Positive electrode active material, lithium ion battery, and method for manufacturing positive electrode active material

Abstract

To disclose a positive electrode active material having an O2-type structure and capable of contributing to reduction of resistance.SOLUTION: The positive electrode active material according to the present disclosure has an O2-type structure and has a carbon amount of 500 ppm at a maximum. The method for manufacturing the positive electrode active material of the present disclosure includes: ion-exchanging at least a part of Na in a Na-containing oxide with a P2-type structure with Li and obtaining a Li-containing oxide with an O2-type structure; and heating the Li-containing oxide and reducing the carbon amount of the Li-containing oxide.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

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

[0003] [Patent Document 1] JP 2011-170994 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional positive electrode active materials having an O2 type structure have room for improvement in terms of resistance. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> A positive electrode active material having an O2 type structure, Has a carbon content of 500 ppm or less; Cathode active material. <Aspect 2> The positive electrode active material of embodiment 1, Has a sulfur content of 300 ppm or less. Cathode active material. <Aspect 3> 1. A lithium ion battery, A positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer includes the positive electrode active material of embodiment 1 or 2. Lithium-ion battery. <Aspect 4> A method for producing a positive electrode active material, comprising the steps of: At least a part of Na in the Na-containing oxide having a P2 type structure is ion-exchanged with Li to obtain a Li-containing oxide having an O2 type structure; and heating the Li-containing oxide to reduce a carbon content of the Li-containing oxide; A method for producing a positive electrode active material comprising the steps of: <Aspect 5> A method for producing a positive electrode active material according to aspect 4, comprising the steps of: The Li-containing oxide is heated in an inert gas atmosphere or an oxygen-containing atmosphere, The temperature at which the Li-containing oxide is heated is 200° C. or higher and 300° C. or lower. A method for producing a positive electrode active material. <Aspect 6> A method for producing a positive electrode active material according to aspect 4 or 5, comprising the steps of: washing the Li-containing oxide with water to reduce the amount of sulfur in the Li-containing oxide; A method for producing a positive electrode active material comprising the steps of: Effect of the Invention

[0006] The positive electrode active material of the present disclosure has an O2 type structure and low resistance. [Brief description of the drawings]

[0007] [Figure 1] 1 shows an example of a method for producing a positive electrode active material having an O2 type structure. [Diagram 2] 1 shows a schematic of the mechanism by which carbon is removed by heating. [Diagram 3] 1 illustrates a schematic diagram of an example of the configuration of a lithium ion battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, one embodiment of the positive electrode active material, the lithium ion battery, and the method for producing the positive electrode active material according to the present disclosure will be described, but the positive electrode active material, the lithium ion battery, and the method for producing the positive electrode active material according to the present disclosure are not limited to the embodiment described below.

[0009] 1.Cathode active material The positive electrode active material according to one embodiment has an O2 type structure and a carbon content of 500 ppm or less.

[0010] 1.1 Crystal structure The positive electrode active material according to an embodiment has at least an O2 type structure (belonging to space group P63mc) as a crystal structure. The positive electrode active material according to an embodiment has an O2 type structure and may have a crystal structure other than the O2 type structure. Examples of the crystal structure other than the O2 type structure include a T♯2 type structure (belonging to space group Cmca) formed when Li is deintercalated from the O2 type structure and an O6 type structure (belonging to space group R-3m, having a c-axis length of 2.5 nm or more and 3.5 nm or less, typically 2.9 nm or more and 3.0 nm or less, and different from the O3 type structure also belonging to space group R-3m). The positive electrode active material according to an embodiment may have an O2 type structure as a main phase. The positive electrode active material according to an embodiment may have one or both of a T♯2 type structure and an O6 type structure together with the O2 type structure. The positive electrode active material according to an embodiment may have a crystal structure serving as a main phase that changes depending on its charge / discharge state.

[0011] 1.2 Chemical composition The chemical composition of the positive electrode active material according to one embodiment is not particularly limited as long as the above-mentioned O2 type structure can be maintained. The positive electrode active material having the O2 type structure may contain at least one element selected from Mn, Ni, and Co, Li, and O as constituent elements. The positive electrode active material is particularly likely to achieve higher performance when it contains at least Li, Mn, one or both of Ni and Co, and O as constituent elements, and particularly when it contains at least Li, Mn, Ni, Co, and O as constituent elements. The positive electrode active material according to one embodiment is Lia So b Mr x-p Ni y-q Co z-r M p+q+rO2 (where 0 < a < 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, and 0 ≤ p + q + r < 0.17, and the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W) may have a chemical composition represented thereby. When the positive electrode active material has such a chemical composition, the O2-type structure is likely to be maintained. In the above chemical composition, a is greater than 0, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and 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. Also, x is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, or 0.40 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less. Also, y is 0 or more, and may be 0.10 or more, or 0.20 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. Also, z is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, or 0.40 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less. The element M has a small contribution to charge and discharge. In this regard, in the above chemical composition, since p + q + r is less than 0.17, a high charge and discharge capacity is likely to be ensured. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, since the element M is included, the O2-type structure is likely to be stabilized. In the above chemical composition, p + q + r is 0 or more, and may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more.The composition of O is approximately 2, but is not necessarily exactly 2.0 and is variable.

[0012] 1.3 Carbon content In conventional positive electrode active materials having an O2 type structure, lithium carbonate is inevitably generated due to the manufacturing process. Specifically, a positive electrode active material having an O2 type structure can be obtained by replacing Na in a Na-containing oxide having a P2 type structure with Li (ion exchange). Here, Li or Li compounds that do not constitute an O2 type structure inevitably remain on the surface of the positive electrode active material after ion exchange. In addition, the O2 type structure is a metastable phase, and Li or Li compounds can be generated by the collapse of a part of the O2 type structure. Such Li or Li compounds react with, for example, carbon dioxide derived from the atmosphere to become lithium carbonate. When a positive electrode active material having an O2 type structure contains a large amount of lithium carbonate, the resistance of the positive electrode active material increases.

