Positive electrode active material, method for producing positive electrode active material, and solid-state battery

Abstract

To provide a positive electrode active material and solid-state battery that can produce a battery with a large discharge capacity in a range including a high potential range and excellent rapid discharge performance, a solid-state battery, and a manufacturing method for a positive electrode active material.SOLUTION: A positive electrode active material is composed of alternating a layer O3 having a crystal structure of an O3-type structure and a layer O2 having at least one crystal structure selected from the group consisting of an O2-type structure, a T#2-type structure, and an O6-type structure. A ratio of a volume of the layer O2 to a total volume of the layer O3 and the layer O2 is greater than or equal to 0.1 and less than or equal to 0.6.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a positive electrode active material, a method for manufacturing the positive electrode active material, and a solid battery.

Background Art

[0002] A positive electrode active material having at least one crystal structure selected from the group consisting of an O2-type structure, a T#2-type structure, and an O6-type structure is stable up to a high potential, and thus has a large charge-discharge capacity in charge-discharge in a high potential region. Patent Document 1 discloses "a positive electrode active material used in a non-aqueous electrolyte secondary battery, which has a layered structure and contains a lithium-containing transition metal oxide in which the main arrangement of transition metal, oxygen, and lithium is represented by an O2 structure, and the lithium-containing transition metal oxide has Li, Mn, and element M in the lithium-containing transition metal layer in the layered structure, and has a general composition formula Li x [Li α (Mn a M b ) 1-α O2, where 0.5 < x < 1.1, 0.1 < α < 0.33, 0.67 < a < 0.97, 0.03 < b < 0.33, and M contains at least one element selected from the group consisting of Ni, Mg, Ti, Fe, Sn, Zr, Nb, Mo, W, and Bi, a positive electrode active material for a non-aqueous electrolyte secondary battery."

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A positive electrode active material having at least one crystal structure selected from the group consisting of an O2-type structure, a T#2-type structure, and an O6-type structure has a slow internal diffusion rate of lithium ions, and thus tends to have poor rapid charge-discharge performance. In recent years, there has been a demand for improved rapid charge-discharge performance, and there is a need to develop a positive electrode active material having at least one crystal structure selected from the group consisting of an O2-type structure, a T#2-type structure, and an O6-type structure, which can provide a battery with excellent rapid charge-discharge performance and a large discharge capacity in a high potential range.

[0005] Therefore, an object of one embodiment of the present disclosure is to provide a positive electrode active material that can provide a battery having excellent rapid charge / discharge performance and a large discharge capacity in a high potential range. Another problem to be solved by another embodiment of the present disclosure is to provide a solid-state battery that has excellent rapid charge and discharge performance and a large discharge capacity in a high potential range. Another problem to be solved by another embodiment of the present disclosure is to provide a method for producing a positive electrode active material that can provide a battery that has excellent rapid charge and discharge performance and a large discharge capacity in a high potential range. [Means for solving the problem]

[0006] The means for solving the above problems include the following means. <1> Layer with O3-type crystal structure O3 and a layer having at least one crystal structure selected from the group consisting of an O2 type structure, a T#2 type structure, and an O6 type structure. O2 and are stacked alternately, The layer O3 and the layer O2 the total volume of the layer O2 The positive electrode active material has a volume of 0.1 or more and 0.6 or less. <2> The average intensity at all midpoints between two adjacent peaks is 0.05 or less relative to the average maximum intensity of all peaks in the intensity profile obtained by integrating each pixel value in a high-angle annular dark-field scanning transmission electron microscope image with the electron beam incident direction set to <1-10> in a direction perpendicular to the c-axis. <1> or <2> The positive electrode active material according to claim 1. <3> <1> or <2> A solid-state battery comprising the positive electrode active material according to claim 1. <4> A method for producing a positive electrode active material, comprising a step of ion-exchanging Na contained in a compound represented by the following formula 2 with Li: Formula 2: Na c Mn x-p Ni y-q Co z-r M p+q+r O2 In the above formula 2, c, x, y, z, p, q, and r are numbers that satisfy 0.82≦c, x+y+z=1, and 0≦p+q+r≦0.20, M represents a metal element selected from the group consisting of Li, B, Mg, Al, K, Ca, Ti, Cr, Ga, Zr, Nb, Mo, and W. [Effects of the Invention]

