Composite active materials and batteries

Abstract

A composite active material having high capacity and low resistance is disclosed. [Solution] The composite active material of this disclosure comprises active material particles and a coating layer. The active material particles have an O2-type structure. The active material particles contain, as constituent elements, Li, at least one transition metal element from Mn, Ni, and Co, and O. The coating layer covers at least a portion of the surface of the active material particles. The coating layer is a layer of oxide containing Li as a constituent element. The particle size (D50) of the composite active material is less than 5.90 μm.

Description

[Technical Field]

[0001] This application discloses a composite active material and a battery. [Background technology]

[0002] Patent Document 1 discloses an electrode active material having an O2-type structure (O: Octahedral). The electrode active material having an O2-type structure is obtained by ion-exchanging at least a portion of the Na in a Na-containing oxide having a P2-type structure with Li. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-085829 [Overview of the project] [Problems that the invention aims to solve]

[0004] Electrode active materials with an O2-type structure have room for improvement in terms of capacitance and resistance. [Means for solving the problem]

[0005] This application discloses several embodiments as means for solving the above-mentioned problems. <Aspect 1> A composite active material comprising active material particles and a coating layer, The active material particles have an O2-type structure, The active material particles consist of the following constituent elements: Li and At least one transition metal element from Mn, Ni, and Co, O and, Includes, The coating layer covers at least a portion of the surface of the active material particles, The aforementioned coating layer is a layer of oxide containing Li as a constituent element. The particle diameter (D50) of the composite active material is less than 5.90 μm. Composite active material. <Aspect 2> The composite active material according to Aspect 1, wherein the coating layer contains Li, B, P, and O as constituent elements. Composite active material. <Aspect 3> The composite active material according to Aspect 1 or 2, wherein the particle diameter (D50) of the composite active material is 5.42 μm or less. Composite active material. <Aspect 4> <00所00067>The composite active material according to any one of Aspects 1 to 3, wherein the active material particles contain Li, Mn, Ni, Co, and O as constituent elements. Composite active material. <Aspect 5> A battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, wherein the positive electrode active material layer contains the composite active material according to any one of Aspects 1 to 4. Battery.

Advantages of the Invention

[0006] The composite active material of the present disclosure has high capacity and low resistance.

Brief Description of the Drawings

[0007] [Figure 1] An example of the internal (cross-sectional) structure of the composite active material is schematically shown. [Figure 2] It is a schematic diagram for explaining a method of specifying the aspect ratio of the cross-sectional shape of the active material particles. [Figure 3] An example of the appearance of the composite active material is shown. [Figure 4] An example of the flow of the manufacturing method of the composite active material is shown. [Figure 5] An example of the configuration of the battery is schematically shown. [Figure 6] It is a SEM image of the composite active material according to Example 1. <000009�> [Figure 7] SEM image of the composite active material according to Example 2. [Figure 8] SEM image of the composite active material according to Comparative Example 1. [Figure 9] SEM image of the composite active material according to Comparative Example 2.

Mode for Carrying Out the Invention

[0008] Hereinafter, an embodiment of the composite active material and the battery of the present disclosure will be described, but the composite active material and the battery of the present disclosure are not limited to the embodiments described below.

[0009] 1. Composite active material As shown in FIG. 1, the composite active material 1 according to an embodiment has active material particles 1a and a coating layer 1b. The active material particles 1a have an O2-type structure. The active material particles 1a contain, as constituent elements, Li, at least one transition metal element among Mn, Ni, and Co, and O. The coating layer 1b covers at least a part of the surface of the active material particles 1a. The coating layer 1b is a layer of an oxide containing Li as a constituent element. The particle diameter (D50) of the composite active material 1 is 5.90 μm or less.

[0010] 1.1 Active material particles The active material particles 1a have an O2-type structure. Also, the active material particles 1a contain, as constituent elements, Li, at least one transition metal element among Mn, Ni, and Co, and O.

[0011] 1.1.1 Crystal structure of the active material particles The active material particle 1a has an O2-type structure (belonging to space group P63mc). In one embodiment, the active material particle 1a may have an O2-type structure as well as a crystal structure other than the O2-type structure. Examples of crystal structures other than the O2-type structure include the T♯2-type structure (belonging to space group Cmca) and the O6-type structure (belonging to space group R-3m, with a c-axis length of 2.5 nm to 3.5 nm, typically 2.9 nm to 3.0 nm, and different from the O3-type structure which also belongs to space group R-3m), which are formed when Li is removed or inserted from the O2-type structure. In one embodiment, the active material particle 1a may have an O2-type structure as its main phase, or it may have a crystal structure other than the O2-type structure as its main phase. In one embodiment, the crystal structure of the main phase of the active material particle 1a may change depending on its charge and discharge state. In one embodiment, the active material particle 1a may be a single crystal consisting of one crystallite, or a polycrystal having multiple crystallites.

[0012] 1.1.2 Chemical composition of active material particles The active material particles 1a contain Li, at least one transition metal element from Mn, Ni, and Co, and O as constituent elements. The active material particles 1a tend to exhibit higher performance, particularly when they contain Li, Mn, one or both of Ni and Co, and O as constituent elements, and especially when they contain Li, Mn, Ni, Co, and O. The active material particles 1a may also contain elements other than Li, Mn, Ni, Co, and O.

