Electrode active materials and batteries

Abstract

This disclosure provides an electrode active material having an O3-type structure, which possesses high capacity and high Coulomb efficiency. [Solution] The electrode active material of this disclosure comprises a Na-containing transition metal oxide. The Na-containing transition metal oxide has an O3-type structure. The Na-containing transition metal oxide comprises Na, Ni, Mn, and O as constituent elements. The X-ray diffraction pattern of the Na-containing transition metal oxide is 0.476 003 / I 104 <0.554(where I 003 This is the diffraction peak intensity of the (003) plane in the aforementioned X-ray diffraction pattern, and I 104 (where is the diffraction peak intensity of the (10⁴) plane in the aforementioned X-ray diffraction pattern.)​

Description

Technical Field

[0001] This application discloses an electrode active material and a battery.

Background Art

[0002] Patent Document 1, Non-Patent Documents 1 and 2 disclose a Na-containing transition metal oxide having an O3-type structure and containing Na, Ni, Mn, and O as constituent elements. The Na-containing transition metal oxide is useful, for example, as an electrode active material of a sodium ion battery.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] An electrode active material containing a Na-containing transition metal oxide having an O3-type structure has room for improvement in terms of capacity and Coulomb efficiency.

Means for Solving the Problems

[0006] As means for solving the above problems, this application discloses the following multiple aspects. <Aspect 1> An electrode active material, comprising a Na-containing transition metal oxide, The Na-containing transition metal oxide has an O3-type structure, The Na-containing transition metal oxide comprises Na, Ni, Mn, and O as constituent elements. The X-ray diffraction pattern of the Na-containing transition metal oxide is related to the following relationship (1): 0.476 003 / I 104 <0.554 …(1) I 003 :Diffraction peak intensity of the (003) plane in the above X-ray diffraction pattern I 104 :Diffraction peak intensity of the (104) plane in the above X-ray diffraction pattern Satisfying Electrode active material. <Aspect 2> An electrode active material according to embodiment 1, The X-ray diffraction pattern of the Na-containing transition metal oxide is as follows (2): 0.492≦I 003 / I 104 ≤0.513 …(2) Satisfying Electrode active material. <Aspect 3> An electrode active material according to embodiment 1 or 2, The Na-containing transition metal oxide contains Fe as a constituent element. Electrode active material. <Aspect 4> A battery comprising a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer includes an electrode active material according to any of embodiments 1 to 3. battery. [Effects of the Invention]

[0007] The electrode active material of this disclosure has high capacity and high Coulomb efficiency. [Brief explanation of the drawing]

[0008] [Figure 1A] This is a schematic diagram illustrating the ionic conductivity of electrode active materials. [Figure 1B] ​It is a schematic diagram for explaining the ionic conductivity in the electrode active material. [Figure 2] An example of a method for manufacturing an electrode active material is shown. [Figure 3] An example of the configuration of a battery is schematically shown. [Figure 4] The X-ray diffraction pattern of a Na-containing transition metal oxide having an O3-type structure is shown.

Mode for Carrying Out the Invention

[0009] Hereinafter, an embodiment of the electrode active material and the battery of the present disclosure will be described, but the electrode active material and the battery of the present disclosure are not limited to the embodiments described below.

[0010] 1. Electrode Active Material The electrode active material according to one embodiment contains a Na-containing transition metal oxide. The Na-containing transition metal oxide has an O3-type structure. The Na-containing transition metal oxide contains, as constituent elements, Na, Ni, Mn, and O. The X-ray diffraction pattern of the Na-containing transition metal oxide satisfies the following relationship (1): 0.476 < I 003 / I 104 < 0.554 …(1) I 003 : Diffraction peak intensity of the (003) plane in the X-ray diffraction pattern I 104 : Diffraction peak intensity of the (104) plane in the X-ray diffraction pattern is satisfied.

[0011] 1.1 Crystal Structure The Na-containing transition metal oxide contained in the electrode active material has at least an O3-type structure as a crystal structure. The Na-containing transition metal oxide may have an O3-type structure and a crystal structure other than the O3-type structure. The Na-containing transition metal oxide may have an O3-type structure as the main phase. The Na-containing transition metal oxide may be one in which a crystal structure other than the O3-type structure is not confirmed in the X-ray diffraction pattern.

[0012] Na-containing transition metal oxides having an O3-type structure have a layered structure in which Na ions exist between layers of transition metal elements. To improve the conductivity of Na ions in these Na-containing transition metal oxides, it is considered effective to align the layers of transition metal elements, as shown in Figure 1A, and to reduce the amount of transition metal elements in the Na ion conduction path and the amount of Na in the layers of transition metal elements (so-called cation mixing). As shown in Figure 1B, if the layers of transition metal elements are significantly distorted or collapsed, or if there is a lot of cation mixing, the Na ion conduction path becomes narrower, and the capacity and Coulomb efficiency as an electrode active material decrease.

[0013] In one embodiment, the Na-containing transition metal oxide contained in the electrode active material satisfies the above relationship (1) in the X-ray diffraction pattern of the Na-containing transition metal oxide. In relationship (1), the (003) plane and the (104) plane in the X-ray diffraction pattern both correspond to the crystal planes of the transition metal element layer in the O3 type structure. The peak intensity ratio of these crystal planes I 003 / I 104 When the ratio is greater than 0.476 and less than 0.554, the extent of the octahedral structure constituting the transition metal element layer is considered to be appropriate, and the transition metal element layer is aligned. In other words, as shown in Figure 1A, Na-containing transition metal oxides that satisfy the above relationship (1) have less collapse and distortion of the transition metal element layer and less cation mixing. As a result, a wide Na ion conduction path is secured, and the capacity and Coulomb efficiency as an electrode active material are increased.