[0007] According to one embodiment of the present disclosure, a positive electrode active material is provided that enables obtaining a battery having excellent rapid charge and discharge performance and a large discharge capacity in a high potential range. According to another embodiment of the present disclosure, a solid-state battery is provided that has excellent rapid charge and discharge performance and a large discharge capacity in a high potential range. According to another embodiment of the present disclosure, there is provided a method for producing a positive electrode active material that can provide a battery that has excellent rapid charge and discharge performance and a large discharge capacity in a high potential range. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0009] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified. The term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.

[0010] <Cathode active material> The positive electrode active material according to the present disclosure is a layer having an O3-type crystal structure. O3 and a layer having at least one crystal structure selected from the group consisting of an O2 type structure, a T#2 type structure, and an O6 type structure. O2 and are stacked alternately.

[0011] The cathode active material according to the present disclosure, as configured above, is a cathode active material that can provide a battery having excellent rapid charge / discharge performance and a large discharge capacity in a region including a high potential region. The reason for this is presumed to be as follows. "Excellent rapid charge / discharge performance" means that the charge rate is 70% or higher at a current value of 5 C. The region including a high potential region refers to a range of 2.0 V or higher and 4.5 V or higher, preferably a range of 2.0 V or higher and 4.8 V or lower.

[0012] The positive electrode active material according to the present disclosure includes a layer having at least one crystal structure selected from the group consisting of an O2 type structure, a T#2 type structure, and an O6 type structure. O2 Therefore, the positive electrode active material according to the present disclosure has a large discharge-charge capacity in a region including a high potential region. O3 The O3-type crystal structure has a fast internal diffusion rate of lithium ions, which is advantageous for improving rapid charge and discharge performance. O3 and the layer O2 and are alternately stacked, which improves both the rapid discharge and charge performance and the discharge capacity in a region including a high potential region. In addition, the layer O3 and the layer O2 the total volume of the layer O2By setting the volume to 0.1 or more and 0.6 or less, the rapid discharge and charge performance and the discharge capacity in a region including a high potential region are likely to be further improved.

[0013] (layer O3 ) The positive electrode active material according to the present disclosure has a layer having an O3-type crystal structure. O3 It has. Here, the O3-type crystal structure refers to a crystal structure that belongs to the space group R-3m, in which lithium is present at the center of an oxygen octahedron, and in which there are three types of overlapping patterns between oxygen and transition metal oxide per unit cell. A crystal structure in which six oxygen layers, three Li layers, and three transition metal layers form one period is preferred.

[0014] (layer O2 ) The positive electrode active material according to the present disclosure includes a layer having at least one crystal structure selected from the group consisting of an O2 type structure, a T#2 type structure, and an O6 type structure. O2 It has. Here, the O2-type crystal structure is a crystal structure that belongs to the space group P63mc, in which lithium is present at the center of an oxygen octahedron, and there are two types of overlapping of oxygen and transition metal atoms per unit cell. A crystal structure in which one period consists of four oxygen layers, two Li layers, and two transition metal layers is preferred. The T#2 type crystal structure belongs to the space group Cmca, in which lithium is present at the center of an oxygen tetrahedron and there are two types of overlapping of oxygen and transition metal atoms per unit cell. A crystal structure in which one period consists of four oxygen layers, two Li layers, and two transition metal layers is preferred. The O6-type crystal structure is a crystal structure that belongs to the space group R-3m, in which lithium is present at the center of an oxygen octahedron, and there are six different ways in which oxygen and transition metals overlap per unit cell. A crystal structure that forms one period with an O12 layer, an Me6 layer, and an Li6 layer is preferred.