[0013] The active material particle 1a is Li a Na b Mn x-p Ni y-q Co z-r M p+q+rIt may have a chemical composition represented by O2 (where 0 < a ≤ 1.40, 0 ≤ b ≤ 0.20, x + y + z = 1, and 0 ≤ p + q + r < 0.17, and the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W). When the active material part 1ax has such a chemical composition, high performance is easily ensured and the O2-type structure is easily maintained. In the above chemical composition, a may be greater than 0, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and is at most 1.40, and may be 1.30 or less, 1.20 or less, 1.10 or less, 1.00 or less, 0.90 or less, 0.80 or less, or 0.70 or less. In the above chemical composition, b is 0 or more, and may be 0.01 or more, 0.02 or more, or 0.03 or more, and is at most 0.20, and may be 0.15 or less, or 0.10 or less. Also, x is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, or 0.40 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less. Also, y is 0 or more, and may be 0.10 or more, or 0.20 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. Also, z is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, or 0.40 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less. The element M has little contribution to charge and discharge. In this regard, in the above chemical composition, since p + q + r is less than 0.17, a high charge-discharge capacity is easily ensured. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, when the element M is included, the O2-type structure is easily stabilized.In the above chemical composition, p+q+r is 0 or greater, and may be 0.01 or greater, 0.02 or greater, 0.03 or greater, 0.04 or greater, 0.05 or greater, 0.06 or greater, 0.07 or greater, 0.08 or greater, 0.09 or greater, or 0.10 or greater. The composition of O is approximately 2, but is not fixed.

[0014] 1.1.3 Shape of active material particles The shape of the active material particles 1a is not particularly limited. The active material particles 1a may be, for example, plate-shaped. As described later, the active material particles 1a can be obtained by substituting Na with Li in a Na-containing oxide having a P2-type structure. Here, the P2-type structure is hexagonal, has a large diffusion coefficient for Na ions, and is prone to crystal growth in a specific direction. In particular, when at least one of Mn, Ni, and Co is included as a transition metal element constituting the P2-type structure, it is prone to plate-shaped crystal growth in a specific direction. Therefore, Na-containing oxides having a P2-type structure tend to become plate-shaped particles with a large aspect ratio, in which the crystal growth direction is biased in a specific direction. The active material particles 1a according to one embodiment may be obtained from such plate-shaped Na-containing oxide particles.

[0015] In this application, the term "plate-shaped" for the active material particle 1a means that the cross-sectional shape of the active material particle 1a has an aspect ratio of 1.5 or greater. Here, the "aspect ratio" of the cross-sectional shape of the active material particle 1a is measured as follows: (1) Multiple composite active materials 1 are press-molded together with resin and metal powder to obtain a sample for cross-sectional observation (or, an electrode containing the composite active material 1 may be used as the sample for cross-sectional observation). The sample is then cross-sectionally processed using a cross-sectional preparation device (Hitachi ion milling device: IM4000II). The cross-section should be aligned with the direction of pressure applied during press molding. (2) The sample that has undergone cross-sectional processing is mounted on an FE-SEM to confirm the cross-section. (3) An elemental mapping analysis (oxygen, sulfur) of the cross-section of composite active material 1 is performed using EDX manufactured by Oxford Instruments, and elemental mappings of each element are obtained using EDX analysis software (AZtecLive) manufactured by Oxford Instruments. (4) The cross-sectional shape of the active material particle 1a is determined from the obtained O Kα1 mapping region, etc. (5) In the identified cross-sectional shape, the largest Ferret diameter is determined and considered to be the "major axis" of the active material particle 1a. For example, as shown in Figure 2, the major axis D in the cross-sectional shape of the active material particle 1a L Identify. (6) Among the line segments connecting two points on the outer circumference of the identified cross-sectional shape, the longest line segment perpendicular to the "major axis" identified in (5) is considered to be the "minor axis" of the active material particle 1a. For example, as shown in Figure 2, the minor axis D in the cross-sectional shape of the active material particle 1a S Identify. (7) The ratio of the specified "major axis" to the "minor axis" (major axis / minor axis) is considered to be the "aspect ratio" of the active material particle 1a in a predetermined cross-sectional shape, and if the "aspect ratio" is 1.5 or greater, the active material particle 1a is considered to be "plate-shaped". However, there is no particular upper limit to the aspect ratio. The aspect ratio may be, for example, 10 or less.

[0016] The particle size (D50) of the active material particles 1a may be, for example, 0.10 μm or more, 1.00 μm or more, 1.50 μm or more, or 2.00 μm or more, or 5.00 μm or less, 4.00 μm or less, or 3.50 μm or less. In this application, the "particle size (D50)" for the active material particles 1a and the composite active material 1 refers to the particle size (median diameter) at 50% of the cumulative value in the volume-based particle size distribution obtained by laser diffraction and scattering. The particle size distribution of the active material particles 1a can be measured wet, while the particle size distribution of the composite active material 1 should be measured dry in order to suppress the elution of the coating layer 1b.

[0017] The particle size (D90) of the active material particle 1a may be, for example, 2.00 μm or more, 3.00 μm or more, or 4.00 μm or more, or 8.00 μm or less, 7.00 μm or less, or 6.00 μm or less. In this application, the "particle size (D90)" for the active material particle 1a and the composite active material 1 refers to the particle size at 90% of the cumulative value in the volume-based particle size distribution obtained by laser diffraction and scattering.

[0018] The particle size (D10) of the active material particle 1a may be, for example, 0.10 μm or more, 0.50 μm or more, or 1.00 μm or more, or it may be 4.00 μm or less, 3.00 μm or less, or 2.00 μm or less. In this application, the "particle size (D10)" for the active material particle 1a and the composite active material 1 refers to the particle size at 10% of the cumulative value in the volume-based particle size distribution obtained by laser diffraction-scattering method.

[0019] 1.2 Coat Layer As shown in Figure 1, at least a portion of the surface of the active material particles 1a is covered by a coating layer 1b. The coating layer 1b is a layer of oxide containing Li as a constituent element. In one embodiment, the coating layer 1b may contain Li, B, P, and O as constituent elements. When the coating layer 1b contains Li, B, P, and O as constituent elements, the resistance and other properties of the composite active material 1 are more easily improved. Alternatively, the coating layer 1b may have a different chemical composition.

