Cathode active material, secondary battery, and manufacturing method of cathode active material

Abstract

To provide a cathode active material capable of improving durability.SOLUTION: The cathode active material includes secondary particles. The secondary particles contain multiple crystallites. The multiple crystallites are arranged radially from the center of the secondary particles to the outside. Each of the multiple crystallites contains a lithium metal composite oxide. The lithium metal composite oxides have a layered rock salt structure. On the surface of the secondary particles, open pores are formed between adjacent crystallites. The open pores have an opening diameter of 20 nm or more.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material, a secondary battery, and a method for producing a positive electrode active material. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2019-145204 discloses a positive electrode active material that contains voids at a rate of 20% or more and that contains long voids that connect to the interior of the particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-145204 Summary of the Invention [Problem to be solved by the invention]

[0004] The secondary particle structure of the positive electrode active material can affect battery performance. For example, the formation of long voids that connect to the interior of the secondary particles can improve output characteristics. However, there is still room for improvement in terms of battery durability.

[0005] The objective of the present disclosure is to improve durability. [Means for solving the problem]

[0006] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action of the present disclosure includes speculation. The mechanism of action does not limit the technical scope of the present disclosure.

[0007] 1. The positive electrode active material includes secondary particles. The secondary particles include a plurality of crystallites. The plurality of crystallites are arranged radially from the center of the secondary particle toward the outside. Each of the plurality of crystallites includes a lithium metal composite oxide. The lithium metal composite oxide has a layered rock salt structure. Open pores are formed between adjacent crystallites on the surface of the secondary particles. The open pores have an opening diameter of 20 nm or more.

[0008] Figure 1 is a conceptual diagram showing a first example of a secondary particle structure. A secondary particle 2 is an aggregate of crystallites 1. The crystallites 1 are also called "primary particles." Within a secondary particle 2, the crystallites 1 are densely packed. Adjacent crystallites 1 are bonded together. With repeated charge and discharge, the crystallites 1 repeatedly expand and contract. Due to volume changes in the crystallites 1, stress can concentrate between the crystallites 1. Due to the concentration of stress, peeling can occur between the crystallites 1. In other words, newly formed surfaces can be exposed. The newly formed surfaces can be active. It is thought that durability decreases when the newly formed surfaces react with the electrolyte.

[0009] FIG. 2 is a conceptual diagram showing a second example of a secondary particle structure. Crystallites 1 are arranged radially. Open pores 3 are formed between the crystallites 1 on the surface of secondary particles 2. The combination of the radial arrangement of crystallites 1 and the open pores 3 on the particle surface can alleviate stress associated with volume changes in the crystallites 1. Therefore, it is expected that peeling between crystallites 1 (exposure of newly formed surfaces) will be less likely to occur. In other words, improved durability is expected. However, the open pores 3 have an opening diameter of 20 nm or more. If the opening diameter is less than 20 nm, the desired durability may not be achieved.

[0010] 2. The positive electrode active material described in "1" above may have the following configuration, for example. In the cross section of the secondary particle, the relationship "θ≦45°" is satisfied. "θ" represents the angle between a first line and a second line. The first line is an extension of the major axis diameter of the crystallite. The second line passes through the intersection of the circumscribing circle of the secondary particle and the extension, and through the center of the circumscribing circle.

[0011] The angle (θ) is an index of the arrangement. The smaller the angle (θ), the more radially the crystallites are thought to be arranged. By keeping the angle (θ) at 45° or less, improved durability is expected.

[0012] 3. The positive electrode active material according to the above item "1" or "2" may have, for example, the following configuration: The open pores have an opening diameter of less than 250 nm.

[0013] When the aperture diameter is less than 250 nm, improved durability is expected.

[0014] 4. The positive electrode active material according to any one of the above items "1" to "3" may have the following structure, for example: In the cross section of the secondary particle, "6.4≦d L / d S ≦17.3" is satisfied. L " indicates the major axis diameter of the crystallite. S " indicates the minor axis diameter of the crystallite.

[0015] "d L / d S " indicates the aspect ratio of the crystallite. When the aspect ratio is between 6.4 and 17.3, improved durability is expected.

[0016] 5. The positive electrode active material according to any one of the above items "1" to "4" may have the following structure, for example: In the cross section of the secondary particle, "4.0≦D / d L ≦9.0". "D" indicates the maximum Feret diameter of secondary particles. "d L " indicates the major axis diameter of the crystallite.

[0017] "D / d L " indicates the size ratio between secondary particles and crystallites. When the size ratio is between 4 and 9, improved durability is expected.

[0018] 6. The positive electrode active material according to any one of the above items 1 to 5 may include, for example, the following structure: The lithium metal composite oxide has a composition represented by the following general formula: Li 1-a MO2 In the formula, the relationship "-0.5≦a≦0.5" is satisfied. M includes at least one selected from the group consisting of Ni, Co, Mn, and Al.

[0019] 7. The positive electrode active material according to any one of the above items 1 to 5 may include, for example, the following structure: The lithium metal composite oxide has a composition represented by the following general formula. Li 1-a MO2B b In the formula, the relationships of "-0.5≦a≦0.5" and "0.002≦b≦0.030" are satisfied. M includes at least one selected from the group consisting of Ni, Co, Mn, and Al.

[0020] For example, the lithium metal composite oxide may contain a specific amount of boron (B). B may be derived from, for example, a crystallinity control material described below.

[0021] 8. A secondary battery includes the positive electrode active material according to any one of the above items "1" to "7."

[0022] 9. A method for producing a positive electrode active material includes the following steps (a) to (d): (a) Prepare a metal hydroxide. (b) A first mixture is formed by mixing a metal hydroxide, a lithium compound, and a crystallization control material. (c) subjecting the first mixture to a first heat treatment to form a second mixture; (d) The second mixture is subjected to a second heat treatment to synthesize a positive electrode active material. The crystallinity control material includes B2O3. The first and second heat treatments are performed in an oxygen atmosphere. The first heat treatment is performed at a temperature of 600 to 700°C for 6 to 12 hours. The second heat treatment is performed at a temperature of 1100 to 1300°C for 1 to 3 hours.

[0023] It is expected that the secondary particle structure described in "1" above will be formed by the combination of the crystallinity control material (B2O3), the first heat treatment, and the second heat treatment.

[0024] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure. The present embodiment and the example are illustrative in all respects. The present embodiment and the example are non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the description of the claims. For example, it is also intended from the beginning that any configuration may be extracted from the present embodiment and arbitrarily combined. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 2 is a conceptual diagram showing a first example of a secondary particle structure. [Figure 2] FIG. 4 is a conceptual diagram showing a second example of a secondary particle structure. [Figure 3] FIG. 2 is a conceptual diagram showing an example of a cross-sectional image of a secondary particle in this embodiment. [Figure 4] FIG. 1 is a conceptual diagram showing a method for measuring the angle (θ). [Figure 5] 1 is a schematic flowchart of a method for producing a positive electrode active material according to the present embodiment. [Figure 6] 1 is a conceptual diagram of a secondary battery according to an embodiment of the present invention. [Figure 7] 1 is a table showing the first battery configuration. [Figure 8] 10 is a table showing the configuration of a second battery. [Figure 9] 10 is a table showing a third battery configuration. [Figure 10] 10 is a table showing experimental results. DETAILED DESCRIPTION OF THE INVENTION

[0026] <Key terms> "Comprise," "include," "have," and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the required elements. "Consisting of" is a closed term. However, even a structure expressed in closed terminology may include additional elements that are normally associated with the technology or that are unrelated to the technology in question. "Consisting essentially of..." is a semi-closed term. Semi-closed terminology allows for the addition of elements that do not substantially affect the basic and novel characteristics of the technology in question.