[0014] The X-ray diffraction patterns of Na-containing transition metal oxides are shown in the following relationships (1-1) to (1-20): 0.480≦I 003 / I 104 ≤0.550 …(1-1) 0.480≦I 003 / I 104 ≤0.545 …(1-2) 0.480≦I 003 / I 104≦0.540 …(1-3) 0.480≦I 003 / I 104 ≦0.535 …(1-4) 0.480≦I 003 / I 104 ≦0.530 …(1-5) 0.480≦I 003 / I 104 ≦0.525 …(1-6) 0.480≦I 003 / I 104 ≦0.520 …(1-7) 0.480≦I 003 / I 104 ≦0.515 …(1-8) 0.482≦I 003 / I 104 ≦0.550 …(1-9) 0.484≦I 003 / I 104 ≦0.550 …(1-10) 0.486≦I 003 / I 104 ≦0.550 …(1-11) 0.488≦I 003 / I 104 ≦0.550 …(1-12) 0.490≦I 003 / I 104 ≦0.550 …(1-13) 0.482≦I 003 / I 104 ≦0.545 …(1-14) 0.484≦I 003 / I 104 ≦0.540 …(1-15) 0.486≦I 003 / I 104 ≦0.535 …(1-16) 0.488≦I 003 / I 104 ≦0.530 …(1-17) 0.490≦I 003 / I 104 ≦0.525 …(1-18) 0.490≦I 003 / I 104 ≦0.520 …(1-19) 0.490≦I 003 / I 104 ≤0.515 …(1-20) It may satisfy any of the following conditions. In particular, as far as the inventors have confirmed, the X-ray diffraction pattern of Na-containing transition metal oxides is related to the following relationship (2): 0.492≦I 003 / I 104 ≤0.513 …(2) When these conditions are met, capacity and Coulomb efficiency tend to be even higher.

[0015] Furthermore, if the Na-containing transition metal oxide does not contain Fe, the X-ray diffraction pattern of the Na-containing transition metal oxide is as follows: (3-1) or (3-2): 0.490≦I 003 / I 104 <0.510 …(3-1) 0.492≦I 003 / I 104 ≤0.503 …(3-2) It may also satisfy the following conditions.

[0016] Furthermore, if the Na-containing transition metal oxide also contains Fe, the X-ray diffraction pattern of the Na-containing transition metal oxide is as follows: (4-1) or (4-2): 0.510≦I 003 / I 104 <0.520 …(4-1) 0.510≦I 003 / I 104 ≤0.513 …(4-2) It may also satisfy the following conditions.

[0017] In this application, the "X-ray diffraction pattern of Na-containing transition metal oxide" and "diffraction peak intensity" refer to those obtained under the following conditions. Specifically, an X-ray diffraction pattern is obtained from a Na-containing transition metal oxide using an X-ray diffractometer (Rigaku, fully automatic multi-purpose X-ray diffractometer SmartLab) with CuKα as the radiation source, at a tube voltage of 40kV, a tube current of 40mA, a step width of 0.02°, and a scan speed of 4° / min, performing a 2θ / θ scan. In this X-ray diffraction pattern, the X-ray diffraction peak originating from the (003) plane of the O3-type structure typically appears at 16.6°±0.5° (however, this may vary depending on the transition metal composition, Na content, etc.). Also, the X-ray diffraction peak originating from the (104) plane of the O3-type structure typically appears at 41.8°±0.5° (however, this may vary depending on the transition metal composition, Na content, etc.). After subtracting the background values ​​near the peaks from the X-ray diffraction pattern using PDXL analysis software, the intensity of each X-ray diffraction peak is used to determine the above I 003 / I 104 We seek.

[0018] 1.2 Chemical composition The Na-containing transition metal oxide having the above-described O3-type structure contains Na, Ni, Mn, and O as constituent elements. For example, the Na-containing transition metal oxide may contain only Na, Ni, Mn, and O as constituent elements. The molar ratio of Na, Ni, and Mn in the Na-containing transition metal oxide is not particularly limited as long as the O3-type structure is maintained. For example, the molar amount of Na contained in the Na-containing transition metal oxide contained in the electrode active material may be M1, the molar amount of Ni contained in the Na-containing transition metal oxide may be M2, the molar amount of Mn contained in the Na-containing transition metal oxide may be M3, and M1 / (M2+M3) may be between 0.97 and 1.09. When M1 / (M2+M3) is between 0.97 and 1.09, the O3-type structure is easily maintained, and the formation of crystalline phases other than the O3 phase is easily suppressed.

[0019] The Na-containing transition metal oxide having the above-described O3-type structure may contain other elements as constituent elements in addition to Na, Ni, Mn, and O. For example, the Na-containing transition metal oxide may contain Na, Ni, Mn, element M, and O as constituent elements. Here, element M may be at least one selected from Fe, Ti, Zn, Co, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, and Cu. As an example, the Na-containing transition metal oxide may contain Fe as a constituent element along with Na, Ni, Mn, and O.