[0013] In contrast, the positive electrode active material according to one embodiment has a carbon content of 500 ppm or less by mass. That is, the positive electrode active material according to one embodiment has a significantly smaller amount of lithium carbonate, which is an impurity, compared to conventional positive electrode active materials. Therefore, the positive electrode active material according to one embodiment has a lower resistance compared to conventional positive electrode active materials. The carbon content of the positive electrode active material according to one embodiment may be 400 ppm or less, 300 ppm or less, or 200 ppm or less. The lower limit of the carbon content is not particularly limited. The carbon content may be 0 ppm or more, 10 ppm or more, 50 ppm or more, 100 ppm or more, or 150 ppm or more. Such a positive electrode active material with a low carbon content can be produced by heating (additional baking) the Li-containing oxide obtained after ion exchange, as described later.

[0014] The carbon content of the positive electrode active material can be measured, for example, by a combustion-infrared absorption method using a carbon-sulfur analyzer (CS844 type) manufactured by LECO Corporation.

[0015] 1.4 Sulfur content The positive electrode active material according to an embodiment may have a sulfur content of 300 ppm or less by mass together with the carbon content. By reducing the sulfur content of the positive electrode active material, the resistance of the positive electrode active material is likely to be further reduced. The lower limit of the sulfur content is not particularly limited. The sulfur content may be 0 ppm or more, 10 ppm or more, 50 ppm or more, 100 ppm or more, 150 ppm or more, or 200 ppm or more. Such a positive electrode active material having a low sulfur content can be produced by washing the Li-containing oxide obtained after ion exchange with water, as described below.

[0016] The amount of sulfur in the positive electrode active material can be measured, for example, by a combustion-ion chromatography method using a sample combustion device (AQF-2100S) manufactured by Mitsubishi Chemical Analytech Co., Ltd. and an ion chromatograph (Compact IC Flex) manufactured by Metrohm Co., Ltd.

[0017] 1.5 Carbon / Sulfur Ratio The mass ratio C / S of carbon to sulfur in the positive electrode active material according to an embodiment may be, for example, 0.70 to 3.50, or 0.74 to 3.46. When the mass ratio of carbon to sulfur in the positive electrode active material is within such a range, the positive electrode active material is likely to have a better balance of performance.

[0018] 1.6 Shape The positive electrode active material according to an embodiment can be obtained by substituting Li for Na in a Na-containing oxide having a P2 type structure. Here, the P2 type structure is a hexagonal crystal system, has a large diffusion coefficient of Na ions, and is prone to crystal growth in a specific direction. In particular, when at least one of Mn, Ni, and Co is included as a transition metal element constituting the P2 type structure, the crystal is prone to grow in a plate-like shape in a specific direction. Therefore, the Na-containing oxide having the P2 type structure is usually a plate-like particle with a large aspect ratio in which the crystal growth direction is biased in a specific direction. The positive electrode active material according to an embodiment may be obtained based on such plate-like Na-containing oxide particles, or, as described later, may be obtained based on spherical Na-containing oxide particles. That is, the shape of the positive electrode active material may be plate-like particles or spherical particles. When the positive electrode active material is spherical particles, the reaction resistance is reduced by reducing the crystallite size, and the diffusion resistance inside the particles is likely to be reduced. Furthermore, when applied to a battery, it is considered that the degree of bending is reduced by spheroidization, and the lithium ion conduction resistance is reduced. This, for example, improves the rate characteristics and tends to increase the reversible capacity. In the present application, the term "spherical particles" refers to particles having a circularity of 0.80 or more. The circularity of the particles may be 0.81 or more, 0.82 or more, 0.83 or more, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 or more, 0.89 or more, or 0.90 or more. The circularity of the particles is 4πS / L 2 Here, 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.

[0019] The positive electrode active material according to one embodiment may be, for example, a solid particle, a hollow particle, or a particle having a void. The size of the positive electrode active material particles is not particularly limited, but it is considered that a smaller size is more advantageous. For example, the average particle diameter (D50) of the positive 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 an integrated value of 50% in the volume-based particle size distribution by a laser diffraction / scattering method.

[0020] 2. Manufacturing method of positive electrode active material As shown in FIG. 1, a method for producing a positive electrode active material according to an embodiment includes the steps of: S1: At least a part of Na in a Na-containing oxide having a P2 type structure is ion-exchanged with Li to obtain a Li-containing oxide having an O2 type structure; and S2: Heating the Li-containing oxide to reduce the carbon content of the Li-containing oxide; It may include.

[0021] 2.1 S1 In S1, at least a part of the Na in the Na-containing oxide having the P2 type structure is ion-exchanged with Li to obtain a Li-containing oxide having the O2 type structure.

[0022] 2.1.1 Preparation of Na-containing oxides with P2-type structure The Na-containing oxide having a P2 type structure is, for example, S1-1: Obtaining a precursor (e.g., a precursor containing at least one element of Mn, Ni, and Co); S1-2: Coating the surface of the precursor with a Na source to obtain a composite; and S1-3: Firing the composite It can be obtained through.

[0023] In S1-1, for example, a precursor containing at least one element of Mn, Ni, and Co is obtained. The precursor may contain at least Mn, one or both of Ni and Co, or may contain at least Mn, Ni, and Co. The precursor may be a salt containing at least one element 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 in the form of particles, or may be spherical particles as described later. The particle size of the particles made of the precursor is not particularly limited. In S1-1, a precipitate as the precursor may be obtained by a coprecipitation method 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 of Mn, Ni, and Co. This makes it easy to obtain spherical particles as the precursor. The "ion source capable of forming a precipitate in an aqueous solution together with transition metal ions" may be at least one selected from, for example, sodium salts such as sodium carbonate and sodium nitrate, sodium hydroxide, and sodium oxide. The transition metal compound may be the above salts or hydroxides containing at least one element of Mn, Ni, and Co. Specifically, in S1-1, the ion source and the transition metal compound may be prepared as solutions, and then each solution may be dropped and mixed to obtain a precipitate as a precursor. In this case, for example, water is used as the solvent. In this case, various sodium compounds may be used as a base, and an aqueous ammonia solution or the like may be added to adjust the basicity. In the case of the coprecipitation method, for example, an aqueous solution of a transition metal compound and an aqueous solution of sodium carbonate are prepared, and each aqueous solution is dropped and mixed to obtain a precipitate as a precursor. Alternatively, the precursor can be obtained by a sol-gel method. In particular, the coprecipitation method makes it easy to obtain spherical particles as a precursor. In S1-1, the precursor may contain the element M.The element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. These elements M have a function of stabilizing, for example, a P2 type structure or an O2 type structure. The method of obtaining a precursor containing element M is not particularly limited. When obtaining a precursor by coprecipitation in S1-1, for example, an aqueous solution of a transition metal compound containing at least one of Mn, Ni, and Co, an aqueous solution of sodium carbonate, and an aqueous solution of a compound of element M are prepared, and each aqueous solution is dropped and mixed to obtain a precursor containing element M together with at least one element of Mn, Ni, and Co. Alternatively, in the manufacturing method of the present disclosure, element M may not be added in S1-1, and element M may be doped when Na-doping baking is performed in S1-2 and S1-3 described later.