[0027] Expressions such as "may" and "may" are used in the permissive sense, meaning "to have the possibility," rather than in the obligatory sense, meaning "to have to."

[0028] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0029] Geometric terms should not be interpreted in their strict sense. Examples of geometric terms include "parallel," "perpendicular," and the like. For example, "parallel" may deviate slightly from the strict meaning of "parallel." For example, directions, angles, distances, etc. may be relatively displaced as long as substantially the same function is obtained. Geometric terms may include, for example, tolerances, errors, etc. in design, work, manufacturing, etc. The dimensional relationships in each figure may not match the actual dimensional relationships. The dimensional relationships in each figure may be changed to aid the reader's understanding. For example, length, width, thickness, etc. may be changed. Some components may be omitted.

[0030] Numerical ranges such as "m to n%" include the upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." "Equal to or more" and "equal to or less" are represented by an inequality sign "≦." "More than" and "less than" are represented by an inequality sign "<" without an equal sign. A numerical value arbitrarily selected from within the numerical range may be used as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described elsewhere in this specification, in a table, a figure, or the like.

[0031] All numerical values ​​are modified by the term "about." The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximate values ​​that may vary depending on the application of the disclosed technology. All numerical values ​​may be expressed with significant figures. Unless otherwise specified, measured values ​​may be average values ​​of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, the more reliable the average value is expected to be. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors, such as those associated with the detection limits of the measuring device.

[0032] A "crystallite" is the smallest unit of a particle and refers to a solid particle with boundaries between particles that cannot be further divided. A "secondary particle" refers to an aggregate of two or more crystallites.

[0033] "Open pore diameter (Pd)", "Long axis diameter of crystallite (d L ) and "minor axis diameter of crystallite (d S), the maximum Feret diameter (D) of the secondary particles, and the angle (θ) are measured in a cross-sectional SEM (Scanning Electron Microscope) image of the secondary particles. The observation magnification can be adjusted depending on the particle size. The observation magnification may be, for example, about 1000x. A cross-sectional sample of the particle can be prepared by a conventionally known method. For example, a cross-sectional sample may be prepared using a CP (Cross Section Polisher), FIB (Focused Ion Beam), or the like. Various dimensions and angles in the image are measured using image analysis software. For example, "ImageJ Fiji" or the like may be used. Note that "ImageJ Fiji" is merely an example. Any image analysis software having equivalent functions to "ImageJ Fiji" may be used. For example, image analysis software included with various SEM devices may be used.

[0034] 3 is a conceptual diagram showing an example of a cross-sectional image of a secondary particle in this embodiment. In the cross-sectional SEM image of a secondary particle 2, the surface of the secondary particle 2 is observed. The gaps between crystallites 1, which are voids that communicate with the outside air, are "open pores 3." The diameter of the opening of the open pore 3 is the "opening diameter (Pd)."

[0035] The distance between the two most distant points on the contour line of the secondary particle 2 is the "maximum Feret diameter (D)."

[0036] The smallest rectangle circumscribing the crystallite 1 (hereinafter also referred to as the "circumscribing rectangle") is identified. The length of the long side of the circumscribing rectangle is called the "major axis diameter (d L )" The length of the short side of the circumscribed rectangle is the "minor axis diameter (d S )".

[0037] FIG. 4 is a conceptual diagram showing a method for measuring the angle (θ). In a cross-sectional SEM image of a secondary particle, the circumscribing circle 4 of the secondary particle is identified. A crystallite 1 exposed on the surface of the secondary particle is selected. The major axis diameter (d L ) is extended to identify the first straight line L1. That is, the first straight line L1 is the major axis diameter (d L) is an extension of the circumscribing circle 4. The intersection 4i between the first line L1 and the circumscribing circle 4 is identified. The second line L2 passing through the intersection 4i and the center 4c of the circumscribing circle 4 is identified. The angle (θ) is the angle (acute angle) between the first line L1 and the second line L2.

[0038] "D50" indicates the particle size at which the cumulative distribution reaches 50% in the volume-based particle size distribution (cumulative distribution). The particle size distribution can be measured by a laser diffraction method.

[0039] The stoichiometric composition formula indicates a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to a compound having a substance ratio (molar ratio) of "Al / O=2 / 3." Unless otherwise specified, "Al2O3" indicates a compound containing Al and O in any molar ratio. For example, the compound may be doped with a trace element. A portion of the Al and O may be substituted with another element.

[0040] The term "derivative" refers to a compound in which a part of a parent compound has been modified by at least one method selected from the group consisting of introduction of a substituent, substitution of an atom, oxidation, reduction, and other chemical reactions. The modification may be at one or more locations. The "substituent" may include at least one selected from the group consisting of, for example, alkyl groups, alkenyl groups, alkynyl groups, cycloalkyl groups, unsaturated cycloalkyl groups, aromatic groups, heterocyclic groups, halogen atoms (such as F, Cl, Br, and I), OH groups, SH groups, CN groups, SCN groups, OCN groups, nitro groups, alkoxy groups, unsaturated alkoxy groups, amino groups, alkylamino groups, dialkylamino groups, aryloxy groups, acyl groups, alkoxycarbonyl groups, acyloxy groups, aryloxycarbonyl groups, acylamino groups, alkoxycarbonylamino groups, aryloxycarbonylamino groups, sulfonylamino groups, sulfamoyl groups, carbamoyl groups, alkylthio groups, arylthio groups, sulfonyl groups, sulfinyl groups, ureido groups, phosphoric acid amide groups, sulfo groups, carboxy groups, hydroxamic acid groups, sulfino groups, hydrazino groups, imino groups, and silyl groups. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different. Multiple substituents may be bonded to each other to form a ring. Derivatives of polymer compounds (resin materials) may also be called "modified products."

[0041] The "copolymer" includes at least one type selected from the group consisting of unspecified type, statistical type, random type, alternating type, periodic type, block type, and graft type.

[0042] <Cathode active material> Hereinafter, the positive electrode active material in this embodiment may be abbreviated as "the present positive electrode active material." The present positive electrode active material is for use in a secondary battery. The positive electrode active material includes secondary particles. The positive electrode active material may be an aggregate (powder) of secondary particles. The D50 of the present positive electrode active material may be, for example, 0.1 μm or more, 1 μm or more, 5 μm or more, or 10 μm or more. The D50 may be, for example, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0043] ·Secondary particles As shown in FIG. 3, the secondary particle 2 is an aggregate of crystallites 1. The secondary particle 2 has any shape. The secondary particle 2 may be, for example, spherical, ellipsoidal, or lumpy. In a cross-sectional SEM image of the secondary particle 2, the outline of the secondary particle 2 may have a circularity of, for example, 0.8 or more. The circularity may be, for example, 0.85 or more, 0.90 or more, or 0.95 or more. The "circularity" is calculated by the following formula. Cr=4πS / L 2 Cr: Circularity π: Pi S: Cross-sectional area of ​​secondary particle 2 (area of ​​the region surrounded by the outline of secondary particle 2) L: Perimeter of secondary particle 2 (length of the outline of secondary particle 2)

[0044] The maximum Feret diameter (D) of the secondary particles 2 may be, for example, 1 μm or more, 5 μm or more, 10 μm or more, 12.8 μm or more, 13.2 μm or more, 13.5 μm or more, 14.8 μm or more, 17.3 μm or more, or 20 μm or more. The maximum Feret diameter (D) may be, for example, 30 μm or less, 25 μm or less, 20 μm or less, 17.3 μm or less, 14.8 μm or less, 13.5 μm or less, 13.2 μm or less, 12.8 μm or less, or 10 μm or less.