[0020] The Na-containing transition metal oxide having the above O3-type structure is Na a Ni x Mn y M zIt may have a chemical composition represented by O2 (where 0.97 ≤ a ≤ 1.09, 0 < x < 1.00, 0 < y < 1.00, 0 ≤ z < 1.00, and the element M is at least one selected from Fe, Ti, Zn, Co, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, and Cu). Here, a is 0.97 or more, may be 0.99 or more, or 1.00 or more, and is 1.09 or less, may be 1.07 or less, 1.05 or less, or 1.03 or less. Also, x is more than 0, may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and is less than 1.00, may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.34 or less. Also, y is more than 0, may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and is less than 1.00, may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.34 or less. Also, z is 0 or more, may be 0.10 or more, 0.20 or more, or 0.30 or more, and is less than 1.00, 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, 0.35 or less, or 0.33 or less. x + y + z is not particularly limited as long as the O3-type structure is maintained. x + y + z may be, for example, 0.99 or more and may be 1.01 or less. The composition of O is approximately 2, but is not necessarily exactly 2.0 and is indefinite.

[0021] 1.3 Others As described above, the electrode active material according to one embodiment has high capacity and high Coulomb efficiency by containing the above-mentioned specific Na-containing transition metal oxide. As mentioned above, the Na-containing transition metal oxide has aligned layers of transition metal elements, and as a result of ensuring a wide Na ion conduction path, it is possible that this has led to an improvement in capacity and Coulomb efficiency. The electrode active material according to one embodiment may consist only of the above-mentioned Na-containing transition metal oxide, or it may contain the above-mentioned Na-containing transition metal oxide along with other components (other components). From the viewpoint of further enhancing the above effects, the proportion of other components in the total electrode active material may be small. For example, with the total electrode active material being 100% by mass, the content of the above-mentioned Na-containing transition metal oxide 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. The electrode active material according to one embodiment may be, for example, a positive electrode active material, and more specifically, a positive electrode active material for a sodium-ion battery.

[0022] The electrode active material may be solid particles, hollow particles, or particles with voids. The size of the electrode active material is not particularly limited. For example, the average particle diameter of the electrode active material may be 0.1 μm to 10 μm, 1.0 μm to 8.0 μm, or 2.0 μm to 6.0 μm. In this application, the average particle diameter refers to the particle diameter (D50, median diameter) at 50% of the cumulative value in the volume-based particle size distribution obtained by laser diffraction-scattering.

[0023] 2. Method for manufacturing electrode active material The Na-containing transition metal oxide having the above-described O3-type structure can be produced, for example, by the following method. As shown in Figure 2, the method for producing the Na-containing transition metal oxide having the O3-type structure according to one embodiment is: S1: Obtain a precursor containing Ni and Mn by coprecipitation. S2: Mixing the precursor and the Na source to obtain a mixture, and S3: The above mixture is calcined to obtain a Na-containing transition metal oxide having an O3-type structure. Includes.

[0024] 2.1 Preparation of Precursors In step S1, a precursor containing Ni and Mn is obtained by coprecipitation. Here, it is preferable to obtain a precursor with a low melting point in step S1. For example, the precursor obtained by coprecipitation in step S1 may be a composite hydroxide containing Ni and Mn. By obtaining a precursor with a low melting point (for example, a composite hydroxide containing Ni and Mn) in step S1, the calcination temperature in step S3 described later can be lowered, the layers of transition metal elements in the Na-containing transition metal oxide having an O3-type structure obtained in the end are aligned, and cation mixing is reduced. The precursor may be in various shapes. For example, the precursor may be particulate.

[0025] In S1, for example, a complex hydroxide as a precursor may be obtained by coprecipitation using an ion source capable of forming a precipitate with transition metal ions in an aqueous solution, a Ni compound, and a Mn compound. The "ion source capable of forming a precipitate with transition metal ions in an aqueous solution" may be, for example, sodium hydroxide. The "Ni compound" may be a salt containing Ni, for example, a sulfate. The "Mn compound" may be a salt containing Mn, for example, a sulfate. In S1, for example, a complex hydroxide containing Ni and Mn may be precipitated as a precursor by dropwise adding and mixing a first aqueous solution in which sodium hydroxide is dissolved and a second aqueous solution in which the Ni compound and Mn compound are dissolved. In this case, various sodium compounds may be added as a base, and aqueous ammonia may be added to adjust the basicity. As far as the inventors have confirmed, the state of the precursor changes depending on the pH of the solution in the coprecipitation method, and the physical properties of the Na-containing transition metal oxide obtained at the end (I 003 / I 104) may change. According to the inventor's findings, when the pH of the solution in the coprecipitation method is less than 12.0, the physical properties of the Na-containing transition metal oxide (I 003 / I 104 ) is likely to fall within the specified range.

[0026] In S1, the precursor may contain element M. Element M is at least one selected from Fe, Ti, Zn, Co, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, and Cu. The method for obtaining the precursor containing element M is not particularly limited. As described above, when obtaining the precursor by coprecipitation in S1, for example, a compound of element M can be further dissolved in the second aqueous solution described above, or a third aqueous solution containing a compound of element M can be prepared separately, and each aqueous solution can be added dropwise and mixed to obtain a precursor containing Mn, Ni, and element M. Alternatively, element M may not be added in S1, and element M may be doped in S2 or S3 described later.

[0027] 2.2 Preparation of the mixture In step S2, a mixture is obtained by mixing the precursor obtained in step S1 with the Na source. In this embodiment, it is preferable to use a Na source with a low melting point. For example, the Na source mixed with the precursor in step S1 may have a melting point of 460°C or lower. Examples of such low-melting-point Na sources include sodium hydroxide and molten salts containing Na (a mixture and melting of multiple types of Na salts). By using a Na source with a low melting point in step S2, the calcination temperature in step S3, described later, can be lowered, resulting in aligned layers of transition metal elements in the Na-containing transition metal oxide having an O3-type structure, and reduced cation mixing. The Na source may take various forms. For example, the Na source may be particulate.

