower than 8 hours, or 5 hours or higher and lower than 7 hours. The pre-firing atmosphere is not particularly limited, and may be, for example, an oxygen-containing atmosphere.

[0027] In S13-2, following the pre-firing, the composite is subjected to main firing at a temperature of 700°C to 1100°C for 30 minutes to 48 hours. In S13-2, the main firing temperature of the composite may be 800°C to 1000°C, or 850°C to 950°C. If the main firing temperature is too low, the P2 phase will not be formed, and if the main firing temperature is too high, an O3 phase or the like will likely form instead of the P2 phase. The temperature rise conditions from the pre-firing temperature to the main firing temperature are not particularly limited. In S13-2, the shape and crystallite size of the Na-containing oxide can be controlled by the main firing temperature and main firing time. If the main firing time is too short, the P2 phase will not be formed sufficiently. On the other hand, if the main firing time is too long, the P2 phase will grow excessively, and the crystallites will likely become coarse.

[0028] In step S13-3, following the main firing, the composite is rapidly cooled (cooled at a cooling rate of 20°C / min or more) from a temperature T1 of 200°C or higher to a temperature T2 of 100°C or lower. The preliminary firing and main firing are performed, for example, in a heating furnace. In step S13-3, for example, the composite is main fired in a heating furnace, then cooled to a temperature T1 of 200°C or higher in the heating furnace. After reaching temperature T1, the fired product is removed from the heating furnace and rapidly cooled outside the furnace to a temperature T2 of 100°C or lower. Temperature T1 may be any temperature of 200°C or higher, or any temperature of 250°C or higher. Temperature T2 may be any temperature of 100°C or lower, or any temperature of 50°C or lower, or may be the cooling end temperature. In the predetermined temperature range between temperature T1 and temperature T2, moisture is likely to penetrate between the layers of the P2 type structure due to atomic vibration, molecular motion, etc. When cooling the sintered composite (a Na-containing oxide having a P2 structure), it is believed that the amount of moisture that penetrates between the layers of the P2 structure can be reduced by shortening the time spent in this temperature range where moisture easily penetrates (i.e., by rapid cooling). In this regard, when cooling the sintered composite in step S13-3, for example, by allowing it to cool in a dry atmosphere outside the furnace from a temperature T1 of 200°C or higher to a temperature T2 of 100°C or lower, the cooling rate from temperature T1 to temperature T2 is high (e.g., 20°C / min or higher), making it difficult for moisture to penetrate between the layers of the P2 structure, thereby preventing the collapse of the P2 structure. As a result, Na can be efficiently ion-exchanged with Li in S2.

[0029] By S13, a Na-containing oxide having a P2 type structure and a predetermined chemical composition can be produced. The Na-containing oxide may contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Na, and O. In particular, when the constituent elements contain at least Na, Mn, at least one element selected from Ni and Co, and O, and especially when the constituent elements contain at least Na, Mn, Ni, Co, and O, the performance of the finally obtained electrode active material is likely to be further improved. The Na-containing oxide may contain Nac Ni x-p Co y-q Mn z-r M p+q+r It may have a chemical composition represented by O2. Here, 0 < c < 1.00, 0.15 < x < 0.35, 0.15 < y < 0.45, 0.25 < z < 0.55, x + y + z = 1, and 0 ≦ p + q + r < 0.17. Also, M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. When the Na-containing oxide has such a chemical composition, the P2-type structure is likely to be maintained. In the above chemical composition, c is greater than 0, and may be 0.10 or more, may be 0.20 or more, may be 0.30 or more, may be 0.40 or more, may be 0.50 or more, or may be 0.60 or more, and is less than 1.00, and may be 0.90 or less, may be 0.80 or less, or may be 0.70 or less; x, y, z, and p + q + r are as described above. The composition of O is approximately 2, but is not necessarily exactly 2.0 and is indefinite.