[0015] (layer structure) The positive electrode active material according to the present disclosure is a layer O3 and layers O2 and are stacked alternately. "layer O3 and layersO2 "Alternately stacked layers" means that the layers O3 or layer O2 and a layer O3 or layer O2 Between the two layers, there is another layer (layer O2 or layer O3 ) (for example, the two layers are layers O3 If so, two layers O3 In between, there is another layer, O2 (having). From the viewpoint of rapid charge / discharge performance and discharge capacity, a layer contained in one primary particle of the positive electrode active material according to the present disclosure O3 The number of layers is not particularly limited, but preferably includes 3 to 400 layers, more preferably includes 10 to 300 layers, and even more preferably includes 50 to 300 layers. From the viewpoint of rapid charge / discharge performance and discharge capacity, a layer contained in one primary particle of the positive electrode active material according to the present disclosure O2 The number of layers is not particularly limited, but preferably includes 3 to 40 layers, more preferably includes 4 to 30 layers, and even more preferably includes 5 to 25 layers.

[0016] ·layer O3 and layer O2 How to determine Layer contained in the positive electrode active material O3 and layer O2 is determined as follows: The positive electrode active material was observed by annular bright-field scanning transmission electron microscopy (ABF-STEM) using a transmission electron microscope under conditions of an acceleration voltage of 200 kV or more and a resolution of 0.2 nm or less. The interface between the region where a structure consistent with the space group P63mc was observed and the region where a structure consistent with the space group R-3m was observed was then identified as a layer. O3 and layer O2 the interface with the O3 / layer O2If there is a region N between a region where a consistent structure is observed for the space group P63mc and a region where a consistent structure is observed for the space group R-3m, where a structure that does not fit into either of these is observed, the midpoint of the region N is defined as a layer. O3 / layer O2 The region where a consistent structure is observed in the space group P63mc and the region N from one end to the layer O3 / layer O2 The area up to the interface is layered. O3 The region where a consistent structure is observed as space group R-3m, and the layer from the other end of region N O3 / layer O2 The area up to the interface is layered. O2 Let's say.

[0017] From the viewpoint of rapid charge / discharge performance and discharge capacity, O3 and layer O2 The total volume of the layer O2 (hereinafter also referred to as "specific volume ratio") is 0.1 or more and 0.6 or less, preferably 0.2 or more and less than 0.6, more preferably 0.2 or more and 0.5 or less, and even more preferably 0.3 or more and 0.4 or less.

[0018] Specific volume ratio calculation method The calculation of the specific volume ratio is O2 The volume of the layer O3 and layer O2 It is calculated by dividing by the "total volume of layer O3 The volume is measured as follows: Acquired in a 10nm x 10nm area <001> From the electron incident ABF-STEM image, the layer O3 For the area that was determined to be a smear, the square of the long side × the short side was calculated, and the sum was taken for the entire area of ​​the ABF-STEM image. Furthermore, the sum of the smears for the 10 ABF-STEM images was used to form a layer. O3 Let the volume be . layer O2 The volume is measured as follows: Acquired in a 10nm x 10nm area <001> From the electron incident ABF-STEM image, the layer O2 For the area that was determined to be a smear, the square of the long side × the short side was calculated, and the sum was taken for the entire area of ​​the ABF-STEM image. Furthermore, the sum of the smears for the 10 ABF-STEM images was used to form a layer. O2 Let the volume be .

[0019] (Characteristics of positive electrode active material) From the viewpoint of rapid charge / discharge performance and discharge capacity, the positive electrode active material according to the present disclosure preferably has an average value of intensities at all midpoints between two adjacent peaks relative to the average value of maximum intensities of all peaks in an intensity profile obtained by integrating each pixel value in a high-angle annular dark-field scanning transmission electron microscope image with the electron beam incident direction set to <1-10> in a direction perpendicular to the c-axis (hereinafter also referred to as the "specific intensity ratio") of 0.05 or less, more preferably 0.01 or more and 0.05 or less, and even more preferably 0.01 or more and 0.03 or less.