[0028] In step S2, for example, the precursor and the Na source are mixed by a mixing means to obtain a mixture. The mixing means are not particularly limited. The precursor and the Na source may be mixed manually using, for example, a mortar and pestle, or mechanically using a mixer.

[0029] In step S2, the mixing ratio of the precursor and the Na source may be adjusted so that the M1 / (M2+M3) of the final Na-containing transition metal oxide is between 0.97 and 1.09, taking into account the Na loss in step S3 described below. Here, M1 is the molar amount of Na in the Na-containing transition metal oxide, M2 is the molar amount of Ni contained in the Na-containing transition metal oxide, and M3 is the molar amount of Mn contained in the Na-containing transition metal oxide. In step S2, if the amount of Na source relative to the precursor is too high, other phases (impurity phases) besides the O3 phase are likely to be formed in the final Na-containing transition metal oxide. Also, in step S2, if the amount of Na source relative to the precursor is too low, it becomes difficult to obtain a sufficient amount of the O3 phase in the final Na-containing transition metal oxide. According to the inventors' findings, when the amount of Na-containing transition metal oxide obtained in the final product is large (for example, 0.05 mol or more), the amount of Na source relative to the precursor is increased, and when the amount of Na-containing transition metal oxide obtained in the final product is small (for example, less than 0.05 mol), the amount of Na source relative to the precursor is decreased, thereby adjusting the M1 / (M2+M3) of the obtained Na-containing transition metal oxide to be between 0.97 and 1.09.

[0030] In S2, the precursor may be mixed with the element M source along with the Na source. For example, in S2, the precursor obtained in S1 may be mixed with the Na source and an element M source containing at least one element M selected from Fe, Ti, Zn, Co, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, and Cu to obtain a mixture. The element M source should preferably have a low melting point, such as a hydroxide or molten salt. The amount of element M source mixed with the precursor should be determined according to the chemical composition of the Na-containing transition metal oxide after calcination.

[0031] 2.3 Calcination of the mixture In S3, the mixture obtained in S2 is calcined to obtain a Na-containing transition metal oxide having an O3-type structure. In S3, for example, the mixture may be pre-calcined before the main calcination. Pre-calcination is optional, and its conditions are not particularly limited.

[0032] The final firing in S3 should be performed at a temperature that yields an O3-type crystal structure, and at a low temperature. As far as the inventors have confirmed, when the final firing temperature is 760°C to 850°C, the layers of transition metal elements are aligned in the Na-containing transition metal oxide having the final O3-type structure, and cation mixing is reduced. If the final Na-containing transition metal oxide having the final O3-type structure contains only Na, Ni, Mn, and O as constituent elements (and does not contain element M such as Fe), the final firing temperature may be, for example, 760°C to 800°C. On the other hand, if the final Na-containing transition metal oxide having the final O3-type structure contains element M (e.g., Fe) in addition to Na, Ni, Mn, and O as constituent elements, the final firing temperature may be, for example, 800°C to 850°C. Furthermore, as far as the inventors have confirmed, the physical properties of the final Na-containing transition metal oxide (I) are affected by the atmosphere of the final firing. 003 / I 104 ) may change. According to the inventors' findings, when the atmosphere of the main firing contains oxygen, the physical properties of the Na-containing transition metal oxide (I 003 / I 104 ) is likely to fall within a predetermined range. In other words, the atmosphere for the main firing may be an oxygen-containing atmosphere such as an air atmosphere or an oxygen atmosphere. The duration of the main firing (holding time at the main firing temperature) is not particularly limited and may be, for example, 12 hours or more and 48 hours or less, or 15 hours or more and 25 hours or less.

[0033] In S3, the pre-firing temperature, the rate of heating up to the main firing temperature, and the rate of cooling down after the main firing are not particularly limited.

[0034] 3.Battery An electrode active material according to one embodiment includes the above-mentioned specific Na-containing transition metal oxide. This electrode active material is suitable, for example, as a positive electrode active material for a battery, and in particular as a positive electrode active material for a sodium-ion battery. Figure 3 schematically shows the configuration of a battery according to one embodiment. As shown in Figure 3, the battery 100 according to one 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 includes the electrode active material according to the above embodiment.

[0035] 3.1 Cathode active material layer The positive electrode active material layer 10 contains at least the electrode active material according to the above embodiment, and may optionally contain an electrolyte, a conductive additive, and a binder. Furthermore, the positive electrode active material layer 10 may also contain various other additives. The respective contents of the active material, electrolyte, conductive additive, and binder in the positive electrode active material layer 10 can be appropriately determined according to the desired battery performance. For example, with the entire positive electrode active material layer 10 (total solid content) as 100% by mass, the active material content may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 100% by mass or less, or 90% by mass or less. The shape of the positive electrode active material layer 10 is not particularly limited, and for example, it may be a sheet-shaped positive electrode active material layer 10 having a substantially flat surface. The thickness of the positive electrode active material layer 10 is not particularly limited, and for example, it may be 0.1 μm or more, 1 μm or more, 2 mm or less, or 1 mm or less.

[0036] 3.1.1 Cathode active material The positive electrode active material is as described above. The positive electrode active material may consist only of the above-mentioned Na-containing transition metal oxide, or it may contain the above-mentioned Na-containing transition metal oxide along with other positive electrode active materials (other positive electrode active materials). From the viewpoint of further enhancing the effects of the technology of this disclosure, the proportion of other positive electrode active materials in the total positive electrode active material may be small. For example, with the total positive electrode active material being 100% by mass, the content of the above-mentioned Na-containing transition metal oxide 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.