[0030] 2.2 S2 In step S2, the Na-containing oxide obtained in step S1 is brought into contact with an ion exchange material to ion-exchange at least a portion of the Na contained in the Na-containing oxide with Li, thereby obtaining a Li-containing oxide having an O2-like structure. For example, a Li compound is used as the ion exchange material. Specifically, lithium salts such as lithium nitrate and lithium halide may be used as the ion exchange material. When the ion exchange material is brought into contact with the Na-containing oxide, the ion exchange material may be in a molten state or a solid state. A molten state is particularly preferable. That is, by mixing the Na-containing oxide having the P2-type structure with the ion exchange material and heating the mixture to a temperature equal to or higher than the melting point of the ion exchange material, at least a portion of the Na in the Na-containing oxide can be ion-exchanged with Li. The ion exchange temperature may be, for example, equal to or higher than the melting point of the ion exchange material and equal to or lower than 600°C, 500°C, 400°C, or 300°C. If the ion exchange temperature is too high, a stable O3-type structure is likely to be formed instead of an O2-like structure. On the other hand, from the viewpoint of shortening the time required for ion exchange, it is preferable that the temperature during ion exchange is as high as possible.

[0031] 3.Battery As shown in FIG. 1 , a battery 100 according to one embodiment includes a positive electrode active material layer 10, an electrolyte layer 20, and a negative electrode active material layer 30. In the battery 100, for example, the positive electrode active material layer 10 may include the electrode active material of the present disclosure. The battery 100 may include a positive electrode current collector 40 and a negative electrode current collector 50. The battery 100 may be a solid-state battery or a liquid-based battery. A solid-state battery refers to a battery that includes a solid electrolyte and can tolerate the presence of a liquid. The battery 100 may also be an all-solid-state battery that is substantially free of liquid. The battery configuration may be the same as a conventional battery, except that the electrode active material of the present disclosure is used. Detailed description will be omitted here. [Example]

[0032] As described above, one embodiment of the electrode active material etc. has been described, but the technology of 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 while showing examples, but the technology of the present disclosure is not limited to the following examples.

[0033] 1. Preparation of Electrode Active Material 1.1 Example 1 1.1.1 Preparation of precursor particles (1) NiSO4·6H2O, CoSO4·7H2O, and MnSO4·5H2O were weighed to achieve the desired composition ratio (Ni:Co:Mn=2:4:4) 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) 1000 mL of pure water was placed in a reaction vessel (with a baffle plate), and 500 mL of the first solution and 500 mL of the second solution were added dropwise thereto at a rate of about 4 mL / min. (3) After the dropwise addition was completed, the mixture was stirred at room temperature for 1 hour at a stirring speed of 150 rpm to obtain a product. (4) The product was washed with pure water, and the solid was separated into liquid using a centrifuge to recover the precipitate. (5) The obtained precipitate was dried overnight at 120°C, crushed in a mortar, and then subjected to air classification to remove coarse particles and fine particles, thereby obtaining precursor particles.

[0034] 1.1.2 Preparation of the complex The obtained precursor particles and Na2CO3 were mixed in a mortar to coat the surfaces of the precursor particles with Na2CO3, thereby obtaining a composite.

[0035] 1.1.3 Firing of the composite The composite was placed in an alumina crucible and fired in an air atmosphere to obtain a Na-containing oxide having a P2 structure under the firing conditions (1) to (7) below. (1) The alumina crucible containing the composite is placed in a heating furnace in an air atmosphere. (2) The temperature inside the heating furnace is raised from room temperature (25°C) to 600°C in 115 minutes. (3) The temperature in the heating furnace is maintained at 600°C for 360 minutes to perform pre-baking. (4) After the preliminary firing, the temperature inside the heating furnace is raised to 900°C and then maintained at 900°C for 12 hours for main firing. (5) After the main firing, the temperature inside the heating furnace is lowered from the main firing temperature to 250°C, and the alumina crucible is removed from the heating furnace at 250°C and allowed to cool outside the furnace in a dry atmosphere until it reaches 25°C in 10 minutes.