[0024] In S1-2, the surface of the precursor obtained by S1-1 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 S1-2, the amount of the Na source coated on the surface of the precursor may be determined taking into account the amount of Na lost during the subsequent firing. In S1-2, the coverage rate of the Na source on the surface of the precursor is not particularly limited. For example, in S1-2, the composite may be obtained by coating 40 area% or more, 50 area% or more, 60 area% or more, or 70 area% or more of the surface of the precursor with a Na source. Here, when the precursor obtained by S1-1 is a spherical particle, and the composite obtained by S1-2 is obtained by coating 40 area% or more of the surface of the precursor with the Na source, the Na-containing oxide having a P2 type structure is likely to become a spherical particle in S1-3 described later. If the coverage rate of the Na source is small, when the composite is fired, P2 type crystals tend to grow on the surface of the composite, and the Na-containing oxide tends to become plate-like. If the coverage rate of the Na source is large, when the composite is fired, the crystallites of the P2 type crystals tend to become small, and the Na-containing oxide tends to become spherical particles corresponding to the shape of the precursor. In S1-2, the method of coating the surface of the precursor with the Na source is not particularly limited. As described above, when 40% or more of the surface of the precursor is coated with the Na source, various methods can be mentioned. For example, the rolling fluidized coating method and the spray drying method can be mentioned. That is, a coating solution in which the Na source is dissolved is prepared, and the coating solution is brought into contact with the surface of the precursor, or the coating solution is dried at the same time as the coating solution is brought into contact with the surface of the precursor. By adjusting the coating conditions (temperature, time, number of times, etc.), 40% or more of the surface of the precursor can be coated with the Na source. In S1-2, the precursor may be coated with the M source together with the Na source. For example, in S1-2, the precursor obtained in S1-1, a Na source, and an M source containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W may be mixed to obtain a composite.The M source may be, for example, a salt containing element M, such as a carbonate or sulfate, or a compound other than a salt, such as an oxide or 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] In S1-3, the composite obtained in S1-2 is fired to obtain a Na-containing oxide having a P2 type structure. S1-3 includes, for example, the following S1-3A, S1-3B, and S1-3C.

[0026] In S1-3A, the composite is pre-fired at a temperature of 300° C. or more and less than 700° C. for 2 hours to 10 hours. In S1-3A, the composite may be optionally molded and then pre-fired. The pre-fire is performed at a temperature lower than that of the main firing. If the pre-fire in S1-3A is insufficient, the P2 phase may not be sufficiently generated in the finally obtained Na-containing oxide. In S1-3A, the pre-fire temperature is 300° C. or more and less than 700° C., and the pre-fire time is 2 hours to 10 hours, so that the composite can be sufficiently pre-fired, the heat uniformity is improved, and the Na-containing oxide obtained through S1-3B and S1-3C described later is likely to be appropriate. The pre-firing temperature may be 400° C. or more and less than 700° C., 450° C. or more and less than 700° C., 500° C. or more and less than 700° C., 550° C. or more and less than 700° C., or 550° C. or more and less than 650° C. The pre-firing time may be 2 hours or more and less than 8 hours, 3 hours or more and less than 8 hours, 4 hours or more and less than 8 hours, 5 hours or more and less than 8 hours, or 5 hours or more and less than 7 hours. The pre-firing atmosphere is not particularly limited, and may be, for example, an oxygen-containing atmosphere.

[0027] In S1-3B, following the above pre-firing, the composite is subjected to main firing at a temperature of 700°C to 1100°C for 30 minutes to 10 hours. In S1-3B, the main firing temperature of the composite is 700°C to 1100°C, preferably 800°C to 1000°C. If the main firing temperature is too low, the P2 phase is not generated, and if the main firing temperature is too high, the O3 phase and the like are likely to be generated instead of the P2 phase. The temperature rise condition from the pre-firing temperature to the main firing temperature is not particularly limited. The main firing time is not particularly limited, and may be, for example, 30 minutes to 48 hours. However, the shape of the Na-containing oxide can be controlled by the main firing time. As described above, in the method of the present disclosure, when the coverage rate of the Na source in the composite is 40 area % or more, when the composite is fired, P2 type crystals with small crystallites are likely to be formed on the surface. In the method of the present disclosure, the P2 type crystals are grown along the surface of the particles so as to connect one P2 type crystallite with another P2 type crystallite, so that the shape of the Na-containing oxide corresponds to the shape of the precursor. For example, when the precursor is a spherical particle, the Na-containing oxide can also be a spherical particle. If the firing time is too short, the generation of the P2 phase is insufficient. On the other hand, if the firing time is too long, the P2 phase grows excessively, resulting in plate-like particles rather than spherical ones. As far as the present inventors have confirmed, spherical particles of the Na-containing oxide are easily obtained when the firing time is 30 minutes or more and 3 hours or less. The Na-containing oxide obtained after firing may have a structure in which a plurality of crystallites are present on the surface and the crystallites are connected to each other.