[0037] 3.1.2 Electrolytes The electrolyte contained in the positive electrode active material layer 10 may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. Any known solid electrolyte may be used. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes have excellent ionic conductivity and heat resistance. An example of an inorganic solid electrolyte is Na3Zr2PSi2O 12 Oxides such as Na2O-11Al2O3; NaBH4, NaB 10 H 10 NaCB9H 10 NaCB 11 H 12 NaB 12 Cl 12 These include hydrides and borides; Na3PS4, Na3SbS4, Na 2.88 S 0.88 W 0.12Examples include at least one selected from sulfides such as S4 and fluorides such as NaPF6 and NaBF4. The solid electrolyte may be in particulate form, for example. The solid electrolyte may be used alone or in combination of two or more types. The electrolyte solution may contain sodium ions as carrier ions, for example. The electrolyte solution may be aqueous or non-aqueous. The composition of the electrolyte solution may be the same as that known for battery electrolyte solutions. For example, a solution of sodium salt dissolved in a carbonate solvent at a predetermined concentration can be used as the electrolyte solution. Examples of carbonate solvents include fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Examples of sodium salts include NaPF6, NaClO4, NaBF4, NaFSI, NaTFSI, and NaBETI.

[0038] 3.1.3 Conductive additives Examples of conductive additives that may be included in the positive electrode active material layer 10 include carbon materials such as vapor-processed carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic materials such as nickel, aluminum, and stainless steel. The conductive additive may be in the form of parts or fibers, and its size is not particularly limited. One type of conductive additive may be used alone, or two or more types may be used in combination.

[0039] 3.1.4 Binder Examples of binders that may be included in the positive electrode active material layer 10 include butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, and polyimide (PI) binders. A single binder may be used alone, or two or more binders may be used in combination.

[0040] 3.2 Electrolyte layer The electrolyte layer 20 contains at least an electrolyte. If the battery 100 is a solid-state battery (a battery containing a solid electrolyte, which may also contain a liquid electrolyte in part, or an all-solid-state battery that does not contain a liquid electrolyte), the electrolyte layer 20 contains a solid electrolyte and may optionally contain a binder or the like. In this case, the content of the solid electrolyte and the binder or the like in the electrolyte layer 20 is not particularly limited. On the other hand, if the battery 100 is an electrolyte battery, the electrolyte layer 20 contains an electrolyte and may also have a separator or the like to hold the electrolyte and prevent 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, or 2 mm or less or 1 mm or less.

[0041] The electrolyte included in the electrolyte layer 20 may be appropriately selected from among the examples of electrolytes that may be included in the positive electrode active material layer 10 described above. Similarly, the binder that may be included in the electrolyte layer 20 may be appropriately selected from among the examples of binders that may be included in the positive electrode active material layer 10 described above. The electrolyte and binder may each be used individually or in combination of two or more types. The separator may be any separator that is normally used in batteries, such as those made of polyethylene (PE), polypropylene (PP), polyester, and polyamide resins. The separator may have a single-layer structure or a multi-layer structure. Examples of multi-layer separators include a PE / PP two-layer separator, or a PP / PE / PP or PE / PP / PE three-layer separator. The separator may also be made of a nonwoven fabric such as cellulose nonwoven fabric, resin nonwoven fabric, or glass fiber nonwoven fabric.

[0042] 3.3 Negative electrode active material layer The negative electrode active material layer 30 contains at least negative electrode active material, and may optionally also contain an electrolyte, a conductive additive, and a binder. Furthermore, the negative electrode active material layer 30 may also contain various other additives. The respective content of the negative electrode active material, electrolyte, conductive additive, and binder in the negative electrode active material layer 30 can be appropriately determined according to the desired battery performance. For example, with the entire negative electrode active material layer 30 (total solid content) as 100% by mass, 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 100% by mass or less, or 90% by mass or less. The shape of the negative electrode active material layer 30 is not particularly limited, and for example, it may be a sheet-like negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer 30 is not particularly limited, and for example, it may be 0.1 μm or more, 1 μm or more, 2 mm or less, or 1 mm or less.

[0043] As the negative electrode active material, various materials can be used whose charge-discharge potential (potential for intercalating and releasing charge compensation ions) is lower than that of the positive electrode active material. The negative electrode active material may be an inorganic negative electrode active material such as metallic sodium, an organic negative electrode active material, or a combination thereof. The negative electrode active material may be used alone or in combination of two or more types. The shape of the negative electrode active material may be any shape common to negative electrode active materials in batteries. For example, the negative electrode active material may be particulate. The negative electrode active material particles may be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle diameter (D50) of the negative electrode active material particles may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, or 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 sodium foil. In other words, the negative electrode active material layer 30 may consist of a sheet of negative electrode active material.

[0044] The electrolyte that may be included in the negative electrode active material layer 30 is the solid electrolyte, electrolyte solution, or a combination thereof as described above. The conductive additive that may be included in the negative electrode active material layer 30 is the carbon material or metal material described above as described above. The binder that may be included in the negative electrode active material layer 30 can be appropriately selected from, for example, the binders exemplified as those that may be included in the positive electrode active material layer 10 described above. The electrolyte and binder may each be used individually or in combination of two or more types.