[0036] The fired product after cooling was pulverized in a mortar in a dry atmosphere to obtain Na-containing oxide particles having a P2 type structure (P2 type particles). 0.8 Ni 0.2 Co 0.4 Mn 0.4 The particles were plate-like and had the chemical composition shown by O2.

[0037] 1.1.4 Ion exchange (1) LiNO3 and LiCl were weighed out to a molar ratio of 50:50, and mixed with the above P2 type particles in a molar ratio that was 10 times the minimum Li amount required for ion exchange to obtain a mixture. (2) Using an alumina crucible, ion exchange was carried out at 280°C for 1 hour in an air atmosphere to obtain a product containing a Li-containing oxide. (3) The salt remaining in the product was washed with pure water, and solid-liquid separation was carried out by vacuum filtration to obtain a precipitate. (4) The obtained precipitate was dried overnight at 120°C to obtain the electrode active material particles according to Example 1. The electrode active material particles contained Li 0.67 Ni 0.2 Co 0.4 Mn 0.4 The particles were plate-like and had the chemical composition shown by O2.

[0038] 1.2 Example 2 1.2.1 Preparation of precursor particles Precursor particles were obtained in the same manner as in Example 1.

[0039] 1.2.2 Preparation of the complex (1) Na2CO3 and distilled water were weighed out so that the concentration was 1150 g / L, and then the mixture was stirred using a stirrer until completely dissolved to prepare an aqueous Na2CO3 solution. (2) The above Na2CO3 aqueous solution and the above precursor particles are mixed, and the composition after calcination described below is Na 0.8 Ni 0.2 Co 0.4 Mn 0.4 The components were weighed and mixed to obtain a slurry. (3) The above slurry was spray-dried to obtain a composite. Specifically, a spray dryer DL410 was used, with a slurry flow rate of 30 mL / min, an inlet temperature of 200°C, and a circulating air volume of 0.8 m. 3 The above slurry was dried by airflow at a flow rate of 1 / min and a spray pressure of 0.3 MPa, thereby coating the surface of the precursor particles with Na2CO3 and obtaining a composite.

[0040] 1.2.3 Firing of the composite The composite was fired and allowed to cool in the same manner as in Example 1, except that the above composite was used. The fired product after cooling was pulverized in a mortar in a dry atmosphere to obtain Na-containing oxide particles having a P2 type structure (P2 type particles). 0.8 Ni 0.2 Co 0.4 Mn 0.4 The particles were spherical and had the chemical composition shown in O2.

[0041] 1.2.4 Ion exchange Ion exchange was carried out in the same manner as in Example 1 except that the P2 type particles were used, thereby obtaining electrode active material particles according to Example 2. The electrode active material particles were Li 0.64 Ni 0.2 Co 0.4 Mn 0.4 The particles were spherical and had the chemical composition shown in O2.

[0042] 1.3 Example 3 1.3.1 Preparation of precursor particles Precursor particles were prepared in the same manner as in Example 2, except that the raw materials were mixed so as to have a composition ratio of Ni:Co:Mn=3:3:4.

[0043] 1.3.2 Preparation of the complex A composite was obtained by spray drying in the same manner as in Example 2, except that the above precursor particles were used.

[0044] 1.3.3 Firing of the composite The composite was fired and cooled under the same conditions as in Example 2, except that the firing time of the composite was changed to 1 hour. The fired product after cooling was pulverized in a mortar in a dry atmosphere to obtain Na-containing oxide particles having a P2 type structure (P2 type particles). 0.9 Ni 0.3 Co 0.3 Mn 0.4 The particles were spherical and had the chemical composition shown in O2.

[0045] 1.3.4 Ion exchange Ion exchange was carried out in the same manner as in Example 1 except that the P2 type particles were used, thereby obtaining electrode active material particles according to Example 3. The electrode active material particles were Li 0.65 Ni 0.3 Co 0.3 Mn 0.4 The particles were spherical and had the chemical composition shown in O2.