[0020] 1.2.1 Types of Coating Layers The coating layer 1b is a layer of an oxide containing Li, or in other words, a layer of an oxide (oxide solid electrolyte) that has Li ion conductivity. That is, the coating layer 1b only needs to be able to suppress direct contact between the active material particles 1a and other materials, while also ensuring a Li ion conduction path. The Li ion conductive material may be an inorganic compound or an organic compound, but high performance is particularly easily ensured when it is an inorganic compound. Furthermore, the coating layer 1b may be substantially free of organic compounds (the organic compound content is less than 0.01% by mass).

[0021] When the coating layer 1b is composed of a lithium-ion conductive inorganic compound, the inorganic compound may contain a lithium-containing oxide and optionally may further contain other inorganic compounds (e.g., lithium-containing halides, etc.). In particular, as described above, high performance is likely to be ensured when the coating layer 1b contains Li, B, P, and O as constituent elements. When the coating layer 1b contains Li, B, P, and O as constituent elements, the proportion of Li contained in the coating layer 1b may be, for example, 20 mol% or more and 50 mol% or less. Also, the proportion of P contained in the coating layer 1b may be, for example, 5 mol% or more and 20 mol% or less. Further, the molar ratio of B to P (B / P) contained in the coating layer 1b may be, for example, 0.5 or more and 2.0 or less. Also, the molar ratio of Li to the total of P and B contained in the coating layer 1b (Li / (P + B)) may be, for example, 0.3 or more and 1.2 or less. The proportions of these elements can be specified, for example, by elemental analysis using SEM-EDX or ICP analysis. Also, the proportion of O contained in the coating layer 1b can be determined as the oxygen concentration, for example, by a heat fusion method. The oxygen concentration determined by the heat fusion method for the coating layer 1b may be, for example, 45 wt% or more and 60 wt% or less. The proportion of O contained in the coating layer 1b may be, for example, 30 mol% or more and 60 mol% or less.

[0022] The lithium-containing oxide constituting the coating layer 1b may be an oxide containing Li and an element A other than Li. The lithium-containing oxide may contain, for example, at least one element A selected from B, C, Al, Si, P, S, Ti, La, Zr, Nb, Mo, Zn, and W, Li, and O. In particular, higher performance is likely to be ensured when the element A contains B and P. The lithium-containing oxide may be an oxynitride containing N. More specifically, the lithium-containing oxide is Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, Li4Ti5O 12It may be at least one selected from Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, Li2WO4, LiPON, Li-BPO, Li2O-LaO2, Li2O-ZnO2, etc. The Li-containing oxide may have some elements substituted by various doping elements.

[0023] The coating layer 1b may contain a Li-containing halide. The Li-containing halide may, for example, contain at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sn, Al, Sc, Ga, Bi, Sb, Zr, Hf, Ti, Ta, Nb, W, Y, Gd, Tb, and Sm, at least one halogen element selected from the group consisting of Cl, Br, I, and F, and Li. The Li-containing halide may also contain at least one element selected from the group consisting of Ti, Al, Gd, Ca, Zr, and Y, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. Furthermore, the Li-containing halide may also contain at least one element selected from the group consisting of Ti and Al, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. In addition, the Li-containing halide may be, for example, a composite halide of Li, Ti, Al, and F.

[0024] 1.2.2 Coverage of the coating layer The coating layer 1b may cover part or all of the surface of the active material particles 1a. For example, the coating layer 1b may cover 70% or more, 80% or more, 90% or more, 95% or more, or 99% or more of the surface of the active material particles 1a. The coverage rate of the coating layer 1b over the active material particles 1a can be determined by performing elemental analysis on the appearance or cross-section of the composite active material 1.

[0025] 1.2.3 Thickness of the coating layer The thickness of the coating layer 1b may be, for example, 0.1 nm to 100 nm, or 1 nm to 50 nm. The thickness of the coating layer 1b can be determined by observing the cross-section of the composite active material 1 using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0026] 1.2.4 Others The coating layer 1b may directly or indirectly cover the active material particles 1a. "Indirectly covering" means that a layer different from the coating layer 1b exists between the active material particles 1a and the coating layer 1b.

[0027] 1.3 Shape of the composite active material The composite active material 1 comprises the active material particles 1a and a coating layer 1b described above. As shown in Figure 3, the composite active material 1 is particulate. The composite active material 1 may also consist of secondary particles formed by the aggregation of multiple active material particles 1a via the coating layer 1b, etc. However, in this embodiment, as will be explained below, it is important that the composite active material 1 as a whole has a small particle size.

[0028] As described above, active material particles having an O2-type structure are produced by ion exchange of a Na-containing oxide having a P2-type structure. Here, the P2-type structure is prone to crystal growth in a specific direction, and the ends in the crystal growth direction can serve as entry and exit points for intercalation. Therefore, active material particles having an O2-type structure obtained after ion exchange tend to have a long bulk Li diffusion distance. According to the inventors' findings, when such active material particles are coated with a coating layer to obtain a composite active material, if the particle size (D50) of the composite active material becomes too large, the Li diffusion distance within the composite active material becomes long, which tends to result in inferior Li conductivity and other properties. In contrast, the composite active material 1 according to one embodiment has a small particle size (D50) of less than 5.90 μm, and the Li diffusion distance of the composite active material 1 as a whole is short. As a result, the composite active material 1 as a whole tends to have high capacity and low resistance. In particular, the effects of the technology of this disclosure become even more pronounced when the active material particles 1a are plate-shaped particles. The particle size (D50) of composite active material 1 may be 5.85 μm or less, 5.80 μm or less, 5.75 μm or less, 5.70 μm or less, 5.65 μm or less, 5.60 μm or less, 5.55 μm or less, 5.50 μm or less, 5.45 μm or less, or 5.42 μm or less. The lower limit of the particle size (D50) of composite active material 1 is not particularly limited. The particle size (D50) of composite active material 1 may be 2.00 μm or more, 3.00 μm or more, 4.00 μm or more, or 5.00 μm or more.