[0045] 3.4 Positive electrode current collector As shown in Figure 3, the battery 100 may include a positive electrode current collector 40 that contacts the positive electrode active material layer 10. The positive electrode current collector 40 can be any of the types commonly used for positive electrode current collectors in batteries. The positive electrode current collector 40 may be in the form of foil, plate, mesh, perforated metal, or foam. The positive electrode current collector 40 may be composed of metal foil or metal mesh, or of a combination of resin and conductive components. Metal foil is particularly advantageous in terms of handling. The positive electrode current collector 40 may consist of multiple foils. Examples of metals that make up the positive electrode current collector 40 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. The positive electrode current collector 40 may have some kind of coating layer on its surface for the purpose of adjusting resistance, etc. The positive electrode current collector 40 may also be a metal foil or a substrate on which the above metals are plated or deposited. Furthermore, if the positive electrode current collector 40 consists of multiple metal foils, there may be some layer between the multiple metal foils. The thickness of the positive electrode current collector 40 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

[0046] 3.5 Negative electrode current collector As shown in Figure 3, the battery 100 may include a negative electrode current collector 50 that contacts the negative electrode active material layer 30. Any of the commonly used negative electrode current collectors for batteries can be used for the negative electrode current collector 50. Furthermore, the negative electrode current collector 50 may be in the form of foil, plate, mesh, perforated metal, or foam. The negative electrode current collector 50 may be a metal foil or metal mesh, or a carbon sheet, or a combination of resin and a conductive component. Metal foil, in particular, offers excellent handling. The negative electrode current collector 50 may consist of multiple foils or sheets. Examples of metals constituting the negative electrode current collector 50 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The negative electrode current collector 50 may have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the negative electrode current collector 50 may be a metal foil or a substrate on which the above-mentioned metal is plated or deposited. Also, if the negative electrode current collector 50 consists of multiple metal foils, there may be some layer between the multiple metal foils. The thickness of the negative electrode current collector 50 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

[0047] 3.6 Other Matters In addition to the above configuration, the battery 100 may also have obvious components for a battery, such as tabs and terminals. The battery 100 may have each of the above components housed inside an outer casing. Any known battery casing can be used. Furthermore, multiple batteries 100 may be electrically connected and stacked as desired to form a battery pack. In this case, the battery pack may be housed inside a known battery case. The battery 100 may also have other obvious components such as necessary terminals. Examples of the shape of the battery 100 include coin type, laminate type, cylindrical type, and prismatic type. As described above, the battery 100 may be a sodium-ion battery. The battery 100 may also be a secondary battery. In one embodiment, the battery 100 is a sodium-ion secondary battery.

[0048] 4. Battery manufacturing method The battery 100 can be manufactured by applying known methods, except for using the specific electrode active material described above. For example, it can be manufactured as follows. However, the manufacturing method of the battery 100 is not limited to the following method, and each layer may be formed by, for example, dry molding. (1) A slurry for the positive electrode layer is obtained by dispersing the positive electrode active material and other materials constituting the positive electrode active material layer in a solvent. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The slurry for the positive electrode layer is applied to the surface of the 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, which serves as the positive electrode. (2) A slurry for the negative electrode layer is obtained by dispersing the negative electrode active material and other materials constituting the negative electrode active material layer in a solvent. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The slurry for the negative electrode layer 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, which serves as the negative electrode. Alternatively, a sheet or foil of metal active material may be used as the negative electrode active material layer. (3) The layers are stacked so that an electrolyte layer (solid electrolyte layer or separator) is sandwiched between the negative electrode and the positive electrode, and a laminate is obtained having the negative electrode current collector, negative electrode active material layer, electrolyte layer, positive electrode active material layer and positive electrode current collector in this order. Other members such as terminals are attached to the laminate as needed. (4) The laminate is housed in a battery case, and in the case of an electrolyte battery, the battery case is filled with electrolyte, the laminate is immersed in the electrolyte, and the laminate is sealed inside the battery case to form a secondary battery. In the case of an electrolyte battery, the negative electrode active material layer, separator and positive electrode active material layer may be made to contain the electrolyte at the stage of (3) above.

[0049] 5. Methods for increasing battery capacity and Coulomb efficiency The technology of this disclosure also has aspects as a method for increasing the capacity and Coulomb efficiency of a battery. That is, the method for increasing the capacity and Coulomb efficiency of a battery of this disclosure is characterized by using the electrode active material of this disclosure in the positive electrode active material layer of the battery.

[0050] 6. Vehicles As described above, the electrode active material of this disclosure has high capacity and high Coulomb efficiency and is suitable as a positive electrode active material for a battery. A battery using such an active material with high capacity and high Coulomb efficiency can be suitably used in at least one type of vehicle selected from, for example, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). In other words, the technology of this disclosure also has an aspect as a vehicle having a battery, wherein the battery has a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, and the positive electrode active material layer contains the electrode active material of this disclosure. [Examples]

[0051] As described above, one embodiment of the electrode active material, etc., has been explained, but the technology of this disclosure can be modified in various ways other than the above embodiment without departing from its gist. The technology of this disclosure will be described in more detail below with reference to examples, but the technology of this disclosure is not limited to the following examples.

[0052] 1. Manufacturing of electrode active material 1.1 Example 1-1 1.1.1 Preparation of Precursors An 8 mol / L sodium hydroxide aqueous solution was added to a reaction vessel set to 40°C, maintaining the pH of the solution at 11.5. A transition metal aqueous solution, a mixture of nickel sulfate aqueous solution and manganese sulfate aqueous solution, and a 28% by mass aqueous ammonia solution were added dropwise to synthesize a complex hydroxide precursor. The synthesized precursor was separated into filtrate and precursor by suction filtration. The precursor was left to stand overnight in a vacuum dryer before being collected.

[0053] 1.1.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.1 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.05.