[0028] In step S1-3C, following the main firing, the composite is rapidly cooled (cooled at a temperature drop rate of 20°C / min or more) from a temperature T1 of 200°C or more to a temperature T2 of 100°C or less. The preliminary firing and main firing are performed, for example, in a heating furnace. In step S3-3, for example, after the main firing of the composite is performed in a heating furnace, it is cooled to an arbitrary temperature T1 of 200°C or more in the heating furnace, and after the temperature T1 is reached, the fired product is removed from the heating furnace and rapidly cooled outside the furnace to an arbitrary temperature T2 of 100°C or less. The temperature T1 may be an arbitrary temperature of 200°C or more, or an arbitrary temperature of 250°C or more. The temperature T2 may be an arbitrary temperature of 100°C or less, or an arbitrary temperature of 50°C or less, or may be the cooling end temperature. In a certain temperature range between the temperature T1 and the temperature T2, moisture is likely to penetrate between the layers of the P2 type structure due to atomic vibration, molecular motion, etc. When cooling the composite (Na-containing oxide having a P2 type structure) after the main firing, it is considered that the amount of moisture that penetrates between the layers of the P2 type structure is reduced by shortening the time in which the temperature range in which moisture easily penetrates (i.e., by cooling quickly). In this regard, when cooling the composite after the main firing in step S3-3, for example, by cooling in a dry atmosphere outside the furnace from an arbitrary temperature T1 of 200°C or higher to an arbitrary temperature T2 of 100°C or lower, the cooling rate from temperature T1 to temperature T2 is high (for example, 20°C / min or higher), making it difficult for moisture to penetrate between the layers of the P2 type structure, and the collapse of the P2 type structure can be suppressed. As a result, Na can be efficiently ion-exchanged with Li in S4.

[0029] As described above, a Na-containing oxide having a P2 type structure and a predetermined chemical composition can be produced by S1-1 to S1-3. The Na-containing oxide contains, for example, at least one transition metal element selected from Mn, Ni, and Co, Na, and O as constituent elements. In particular, when the constituent elements contain at least Na, Mn, at least one of Ni and Co, and O, and especially when the constituent elements contain at least Na, Mn, Ni, Co, and O, the performance of the positive electrode active material is likely to be further improved. The Na-containing oxide contains Nac Mn x-p Ni y-q Co z-r M p+q+r It may have a chemical composition represented by O2. Here, 0 < c < 1.00, x + y + z = 1, and 0 ≤ p + q + r < 0.17. Also, M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. When the Na-containing oxide has such a chemical composition, the P2-type structure is more likely to be maintained. In the above chemical composition, c is greater than 0, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and less than 1.00, and may be 0.90 or less, 0.80 or less, or 0.70 or less. x is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, or 0.40 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less. Also, y is 0 or more, and may be 0.10 or more or 0.20 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. Also, z is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, or 0.40 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less. The contribution of element M to charge and discharge is small. In this regard, in the above chemical composition, when p + q + r is less than 0.17, a high charge and discharge capacity is likely to be ensured. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, when element M is included, the P2-type structure and the O2-type structure are likely to be stabilized. In the above chemical composition, p + q + r is 0 or more, and may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more. The composition of O is approximately 2, but is not necessarily exactly 2.0 and is indefinite.

[0030] 2.1.2 Ion exchange In S1, at least a part of Na in the Na-containing oxide obtained as described above is ion-exchanged with Li to obtain a Li-containing oxide having an O2 type structure. For example, there are a method using an aqueous solution containing lithium halide and a method using a mixture of lithium halide and other lithium salts (for example, molten salt) for ion exchange. From the viewpoint that the P2 type structure is easily broken by the intrusion of water and from the viewpoint of crystallinity, the method using a molten salt is preferable among the above two methods. That is, by mixing the Na-containing oxide having the above-mentioned P2 type structure with the molten salt and heating it to a temperature equal to or higher than the melting point of the molten salt, at least a part of Na in the Na-containing oxide can be replaced with Li by ion exchange. The lithium halide constituting the molten salt is preferably at least one of lithium chloride, lithium bromide, and lithium iodide. The other lithium salt constituting the molten salt is preferably lithium nitrate. By using a molten salt, the melting point becomes lower than when lithium halide or other lithium salts are used alone, and ion exchange can be performed at a lower temperature. The temperature in the ion exchange may be, for example, above the melting point of the molten salt and below 600°C, below 500°C, below 400°C, or below 300°C. If the temperature in the ion exchange is too high, the stable O3 structure is likely to be formed instead of the O2 structure. On the other hand, from the viewpoint of shortening the time required for the ion exchange, it is preferable that the temperature in the ion exchange is as high as possible.

[0031] 2.2 S2 In S2, the Li-containing oxide obtained in S1 is heated to reduce the carbon content of the Li-containing oxide. That is, the Li-containing oxide having the O2 type structure obtained after the ion exchange is additionally calcined to remove at least a part of the carbon (lithium carbonate) present on the surface of the Li-containing oxide.

[0032] The Li-containing oxide having an O2-type structure adopts a Li-deficient crystal structure. That is, in the positive electrode active material having an O2-type structure, the composition ratio Li / O of Li and O is less than 0.5 (for example, "a" in the above composition formula is less than 1.0), and there is room for Li to be inserted into the crystal structure. When such a Li-deficient Li-containing oxide is heated, as shown in FIG. 2, the lithium carbonate on the surface of the Li-containing oxide is converted into Li and CO. x and Li is incorporated into the crystal structure, while CO x It is considered that the Li-containing oxide is removed from the Li-containing oxide. That is, by subjecting the Li-containing oxide having an O2-type structure obtained after ion exchange to additional baking, at least a part of the carbon (lithium carbonate) present on the surface of the Li-containing oxide is removed, and the carbon amount of the finally obtained positive electrode active material becomes 500 ppm or less. Such an action and effect are unique to the case where the Li-containing oxide having an O2-type structure is heated.

[0033] In S2, the atmosphere in which the Li-containing oxide is heated may be any atmosphere in which the O2 type structure of the Li-containing oxide is maintained and the amount of carbon in the Li-containing oxide can be reduced. For example, the heating atmosphere may be an inert gas atmosphere such as an Ar atmosphere, or an oxygen-containing atmosphere such as air atmosphere.

[0034] In S2, the temperature at which the Li-containing oxide is heated may be any temperature at which the O2-type structure of the Li-containing oxide is maintained and the amount of carbon in the Li-containing oxide can be reduced. If the temperature is too low, the carbon removal reaction described above is difficult to occur. On the other hand, if the temperature is too high, the metastable O2-type structure is likely to change to the stable O3-type structure. From the viewpoint of appropriately removing carbon while maintaining the O2-type structure, the temperature in S2 may be, for example, 200°C or higher and 300°C or lower. The temperature may be 220°C or higher or 240°C or higher, and may be 280°C or lower or 260°C or lower.

[0035] In S2, the time for heating the Li-containing oxide may be a time for which the O2-type structure of the Li-containing oxide is maintained and the carbon content in the Li-containing oxide can be reduced. The time in S2 (holding time at the heating temperature) may be, for example, 30 minutes to 10 hours, 2 hours to 8 hours, or 4 hours to 6 hours.