[0029] The particle size (D90) of the composite active material 1 may be, for example, greater than 2.00 μm, 3.00 μm or more, 4.00 μm or more, or 5.00 μm or more, and may also be 10.00 μm or less, 9.50 μm or less, or 9.00 μm or less.

[0030] The particle size (D10) of the composite active material 1 may be, for example, greater than 1.00 μm, 2.00 μm or more, or 3.00 μm or more, and may also be 5.00 μm or less, 4.50 μm or less, 4.00 μm or less, or 3.50 μm or less.

[0031] 2. Method for producing composite active material The composite active material 1 described above can be manufactured, for example, by the following method. That is, as shown in Figure 4, the method for manufacturing the composite active material 1 according to one embodiment is: S1: To obtain active material particles 1a, and S2: Coating at least a portion of the surface of the active material particles 1a with a coating layer 1b by spray drying (oxide coating), This includes the active material particles 1a having an O2-type structure. The active material particles 1a contain Li, at least one transition metal element from Mn, Ni, and Co, and O as constituent elements. The coating layer 1b is a layer of oxide containing Li as a constituent element. In this embodiment, it is preferable to control the spray drying conditions in S2 (especially the atomizing air pressure) so that the particle size (D50) of the final composite active material 1 is less than 5.90 μm.

[0032] 2.1 S1 In S1, active material particles 1a having an O2-type structure and containing predetermined constituent elements can be obtained, for example, by the following method. As shown in Figure 4, S1 is S11: To obtain a precursor containing at least one transition metal element from Mn, Ni, and Co. S12: Mix the precursor and the Na source to obtain a mixture. S13: Obtaining Na-containing oxide particles having a P2-type structure by calcining the above mixture, and S14: This may include obtaining Li-containing oxide particles having an O2-type structure by ion-exchanging at least a portion of the Na in the Na-containing oxide particles with Li.

[0033] 2.1.1 Preparation of Precursors The precursor contains at least one transition metal element from among Mn, Ni, and Co. The precursor may contain Mn and one or both of Ni and Co, or it may contain at least Mn, Ni, and Co. The precursor may be a salt containing at least one element from among Mn, Ni, and Co. For example, the precursor may be at least one of carbonates, sulfates, nitrates, and acetates. Alternatively, the precursor may be a compound other than a salt. For example, the precursor may be a hydroxide. The precursor may be a hydrate. The precursor may be a combination of multiple compounds. The precursor may be in various shapes. For example, the precursor may be particulate, or it may be spherical particles as described later. The particle size of the particles made up of the precursor is not particularly limited.

[0034] In S11, a precipitate as a precursor may be obtained by coprecipitation using an ion source capable of forming a precipitate with transition metal ions in aqueous solution and a transition metal compound containing at least one element from Mn, Ni, and Co. This makes it easier to obtain spherical particles as a precursor. The "ion source capable of forming a precipitate with transition metal ions in aqueous solution" may be at least one selected from, for example, sodium salts such as sodium carbonate and sodium nitrate, sodium hydroxide, and sodium oxide. The transition metal compound may be the above salts or hydroxides containing at least one element from Mn, Ni, and Co. Specifically, in S1, the precipitate as a precursor may be obtained by preparing solutions of the ion source and the transition metal compound separately, and then adding and mixing each solution dropwise. In this case, water may be used as the solvent. Various sodium compounds may be used as the base, and aqueous ammonia may be added to adjust the basicity. In the case of coprecipitation, for example, an aqueous solution of the transition metal compound and an aqueous solution of sodium carbonate are prepared, and the precipitate as a precursor is obtained by adding and mixing each aqueous solution dropwise. Alternatively, the precursor can be obtained by the sol-gel method.

[0035] In S11, the precursor may contain element M. Element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. These elements M have functions such as stabilizing P2-type or O2-type structures. The method for obtaining a precursor containing element M is not particularly limited. When obtaining a precursor by coprecipitation in S1, for example, an aqueous solution of a transition metal compound containing at least one of Mn, Ni, and Co, an aqueous solution of sodium carbonate, and an aqueous solution of a compound of element M are prepared, and each aqueous solution is added dropwise and mixed to obtain a precursor containing element M along with at least one of Mn, Ni, and Co. Alternatively, in the manufacturing method of this disclosure, element M may not be added in S11, and element M may be doped in S12 and S13 as described below.

[0036] 2.1.2 Preparation of mixtures (complexes) In S12, the precursor obtained in S11 and the Na source are mixed to obtain a mixture. In S12, the surface of the precursor may be coated with the Na source to obtain a composite. The Na source may be a salt containing Na, such as a carbonate or nitrate, or a compound other than a salt, such as sodium oxide or sodium hydroxide. In S12, the amount of Na source relative to the precursor should be determined taking into account the amount of Na lost during subsequent calcination. In S12, when the surface of the precursor is coated with the Na source, the coverage rate of the Na source on the surface of the precursor is not particularly limited. In S12, the method of coating the surface of the precursor with the Na source is not particularly limited. For example, the precursor and the Na source may be mixed using a mortar and pestle or a mixing device, or the solution containing the Na source may be brought into contact with the precursor using a rolling flow coating method or a spray drying method, and then dried.