[0054] 1.1.3 Calcination of the mixture The above mixture was placed in an electric furnace and pre-fired under an atmospheric atmosphere, followed by main firing at 800°C for 20 hours under the same atmospheric atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0055] 1.2 Examples 1-2 1.2.1 Preparation of Precursors The precursor was prepared under the same conditions as in Example 1-1.

[0056] 1.2.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.1 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.02.

[0057] 1.2.3 Firing of the mixture The above mixture was placed in an electric furnace and pre-fired under an atmospheric atmosphere, followed by main firing at 800°C for 20 hours under the same atmospheric atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0058] 1.3 Examples 1-3 1.3.1 Preparation of Precursors The precursor was prepared under the same conditions as in Example 1-1.

[0059] 1.3.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.03 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.05.

[0060] 1.3.3 Firing of the mixture The above mixture was placed in a tubular furnace and pre-fired under an oxygen atmosphere, followed by main firing at 780°C for 20 hours under the same oxygen atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0061] 1.4 Examples 1-4 1.4.1 Preparation of Precursors The precursor was prepared under the same conditions as in Example 1-1.

[0062] 1.4.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.03 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.05.

[0063] 1.4.3 Calcination of the mixture The above mixture was placed in an electric furnace and pre-fired under an atmospheric atmosphere, followed by main firing at 800°C for 20 hours under the same atmospheric atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0064] 1.5 Comparative Example 1-1 1.5.1 Preparation of Precursors An 8 mol / L sodium hydroxide aqueous solution was added to a reaction vessel set at 25°C, maintaining the pH of the solution at 12.0. A transition metal aqueous solution, a mixture of nickel sulfate aqueous solution and manganese sulfate aqueous solution, and a 28% by mass aqueous ammonia solution were added dropwise to synthesize a complex hydroxide precursor. The synthesized precursor was separated into filtrate and precursor by suction filtration. The precursor was left to stand overnight in a vacuum dryer before being collected.

[0065] 1.5.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.03 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.05.

[0066] 1.5.3 Firing of the mixture The above mixture was placed in an electric furnace and pre-fired under an atmospheric atmosphere, followed by main firing at 800°C for 20 hours under the same atmospheric atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0067] 1.6 Comparative Example 1-2 1.6.1 Preparation of Precursors An 8 mol / L sodium hydroxide aqueous solution was added to a reaction vessel set to 40°C, maintaining the pH of the solution at 12.5. A transition metal aqueous solution, a mixture of nickel sulfate aqueous solution and manganese sulfate aqueous solution, and a 28% by mass aqueous ammonia solution were added dropwise to synthesize a complex hydroxide precursor. The synthesized precursor was separated into filtrate and precursor by suction filtration. The precursor was left to stand overnight in a vacuum dryer before being collected.

[0068] 1.6.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.06 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.05.

[0069] 1.6.3 Firing of the mixture The above mixture was placed in an electric furnace and pre-fired under an atmospheric atmosphere, followed by main firing at 800°C for 20 hours under the same atmospheric atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0070] 1.7 Comparative Examples 1-3 1.7.1 Preparation of Precursors The precursor was prepared under the same conditions as in Comparative Example 1-1.

[0071] 1.7.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.03 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.05.

[0072] 1.7.3 Calcination of the mixture The above mixture was placed in a tubular furnace and pre-calcined under an argon atmosphere, followed by main calcination at 750°C for 20 hours under the same argon atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0073] 1.8 Comparative Examples 1-4 1.8.1 Preparation of Precursors The precursor was prepared under the same conditions as in Comparative Example 1-1.

[0074] 1.8.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.03 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.05.

[0075] 1.8.3 Firing of the mixture The above mixture was placed in a tubular furnace and pre-calcined under an argon atmosphere, followed by main calcination at 800°C for 20 hours under the same argon atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0076] 1.9 Example 2-1 1.9.1 Preparation of Precursors An 8 mol / L sodium hydroxide aqueous solution was added to a reaction vessel set to 40°C, maintaining the pH of the solution at 11.5. A transition metal aqueous solution, a mixture of nickel sulfate aqueous solution, manganese sulfate aqueous solution, and iron sulfate aqueous solution, along with a 28% by mass ammonia aqueous solution, was added dropwise to synthesize a complex hydroxide precursor. The synthesized precursor was separated into filtrate and precursor by suction filtration. The precursor was left to stand overnight in a vacuum dryer before being collected.

[0077] 1.9.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.03 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.05.

[0078] 1.9.3 Firing of the mixture The above mixture was placed in a tubular furnace and pre-fired under an oxygen atmosphere, followed by main firing at 800°C for 20 hours under the same oxygen atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0079] 1.10 Example 2-2 1.10.1 Preparation of Precursors An 8 mol / L sodium hydroxide aqueous solution was added to a reaction vessel set to 40°C, maintaining the pH of the solution in the vessel at 11.1. A transition metal aqueous solution, a mixture of nickel sulfate aqueous solution, manganese sulfate aqueous solution, and iron sulfate aqueous solution, along with a 28% by mass aqueous ammonia solution, was added dropwise to synthesize a complex hydroxide precursor. The synthesized precursor was separated into filtrate and precursor by suction filtration. The precursor was left to stand overnight in a vacuum dryer before being collected.

[0080] 1.10.2 Preparation of the mixture A mixture was obtained by mixing the composite hydroxide, which served as the precursor, with sodium hydroxide, which served as the Na source. Here, the composite hydroxide and sodium hydroxide were weighed so that the final amount of sodium-containing transition metal oxide obtained was 0.1 mol. The molar amounts of Na M1, Ni M2, and Mn M3 in the mixture were set to M1 / (M2+M3) = 1.02.