[0036] 2.3 Other processes According to the method including S1 and S2, a positive electrode active material having an O2 type structure and a carbon content of 500 ppm or less can be manufactured. The method for manufacturing a positive electrode active material according to an embodiment may include washing the Li-containing oxide obtained by S1 with water to reduce the sulfur content of the Li-containing oxide. The washing of the Li-containing oxide with water may be performed before or after S2. In particular, it is considered that washing with water before S2 and then performing S2 can reduce the water content as well as the carbon content and sulfur content in the positive electrode active material. By washing the Li-containing oxide with water, the sulfur content of the finally obtained positive electrode active material is 300 ppm. Although washing the Li-containing oxide with water is effective for reducing the sulfur content of the finally obtained positive electrode active material, it is substantially ineffective for reducing the carbon content. In order to reduce the carbon content of the finally obtained positive electrode active material, for example, additional baking as described above is necessary.

[0037] 3. Lithium-ion battery A configuration of a lithium-ion battery according to an embodiment is shown in FIG. 3. As shown in FIG. 3, a lithium-ion battery 100 according to an embodiment has a positive electrode active material layer 10, an electrolyte layer 20, and a negative electrode active material layer 30. Here, the positive electrode active material layer 10 contains the positive electrode active material according to the above embodiment. As shown in FIG. 3, the lithium-ion battery 100 may include a positive electrode current collector 40 and a negative electrode current collector 50.

[0038] 3.1 Cathode active material layer The positive electrode active material layer 10 includes a positive electrode active material having the above-mentioned O2 type structure. The positive electrode active material layer 10 may optionally include other positive electrode active materials, electrolytes, conductive assistants, binders, and the like. The positive electrode active material layer 10 may also include various other additives. The contents of the positive electrode active material, electrolytes, conductive assistants, binders, and the like in the positive electrode active material layer 10 may be appropriately determined according to the intended battery performance. For example, the content of the positive electrode active material may be 40% by mass or more and 100% by mass or less, assuming that the entire solid content contained in the positive electrode active material layer 10 is 100% by mass.

[0039] An ion-conductive protective layer may be formed on the surface of the positive electrode active material. That is, the positive electrode active material layer 10 may include a complex of the positive electrode active material and a protective layer, and in the complex, at least a part of the surface of the positive electrode active material may be covered with the protective layer. The ion-conductive protective layer may include various ion-conductive compounds. The ion-conductive compound may be, for example, at least one selected from ion-conductive oxides and ion-conductive halides. The coverage (area ratio) of the protective layer to the surface of the positive electrode active material may be, for example, 70% or more, 80% or more, or 90% or more. The thickness of the protective layer may be, for example, 0.1 nm or more or 1 nm or more, and may be 100 nm or less, or 20 nm or less.

[0040] The positive electrode active material contained in the positive electrode active material layer 10 may be composed of only the positive electrode active material having the above O2 type structure, or may contain other positive electrode active materials (other positive electrode active materials) together with the positive electrode active material. From the viewpoint of further enhancing the effect of the technology of the present disclosure, the ratio of other positive electrode active materials in the entire positive electrode active material may be small. For example, the content of the positive electrode active material having the above O2 type structure may be 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, or 99% by mass or more and 100% by mass or less, based on the entire positive electrode active material being 100% by mass.

[0041] The electrolyte that can be included in the positive electrode active material layer 10 may be a solid electrolyte, a liquid electrolyte, or a combination of these. In particular, when the positive electrode active material layer 10 includes a solid electrolyte, particularly when it includes a sulfide solid electrolyte, high performance is likely to be ensured. The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte (sulfide glass), a glass ceramic-based sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. The sulfide glass is amorphous. The sulfide glass may have a glass transition temperature (Tg). In addition, when the sulfide solid electrolyte has a crystalline phase, examples of the crystalline phase include a Thio-LISICON type crystalline phase, a LGPS type crystalline phase, and an Argyrodite type crystalline phase. The sulfide solid electrolyte may contain, for example, a Li element, a P element, and an S element. The sulfide solid electrolyte may further contain an X element (X is at least one of As, Sb, Si, Ge, Sn, B, Al, Ga, and In). The sulfide solid electrolyte may further contain at least one of an O element and a halogen element. The sulfide solid electrolyte may further contain an S element as a main component of an anion element. Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2-P2S5-LiI, Li2S-P2S5-ZmSn (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y(However, x and y are positive numbers. M may be at least one selected from P and optionally any one of Si, Ge, B, Al, Ga, and In.) It may be at least one selected. Alternatively, the sulfide solid electrolyte is not particularly limited. For example, it may have at least one chemical composition selected from xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30), etc. Alternatively, the sulfide solid electrolyte has the general formula: Li 4-x Ge 1-x P x S4 (0 < x < 1). In the above general formula, at least a part of Ge may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, a part of P may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, a part of Li may be substituted with at least one of Na, K, Mg, Ca, and Zn. In the above general formula, a part of S may be substituted with a halogen (at least one of F, Cl, Br, and I). Alternatively, the sulfide solid electrolyte has the formula Li 7-a PS 6-a X a (X is at least one of Cl, Br, and I, and a is a number from 0 or more to 2 or less). a may be 0, or may be greater than 0. In the latter case, a may be 0.1 or more, may be 0.5 or more, or may be 1 or more. Also, a may be 1.8 or less, may be 1.5 or less. The sulfide solid electrolyte may be in particulate form. The average particle diameter (D50) of the sulfide solid electrolyte may be, for example, 10 nm or more and 100 μm or less.

[0042] Examples of the conductive assistant that may be included in the positive electrode active material layer 10 include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metal materials such as nickel, titanium, aluminum, and stainless steel. The conductive assistant may be, for example, particulate or fibrous, and the size thereof is not particularly limited. Only one type of conductive assistant may be used alone, or two or more types may be used in combination.

[0043] Examples of binders that can be included in the positive electrode active material layer 10 include butadiene rubber (BR)-based binders, butylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, etc. Only one type of binder may be used alone, or two or more types may be used in combination.

[0044] The positive electrode active material layer 10 may contain various additives in addition to the above components, such as a dispersant and a lubricant.