[0020] Specific intensity ratio measurement method The specific intensity ratio is measured as follows. At a position 10 nm or more away from the particle surface of the positive electrode active material, a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image is acquired over a 10 nm x 10 nm area with a resolution of 512 x 512 or more, using a transmission electron microscope with a resolution of 0.2 nm or less and an electron beam incident direction of <1-10>. An HAADF-STEM image is acquired under the same conditions in a vacuum region without any measurement samples, and the root mean square of the background noise is calculated. The S / N ratio is defined as the maximum intensity of the obtained HAADF-STEM image minus the root mean square and then divided by the root mean square. The image is acquired so that the S / N ratio is 100 or more. However, the maximum intensity of the obtained HAADF-STEM image is acquired so that it does not reach the maximum value of the image, such as 255 for an 8-bit image or 65535 for a 16-bit image, and the HAADF-STEM image is acquired without nonlinear correction such as gamma correction. In addition, the following processing is performed on the obtained HAADF-STEM image without correction. An intensity profile is obtained by integrating each pixel value of the HAADF-STEM image over 2 nm or more in the direction perpendicular to the c-axis. For the peaks that appear in the intensity profile at a period of approximately 0.48 nm, the maximum intensity of the peaks is calculated, and the arithmetic mean of these is calculated to obtain the "average maximum intensity of each peak." Next, the intensity at the midpoint between two adjacent peaks is calculated, and the arithmetic mean of these is calculated to obtain the "average intensity at the midpoint between two adjacent peaks." The "specific intensity ratio" is calculated by calculating the ratio of the "average maximum intensity of each peak" to the "average intensity at the midpoint between two adjacent peaks."

[0021] (Composition formula of positive electrode active material) The composition of the positive electrode active material according to the present disclosure is O3 and layers O2 The compositions of the layers may be different or the same. O3 and layer O2 It is preferable that the compositions of the two are the same.

[0022] From the viewpoint of rapid charge / discharge performance and discharge capacity, the positive electrode active material according to the present disclosure is preferably a compound represented by the following formula 1. Formula 1: Li a Na b Mn x-p Ni y-q Co z-r M p+q+r O2 In the above formula 1, a, b, x, y, z, p, q, and r are numbers that satisfy 0≦a≦1 (preferably 0.6≦a≦1), 0≦b≦0.05 (preferably 0≦b≦0.01), and x+y+z=1 and 0≦p+q+r≦0.20 (preferably 0≦p+q+r≦0.10), and M represents at least one element selected from the group consisting of B, Mg, Al, K, Ca, Ti, Cr, Ga, Zr, Nb, Mo, and W. M preferably represents at least one selected from the group consisting of B, Mg, Al, K, Ca, Ti, Cr, Ga, Zr, Nb, Mo and W, and more preferably represents Al.

[0023] x is preferably a number that satisfies 0≦x≦1, and more preferably a number that satisfies 0.1≦x≦1. y is preferably a number that satisfies 0≦y≦0.5, and more preferably a number that satisfies 0≦y≦0.33. It is preferable that z is a number that satisfies 0≦z≦1, and it is more preferable that z is a number that satisfies 0≦z≦0.67. It is preferable that p is a number that satisfies 0≦p≦0.10. It is preferable that q is a number that satisfies 0≦q≦0.10. It is preferable that r is a number that satisfies 0≦r≦0.10.

[0024] Specifically, the composition formula of the positive electrode active material according to the present disclosure is Li 0.82 Na0Mn 0.5 Ni 0.2 Co 0.3 O2, Li 1.0 Na0Mn 0.5 Ni 0.2 Co 0.3 O2, Li 0.9 Na 0.05 Mn0.5 Ni 0.2 Co 0.3 O2, Li 0.9 Na0Mn 0.67 Ni 0.33 Co0O2, Li 0.9 Na0Mn 0.5 Ni 0.2 Co 0.2 Al 0.1 O2, Li 0.9 Na0Mn 0.5 Ni 0.1 Co 0.3 Mg 0.1 Examples include O2.