[0045] Crystallites The secondary particle 2 includes a plurality of crystallites 1. In a cross-sectional SEM image of the secondary particle 2, the number of crystallites 1 included in one secondary particle 2 may be, for example, 10 or more, 50 or more, 100 or more, 150 or more, or 200 or more. The number of crystallites 1 included in one secondary particle 2 may be, for example, 500 or less, 250 or less, 200 or less, 150 or less, 100 or less, or 50 or less.

[0046] For example, 4.0≦D / d L The relationship of ≦9.0 may be satisfied. L) may be, for example, 5.1 or more, 5.5 or more, or 6.8 or more. L ) may be, for example, 6.8 or less, 5.5 or less, or 5.1 or less.

[0047] The crystallite 1 may be, for example, rod-shaped, column-shaped, needle-shaped, etc. For example, 6.4≦d L / d S The aspect ratio (d L / d S The aspect ratio (d) may be, for example, 7.5 or more, 10.4 or more, or 13.5 or more. L / d S ) may be, for example, 13.5 or less, 10.4 or less, or 7.5 or less.

[0048] The multiple crystallites 1 are arranged radially from the center of the secondary particle 2 outward. For example, the relationship θ≦45° may be satisfied. The angle (θ) may be, for example, 47.3° or less, 44.3° or less, 30° or less, 26.8° or less, 15° or less, 10° or less, 5.6° or less, 2.1° or less, or 1° or less. The angle (θ) may be, for example, 0° or more, 1° or more, 2.1° or more, 5.6° or more, 10° or more, 15° or more, 26.8° or more, 30° or more, or 44.3° or more.

[0049] Open pores On the surface of the secondary particle 2, open pores 3 are formed between adjacent crystallites 1. The open pores 3 may extend from the particle surface toward the particle center. The open pores 3 have an opening diameter (Pd) of 20 nm or more. The opening diameter (Pd) may be, for example, 50 nm or more, 87 nm or more, 100 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, or 248 nm or more. The opening diameter (Pd) may be, for example, less than 250 nm, 248 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 100 nm or less, 87 nm or less, or 50 nm or less. That is, the relationship 20 nm≦Pd<250 nm may be satisfied.

[0050] The maximum depth of the open pores 3 from the surface of the secondary particles 2 may be, for example, 0.01D or more, 0.05D or more, 0.1D or more, 0.2D or more, 0.3D or more, or 0.4D or more. "D" indicates the maximum Feret diameter of the secondary particles 2. For example, "0.1D" indicates 0.1 times D. The maximum depth of the open pores 3 may be, for example, 0.5D or less, 0.4D or less, 0.3D or less, 0.2D or less, 0.1D or less, or 0.05D or less.

[0051] Crystal structure Crystallite 1 may consist of a single crystal (single crystal). The lithium metal composite oxide has a layered rock-salt structure. The layered rock-salt structure is also referred to as an "α-NaFeO2 structure." The space group of the layered rock-salt structure is "R-3m." Note that the "- (bar)" is normally placed above the "3," but is placed before the "3" for convenience. The crystal structure can be identified by powder X-ray diffraction (XRD). The layered rock-salt structure has 100 and 003 faces. The 100 face may be detected on the end face of crystallite 1 (columnar body). The 003 face may be detected on the side face (peripheral face) of crystallite 1. The crystal faces can be detected, for example, by transmission electron microscopy (TEM) analysis.

[0052] ·Chemical composition The lithium metal composite oxide may have any chemical composition, for example, a composition represented by the following general formula: Li 1-a MO2 In the formula, the relationship of -0.5≦a≦0.5 is satisfied, and M includes at least one element selected from the group consisting of Ni, Co, Mn, and Al.

[0053] The lithium metal composite oxide may be doped with B or the like. That is, the lithium metal composite oxide may have a composition represented by the following general formula, for example. Li 1-a MO2B b In the formula, the relationship of -0.5 ≤ a ≤ 0.5 and 0.002 ≤ b ≤ 0.030 is satisfied. M contains at least one selected from the group consisting of Ni, Co, Mn, and Al. For example, the relationship of 0.002 ≤ b ≤ 0.005, 0.005 ≤ b ≤ 0.010, or 0.010 ≤ b ≤ 0.030 may be satisfied.

[0054] B may be diffused throughout the particles or may be locally distributed. For example, B may be unevenly distributed on the particle surface. B may be a substitutional solid solution atom or an interstitial solid solution atom.

[0055] The composition of the lithium metal composite oxide may be represented by, for example, the following general formula. Li 1-a Ni x M 1-x O2 In the formula, the relationship of -0.5 ≤ a ≤ 0.5 and 0 ≤ x ≤ 1 is satisfied. M may contain, for example, at least one selected from the group consisting of Co, Mn, and Al. For example, the relationship of 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x ≤ 1 may be satisfied. For example, the relationship of -0.4 ≤ a ≤ 0.4, -0.3 ≤ a ≤ 0.3, -0.2 ≤ a ≤ 0.2, or -0.1 ≤ a ≤ 0.1 may be satisfied.

[0056] The lithium metal composite oxide may contain, for example, at least one selected from the group consisting of LiCoO2, LiMnO2, LiNi 0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O2, and LiNiO2.

[0057] The composition of the lithium metal composite oxide may be represented by, for example, the following general formula. The compound represented by the following general formula may also be referred to as "NCM". Li 1-a Nix Co y Mn z O2 In the formula, the relationships of -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied. For example, the relationship of 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x < 1 may be satisfied. For example, the relationship of 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9, or 0.9 ≤ y < 1 may be satisfied. For example, the relationship of 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1 may be satisfied.

[0058] NCM is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and LiNi 0.9 Co 0.05 Mn 0.05 It may contain at least one selected from the group consisting of O2.

[0059] The composition of the lithium metal composite oxide may be represented by, for example, the following general formula. The compound represented by the following general formula may also be referred to as "NCA". Li 1-a Ni x Co y Al z O2 In the formula, the relationships of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied. For example, the relationships of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1 may be satisfied. For example, the relationships of 0 < y ≦ 0.1, 0.1 ≦ y ≦ 0.2, 0.2 ≦ y ≦ 0.3, 0.3 ≦ y ≦ 0.4, 0.4 ≦ y ≦ 0.5, 0.5 ≦ y ≦ 0.6, 0.6 ≦ y ≦ 0.7, 0.7 ≦ y ≦ 0.8, 0.8 ≦ y ≦ 0.9, or 0.9 ≦ y < 1 may be satisfied. For example, the relationships of 0 < z ≦ 0.1, 0.1 ≦ z ≦ 0.2, 0.2 ≦ z ≦ 0.3, 0.3 ≦ z ≦ 0.4, 0.4 ≦ z ≦ 0.5, 0.5 ≦ z ≦ 0.6, 0.6 ≦ z ≦ 0.7, 0.7 ≦ z ≦ 0.8, 0.8 ≦ z ≦ 0.9, or 0.9 ≦ z < 1 may be satisfied.