[0045] 3.2 Electrolyte layer The electrolyte layer 20 is disposed between the positive electrode active material layer 10 and the negative electrode active material layer 30. The electrolyte layer 20 includes at least an electrolyte. The electrolyte layer 20 may include at least one of a solid electrolyte and a liquid electrolyte, and may further include a binder or the like. In particular, when the electrolyte layer 20 includes a solid electrolyte, particularly when the electrolyte layer 20 includes a sulfide solid electrolyte, higher performance is likely to be ensured. The content of the electrolyte and the binder or the like in the electrolyte layer 20 is not particularly limited. Alternatively, the electrolyte layer 20 may have a separator or the like for holding the electrolytic solution and preventing contact between the positive electrode active material layer 10 and the negative electrode active material layer 30. The thickness of the electrolyte layer 20 is not particularly limited, and may be, for example, 0.1 μm or more or 1 μm or more, and may be 2 mm or less or 1 mm or less.

[0046] The electrolyte contained in the electrolyte layer 20 may be appropriately selected from those exemplified as electrolytes that may be contained in the above-mentioned positive electrode active material layer 10 (solid electrolytes and / or liquid electrolytes). The binder that may be contained in the electrolyte layer 20 may also be appropriately selected from those exemplified as binders that may be contained in the above-mentioned 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 that is commonly used in lithium ion batteries, and examples of the separator include those made of resins such as polyethylene (PE), polypropylene (PP), polyester, and polyamide. The separator may have a single layer structure or a multilayer structure. Examples of the multilayer separator include a separator with a two-layer structure of PE / PP, or a separator with 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.

[0047] 3.3 Negative electrode active material layer The negative electrode active material layer 30 includes at least a negative electrode active material. The negative electrode active material layer 30 may also include an electrolyte, a conductive assistant, a binder, various additives, and the like. The content of each component in the negative electrode active material layer 30 may be appropriately determined according to the intended battery performance. For example, the content of the negative electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or 100% by mass or less, less than 100% by mass, 95% by mass or less, or 90% by mass or less, based on the entire solid content of the negative electrode active material layer 30 being 100% by volume. Alternatively, the negative electrode active material and optionally the electrolyte, the conductive assistant, and the binder may be included in a total amount of 85% by volume or more, 90% by volume or more, or 95% by volume or more, based on the entire negative electrode active material layer 30 being 100% by volume, and the remainder may be voids or other components. The shape of the negative electrode active material layer 30 is not particularly limited, and may be, for example, a sheet having a substantially flat surface. The thickness of the negative electrode active material layer 30 is not particularly limited, and may be, for example, 0.1 μm or more, 1 μm or more, 10 μm or more, or 30 μm or more, and may be 2 mm or less, 1 mm or less, 500 μm or less, or 100 μm or less.

[0048] The negative electrode active material contained in the negative electrode active material layer 30 can be any of those known as negative electrode active materials for lithium ion batteries. Of the known active materials, various materials can be used that have a potential (charge / discharge potential) for absorbing and releasing lithium ions that is lower than the above-mentioned positive electrode active material. For example, silicon-based active materials such as Si, Si alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium, lithium alloys, and the like can be used. Among them, when the negative electrode active material layer 30 contains Si as the negative electrode active material, the performance of the lithium ion battery 100 is likely to be improved. Only one type of negative electrode active material may be used alone, or two or more types may be used in combination. The shape of the negative electrode active material may be any shape that is common as a negative electrode active material for lithium ion batteries. For example, the negative electrode active material may be in the form of particles. The negative electrode active material particles may be primary particles, or may be secondary particles formed by agglomeration of a plurality of primary particles. The average particle diameter (D50) of the negative electrode active material particles may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Alternatively, the negative electrode active material may be in the form of a sheet (foil or film) such as a lithium foil. That is, the negative electrode active material layer 30 may be made of a sheet of the negative electrode active material.

[0049] Examples of the electrolyte that can be contained in the negative electrode active material layer 30 include the above-mentioned solid electrolyte, electrolytic solution, or a combination thereof. The conductive assistant that can be contained in the negative electrode active material layer 30 may be appropriately selected from, for example, those exemplified as the conductive assistant that can be contained in the above-mentioned positive electrode active material layer. The binder that can be contained in the negative electrode active material layer 30 may be appropriately selected from, for example, those exemplified as the binder that can be contained in the above-mentioned positive electrode active material layer. Each of the electrolyte, conductive assistant, and binder may be used alone or in combination of two or more kinds.

[0050] 3.4 Other configurations As shown in FIG. 3, the lithium ion battery 100 may include a positive electrode collector 40 in contact with the positive electrode active material layer 10 and a negative electrode collector 50 in contact with the negative electrode active material layer 30. The configuration of the collector itself is known. The lithium ion battery 100 may include a general configuration as a battery in addition to the above configuration. For example, a tab or a terminal. The lithium ion battery 100 may be one in which each of the above configurations is housed inside an exterior body. Any known exterior body for a battery can be used as the exterior body. In addition, a plurality of batteries 100 may be electrically connected and stacked in any order to form a battery pack. In this case, the battery pack may be housed inside a known battery case. The shape of the lithium ion battery 100 may be, for example, a coin type, a laminate type, a cylindrical type, a square type, or the like. The lithium ion battery 100 may be a secondary battery.

[0051] The lithium ion battery 100 can be manufactured by applying a known method, except for using the above-mentioned specific positive electrode active material. For example, it can be manufactured as follows. (1) The positive electrode active material constituting the positive electrode active material layer is 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, thereby forming a positive electrode. (2) The negative electrode active material constituting the negative electrode active material layer is 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, thereby forming a negative electrode. (3) The layers are laminated 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 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 in this order. 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 electrolyte, and the laminate is immersed in the electrolyte and sealed in the battery case to form a battery. In the case of an electrolyte battery, the electrolyte may be impregnated in the negative electrode active material layer, the separator, and the positive electrode active material layer at the above step (3). EXAMPLES

[0052] The technology of the present disclosure will be described in more detail below with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0053] 1. Preparation of Positive Electrode Active Material 1.1 Example 1 1.1.1 Preparation of precursor particles (1) MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed out to obtain the desired composition ratio, and dissolved in distilled water to obtain a concentration of 1.2 mol / L to obtain a first solution. In a separate container, Na2CO3 was dissolved in distilled water to obtain 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 each added dropwise at a rate of about 4 mL / min. (3) After the dropwise addition was completed, the mixture was stirred at room temperature at a stirring speed of 100 rpm for 1 hour to obtain a product. (4) The product was washed with pure water, subjected to solid-liquid separation using a centrifuge, and the precipitate was collected. (5) The obtained precipitate was dried overnight at 120°C, crushed in a mortar, and then separated into coarse particles and fine particles by air classification. Here, both the coarse particles and the fine particles are composite salts containing Mn, Ni, and Co. In Example 1, the above coarse particles were used as precursor particles.