[0025] <Method of manufacturing positive electrode active material> The method for producing a positive electrode active material according to the present disclosure includes a step of ion-exchanging Na contained in a compound represented by the following formula 2 with Li (ion-exchange step).

[0026] Formula 2: Na c Mn x-p Ni y-q Co z-r M p+q+r O2 In the above formula 2, c, x, y, z, p, q, and r are numbers that satisfy 0.82≦c, x+y+z=1, and 0≦p+q+r≦0.20, M represents a metal element selected from the group consisting of Li, B, Mg, Al, K, Ca, Ti, Cr, Ga, Zr, Nb, Mo, and W. Preferably, c is a number that satisfies 0.82≦c≦1.05, and more preferably 0.82≦c≦1.00.

[0027] x is preferably a number that satisfies 0≦x≦1, and more preferably a number that satisfies 0.1≦x≦1. y is preferably a number that satisfies 0≦y≦0.5, and more preferably a number that satisfies 0≦y≦0.33. It is preferable that z is a number that satisfies 0≦z≦1, and it is more preferable that z is a number that satisfies 0≦z≦0.67. It is preferable that p is a number that satisfies 0≦p≦0.10. It is preferable that q is a number that satisfies 0≦q≦0.10. It is preferable that r is a number that satisfies 0≦r≦0.10.

[0028] (Na-doped precursor synthesis process) The method for producing a positive electrode active material according to the present disclosure may include a step of synthesizing a compound represented by the above formula 2 (hereinafter also referred to as a Na-doped precursor) as needed. Alternatively, a commercially available Na-doped precursor may be purchased and used. In the former case, the Na-doped precursor is synthesized by a known method. Specifically, it is preferable to use salts containing the metals that constitute the Na-doped precursor as raw materials and mix and react these salts to obtain the Na-doped precursor. Examples of the salt include sodium-containing carbonates, manganese-containing nitrates, nickel-containing nitrates, cobalt-containing nitrates, manganese-containing sulfates, nickel-containing sulfates, cobalt-containing sulfates, manganese-containing oxalates, nickel-containing oxalates, cobalt-containing oxalates, sodium-containing hydroxides, and sodium-containing hydrogen carbonates.

[0029] The Na-doped precursor is specifically Na 0.82 Mn 0.5 Ni 0.2 Co 0.3 O2, Na 1.0 Mn 0.5 Ni 0.2 Co 0.3 O2, Na 0.9 Mn 0.67 Ni 0.33 Co0O2, Na 0.9 Mn 0.5 Ni 0.2 Co 0.2 Al 0.1 O2, Na 0.9 Mn 0.5 Ni 0.1 Co 0.3 Mg 0.1 O2, NaMnNiCoO2, etc.

[0030] (Ion exchange process) The ion exchange step is a step of ion-exchanging Na contained in the Na-doped precursor with Li. Ion exchange of the Na-doped precursor can be performed using a molten salt bed containing a mixture of lithium nitrate and lithium chloride. The temperature conditions during ion exchange are preferably in the range of not less than the temperature at which the molten salt bed melts but less than 320°C.

[0031] <Solid battery> A solid-state battery according to the present disclosure includes a positive electrode active material according to the present disclosure. The solid-state battery according to the present disclosure preferably includes a positive electrode layer, a negative electrode layer, and an electrolyte layer or a separator disposed between the positive electrode layer and the negative electrode layer, and the positive electrode layer contains the positive electrode active material according to the present disclosure. Solid-state batteries include so-called all-solid-state batteries (in which the content of electrolytic solution as electrolyte is less than 10 mass % of the total amount of electrolyte) that use an inorganic solid electrolyte as the electrolyte.