[0060] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O2, LiNi0.7 Co 0.2 Al 0.1 O2, LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi 0.8 Co 0.17 Al 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and LiNi 0.9 Co 0.05 Al 0.05 O2.

[0061] For NCM, NCA, etc., for example, the general formula "Li 1-a Ni x M 1-x O2B b ”, general formula “Li 1-a Ni x Co y Mn z O2B b ”, general formula “Li 1-a Ni x Co y Al z O2B b ", it may contain B.

[0062] A dopant other than B may be added to the lithium metal composite oxide. A dopant other than B may be added alone, or both a dopant other than B and B may be added. The amount of dopant other than B added (substance amount fraction relative to the entire positive electrode active material) may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%. Two or more dopants other than B may be used.

[0063] The dopant other than B may include at least one selected from the group consisting of, for example, C, N, halogen, Si, Na, Mg, Al, Mn, Co, Cr, Sc, Ti, V, Cu, Zn, Ga, Ge, Se, Sr, Y, Zr, Nb, Mo, In, Pb, Bi, Sb, Sn, W, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and actinides.

[0064] <Method of manufacturing positive electrode active material> 5 is a schematic flowchart of a method for producing a positive electrode active material according to this embodiment. Hereinafter, the method for producing a positive electrode active material according to this embodiment may be abbreviated as "this production method." This production method includes "(a) preparation of metal hydroxide," "(b) mixing," "(c) first heat treatment," and "(d) second heat treatment." This production method may further include, for example, "(e) crushing."

[0065] (a) Preparation of metal hydroxides The production method includes preparing a metal hydroxide. The metal hydroxide is a precursor of a lithium metal composite oxide. The metal hydroxide may be synthesized, for example, by a coprecipitation method. For example, a sulfate may be prepared. The sulfate may include, for example, at least one selected from the group consisting of NiSO4, CoSO4, MnSO4, and Al2(SO4)3. A raw material solution is prepared by dissolving the sulfate in water. The mass concentration of the raw material solution may be, for example, 10 to 50%. A precipitate of the metal hydroxide may be generated by dropping the raw material solution into an alkaline aqueous solution. For example, the precipitate (metal hydroxide) may be collected by filtration. After collection, the metal hydroxide may be washed with water. After washing with water, the metal hydroxide may be dried.

[0066] ·(b) Mixture The method includes mixing a metal hydroxide, a lithium compound, and a crystallization control material to form a first mixture. For example, the materials may be mixed and ground in a mortar or the like.

[0067] "Lithium compound" refers to a compound containing Li. The lithium compound may, for example, contain at least one selected from the group consisting of LiOH and Li2CO3. The lithium compound is a Li source for a lithium metal composite oxide. The ratio of the substance amount of Li to the substance amount of the metal hydroxide (precursor) may, for example, be 0.5 or more, 0.75 or more, 1 or more, 1.1 or more, or 1.25 or more. The ratio may, for example, be 1.5 or less, 1.25 or less, 1.1 or less, 1 or less, or 0.75 or less.

[0068] The crystallinity control material includes B2O3. It is believed that secondary particles having radially arranged crystallites and open pores can be formed by combining the crystallinity control material, the first heat treatment, and the second heat treatment. The ratio of the amount of substance of the crystallinity control material to the amount of substance of the metal hydroxide (precursor) may be, for example, 0.001 to 0.015. This ratio may be, for example, 0.0025 or more, 0.005 or more, or 0.010 or more. This ratio may be, for example, 0.010 or less, 0.005 or less, or 0.0025 or less.

[0069] (c) First heat treatment, (d) Second heat treatment The method includes subjecting the first mixture to a first heat treatment to form a second mixture. The method further includes subjecting the second mixture to a second heat treatment to synthesize a positive electrode active material. The first and second heat treatments are performed in an oxygen atmosphere.

[0070] The first heat treatment is carried out at a temperature of 600 to 700°C for 6 to 12 hours. The temperature of the first heat treatment may be, for example, 650°C or higher or 650°C or lower. The time of the first heat treatment may be, for example, 8 hours or higher, 9 hours or higher, 10 hours or higher, or 11 hours or higher. The time of the first heat treatment may be, for example, 11 hours or lower, 10 hours or lower, 9 hours or lower, or 8 hours or lower.

[0071] The second heat treatment is carried out at a temperature of 1100 to 1300°C for 1 to 3 hours. The temperature of the second heat treatment may be, for example, 1150°C or higher, 1200°C or higher, or 1250°C or higher. The temperature of the second heat treatment may be, for example, 1250°C or lower, 1200°C or lower, or 1150°C or lower. The duration of the second heat treatment may be, for example, 1.5 hours or higher, 2 hours or higher, or 2.5 hours or higher. The duration of the second heat treatment may be, for example, 2.5 hours or lower, 2 hours or lower, or 1.5 hours or lower.

[0072] (e) Crushing The present production method may include crushing the lithium metal composite oxide. Any crusher (e.g., a jet mill, etc.) can be used. By crushing, the particle size of the lithium metal composite oxide can be adjusted.

[0073] ·others For example, when the present positive electrode active material is for an all-solid-state battery, a coating treatment may be applied to the secondary particles 2. The coating material may contain, for example, LiNbO3, LiTiO3, Li3PO4, etc. The coating treatment may be performed by, for example, a mechanochemical method, a spray-drying method, etc.

[0074] <Secondary battery> FIG. 6 is a conceptual diagram of a secondary battery according to this embodiment. The battery 100 is a secondary battery. "Secondary battery" refers to a rechargeable battery. The battery 100 includes a positive electrode 10, a negative electrode 20, and an electrolyte. The battery 100 may further include a separator 30. The positive electrode 10 includes the present positive electrode active material. That is, the battery 100 includes the present positive electrode active material. The battery 100 may have any configuration as long as it includes the present positive electrode active material. The battery 100 may be, for example, a liquid battery, a polymer battery, or an all-solid-state battery. The battery 100 may be, for example, a monopolar battery or a bipolar battery. The positive electrode 10 and the negative electrode 20 may form a power generating element. The "power generating element" may also be referred to as a storage element, an electrode body, an electrode group, or the like. The power generating element may be, for example, a wound type or a stacked type.

[0075] Exterior body The battery 100 may include an exterior body. The exterior body may house a power generating element. The exterior body may be, for example, a metal case or a laminated film pouch. The case may have any shape. For example, the case may be cylindrical, rectangular, flat, coin-shaped, or the like. The exterior body may contain, for example, Al.