[0054] 1.1.2 Preparation of composite particles (1) Na2CO3 and distilled water were weighed out so that the total concentration was 1,150 g / L, and then the mixture was stirred using a stirrer until it was completely dissolved, thereby preparing an aqueous Na2CO3 solution. (2) The above precursor particles were mixed in an aqueous Na2CO3 solution to prepare a slurry. The Na2CO3 and the above precursor particles were mixed in an aqueous Na2CO3 solution to prepare a slurry. 0.7 Mn 0.4 Ni 0.2 Co 0.4 Mix to give O2. (3) The obtained slurry was dried by spray drying. Specifically, a spray drying apparatus DL410 was used, with a slurry delivery rate of 30 mL / min, an inlet temperature of 200°C, and a circulating air volume of 0.8 m 3 At a spray air pressure of 0.3 MPa, more than 70% of the surface area of ​​the precursor particles was covered with Na2CO3 to obtain composite particles.

[0055] 1.1.3 Sintering of composite particles The composite particles were placed in an alumina crucible and sintered in an air atmosphere to obtain a Na-containing oxide having a P2 structure under the following sintering conditions (1) to (7). (1) The alumina crucible containing the composite particles 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 kept at 600°C for 360 minutes to perform pre-baking. (4) After preliminary firing, the temperature inside the heating furnace is raised from 600°C to 800°C in 60 minutes. (5) The temperature in the heating furnace is kept at 800°C for 60 minutes to carry out the main firing. (6) After the main firing, the temperature in the heating furnace is lowered from 800°C to 250°C in 80 minutes. (7) At 250°C, the alumina crucible is removed from the heating furnace and allowed to cool in a dry atmosphere.

[0056] 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.

[0057] 1.1.4 Ion exchange (1) LiNO3 and LiCl were weighed out to have a molar ratio of 50:50, and mixed with the above-mentioned Na-containing oxide 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 Li-containing oxide particles. (3) The salt remaining in the product was washed with pure water, and solid-liquid separation was performed by vacuum filtration to obtain a precipitate. (4) The obtained precipitate was dried overnight at 120°C to obtain Li-containing oxide particles having an O2-type structure.

[0058] 1.1.5 Additional firing The obtained Li-containing oxide particles were placed in an alumina crucible and baked in an Ar atmosphere at 250° C. for 5 hours to obtain the positive electrode active material according to Example 1. When confirmed by XRD, the positive electrode active material according to Example 1 had an O2 type structure.

[0059] 1.2 Example 2 1.2.1 Preparation of precursor particles Precursor particles were prepared in the same manner as in Example 1.

[0060] 1.2.2 Preparation of composite particles The target composition after firing is Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 Composite particles were prepared in the same manner as in Example 1, except that Na2CO3 and the above precursor particles were mixed to obtain a slurry so as to obtain O2.

[0061] 1.2.3 Sintering of composite particles The composite particles were placed in an alumina crucible and sintered in an air atmosphere to obtain a Na-containing oxide having a P2 structure under the following sintering conditions (1) to (7). (1) The alumina crucible containing the composite particles 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 kept at 600°C for 360 minutes to perform pre-baking. (4) After preliminary firing, the temperature inside the heating furnace is raised from 600°C to 900°C in 100 minutes. (5) The temperature in the heating furnace is kept at 900°C for 60 minutes to perform the main firing. (6) After the main firing, the temperature in the heating furnace is lowered from 900°C to 250°C in 120 minutes. (7) At 250°C, the alumina crucible is removed from the heating furnace and allowed to cool in a dry atmosphere.

[0062] 1.2.4 Ion exchange and additional calcination As in Example 1, after crushing in a mortar, ion exchange and additional baking were performed to obtain a positive electrode active material according to Example 2. When confirmed by XRD, the positive electrode active material according to Example 2 had an O2 type structure.

[0063] 1.3 Example 3 The process up to the ion exchange was the same as in Example 2. The Li-containing oxide particles obtained after the ion exchange were placed in an alumina crucible and baked at 250° C. for 5 hours in an atmospheric air atmosphere to obtain a positive electrode active material according to Example 3. When confirmed by XRD, the positive electrode active material according to Example 3 had an O2 type structure.

[0064] 1.4 Comparative Example 1 Except for not carrying out the additional baking, the results were the same as in Examples 2 and 3. When confirmed by XRD, the positive electrode active material according to Comparative Example 1 had an O2 type structure.

[0065] 1.5 Comparative Examples 2 and 3 A positive electrode active material having an O3 type structure was prepared as a Li-non-deficient positive electrode active material. The positive electrode active material according to Comparative Example 2 was an NCA type positive electrode active material (LiNi 0.85 Co 0.10 Al 0.05 O2), and the positive electrode active material according to Comparative Example 3 is an NCM-based positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3The positive electrode active materials according to Comparative Examples 2 and 3 were both obtained by mixing a Li source and a transition metal source and baking the mixture at a high temperature.

[0066] 2. Quantitative analysis of impurities contained in the positive electrode active material For each of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3, the carbon amount, sulfur amount, chlorine amount, and nitrogen amount were quantified by the following method. (1) The carbon content in the samples was measured by the combustion-infrared absorption method using a LECO carbon-sulfur analyzer (CS844). (2) The amounts of sulfur and chlorine in the samples were measured by combustion-ion chromatography using a sample combustion device (AQF-2100S) manufactured by Mitsubishi Chemical Analytech Co., Ltd. and an ion chromatograph (Compact IC Flex) manufactured by Metrohm Co., Ltd. (3) The amount of nitrogen in the samples was measured by the inert gas fusion method using a Horiba EMGA-920 Type-Ar measuring device.