[0081] 1.10.3 Firing of the mixture The above mixture was placed in an electric furnace and pre-fired under an atmospheric atmosphere, followed by main firing at 850°C for 20 hours under the same atmospheric atmosphere. After that, it was cooled to room temperature and crushed to obtain a Na-containing transition metal oxide for evaluation.

[0082] 1.11 Examples 2-3 1.11.1 Preparation of Precursors The precursor was prepared under the same conditions as in Example 2-2.

[0083] 1.11.2 Preparation of the mixture The composite hydroxide as the above-mentioned precursor and sodium hydroxide as the Na source were mixed to obtain a mixture. Here, each of the composite hydroxide and sodium hydroxide was weighed so that the amount of the finally obtained sodium-containing transition metal oxide would be 0.1 mol. The molar amount M1 of Na, the molar amount M2 of Ni, and the molar amount M3 of Mn in the mixture were made such that M1 / (M2 + M3) = 1.05.

[0084] 1.11.3 Firing of the mixture The above-mentioned mixture was put into an electric furnace, pre-fired in an air atmosphere, and then main-fired at a temperature of 800 °C for 20 hours in the same air atmosphere. Thereafter, it was cooled to room temperature and subjected to a crushing treatment to obtain a sodium-containing transition metal oxide for evaluation.

[0085] 2. Confirmation of the chemical composition and crystal structure of the electrode active material The chemical composition of each of the sodium-containing transition metal oxides obtained as described above was confirmed. Each of the sodium-containing transition metal oxides had the composition shown in Table 1 below. Also, when X-ray diffraction patterns were obtained for each of the sodium-containing transition metal oxides, all of them had an O3-type structure. From each of the X-ray diffraction patterns, the peak intensity ratio I 003 / I 104 (where I 003 is the diffraction peak intensity of the (003) plane in the X-ray diffraction pattern, and I 104 is the diffraction peak intensity of the (104) plane in the X-ray diffraction pattern) was determined, and it was as shown in Table 1 below. Incidentally, the acquisition conditions of the X-ray diffraction pattern are as described in the embodiment. For reference, FIG. 4 shows the X-ray diffraction pattern of the sodium-containing transition metal oxide having an O3-type structure.

[0086]

Table 1

[0087] 3. Fabrication of the battery [[ID=Each electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder were mixed in a mass ratio of active material:conductive additive:binder = 85:10:5 to obtain an electrode composite. The paste containing the obtained electrode composite was coated onto aluminum foil and air-dried at 80°C for 30 minutes to obtain a laminate. The obtained laminate was punched out to a diameter of φ16 mm, pressed, and vacuum-dried at 120°C to obtain electrodes for evaluation. A 2032 type coin cell was fabricated using the obtained electrodes and Na metal. A 1M NaPF6 non-electrolyte solution was used as the electrolyte. A mixed solvent of EC, DMC, and EMC was used as the solvent for the electrolyte.

[0088] 4. Charge / Discharge Test The obtained coin cells were subjected to charge-discharge tests at 25°C in the range of 4.2V to 2.0V at Na potential, and the initial charge capacity, initial discharge capacity, and reversibility (Coulomb efficiency) were determined. The C rate in the charge-discharge tests was set to 0.3C.

[0089] 5. Evaluation Results Table 2 below shows the results of the charge and discharge tests.

[0090] [Table 2]

[0091] As is clear from the results shown in Table 2, electrode active materials containing Na-containing transition metal oxides that satisfy the following requirements (A) to (C) can be said to have high capacity and high Coulomb efficiency.

[0092] (A) The Na-containing transition metal oxide has an O3-type structure. (B) The Na-containing transition metal oxide contains Na, Ni, Mn, and O as constituent elements. (C) The X-ray diffraction pattern of a Na-containing transition metal oxide satisfies the following relationship (1). 0.476 003 / I 104 <0.554 …(1)​ I 003 :Diffraction peak intensity of the (003) plane in the above X-ray diffraction pattern I 104 :Diffraction peak intensity of the (104) plane in the above X-ray diffraction pattern

[0093] In the above examples, electrode active materials consisting of Na, Ni, Mn, and O, or electrode active materials consisting of Na, Ni, Mn, Fe, and O, were given as examples, but the constituent elements of the electrode active material are not limited to these. Even if any other doping elements are included, it is believed that high capacity and high Coulomb efficiency can be ensured as long as the above requirements (B) and (C) are met. [Explanation of symbols]

[0094] 100 batteries 10 Cathode active material layer 20 Electrolyte layer 30 Negative electrode active material layer 40 Positive electrode current collector 50 Negative electrode current collector

Claims

1. An electrode active material comprising a Na-containing transition metal oxide, The Na-containing transition metal oxide has an O3-type structure, The Na-containing transition metal oxide comprises Na, Ni, Mn, and O as constituent elements. The X-ray diffraction pattern of the Na-containing transition metal oxide is as follows: (1) 0.476<I ００３ / I １０４ <0.554 …(1) I ００３ : Diffraction peak intensity of the (003) plane in the above X-ray diffraction pattern I １０４ : Diffraction peak intensity of the (104) plane in the above X-ray diffraction pattern Satisfying Electrode active material.

2. The electrode active material according to claim 1, The X-ray diffraction pattern of the Na-containing transition metal oxide is as follows (2): 0.492≦I ００３ / I １０４ ≦0.513 …(2) Satisfying Electrode active material.

3. The electrode active material according to claim 1, The Na-containing transition metal oxide contains Fe as a constituent element. Electrode active material.

4. A battery comprising a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer comprises the electrode active material described in any one of claims 1 to 3. battery.

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