[0076] ·Positive electrode The positive electrode may be, for example, in the form of a sheet. The positive electrode may include, for example, a substrate and a positive electrode active material layer. The substrate is conductive. The substrate can support the positive electrode active material layer. The substrate may be, for example, in the form of a sheet. The substrate may have a thickness of, for example, 5 to 50 μm. The substrate may include, for example, a metal foil. The substrate may include, for example, at least one selected from the group consisting of Al, Mn, Ti, Fe, and Cr. The substrate may include, for example, Al foil, Al alloy foil, Ti foil, stainless steel (SUS) foil, etc.

[0077] An intermediate layer may be formed between the substrate and the positive electrode active material layer. The intermediate layer does not contain a positive electrode active material. The intermediate layer may have a thickness of, for example, 0.1 to 5 μm. The intermediate layer may contain, for example, a conductive material, an insulating material, a binder, etc. The conductive material may contain, for example, carbon black, etc. The insulating material may contain, for example, alumina, boehmite, aluminum hydroxide, etc. The binder may contain, for example, polyvinylidene fluoride (PVdF), etc.

[0078] The positive electrode active material layer may be disposed on the surface of the substrate. The positive electrode active material layer may be disposed on only one side of the substrate. The positive electrode active material layer may be disposed on both sides of the substrate. The thickness of the positive electrode active material layer may be, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The positive electrode active material layer includes the present positive electrode active material. The positive electrode active material layer may further include other positive electrode active materials in addition to the present positive electrode active material. The other positive electrode active materials may include, for example, lithium iron phosphate. The mass fraction of the present positive electrode active material relative to the total positive electrode active material may be, for example, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0079] The positive electrode active material layer may further contain, for example, a conductive material and a binder. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material. The conductive material may contain any component. The conductive material may include, for example, at least one selected from the group consisting of graphite, acetylene black (AB), Ketjen Black (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF).

[0080] The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of PVdF, vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), (PTFE), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, and derivatives thereof.

[0081] The positive electrode active material layer may further contain, for example, an inorganic filler, an organic filler, a solid electrolyte, a surface modifier, a dispersant, a lubricant, a flame retardant, a protective agent, a fluxing agent, a coupling agent, an adsorbent, etc. The positive electrode active material layer may also contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, a silane coupling agent, MoS2, WO3, etc.

[0082] ·Negative electrode The negative electrode 20 may be, for example, in the form of a sheet. The negative electrode may include, for example, a substrate and a negative electrode active material layer. The substrate can support the negative electrode active material layer. The substrate may have a thickness of, for example, 5 to 50 μm. The substrate may include, for example, at least one selected from the group consisting of Cu and Ni. The substrate may include, for example, Cu foil, Cu alloy foil, Ni foil, etc.

[0083] The negative electrode active material layer may be disposed on the surface of the substrate. The negative electrode active material layer may be disposed on only one side of the substrate. The negative electrode active material layer may be disposed on both sides of the substrate. The thickness of the negative electrode active material layer may be, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material layer may further include, for example, a conductive material, a binder, etc.

[0084] The conductive material may be blended in an amount of, for example, 0.1 to 10 parts by mass per 100 parts by mass of the negative electrode active material. The conductive material may contain any component. For example, the conductive material may contain at least one selected from the group consisting of AB, Ketjen Black, VGCF, CNT, and GF.

[0085] The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the negative electrode active material. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of styrene butadiene rubber (SBR), acrylate butadiene rubber (ABR), sodium alginate, CMC (CMC-H, CMC-Na, CMC-Li, CMC-NH4, etc.), PAA (PAA-H, PAA-Na, PAA-Li, etc.), polyacrylonitrile (PAN), PVdF, PTFE, acrylic resin, methacrylic resin, PVP, PVA, and derivatives thereof. For example, "CMC-Na" refers to the Na salt of CMC. For example, "CMC-H" refers to acid-type CMC. The same applies to "PAA-Na" and the like.

[0086] The negative electrode active material layer may further contain, for example, an inorganic filler, an organic filler, a solid electrolyte, a surface modifier, a dispersant, a lubricant, a flame retardant, a protective agent, a fluxing agent, a coupling agent, an adsorbent, etc. The negative electrode active material layer may also contain, for example, a layered silicate (smectite, montmorillonite, bentonite, hectorite, etc.), an inorganic filler (solid alumina, hollow silica, boehmite, etc.), a polysiloxane compound, etc.

[0087] The negative electrode active material may be in the form of, for example, particles or a sheet. The D50 of the negative electrode active material may be, for example, 1 to 30 μm, 10 to 20 μm, or 1 to 10 μm.

[0088] The negative electrode active material may include, for example, a carbon-based active material. The carbon-based active material may include, for example, at least one selected from the group consisting of graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. The graphite may be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1," "natural graphite / artificial graphite = 2 / 8 to 8 / 2," or "natural graphite / artificial graphite = 3 / 7 to 7 / 3."

[0089] Graphite may contain a dopant. The dopant may include, for example, at least one selected from the group consisting of B, N, P, Li, and Ca. The addition amount may be, in terms of the amount-of-substance fraction, for example, from 0.01 to 5%, from 0.1 to 3%, or from 0.1 to 1%.

[0090] The surface of the graphite may be coated with, for example, amorphous carbon. The surface of the graphite may be coated with, for example, a different material. The different material may include, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may include, for example, at least one selected from the group consisting of Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO 3、 and Li3PO4.

[0091] The negative electrode active material may include, for example, an alloy-based active material. The negative electrode active material may include, for example, at least one selected from the group consisting of Si, Li silicate, SiO, Si-based alloy, Sn, SnO, and Sn-based alloy.

[0092] SiO may be represented, for example, by the following general formula. SiO x In the formula, the relationship 0 < x < 2 is satisfied. For example, the relationship 0.5 ≤ x ≤ 1.5, or 0.8 ≤ x ≤ 1.2 may be satisfied.

[0093] Li silicate may include, for example, at least one selected from the group consisting of Li4SiO4, Li2SiO3, Li2Si2O5, and Li8SiO6. The negative electrode active material may include, for example, a mixture of Si and Li silicate. The mixing ratio (mass ratio) may be, for example, "Si / Li silicate = 1 / 9 to 9 / 1", "Si / Li silicate = 2 / 8 to 8 / 2", "Si / Li silicate = 3 / 7 to 7 / 3", or "Si / Li silicate = 4 / 6 to 6 / 4".

[0094] The alloy-based active material (e.g., Si, SiO) may contain an additive. The additive may be, for example, a substitutional solute atom or an interstitial solute atom. The additive may be a deposit attached to the surface of the alloy-based active material. The deposit may be, for example, an element, an oxide, a carbide, a nitride, a halide, or the like. The amount of the additive may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1% in terms of substance fraction. The additive may include, for example, at least one selected from the group consisting of Li, Na, K, Rb, Be, Mg, Ca, Sr, Fe, Ba, B, Al, Ga, In, C, Ge, Sn, Pb, N, P, As, Y, Sb, and S. That is, SiO may be doped with Mg or Na. For example, Mg silicate, Na silicate, etc. may be formed. For example, boron oxide (for example, B2O3, etc.), yttrium oxide (for example, Y2O3, etc.), etc. may be added to SiO.

[0095] The negative electrode active material may include, for example, a composite material of a carbon-based active material (such as graphite) and an alloy-based active material (such as Si). A composite material containing Si and carbon may also be referred to as a "Si-C composite material." For example, Si fine particles may be dispersed within carbon particles. For example, Si fine particles may be dispersed within graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon).