[0032] (positive electrode layer) The positive electrode layer contains the positive electrode active material according to the present disclosure, and may contain a conductive additive, a solid electrolyte, a binder, and other components as necessary. Examples of the conductive additive include carbon materials, metal materials, and conductive polymer materials. As the solid electrolyte, a solid electrolyte contained in an electrolyte layer, which will be described later, can be used. Examples of binders include vinyl halide resins, rubbers, and polyolefin resins. Examples of other components include oxide solid electrolytes, halide solid electrolytes, thickeners, surfactants, dispersants, wetting agents, antifoaming agents, and solvents.

[0033] (negative electrode layer) The negative electrode layer contains a negative electrode active material. The negative electrode layer may contain at least one of a negative electrode solid electrolyte, a conductive additive, and a binder, as necessary. Examples of the negative electrode active material include Li-based active materials such as metallic lithium, carbon-based active materials such as graphite, oxide-based active materials such as lithium titanate, and Si-based active materials such as elemental Si. The conductive additive, negative electrode solid electrolyte, and binder used in the negative electrode layer are the same as those contained in the positive electrode layer.

[0034] (Electrolyte layer and separator) A solid-state battery includes an electrolyte layer or separator. The electrolyte layer may be a layer containing a solid electrolyte. In the case of a layer containing a solid electrolyte (solid electrolyte layer), the solid electrolyte layer preferably contains one selected from the group consisting of a sulfide solid electrolyte, an oxide solid electrolyte, and a halide solid electrolyte. As the separator, a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide can be used.

[0035] (Positive electrode current collector and negative electrode current collector) The solid-state battery may further include a positive electrode current collector and a negative electrode current collector. The positive electrode current collector collects current from the positive electrode layer. The negative electrode current collector collects current from the negative electrode layer. Examples of the positive electrode current collector include stainless steel, aluminum, copper, nickel, iron, titanium, and carbon, and aluminum alloy foil or aluminum foil is preferred. The negative electrode current collector may be made of, for example, stainless steel, aluminum, copper, nickel, iron, titanium, or carbon, with copper being preferred. The positive electrode current collector and the negative electrode current collector may be, for example, in the form of a foil or mesh.

[0036] <Solid-state battery manufacturing method> A method for manufacturing a solid-state battery according to the present disclosure includes: a step of preparing a positive electrode, a negative electrode, and an electrolyte layer (preparation step); and a step of stacking a positive electrode, an electrolyte layer, and a negative electrode in this order (stacking step).

[0037] (preparation process) The preparation step is a step of preparing a positive electrode, a negative electrode, and an electrolyte layer or a separator.

[0038] The method for producing the positive electrode, negative electrode, and electrolyte layer is not particularly limited, and it is preferable to produce them by kneading components that can be contained in the positive electrode layer, negative electrode layer, and electrolyte layer to obtain a slurry, applying the slurry to a substrate, and pressing the dried film obtained by drying.

[0039] Methods for pressing the dried film include roll pressing and cold isostatic pressing (CIP).

[0040] (Lamination process) The lamination step is a step of laminating a positive electrode, an electrolyte layer or a separator, and a negative electrode in this order. In the lamination step, the positive electrode prepared in the preparation step, the electrolyte layer or separator, and the negative electrode are preferably laminated in this order, and pressed as necessary to obtain a laminate (electrode body).

[0041] It is preferable to fabricate the solid state battery according to the present disclosure through the above steps. [Example]

[0042] Examples will be described below, but the present invention is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are by mass.