[0037] In S12, the precursor may be mixed with the Na source and the M source. For example, in S12, the precursor obtained in S1 may be mixed with the Na source and the M source containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W to obtain a mixture. The M source may be a salt containing element M, such as a carbonate or sulfate, or a compound other than a salt, such as an oxide or hydroxide. The amount of the M source relative to the precursor should be determined according to the chemical composition of the Na-containing oxide after calcination.

[0038] 2.1.3 Preparation of P2-type Na-containing oxide particles In S13, the mixture (composite) obtained in S12 is calcined to obtain a Na-containing oxide having a P2-type structure. S13-1: The mixture is pre-fired at a temperature of 300°C or higher but less than 700°C for a period of 1 hour or more but not more than 10 hours. S13-2: Following the pre-firing, the mixture is subjected to a main firing at a temperature of 700°C to 1100°C for 30 minutes to 48 hours, and S13-3: Following the above-mentioned firing, the composite is rapidly cooled from a temperature T1 of 200°C or higher to a temperature T2 of 100°C or lower. It may include [something].

[0039] In S13-1, the mixture (composite) is pre-fired at a temperature of 300°C or higher but less than 700°C for a period of 2 hours or more but less than 10 hours. In S13-1, the mixture may be arbitrarily molded before pre-fired. Pre-fired is performed at a temperature lower than that of the main firing. If the pre-fired in S13-1 is insufficient, the formation of the P2 phase in the final Na-containing oxide may be insufficient. In S13-1, by setting the pre-fired temperature to 300°C or higher but less than 700°C and the pre-fired time to 2 hours or more but less than 10 hours, the mixture can be sufficiently pre-fired, the uniformity of the heat is increased, and the Na-containing oxide obtained via S13-2 and S13-3 described below is more likely to be suitable. The pre-firing temperature may be between 400°C and 700°C, 450°C and 700°C, 500°C and 700°C, 550°C and 700°C, or 550°C and 650°C. The pre-firing time may be between 2 hours and 8 hours, 3 hours and 8 hours, 4 hours and 8 hours, 5 hours and 8 hours, or 5 hours and 7 hours. The pre-firing atmosphere is not particularly limited and may be, for example, an oxygen-containing atmosphere.

[0040] In S13-2, following the pre-sintering described above, the mixture (composite) is subjected to main firing at a temperature of 700°C to 1100°C for a period of 30 minutes to 48 hours. In S13-2, the main firing temperature may be 800°C to 1000°C. If the main firing temperature is too low, the P2 phase will not be formed, and if the main firing temperature is too high, other phases besides the P2 phase are likely to be formed. The heating conditions from the pre-sintering temperature to the main firing temperature are not particularly limited. In S13-2, the shape of the Na-containing oxide can be controlled by the main firing time. If the main firing time is too short, the formation of the P2 phase will be insufficient. In this embodiment, by setting the main firing time above a certain level, the P2 phase grows and plate-shaped Na-containing oxide particles are easily obtained.

[0041] In step S13-3, the fired product after the main firing described above is rapidly cooled (cooled at a cooling rate of 20°C / min or more) from a temperature T1 of 200°C or higher to a temperature T2 of 100°C or lower. The above pre-firing and main firing are performed, for example, in a heating furnace. In step S13-3, for example, after the main firing of the mixture (composite) is performed in a heating furnace, it is cooled in the heating furnace to an arbitrary temperature T1 of 200°C or higher, and after reaching that temperature T1, the fired product is removed from the heating furnace and rapidly cooled outside the furnace to an arbitrary temperature T2 of 100°C or lower. Temperature T1 is any temperature of 200°C or higher, and may also be any temperature of 250°C or higher. Temperature T2 is any temperature of 100°C or lower, and may also be any temperature of 50°C or lower, and may also be the cooling completion temperature. In the predetermined temperature range between temperature T1 and temperature T2, moisture easily penetrates between the layers of the P2 type structure due to atomic vibrations, molecular motion, etc. When cooling the calcined product (Na-containing oxide having a P2-type structure) after the main calcination, it is thought that reducing the time spent in the temperature range where moisture easily penetrates (i.e., rapid cooling) will reduce the amount of moisture penetrating into the interlayers of the P2-type structure. In this regard, in step S13-3, when cooling the calcined product after the main calcination, if the cooling is performed in a dry atmosphere outside the furnace from an arbitrary temperature T1 of 200°C or higher to an arbitrary temperature T2 of 100°C or lower, the cooling rate from temperature T1 to temperature T2 becomes high (e.g., 20°C / min or higher), making it difficult for moisture to penetrate into the interlayers of the P2-type structure and suppressing the collapse of the P2-type structure. As a result, Na can be efficiently ion-exchanged for Li in S14.

[0042] 2.1.4 Ion exchange In step S14, Li-containing oxide particles having an O2-type structure are obtained by ion exchange of at least a portion of the Na in the Na-containing oxide particles obtained in step S13 with Li. For ion exchange, there are methods such as using an aqueous solution containing lithium halide and using a mixture of lithium halide and other lithium salts (e.g., a molten salt). From the viewpoint that the P2-type structure is easily broken by the intrusion of water and from the viewpoint of crystallinity, the method using a molten salt is preferred among the two methods above. That is, by mixing the Na-containing oxide having the above-mentioned P2-type structure with the molten salt and heating it to a temperature above the melting point of the molten salt, at least a portion of the Na in the Na-containing oxide can be replaced with Li by ion exchange. The lithium halide constituting the molten salt is preferably at least one of lithium chloride, lithium bromide, and lithium iodide. The other lithium salt constituting the molten salt is preferably lithium nitrate. By using a molten salt, the melting point becomes lower than when lithium halide or other lithium salts are used alone, and ion exchange becomes possible at lower temperatures. The temperature during ion exchange may be, for example, above the melting point of the molten salt and below 600°C, 500°C, 400°C, or 300°C. If the temperature during ion exchange is too high, the stable O3-type structure is more likely to form than the O2-type structure. On the other hand, from the viewpoint of minimizing the time required for ion exchange, it is desirable for the temperature during ion exchange to be as high as possible.