[0096] The negative electrode active material is, for example, Li metal, Li-based alloy, and Li4Ti5O 12 The negative electrode active material may contain at least one selected from the group consisting of: The negative electrode active material may contain, for example, Li foil or the like.

[0097] ·Liquid electrolyte (electrolyte) The battery 100 may include an electrolyte. That is, the battery 100 may be a liquid-based battery. The electrolyte includes a supporting salt and a solvent. The supporting salt is also called a "supporting electrolyte." The concentration of the supporting salt (salt concentration) may be, for example, 0.5 to 1 mol / L, 1 to 1.5 mol / L, 1.5 to 2 mol / L, 2 to 2.5 mol / L, or 2.5 to 3 mol / L. "mol / L" may also be written as "M." The supporting salt may include, for example, an inorganic acid salt, an imide salt, an oxalate complex, a halide, or the like. The supporting salt may include at least one selected from the group consisting of, for example, LiPF6, LiBF4, LiClO4, LiAsF6, LiSbF6, LiN(SO2F)2 "LiFSI", LiN(SO2CF3)2 "LiTFSI", LiB(C2O4)2 "LiBOB", LiBF2(C2O4) "LiDFOB", LiPF2(C2O4)2 "LiDFOP", LiPO2F2, FSO3Li, LiI, LiBr, and derivatives thereof.

[0098] The electrolytic solution may contain, for example, a carbonate-based solvent (carbonate ester-based solvent). The solvent may contain, for example, a cyclic carbonate, a chain carbonate, a fluorinated carbonate, or the like. The solvent may contain, for example, at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (FEC), difluoroethylene carbonate, 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene carbonate, fluoropropylene carbonate, difluoropropylene carbonate, and derivatives thereof.

[0099] The solvent may contain a cyclic carbonate (EC, PC, FEC, etc.) and a chain carbonate (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate to the chain carbonate may be, for example, "cyclic carbonate / chain carbonate = 1 / 9 to 4 / 6," "cyclic carbonate / chain carbonate = 2 / 8 to 3 / 7," or "cyclic carbonate / chain carbonate = 3 / 7 to 4 / 6."

[0100] The solvent may contain a cyclic carbonate (EC, PC, etc.) and a fluorinated cyclic carbonate (FEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate to the fluorinated cyclic carbonate may be, for example, "cyclic carbonate / fluorinated cyclic carbonate = 99 / 1 to 90 / 10," "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 1 / 9," "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 7 / 3," or "cyclic carbonate / fluorinated cyclic carbonate = 3 / 7 to 1 / 9."

[0101] The solvent may contain, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy, for example, the relationship represented by the following formula: V EC +V FEC +V EMC +V DMC +V DEC =10 In the formula, V EC , V FEC , V EMC , V DMC , V DEC indicates the volume ratio of EC, FEC, EMC, DMC, and DEC, respectively. 1≦V EC ≦4, 0≦V FEC ≦3, V EC +V FEC ≦4, 0≦V EMC ≦9, 0≦V DMC ≦9, 0≦V DEC ≦9, 6≦V EMC +V DMC +V DEC ≦9 The relationship is satisfied. For example, 1 ≤ V EC ≦2, or 2≦V EC The relationship ≦3 may be satisfied. For example, 1 ≤ V FEC ≦2, or 2≦V FEC The relationship ≦4 may be satisfied. For example, 3≦V EMC ≦4, or 6≦V EMC The relationship ≦8 may be satisfied. For example, 3≦V DMC ≦4, or 6≦V DMC The relationship ≦8 may be satisfied. For example, 3≦V DEC ≦4, or 6≦V DEC The relationship ≦8 may be satisfied.

[0102] The solvent may have a composition, for example, in volume ratios of "EC / EMC=3 / 7," "EC / DMC=3 / 7," "EC / FEC / DEC=1 / 2 / 7," "EC / DMC / EMC=3 / 4 / 3," "EC / DMC / EMC=3 / 3 / 4," "EC / FEC / DMC / EMC=2 / 1 / 4 / 3," "EC / FEC / DMC / EMC=1 / 2 / 4 / 3," "EC / FEC / DMC / EMC=2 / 1 / 3 / 4," or "EC / FEC / DMC / EMC=1 / 2 / 3 / 4."

[0103] The electrolyte may contain an ether-based solvent, such as at least one selected from the group consisting of tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), hydrofluoroether (HFE), ethylglyme, triglyme, tetraglyme, and derivatives thereof.

[0104] The electrolyte may contain any additive. The amount of additive (mass fraction relative to the total amount of the electrolyte) may be, for example, 0.01 to 5%, 0.05 to 3%, or 0.1 to 1%. The additive may include, for example, an SEI (Solid Electrolyte Interphase) formation promoter, an SEI formation inhibitor, a gas generating agent, an overcharge inhibitor, a flame retardant, an antioxidant, an electrode protectant, a surfactant, etc.

[0105] Examples of the additives include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfite (ES), ethylene sulfate (DTD), γ-butyrolactone, phosphazene compounds, carboxylic acid esters (e.g., methyl formate (MF), methyl acetate (MA), methyl propionate (MP), diethyl malonate (DEM), etc.), fluorobenzenes (e.g., monofluorobenzene (FB), 1,2-difluoropropane (DEM), etc.), and the like. fluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, etc.), fluorotoluenes (e.g., 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene, 3,4-difluorotoluene, octafluorotoluene, etc.), benzotrifluorides (e.g., benzotrifluoride, 2-fluorobenzotrifluoride, 3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, 2-methylbenzotrifluoride, 3-methylbenzotrifluoride, 4-methylbenzotrifluoride, etc.), fluoroxylenes (e.g., 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m-xylene, etc.), sulfur-containing heterocyclic compounds (e.g., benzothiazole, 2-methylbenzotrifluoride, The solvent may contain at least one selected from the group consisting of benzotriazole, benzotriazole, tetrathiafulvalene, etc.), nitrile compounds (e.g., adiponitrile, succinonitrile, etc.), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate, etc.), carboxylic acid anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, etc.), alcohols (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, diethylene glycol monomethyl ether, etc.), and derivatives thereof.

[0106] The components described above as the supporting salt and the solvent may be used as minor components (additives). The additives may include, for example, at least one selected from the group consisting of LiBF, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPOF, FSOLi, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0107] The electrolyte may contain an ionic liquid, which may include, for example, at least one selected from the group consisting of sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, imidazolium salts, and derivatives thereof.

[0108] Gel electrolyte The electrolyte and the polymer material may form a gel electrolyte. That is, the battery 100 may be a polymer battery. The polymer material may form a polymer matrix. The polymer material may include, for example, at least one selected from the group consisting of PVdF, PVdF-HFP, PAN, PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0109] ·Solid electrolyte The battery 100 may include a solid electrolyte. That is, the battery 100 may be an all-solid-state battery. The solid electrolyte may be, for example, a powder. The D50 of the solid electrolyte may be, for example, 0.1 to 3 μm.

[0110] The solid electrolyte may include, for example, a sulfide solid electrolyte. The sulfide solid electrolyte may be, for example, glass ceramics or argyrodite. Examples of sulfide solid electrolytes include LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-GeS2-P2S5, Li2S-P2S5, and Li 10 GeP2S 12 , Li4P2S6, Li7P3S 11 , Li3PS4, Li7PS6, and Li6PS5X (X = Cl, Br, I).