[0046] 1.4 Example 4 1.4.1 Preparation of precursor particles Precursor particles were prepared in the same manner as in Example 2, except that the raw materials were mixed so as to have a composition ratio of Ni:Co:Mn=3:2:5.

[0047] 1.4.2 Preparation of the complex A composite was obtained by spray drying in the same manner as in Example 2, except that the above precursor particles were used.

[0048] 1.4.3 Firing of the composite The composite was fired and cooled under the same conditions as in Example 2, except that the firing time of the composite was changed to 1 hour. The fired product after cooling was pulverized in a mortar in a dry atmosphere to obtain Na-containing oxide particles having a P2 type structure (P2 type particles). 0.8 Ni 0.3 Co 0.2 Mn 0.5 The particles were spherical and had the chemical composition shown in O2.

[0049] 1.4.4 Ion exchange Ion exchange was carried out in the same manner as in Example 1 except that the P2 type particles were used, thereby obtaining electrode active material particles according to Example 4. The electrode active material particles were Li 0.66 Ni 0.3 Co 0.2 Mn 0.5 The particles were spherical and had the chemical composition shown in O2.

[0050] 1.5 Comparative Example 1 1.5.1 Preparation of precursor particles and composites Precursor particles and a composite were prepared in the same manner as in Example 2.

[0051] 1.5.2 Sintering of the composite The composite was fired and allowed to cool under the same conditions as in Example 2, except that the firing temperature was changed to 800°C. The fired product after cooling was pulverized in a mortar in a dry atmosphere to obtain Na-containing oxide particles having a P2 type structure (P2 type particles). 0.8 Ni 0.2 Co 0.4 Mn 0.4 The particles were spherical and had the chemical composition shown in O2.

[0052] 1.5.3 Ion exchange Ion exchange was carried out in the same manner as in Example 1 except that the P2 type particles were used, to obtain electrode active material particles according to Comparative Example 1. The electrode active material particles were Li 0.64 Ni 0.2 Co 0.4 Mn 0.4The particles were spherical and had the chemical composition shown in O2.

[0053] 1.6 Comparative Example 2 Precursor particles and a composite were prepared in the same manner as in Example 3.

[0054] 1.6.2 Firing of the composite The composite was fired and allowed to cool under the same conditions as in Example 3, except that the firing temperature was changed to 800°C. The fired product after cooling was pulverized in a mortar in a dry atmosphere to obtain Na-containing oxide particles having a P2 type structure (P2 type particles). 0.9 Ni 0.3 Co 0.3 Mn 0.4 The particles were spherical and had the chemical composition shown in O2.

[0055] 1.6.3 Ion exchange Ion exchange was carried out in the same manner as in Example 1 except that the P2 type particles were used, to obtain electrode active material particles according to Comparative Example 2. The electrode active material particles were Li 0.65 Ni 0.3 Co 0.3 Mn 0.4 The particles were spherical and had the chemical composition shown in O2.

[0056] 1.7 Summary of conditions Table 1 below shows the conditions for producing the P2 particles in Examples 1 to 4 and Comparative Examples 1 and 2. [Table 1]

[0057] 2. Coin Cell Fabrication Coin cells (CR2032) were fabricated using each electrode active material. The coin cell fabrication procedure is as follows. (1) The above electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder were weighed out in a mass ratio of electrode active material:AB:PVdF = 85:10:5, and dispersed and mixed in N-methyl-2-pyrrolidone to obtain a positive electrode composite slurry. The positive electrode composite slurry was coated on aluminum foil and vacuum dried overnight at 120°C to obtain a positive electrode, which is a laminate of a positive electrode active material layer and a positive electrode current collector. (2) An electrolyte solution was obtained by dissolving LiPF6 at a concentration of 1 M in a mixed solvent of trifluoropropylene carbonate (TFPC) and trifluoroethyl methyl carbonate (TFEMC) in a ratio of TFPC:TFEMC = 30 vol%:70 vol%. (3) Metallic lithium foil was prepared as the negative electrode. (4) A coin cell (CR2032) was fabricated using the positive electrode, electrolyte, and negative electrode.