[0043] 2.2 S2 In step S2, at least a portion of the surface of the active material particles 1a obtained in step S1 is covered with a coating layer 1b. For example, at least a portion of the surface of the Li-containing oxide particles after ion exchange as described above, or the Li-containing oxide particles after further Li doping as described later, is covered with a coating layer 1b. This yields a composite active material 1 as shown in Figure 1.

[0044] In S2, one method for coating at least a portion of the surface of the active material particles 1a with the coating layer 1b is by spray drying. That is, S2 is S2-1: Obtain a solution in which raw materials (e.g., Li source, B source, P source, etc.) for forming the coating layer 1b are dissolved. S2-2: Mixing the solution and the active material particles 1a to obtain a slurry, and S2-3: The slurry is spray-dried together with atomized air to coat at least a portion of the surface of the active material particles 1a with the coating layer 1b. It may include [something].

[0045] In S2-1, various Li compounds such as lithium hydroxide (LiOH) can be used as the Li source to be dissolved in the solvent. Various B compounds such as boric acid (H3BO3) can be used as the B source. Various P compounds such as orthophosphoric acid (H3PO4) and metaphosphoric acid (HPO3) can be used as the P source. In addition, other element sources may be dissolved in the solvent depending on the composition of the desired coating layer 1b. Examples of solvents include water and various organic solvents. The concentrations of the various element sources in the solution should be adjusted as appropriate according to the composition of the desired coating layer 1b.

[0046] In S2-2, the solid content concentration in the slurry is not particularly limited; it should be adjusted to a solid content concentration sufficient for spray drying.

[0047] In steps S2-3, the particle size (D50) of the final composite active material 1 can be controlled by controlling the spray drying conditions. Specifically, the particle size (D50) of the final composite active material 1 can be changed by the atomizing air pressure during spray drying. According to the inventors' findings, the higher the atomizing air pressure, the more the aggregation of active material particles 1a is suppressed, and the smaller the particle size (D50) of the composite active material 1 tends to be. In steps S2-3, the atomizing air pressure during spray drying should be increased so that the particle size (D50) of the composite active material 1 is less than 5.90 μm. Other spray drying conditions are not particularly limited.

[0048] 2.3 Li-doped A method for producing a composite active material according to one embodiment is, for example, S3: Further doping of Li with the Li-containing oxide particles described above. It may also contain [a certain substance]. Here, further Li doping of the Li-containing oxide particles may be performed before or after the spray drying described above. This may further increase the capacity as an active material.

[0049] In step S3, for example, the Li-containing oxide particles after ion exchange as described above, or the composite active material after spray drying as described above, are brought into contact with a reducing solution containing Li ions. "Reducing solution" means a solution that has reducing properties, and may, for example, be a solution containing an electrophile. The reducing solution may be obtained, for example, by dissolving an electrophile and a Li source in a solvent. Various organic solvents capable of dissolving the electrophile and Li source can be used as the solvent. Various substances that dissolve in the above solvent can be used as the electrophile. The electrophile may be an aromatic organic compound. Various substances that dissolve in the above solvent to produce Li ions can be used as the Li source. The Li source may be metallic lithium or a Li compound. The concentration of the electrophile and Li ions contained in the reducing solution should be appropriately determined according to the desired doping amount. The greater the amount of Li ions contained in the reducing solution relative to the amount of particles brought into contact with the reducing solution, the greater the amount of Li doping to the particles tends to be. The molar ratio of electrophile to Li ions (electrophile / Li ions) contained in the reducing solution is not particularly limited. The form of contact between the reducing solution and the particles is not particularly limited. For example, the particles may be immersed in the reducing solution, or the reducing solution may be sprayed onto the particles. There are no particular restrictions on the temperature at contact; heating may be used or not. The particles may also be immersed in the reducing solution and then stirred. There are no particular restrictions on the contact time between the particles and the reducing solution; it should be determined appropriately according to the desired doping amount.

[0050] 3.Battery A battery according to one embodiment has the composite active material of the present disclosure described above. The composite active material of the present disclosure is used, for example, as a positive electrode active material of a lithium-ion battery. As shown in Figure 5, a 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, and the positive electrode active material layer 10 may contain the composite active material 1 of the present disclosure. The battery 100 may include a positive electrode current collector 40 and a negative electrode current collector 50. The battery 100 may be a solid-state battery or a liquid-system battery. A solid-state battery is a battery that includes a solid electrolyte and may allow the presence of liquid. For example, a solid-state battery may include a liquid component (lubricant) to enhance the lubricity between solid materials. The proportion of the solid electrolyte (e.g., sulfide solid electrolyte) in the total electrolyte of the battery 100 may be more than 50% by mass, and the battery 100 may contain only a solid electrolyte (e.g., sulfide solid electrolyte) as the electrolyte (i.e., it may not contain a liquid electrolyte). The battery 100 may be an all-solid-state battery that is substantially free of liquid. The positive electrode active material layer 10 of the battery 100 may contain a solid electrolyte (e.g., a sulfide solid electrolyte) together with the composite active material 1 of this disclosure. The electrolyte layer 20 of the battery 100 may contain a solid electrolyte (e.g., a sulfide solid electrolyte) and a binder. The negative electrode active material layer 30 of the battery 100 may contain a solid electrolyte (e.g., a sulfide solid electrolyte) together with the negative electrode active material. [Examples]

[0051] As described above, one embodiment of the composite 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. Preparation of the composite active material 1.1 Example 1, Comparative Examples 1 and 2 The composite active materials according to Example 1, Comparative Examples 1 and 2 were prepared using the following procedure.