[0067] 3. Preparation of Evaluation Cell Using each of the above positive electrode active materials, an evaluation cell was produced according to the following procedure. (1) A positive electrode active material, a sulfide solid electrolyte (Li2S-P2S5-LiI-LiBr), PVDF, and VGCF were weighed and mixed so that the positive electrode active material:sulfide solid electrolyte:PVDF:VGCF=81.1:15.9:0.6:2.4 (mass ratio) to obtain a positive electrode composite. The obtained positive electrode composite was dispersed in a solvent (butyl butyrate) to obtain a positive electrode slurry. The obtained positive electrode slurry was applied to a positive electrode current collector (Al foil) and dried. Thereafter, the positive electrode active material layer was formed on the surface of the positive electrode current collector by pressing with a roll press at a pressing temperature shown in Table 1 below and a linear pressure of 100 kN. (2) A negative electrode active material (lithium titanate), a sulfide solid electrolyte (Li2S-P2S5-LiI-LiBr), PVDF, and VGCF were weighed and mixed so that the ratio of the negative electrode active material:sulfide solid electrolyte:PVDF:VGCF=72.1:22.7:3.5:1.7 (mass ratio) to obtain a negative electrode composite. The obtained negative electrode composite was dispersed in a solvent (butyl butyrate) to obtain a negative electrode slurry. The obtained negative electrode slurry was applied to a negative electrode current collector (Cu foil) and dried. After that, the negative electrode active material layer was formed on the surface of the negative electrode current collector by pressing at room temperature (25°C) and linear pressure of 60 kN using a roll press. (3) The sulfide solid electrolyte (Li2S-P2S5-LiI-LiBr) and acrylate butadiene rubber (ABR) were weighed and mixed in a sulfide solid electrolyte:ABR = 99.4:0.6 (mass ratio) to obtain an electrolyte mixture. (4) An electrolyte mixture was sandwiched between the positive electrode active material layer and the negative electrode active material layer to obtain a laminate having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector in this order. The obtained laminate was pressed to obtain an evaluation cell (solid-state battery).

[0068] 4.Charge / Discharge Characteristics Evaluation For each of the evaluation cells of Examples 1 to 3 and Comparative Example 1, a two-cycle charge-discharge test was performed at 0.1C (1C=220mA / g) in a voltage range of 1.8-4.6V in a thermostatic chamber maintained at 25°C. Then, in a thermostatic chamber maintained at 25°C, a current equivalent to 3C was applied for 10 seconds in a SOC50% state (2.35V vs. LTO) to measure the DCIR resistance. The measurement results are shown in Table 1 below.

[0069] 5. Evaluation Results Table 1 below shows, for each of Examples 1 to 3 and Comparative Examples 1 to 3, the crystal structure and chemical composition of the positive electrode active material, the atmosphere of the additional baking after ion exchange, the amount of impurities (amount of carbon, sulfur, chlorine, and nitrogen) contained in the positive electrode active material, the results of identifying the impurities by XPS, the position of the (002) plane peak top by XRD, and the resistance measurement results of the evaluation cells.

[0070] [Table 1]

[0071] As is clear from the results shown in Table 1, the positive electrode active material according to Comparative Example 1 had a large carbon amount of 900 ppm, and as a result, the resistance of the evaluation cell was large. In contrast, the positive electrode active materials according to Examples 1 to 3 had a small carbon amount of 500 ppm or less, and as a result, the resistance of the evaluation cell was small. In the positive electrode active materials according to Examples 1 to 3, the Li-containing oxide after ion exchange was subjected to additional baking, and as a result, a part of the lithium carbonate, which is an impurity, was decomposed, and the carbon amount was reduced (FIG. 2). When comparing Comparative Example 1 with Examples 1 to 3, the peak top of the 002 plane in the X-ray diffraction pattern shifted, and this is considered to be due to the lithium generated by the decomposition of the lithium carbonate, which is an impurity, being incorporated into the O2 type structure and changing the c-axis length. Such decomposition and removal of impurities by additional baking is specific to a positive electrode active material having an O2 type structure, which is a Li-deficient structure.

[0072] The positive electrode active material according to Comparative Example 2 had a large amount of both carbon and sulfur. The positive electrode active material according to Comparative Example 3 had a small amount of carbon but a large amount of sulfur. The positive electrode active materials according to Comparative Examples 2 and 3 have a Li-non-deficient O3 type structure, and it is considered that it is difficult to reduce the amount of carbon even if additional baking is performed.

[0073] 6. Supplementary Information In the above examples, the precursor particles are obtained by coprecipitation, but the precursor particles can be obtained by other methods. In the above examples, the precursor particles are mixed with a Na2CO3 solution to obtain composite particles, but the composite particles can be obtained by other methods. In the above examples, the Na-containing oxide having a P2 type structure and the Li-containing oxide having an O2 type structure are exemplified as those having a predetermined chemical composition, but the chemical composition of the Na-containing oxide and the Li-containing oxide is not limited to this. For example, the Na-containing oxide and the Li-containing oxide may be doped with an element M other than Mn, Ni, and Co. The element M is as described in the embodiment. [Explanation of symbols]

[0074] 100 Lithium-ion secondary battery 10 Cathode active material layer 20 Electrolyte layer 30 Negative electrode active material layer 40 Positive electrode current collector 50 Negative electrode current collector

Claims

1. A positive electrode active material having an O2 type structure, having a carbon content of 500 ppm or less; Cathode active material.

2. The positive electrode active material according to claim 1 , having a sulfur content of 300 ppm or less; Cathode active material.

3. 1. A lithium ion battery, A positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer comprises the positive electrode active material according to claim 1 or 2. Lithium-ion battery.

4. A method for producing a positive electrode active material, comprising: At least a part of Na in the Na-containing oxide having a P2 type structure is ion-exchanged with Li to obtain a Li-containing oxide having an O2 type structure; and Heating the Li-containing oxide to reduce the carbon content of the Li-containing oxide; A method for producing a positive electrode active material comprising the steps of:

5. A method for producing a positive electrode active material according to claim 4, The atmosphere in which the Li-containing oxide is heated is an inert gas atmosphere or an oxygen-containing atmosphere, The temperature when the Li-containing oxide is heated is 200° C. or more and 300° C. or less. A method for producing a positive electrode active material.

6. A method for producing a positive electrode active material according to claim 4 or 5, washing the Li-containing oxide with water to reduce the amount of sulfur in the Li-containing oxide; A method for producing a positive electrode active material comprising the steps of:

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