[0111] For example, "LiI-LiBr-Li3PS4" refers to a sulfide solid electrolyte produced by mixing "LiI, LiBr, and Li3PS4" in any molar ratio. For example, the sulfide solid electrolyte may be produced by a mechanochemical method. "Li2S-P2S5" includes Li3PS4. Li3PS4 can be produced, for example, by mixing Li2S and P2S5 in a molar ratio of Li2S / P2S5 = 75 / 25.

[0112] The solid electrolyte may, for example, contain a halide solid electrolyte. The halide solid electrolyte may, for example, have a composition represented by the following general formula. Li 6-na M a X6 In the formula, n represents the oxidation number of M. M may, for example, contain an atom having an oxidation number of +3. M may, for example, contain an atom having an oxidation number of +4. M may, for example, contain at least one selected from the group consisting of Y, Al, Ti, Zr, Ca, and Mg. The relationship 0 < a < 2 may be satisfied. X may, for example, contain at least one selected from the group consisting of F, Cl, Br, and I.

[0113] The halide solid electrolyte may, for example, have a composition represented by the following general formula. Li 3-a Ti a Al 1-a F6 In the formula, for example, the relationship 0 ≦ a ≦ 0.1, 0.1 ≦ a ≦ 0.2, 0.2 ≦ a ≦ 0.3, 0.3 ≦ a ≦ 0.4, 0.4 ≦ a ≦ 0.5, 0.5 ≦ a ≦ 0.6, 0.6 ≦ a ≦ 0.7, 0.7 ≦ a ≦ 0.8, 0.8 ≦ a ≦ 0.9, or 0.9 ≦ a ≦ 1 may be satisfied.

[0114] The halide solid electrolyte may, for example, have a composition represented by the following general formula. Li3YCl a Br b I 6-a-b In the formula, the relationship 0 ≦ a + b ≦ 6 is satisfied. For example, the relationship 0 ≦ a ≦ 1, 1 ≦ a ≦ 2, 2 ≦ a ≦ 3, 3 ≦ a ≦ 4, 4 ≦ a ≦ 5, or 5 ≦ a ≦ 6 may be satisfied. For example, the relationship 0 ≦ b ≦ 1, 1 ≦ b ≦ 2, 2 ≦ b ≦ 3, 3 ≦ b ≦ 4, 4 ≦ b ≦ 5, or 5 ≦ b ≦ 6 may be satisfied.

[0115] The solid electrolyte may, for example, contain an oxide solid electrolyte. The oxide solid electrolyte is, for example, LiNbO3, Li 1.5Al 0.5 Ge 1.5 (PO4)3, La 2 / 3-x Li 3x TiO3 and Li7La3Zr2O 12 It may contain at least one selected from the group consisting of:

[0116] The solid electrolyte may include, for example, a hydride solid electrolyte. The hydride solid electrolyte may include, for example, LiBH4 or the like. The solid electrolyte may include, for example, a nitride solid electrolyte. The nitride solid electrolyte may include, for example, Li3N, Li3BN2 or the like.

[0117] Separator The battery 100 may include a separator 30. The separator 30 can separate the positive electrode 10 from the negative electrode 20. The separator 30 has electrical insulation properties. The separator 30 may include, for example, a resin film. The resin film is porous. The resin film may include, for example, a microporous film, a nonwoven fabric, or the like. The resin film includes a resin skeleton. The resin skeleton may be continuous, for example, in a network form. Pores are formed in the gaps in the resin skeleton. The average pore diameter of the resin film may be, for example, 0.01 to 1 μm, or 0.1 to 0.5 μm. The "average pore diameter" can be measured by mercury intrusion porosimetry. The Gurley value of the resin film is, for example, 50 to 250 s / 100 cm. 3 The "Gurley value" can be measured by the Gurley test method.

[0118] The resin film may contain at least one selected from the group consisting of, for example, olefin-based resins, polyurethane-based resins, polyamide-based resins, cellulose-based resins, polyether-based resins, acrylic-based resins, and polyester-based resins. The resin film may contain at least one selected from the group consisting of, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and derivatives thereof. The resin film may be formed by, for example, a stretching method, a phase separation method, or the like. The thickness of the resin film may be, for example, 5 to 50 μm, or 10 to 25 μm.

[0119] The resin film may have, for example, a single-layer structure. The resin film may be composed of, for example, a PE layer. The skeleton of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multi-layer structure. The resin film may include, for example, a PP layer and a PE layer. The skeleton of the PP layer is formed of PP. The resin film may have, for example, a three-layer structure. The resin film may be formed by laminating, for example, a PP layer, a PE layer, and a PP layer in this order. The thickness of the PE layer may be, for example, 5 to 20 μm. The thickness of the PP layer may be, for example, 3 to 10 μm.

[0120] In an all-solid-state battery, the solid electrolyte layer can function as the separator 30.

[0121] Battery configuration FIG. 7 is a table showing a first battery configuration. FIG. 8 is a table showing a second battery configuration. FIG. 9 is a table showing a third battery configuration. Each battery configuration is an example of a liquid-based battery or a polymer battery configuration. A portion of each battery configuration may be applied to an all-solid-state battery. In each figure, when multiple materials are listed in a box, the description includes each material alone and combinations thereof. For example, when materials "α, β, γ" are listed in a box, the description indicates "at least one selected from the group consisting of α, β, and γ." Any element may be extracted from each battery configuration and combined in any manner. [Example]

[0122] <Production of positive electrode active material> No.1 FIG. 10 is a table showing the experimental results. No. 1 positive electrode active material was produced by the first synthesis method. NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to form a raw material solution. In the raw material solution, the molar ratio of Ni, Co, and Mn was "Ni / Co / Mn=1 / 1 / 1." The solute concentration in the raw material solution was 30% (mass fraction).

[0123] Ammonia water was placed in a reaction vessel. While stirring the ammonia water with a stirrer, the atmosphere in the reaction vessel was replaced with nitrogen. NaOH was then added to the reaction vessel to form a reaction liquid.

[0124] The raw material solution and ammonia water were added dropwise to the reaction solution so that the pH of the reaction solution remained within a certain range, thereby forming a precipitate (metal hydroxide). The reaction solution was filtered, thereby recovering the metal hydroxide. The metal hydroxide was dispersed in ion-exchanged water, thereby forming a dispersion. The dispersion was thoroughly stirred with a spatula. That is, the metal hydroxide was washed with water. After washing with water, the dispersion was filtered, thereby recovering the metal hydroxide. The metal hydroxide was dried at 120°C for 16 hours, thereby forming a dried product.

[0125] The dried material and a lithium compound (Li2CO3) were mixed in a mortar to form a mixture. The ratio of the amount of Li to the amount of metal hydroxide was 1.1.

[0126] The mixture was subjected to heat treatment in a muffle furnace to synthesize a lithium metal composite oxide. The heat treatment consisted of one stage. The heat treatment conditions were as follows. After the heat treatment, the particle size of the lithium metal composite oxide was adjusted using a jet mill.