[0053] 1.1.1 Preparation of Precursor Particles (1) MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed to the desired composition ratio (Mn:Ni:Co=4:2:4) and dissolved in distilled water to a concentration of 1.2 mol / L to obtain the first solution. In a separate container, Na2CO3 was dissolved in distilled water to a concentration of 1.2 mol / L to obtain the second solution. (2) 1000 mL of pure water was placed in a reaction vessel (with baffles), and 500 mL of the first solution and 500 mL of the second solution were added dropwise, each at a rate of approximately 4 mL / min. (3) After the dropwise addition was complete, the mixture was stirred at room temperature at a stirring speed of 150 rpm for 1 hour to obtain the product. (4) The product was washed with pure water, and solid-liquid separation was performed using a centrifuge to recover the precipitate. (5) The obtained precipitate was dried overnight at 120°C, ground in a mortar, and then the coarse powder was recovered by air classification to obtain precursor particles.

[0054] 1.1.2 Preparation of mixtures (complexes) The above-mentioned precursor particles and Na2CO3 were mixed using a mortar and pestle to coat the surface of the precursor particles with Na2CO3, thereby obtaining a mixture (composite).

[0055] 1.1.3 Preparation of P2-type Na-containing oxide particles The above mixture (composite) was placed in an alumina crucible and calcined under an atmospheric environment to obtain a Na-containing oxide having a P2-type structure. The calcination conditions were as follows (1) to (6). (1) Place an alumina crucible containing the above mixture (composite) in a heating furnace in an atmospheric environment. (2) Heat the furnace from room temperature (25°C) to 600°C in 120 minutes. (3) Maintain the temperature inside the heating furnace at 600°C for 360 minutes to perform pre-firing. (4) After pre-firing, raise the temperature inside the furnace to 900°C in 100 minutes. (5) Maintain the temperature inside the heating furnace at 900°C for 120 minutes to perform the final firing. (6) After the main firing, the temperature inside the furnace is lowered from the main firing temperature to 250°C. At 250°C, the alumina crucible is removed from the furnace and allowed to cool outside the furnace in a dry atmosphere until it reaches 25°C in 10 minutes.

[0056] By crushing the calcined material after cooling in a dry atmosphere using a mortar, Na-containing oxide particles having a P2-type structure (P2-type particles) were obtained. These Na-containing oxide particles were plate-shaped particles with an aspect ratio of 1.5 or more in their cross-sectional shape.

[0057] 1.1.4 Ion exchange (1) LiNO3 and LiCl were weighed in a molar ratio of 50:50 and mixed with the above P2 type particles in a molar ratio that was 10 times the minimum amount of Li required for ion exchange to obtain a mixture. (2) Using an alumina crucible, ion exchange was performed at 280°C for 1 hour under an atmospheric atmosphere to obtain a product containing a Li-containing oxide. (3) The salt remaining in the product was washed with pure water, and solid-liquid separation was performed by vacuum filtration to obtain a precipitate. (4) The obtained precipitate was dried overnight at 120°C to obtain Li-containing oxide particles having an O2-type structure.

[0058] 1.1.5 Oxide Coating (1) 4.52 g of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries) was dissolved in 191.8 g of deionized water. Next, boric acid (manufactured by Nacalai Tesque) was added and dissolved so that the molar ratio (B / P) was 1.0. Furthermore, lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries) was added and stirred so that the molar ratio (Li / (P+B)) was 1.00. This yielded a coating solution containing Li, P, and B sources. (2) The above-mentioned Li-containing oxide particles were mixed with the coating liquid to obtain a slurry. (3) The slurry was dried using a spray drying device to obtain solid components. Here, the particle size of the solid components could be changed by changing the atomizing air pressure of the spray drying device. (4) The solid was heat-treated at 200°C for 5 hours in an air atmosphere. This coated the entire surface of the active material particles with a coating layer. The coating layer contained Li, B, P, and O as constituent elements.

[0059] 1.1.6 Li-doping (1) In a glove box (Ar atmosphere), 9-fluorenone was mixed and dissolved in tetrahydrofuran (THF) to obtain a fluorenone solution. (2) Li foil was added to the fluorenone solution and stirred for 2 hours to obtain a reducing solution containing Li ions. (3) The Li-containing oxide particles that had been coated with oxide were added to the obtained reducing solution, immersed in it, and stirred for 24 hours. (4) The particles after stirring were washed with THF and solid-liquid separation was performed by vacuum filtration. The resulting precipitate was dried overnight at 120°C to obtain a composite active material for evaluation.

[0060] 1.2 Example 2 Fine precursor particles were obtained by recovering the fine powder using an air-flow particle scale. Using the obtained precursor particles, a mixture (composite) was prepared, P2-type Na-containing oxide particles were prepared, ion exchange, oxide coating and Li doping were performed under the same conditions as in Example 1 to obtain a composite active material for evaluation.

[0061] 2. Confirmation of the chemical composition and crystal structure of the active material particles. When the chemical composition of the active material particles was examined for each of Examples 1 and 2 and Comparative Examples 1 and 2, it was found that in all cases, Li 1.0 Mn 0.4 Ni 0.2 Co 0.4 The substance was represented by O2. Furthermore, XRD analysis confirmed that the crystalline phase contained in the active material particles had an O2-type structure. In addition, the active material particles were plate-shaped particles with an aspect ratio of 1.5 or more in their cross-sectional shape. The method of cross-sectional observation was as described in the embodiments of this specification.