[0058] 3. Evaluation Method 3.1 Crystallite size X-ray diffraction patterns using CuKα as a radiation source were obtained for each electrode active material. FIG. 2 shows the X-ray diffraction patterns of the electrode active materials of Examples 1 and 2 and Comparative Example 1. FIG. 3 shows the X-ray diffraction patterns of the electrode active materials of Example 3 and Comparative Example 2. FIG. 4 shows the X-ray diffraction pattern of the electrode active material of Example 4. As shown in FIGS. 2 to 4, the electrode active materials of Examples 1 to 4 and Comparative Examples 1 and 2 all had an O2-like structure. In each X-ray diffraction pattern, the crystallite size of the O2-like structure was calculated based on the Scherrer equation using PDXL2 software (manufactured by Rigaku Co., Ltd.) from the X-ray diffraction peaks derived from the (002) plane of the O2-type structure, the (002) plane of the T#2-type structure, and the (006) plane of the O6-type structure. In the X-ray diffraction pattern, when multiple X-ray diffraction peaks were observed, including the X-ray diffraction peaks derived from the (002) plane of the O2 type structure, the X-ray diffraction peaks derived from the (002) plane of the T#2 type structure, and the X-ray diffraction peaks derived from the (006) plane of the O6 type structure, the crystallite size was determined based on the main peak (the peak with the highest intensity) among the multiple peaks.

[0059] 3.2 Electrochemical measurements Each coin cell was charged and discharged in a thermostatic chamber maintained at 25°C at a voltage range of 2.0 to 4.8 V and a 0.1 C rate (1 C = 220 mA / g), and the initial discharge capacity was measured. The percentage of the initial discharge capacity at 3 V or higher was calculated.

[0060] 4. Evaluation Results Table 2 below shows the transition metal composition, crystallite size of the O2-like structure, initial discharge capacity, and the percentage of the capacity at 3 V or higher in the discharge capacity (total capacity) for each of the electrode active materials of Examples 1 to 4 and Comparative Examples 1 and 2. Figure 5 also shows the relationship between the crystallite size of the O2-like structure measured by XRD and the percentage of the capacity at 3 V or higher in the total capacity. [Table 2]

[0061] The results shown in Table 2 and Figure 5 indicate that when the crystallite size of the O2-like structure in the electrode active material is 400 Å or more, the proportion of high-potential capacity in the total capacity of the electrode active material increases. Furthermore, when the crystallite size exceeds 1000 Å, it may be difficult to measure the crystallite size by XRD. In this regard, the upper limit of the crystallite size of the O2-like structure in the electrode active material of the present disclosure is 1000 Å or less. [Explanation of symbols]

[0062] 100 batteries 10 Cathode active material layer 20 Electrolyte layer 30 Negative electrode active material layer 40 Positive electrode current collector 50 Negative electrode current collector

Claims

1. An electrode active material, having at least one O2-like structure selected from the group consisting of an O2-type structure, a T#2-type structure, and an O6-type structure; The crystallite size of the O2-like structure measured by XRD is 400 Å or more and 1000 Å or less. Electrode active material.

2. The electrode active material according to claim 1, The ratio of the capacity at 3 V or more to the total capacity is 75.0% or more. Electrode active material.

3. The electrode active material according to claim 1, Constituent elements include at least one element selected from Ni, Mn, and Co, Li, and O. Electrode active material.

4. The electrode active material according to claim 3, Li ａ Na ｂ Ni ｘ－ｐ Co ｙ－ｑ Mn ｚ－ｒ M ｐ＋ｑ＋ｒ O ２ (wherein 0<a<1.00, 0≦b≦0.20, 0.15<x<0.35, 0.15<y<0.45, 0.25<z<0.55, x+y+z=1, and 0≦p+q+r<0.17, and the element 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), Electrode active material.

5. The electrode active material according to claim 4, 0.70<a<1.00; Electrode active material.

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