[0127] Atmosphere: Oxygen atmosphere Temperature: 800 to 1100°C Duration: 10 hours

[0128] No.2 No. 2 positive electrode active material was produced by the second synthesis method. The second synthesis method differs from the first synthesis method in the heat treatment. A raw material solution was formed by dissolving NiSO4, CoSO4, and MnSO4 in ion-exchanged water. In the raw material solution, the molar ratio of Ni, Co, and Mn was "Ni / Co / Mn = 8 / 1 / 1." The solute concentration in the raw material solution was 30% (mass fraction).

[0129] Ammonia water was placed in a reaction vessel. While stirring the ammonia water with a stirrer, the atmosphere in the reaction vessel was replaced with nitrogen. NaOH was then added to the reaction vessel to form a reaction liquid.

[0130] The raw material solution and ammonia water were added dropwise to the reaction solution so that the pH of the reaction solution remained within a certain range, thereby forming a precipitate (metal hydroxide). The reaction solution was filtered, thereby recovering the metal hydroxide. The metal hydroxide was dispersed in ion-exchanged water, thereby forming a dispersion. The dispersion was thoroughly stirred with a spatula. That is, the metal hydroxide was washed with water. After washing with water, the dispersion was filtered, thereby recovering the metal hydroxide. The metal hydroxide was dried at 120°C for 16 hours, thereby forming a dried product.

[0131] The dried material and a lithium compound (Li2CO3) were mixed in a mortar to form a mixture. The ratio of the amount of Li to the amount of metal hydroxide was 1.1.

[0132] A lithium metal composite oxide was synthesized by carrying out a first heat treatment and a second heat treatment in this order in a muffle furnace. The heat treatment conditions were as follows. After the heat treatment, the particle size of the lithium metal composite oxide was adjusted using a jet mill.

[0133] First heat treatment Atmosphere: Oxygen atmosphere Temperature: 600 to 700°C Duration: 10 hours

[0134] Second heat treatment Atmosphere: Oxygen atmosphere Temperature: 1100 to 1300°C Duration: 2 hours

[0135] No.3 A positive electrode active material was produced in the same manner as in No. 1, except that a crystallinity control material (BO) was added when the dried material (metal hydroxide) and the lithium compound (LiCO) were mixed in a mortar. The ratio of the amount of crystallinity control material to the amount of metal hydroxide was 0.100.

[0136] No.4 A positive electrode active material was produced in the same manner as in No. 2, except that a crystallinity control material (BO) was added when the dried material (metal hydroxide) and the lithium compound (LiCO) were mixed in a mortar. The ratio of the amount of crystallinity control material to the amount of metal hydroxide was 0.001.

[0137] No.5 to No.8 A positive electrode active material was prepared in the same manner as in No. 4, except that the amount of crystallinity control material (B2O3) added was changed.

[0138] <Evaluation> A cylindrical lithium-ion secondary battery (evaluation cell) was manufactured. The evaluation cell had the following configuration:

[0139] Power generating element: Wound type Positive electrode: Positive electrode active material / AB / PVDF=88 / 10 / 2 (mass ratio) Negative electrode: Negative electrode active material (natural graphite), CMC, SBR Electrolyte: LiPF6 (1 mol / L), EC / DMC / EMC = 3 / 4 / 3 (volume ratio)

[0140] The positive and negative electrodes were manufactured by coating the surface of the substrate (metal foil) with the slurry. An Allgood film applicator (with film thickness adjustment function) was used as the coating device. After coating the slurry, the coating was dried at 80°C for 5 minutes.

[0141] A durability test was conducted on the evaluation cell. Specifically, the cell was charged and discharged 200 times at a constant current of 2C in a voltage range of 3.0 to 4.1V at room temperature. The capacity retention rate (percentage) was calculated by dividing the 200th discharge capacity by the initial discharge capacity. A higher capacity retention rate is considered to indicate better durability.

[0142] <Result> As shown in Figure 10, samples No. 4 to No. 8 have improved durability compared to samples No. 1 to No. 3. In samples No. 4 to No. 8, the crystallites were radially arranged. In samples No. 4 to No. 8, open pores with opening diameters of 20 nm or more were observed.

[0143] No. 4 to No. 7 have improved durability compared to No. 8. L / d S In No. 4 to No. 7, the open pore diameter is less than 250 nm. In No. 4 to No. 7, the relationship of "4.0 ≦ D / d L In No. 4 to No. 7, the relationship of "θ≦45°" is satisfied. [Explanation of symbols]

[0144] 1 crystallite, 2 secondary particle, 3 open pore, 4 circumscribed circle, 4c center, 4i intersection, 10 positive electrode, 20 negative electrode, 30 separator, 100 battery, L1 first line, L2 second line.

Claims

1. Contains secondary particles, the secondary particles include a plurality of crystallites, the plurality of crystallites are arranged radially from the center of the secondary particle to the outside, each of the plurality of crystallites includes a lithium metal composite oxide; The lithium metal composite oxide has a layered rock salt structure, open pores are formed between adjacent crystallites on the surfaces of the secondary particles, and The open pores have an opening diameter of 20 nm or more. Cathode active material.

2. In the cross section of the secondary particle, θ≦45° The relationship is satisfied, The θ indicates the angle between the first line and the second line, The first straight line is an extension line of the major axis diameter of the crystallite, and the second straight line passes through an intersection point between the circumscribing circle of the secondary particle and the extension line and through the center of the circumscribing circle; The positive electrode active material according to claim 1 .

3. The open pores have an opening diameter of less than 250 nm. The positive electrode active material according to claim 1 .

4. In the cross section of the secondary particle, 6.4≦d L / d S ≦17.3 The relationship is satisfied, The above d L indicates the major axis diameter of the crystallite, and The above d S indicates the minor axis diameter of the crystallite, The positive electrode active material according to claim 1 .

5. In the cross section of the secondary particle, 4.0≦D / d L ≦9.0 The relationship is satisfied, The D indicates the maximum Feret diameter of the secondary particles, and The above d L indicates the major axis diameter of the crystallite, The positive electrode active material according to claim 1 .

6. The lithium metal composite oxide has the general formula: Li 1-a MO 2 It has a composition represented by In the general formula, The relationship of -0.5≦a≦0.5 is satisfied, and M includes at least one selected from the group consisting of Ni, Co, Mn, and Al; The positive electrode active material according to claim 1 .

7. The lithium metal composite oxide has the general formula: Li 1-a MO 2 B b It has a composition represented by In the general formula, -0.5≦a≦0.5, 0.002≦b≦0.030 The relationship is satisfied, and M includes at least one selected from the group consisting of Ni, Co, Mn, and Al; The positive electrode active material according to claim 1 .

8. The positive electrode active material according to claim 1, Secondary battery.

9. (a) providing a metal hydroxide; (b) forming a first mixture by mixing the metal hydroxide, a lithium compound, and a crystallization control material; (c) subjecting the first mixture to a first heat treatment to form a second mixture; and (d) synthesizing a positive electrode active material by subjecting the second mixture to a second heat treatment; Including, The crystallinity control material is B 2 O 3 Including, the first heat treatment and the second heat treatment are performed in an oxygen atmosphere; The first heat treatment is carried out at a temperature of 600 to 700° C. for a period of 6 to 12 hours; and The second heat treatment is carried out at a temperature of 1100 to 1300°C for 1 to 3 hours. A method for producing a positive electrode active material.

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