[0062] 3. Measurement of particle size and visual inspection For each of Examples 1 and 2 and Comparative Examples 1 and 2, the particle sizes (D10, D50, D90) of the active material particles before oxide coating and the particle sizes (D10, D50, D90) of the composite active material were measured. In addition, each composite active material was coated onto carbon tape, attached to a jig, and mounted on an FE-SEM to confirm the appearance of the composite active material. Figures 6 to 9 show SEM images of the appearance of each composite active material from Examples 1 and 2 and Comparative Examples 1 and 2.

[0063] 4. Creating cells for evaluation (1) The composite active material, sulfide solid electrolyte, vapor-grown carbon fiber (VGCF), and PVdF-based binder described above were weighed in mass ratios of active material:sulfide solid electrolyte:VGCF:binder = 81:16:1:2. A positive electrode slurry was obtained by dispersing and mixing each weighed component in DIBK. This positive electrode slurry was coated onto an Al foil, which served as the positive electrode current collector foil, using the blade method, and this was dried on a hot plate to form a positive electrode active material layer on the Al foil. (2) Lithium titanate (LTO) as the negative electrode active material, sulfide solid electrolyte, VGCF, and PVdF-based binder were weighed in a ratio of negative electrode active material:sulfide solid electrolyte:VGCF:binder = 72:23:3:2 and dispersed and mixed in butyl butyrate to obtain a negative electrode slurry. This negative electrode slurry was coated onto a Ni foil, which was to be used as the negative electrode current collector foil, by the blade method, and this was dried on a hot plate to form a negative electrode active material layer on the Ni foil. (3) A solid electrolyte slurry was obtained by stirring a sulfide solid electrolyte, a PVdF-based binder, and butyl butyrate using an ultrasonic dispersion device. The mass ratio of the sulfide solid electrolyte to the PVdF-based binder was 99.4:0.6. The solid electrolyte slurry was coated onto an Al foil substrate using the blade method, and this was dried on a hot plate at 100°C for 30 minutes to obtain a peelable solid electrolyte layer. (4) The above positive electrode active material layer and solid electrolyte layer are laminated and pressed in a roll press machine at a press pressure of 50 kN / cm and a temperature of 160°C, after which the Al foil is peeled off from the solid electrolyte layer, and 1 cm 2A positive electrode laminate was obtained by punching out the material to the specified size. (5) The above-mentioned negative electrode active material layer and solid electrolyte layer were laminated and pressed in a roll press machine at a press pressure of 50 kN / cm and a temperature of 160°C, after which the Al foil was peeled off from the solid electrolyte layer to obtain a negative electrode laminate. Furthermore, an additional solid electrolyte layer was laminated on the solid electrolyte side of the above negative electrode laminate and pre-pressed in a flat single-axis press machine at a press pressure of 100 MPa and a temperature of 25°C, after which the Al foil was peeled off from the solid electrolyte layer, and 1.08 cm 2 By punching out the material to the specified size, a negative electrode laminate having an additional solid electrolyte layer was obtained. (6) The positive electrode laminate and the negative electrode laminate having an additional solid electrolyte layer were stacked so that their composite material surfaces overlapped, and pressed in a planar single-axis press at a pressing pressure of 200 MPa and a temperature of 120°C to obtain a battery laminate. (7) The battery stack was sandwiched between two restraining plates, and these two restraining plates were fastened together with fasteners to fix the distance between them, thereby obtaining a cell for evaluation.

[0064] 5. Measurement of volume For the evaluation cells, charging and discharging were performed at a voltage range of 0.45-3.25V and a current of 0.1C (1C = 220mA / g) in a constant temperature bath maintained at 25°C, and the initial discharge capacity was measured.

[0065] 6. Measuring Resistance For the evaluation cells, they were charged at 0.1C (1C = 220mA / g) in a constant temperature bath maintained at 25°C at a voltage range of 0.45-3.25V, then discharged until the state of charge (SOC) reached 50%, and after reaching 50% SOC, discharged again at 3.0C for 10 seconds. The 0.1s resistance and 10s resistance values ​​at 50% SOC were then measured.

[0066] 7. Evaluation Results Table 1 below shows the particle sizes of the active material particles before oxide coating (D10, D50, D90), the particle sizes of the composite active material after oxide coating and Li doping (D10, D50, D90), the initial discharge capacity of the evaluation cell, and the 0.1s resistance and 10s resistance values ​​at SOC 50% for each of Examples 1 and 2 and Comparative Examples 1 and 2. [Table 1]

[0067] The results shown in Table 1 indicate the following: When the particle size (D50) of the composite active material is less than 5.90 μm (Examples 1 and 2), the resistance is lower and the capacity is higher compared to when the particle size (D50) of the composite active material is 5.90 μm or more (Comparative Examples 1 and 2). In the above examples, evaluation active materials having a predetermined chemical composition were used as examples, but the chemical composition of the active material is not limited to this. It is believed that similar effects will be achieved if the active material contains at least one transition metal element from Mn, Ni, and Co as constituent elements. [Explanation of symbols]

[0068] 1 Composite active material 1a Active material particles 1b Coat layer 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. A composite active material comprising active material particles and a coating layer, The active material particles have an O2 type structure, The active material particles consist of the following constituent elements: Li and, At least one transition metal element from Mn, Ni, and Co, O and, Includes, The coating layer covers at least a portion of the surface of the active material particles, The aforementioned coating layer is a layer of oxide containing Li as a constituent element. The particle size (D50) of the composite active material is less than 5.90 μm. Composite active material.

2. A composite active material according to claim 1, The coating layer comprises Li, B, P, and O as constituent elements. Composite active material.

3. A composite active material according to claim 1, The particle size (D50) of the composite active material is 5.42 μm or less. Composite active material.

4. A composite active material according to claim 1, The active material particles contain Li, Mn, Ni, Co, and O as constituent elements. Composite active material.

5. 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 the composite active material described in any one of claims 1 to 4. battery.

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