[0043] Example 1 (Na-doped precursor synthesis process) Mn(NO3)2·6H2O, Ni(NO3)2·6H2O, and Co(NO3)2·6H2O were used as raw materials and dissolved in pure water to a molar ratio of Mn, Ni, and Co of 5:2:3. A 12% by mass Na2CO3 solution was prepared, and these two solutions were simultaneously titrated into a beaker. The titration rate was controlled so that the pH was between 7.0 and 7.1. After the titration, the mixed solution was stirred at 50°C and 300 rpm for 24 hours. The resulting reaction product was washed with pure water, and the precipitated powder was separated by centrifugation. The resulting powder was dried at 120°C for 48 hours and then crushed in an agate mortar to obtain a powder (hereinafter referred to as the "intermediate powder"). The obtained intermediate powder was mixed with Na2CO3 in a composition ratio of Na 0.82 Mn 0.5 Ni 0.2 Co 0.3 The mixed powder was pressed under a load of 2 tons by cold isostatic pressing to produce pellets. The pellets were pre-baked in air at 600°C for 6 hours and then sintered at 700°C for 24 hours. After that, they were cooled to 250°C at a rate of 3°C / min and allowed to cool to obtain the Na-doped precursor (Na 0.82 Mn 0.5 Ni 0.2 Co 0.3 O2) was synthesized.

[0044] (Ion exchange process) LiNO3 and LiCl were mixed at a mass ratio of 88:12 to obtain a mixed powder. The Na-doped precursor was weighed so that the ratio of the number of moles of Li contained in the mixed powder was 10 times the number of moles of the Na-doped precursor. The Na-doped precursor and the mixed powder were mixed, and ion exchange was carried out in air at 280°C for 1 hour. After the ion exchange, water was added to dissolve the salt, and the mixture was washed with water to obtain a layer. O3 and layer O2 Positive electrode active material 1 (Li 0.82 Mn 0.50 Ni 0.20 Co 0.30 O2) was obtained.

[0045] [Solid-state battery manufacturing] (preparation process) -Preparation of the positive electrode layer- 85 g of positive electrode active material 1 (powdered by ball milling) and 10 g of carbon black (conductive additive) were added to 125 mL of n-methylpyrrolidone solution containing 5 g of polyvinylidene fluoride (PVDF) as a binder, and the mixture was kneaded until uniformly mixed to prepare a slurry. This slurry was applied to a 15 μm thick Al positive electrode current collector as a substrate in a weight ratio of 6 mg / cm. 2 The electrode was then pressed to a thickness of 45 μm and a density of 2.4 g / cm. 3Finally, this electrode was cut into a piece having a diameter of 16 mm to obtain a positive electrode having a positive electrode layer and a positive electrode current collector.

[0046] -Preparation of the negative electrode layer- The Li foil was cut to a diameter of 19 mm to obtain a negative electrode layer.

[0047] -Preparing the separator- A porous PP sheet was prepared as a separator.

[0048] (Lamination process) A positive electrode, a separator, and a negative electrode layer were stacked in this order to obtain a laminate. The positive electrode was stacked so that the positive electrode layer faced the separator. The laminate and a nonaqueous electrolyte (a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) in a volume ratio of 3:7, with lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L as a supporting electrolyte) were placed in a coin cell to prepare a CR2032 coin cell battery.

[0049] <Comparative Example 1> In the (Na-doped precursor synthesis process), the amount of Na2CO3 added to the intermediate powder is changed to obtain the Na-doped precursor (Na 0.75 Mn 0.5 Ni 0.2 Co 0.3 A positive electrode active material C1 and a CR2032 coin cell battery using the same were produced in the same manner as in Example 1, except that O2 (P63mc) was synthesized. The obtained positive electrode active material had a structure of O2 (P63mc), and the layer O3 and layer O2 The structure did not have an alternating stack of layers.

[0050] <Comparative Example 2> A positive electrode active material C2 and a CR2032 coin cell battery using the same were produced in the same manner as in Example 1, except that in the ion exchange step, LiNO3 and LiI were mixed in a mass ratio of 88:12 to obtain a mixed powder. O3 and layer O2Although the structure has an alternately laminated structure, the specific volume ratio was 0.81.

[0051] <Comparative Example 3> In the (Na-doped precursor synthesis process), Na2CO3 is added to the intermediate powder in a composition ratio of Na 1.00 Mn 0.5 Ni 0.2 Co 0.3 By adding O2, the Na-doped precursor (Na 1.00 Mn 0.5 Ni 0.2 Co 0.3 A positive electrode active material C3 and a CR2032 coin cell battery using the same were produced in the same manner as in Example 1, except that O2) was synthesized. O3 and layer O2 Although the structure has an alternately laminated structure, the specific volume ratio was 0.08.

[0052] <Evaluation> (Layer structure, specific volume ratio and specific strength ratio) The positive electrode active material obtained in each example was layered. O3 and layers O2 The above-mentioned "layer" indicates whether or not the layers are alternately stacked. O3 and layer O2 When the crystals are alternately stacked, it is described in Table 1 as "O3 / O2 mixed phase," and when the crystals consist of only at least one type of crystal structure selected from the group consisting of the O2 type structure, the T#2 type structure, and the O6 type structure, it is described in Table 1 as "O2 single phase." The specific volume ratio of the positive electrode active material obtained in each example was measured according to the above-mentioned "Method for calculating specific volume ratio." The results are shown in Table 1. The specific intensity ratio of the positive electrode active material obtained in each example was measured according to the above-mentioned "Method for measuring specific intensity ratio." The results are shown in Table 1.

[0053] (Initial discharge capacity) A charge-discharge test was carried out using a galvanostat under the conditions of a current of 0.1 C, a charge cut-off voltage of 4.8 V, and a discharge cut-off voltage of 2.0 V. Starting with charging, after the first charge was completed, the amount of current required for discharging down to 2.0 V was calculated, and the initial discharge capacity was calculated by dividing this by the weight of the active material used in the measurement.

[0054] (Discharge capacity at 5C) A charge-discharge test was carried out using a galvanostat under the conditions of a current of 5 C, a charge cut-off voltage of 4.8 V, and a discharge cut-off voltage of 2.0 V. Starting with charging, after the first charge was completed, the amount of current required for discharging down to 2.0 V was calculated, and the discharge capacity at 5 C was calculated by dividing this by the weight of the active material used in the measurement.

[0055] (Capacity retention rate after 50 cycles) A charge-discharge test was carried out under the same conditions as for the initial discharge capacity, and the first discharge capacity and the 50th discharge capacity were calculated. The 50th discharge capacity was divided by the first discharge capacity to obtain the capacity retention rate after 50 cycles.

[0056] [Table 1]

[0057] From the above results, it can be seen that the positive electrode active material of this example is a positive electrode active material that can provide a battery having excellent rapid charge and discharge performance and a large discharge capacity in a region including a high potential region.

Claims

1. Layer having an O3-type crystal structure Ｏ３ and a layer having at least one crystal structure selected from the group consisting of an O2 type structure, a T#2 type structure, and an O6 type structure. Ｏ２ and are alternately stacked, Ｏ３ and the layer Ｏ２ the total volume of the layer Ｏ２ The volume of is 0.1 or more and 0.6 or less, A positive electrode active material in which the average value of the intensities at all midpoints between two adjacent peaks is 0.05 or less relative to the average value of the maximum intensities of all peaks in an intensity profile obtained by integrating each pixel value in a direction perpendicular to the c-axis in a high-angle annular dark-field scanning transmission electron microscope image in which the electron beam incidence direction is <1-10>.

2. A solid-state battery comprising the positive electrode active material described in claim 1.

3. A method for producing a positive electrode active material according to claim 1, comprising: A method for producing a positive electrode active material, comprising a step of ion-exchanging Na contained in a compound represented by the following formula 2 with Li: Formula 2: Na ｃ Mn ｘ－ｐ Ni ｙ－ｑ Co ｚ－ｒ M ｐ＋ｑ＋ｒ O ２ (In the above formula 2, c, x, y, z, p, q, and r are numbers that satisfy 0.82≦c, x+y+z=1, and 0≦p+q+r≦0.20, M represents a metal element selected from the group consisting of Li, B, Mg, Al, K, Ca, Ti, Cr, Ga, Zr, Nb, Mo, and W.

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