Positive electrode active material, electrode and battery

Abstract

This disclosure provides a positive electrode active material, an electrode, and a battery for reducing battery resistance. A positive electrode active material comprises secondary particles, said secondary particles comprising a first particle group and a second particle group, both of said first and second particle groups being composed of primary particles. The average particle size of the second particle group is larger than that of the first particle group. Within the secondary particles, the first and second particle groups are dispersed from each other. The primary particles belonging to the first particle group comprise a first olivine-type compound, and the primary particles belonging to the second particle group comprise a second olivine-type compound. Furthermore, the Mn composition ratio of the second olivine-type compound is lower than that of the first olivine-type compound.

Description

Technical Field

[0001] This disclosure relates to positive electrode active materials, electrodes, and batteries. Background Technology

[0002] Japanese Patent Application Publication No. 2021-009838 discloses granulated forms of manganese-rich lithium iron phosphate particles (average particle size ≥10nm and ≤80nm) and iron-rich lithium iron phosphate particles (average particle size ≥80nm and ≤150nm). Summary of the Invention

[0003] As positive electrode active materials, olivine-type compounds such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP) are being studied. For example, from the viewpoint of energy density and cycle resistance, it has been proposed to form secondary particles (also known as "granules," "agglomerated particles," etc.) by using two types of primary particles with different average particle sizes. However, there is still room for improvement in terms of battery resistance.

[0004] This disclosure provides positive electrode active materials, electrodes, and batteries for reducing battery resistance.

[0005] The following describes the technical solution and effects of this disclosure. However, the mechanism of action includes presumptions. The mechanism of action does not limit the technical scope of this disclosure.

[0006] The first aspect of this disclosure is a positive electrode active material. The positive electrode active material comprises secondary particles. The secondary particles comprise a first particle group and a second particle group. Both the first and second particle groups are composed of primary particles. The average particle size of the second particle group is larger than that of the first particle group. Within the secondary particles, the first and second particle groups are dispersed. The primary particles belonging to the first particle group comprise a first olivine-type compound. The primary particles belonging to the second particle group comprise a second olivine-type compound. The Mn composition ratio of the second olivine-type compound is lower than that of the first olivine-type compound.

[0007] Hereinafter, "primary particles belonging to the first particle group" will also be referred to as "small particles". "Primary particles belonging to the second particle group" will also be referred to as "large particles".

[0008] Olivine-type compounds tend to have a high resistance. To achieve a practical resistance, it is required to reduce the primary particles from the sub-micron scale to the nano scale. The fine primary particles tend to aggregate very easily. Conventionally, a scheme has been proposed to separately prepare small particles and large particles and form secondary particles from the small particles and the large particles. However, as described above, it is considered that since the primary particles aggregate very easily, the small particles and the large particles respectively form primary aggregates, and then the primary aggregates aggregate, thereby forming secondary aggregates. It is considered that when the electrode is compressed, it is difficult for the small particles to enter the gaps between the large particles in the primary aggregate composed of the large particles. That is, there is room for improvement in the filling property. In addition, it is considered that the ion conduction distance in the primary particles is longer for the large particles than for the small particles. It is considered that by forming an aggregate of large particles, ions tend to stagnate and the tortuosity increases. "Tortuosity" is one of the indexes of the ion conductivity in the electrode. It is considered that the smaller the tortuosity, the better the ion conductivity. The combination of low filling property and large tortuosity may not result in a sufficiently low battery resistance.

[0009] In the secondary particles of the present disclosure, the small particles and the large particles are dispersed from each other. Therefore, it is considered that when the electrode is compressed, the primary particles are easily filled tightly by the small particles entering the gaps between the large particles. In addition, by dispersing the large particles, an improvement in the tortuosity can be expected. Furthermore, the Mn composition ratio of the large particles is lower than that of the small particles. The lower the Mn composition ratio, the lower the resistance that the primary particles can have. By the large particles having a low Mn composition ratio, a further improvement in the tortuosity can be expected. Through the synergistic effect of these actions, a reduction in the battery resistance can be expected.

[0010] The positive electrode active material described in the above scheme may also include the following constitution, for example. In the FE-SEM / EDX (Field Emission-Scanning Electron Microscope Energy / Dispersive X-ray Spectroscopy) analysis of the secondary particles, the relationship of "I2 < I1" is satisfied. "I1" represents the detection intensity of Mn in the primary particles belonging to the first particle group. "I2" represents the detection intensity of Mn in the primary particles belonging to the second particle group.

[0011] The difference in the Mn composition ratio between the small particles and the large particles can be determined by, for example, FE-SEM / EDX analysis.

[0012] The positive electrode active material described in the above scheme may also include the following constitution, for example. The first olivine-type compound has a composition represented by Formula 1 "Li x Mn a Fe 1-a PO4". The second olivine-type compound has a composition represented by Formula 2 "Liy Mn b Fe 1-b A composition represented by "PO4". In Formulas 1 and 2, the relationships of "0.5 ≤ x ≤ 1.5", "0.00 < a ≤ 1.00", "0.5 ≤ y ≤ 1.5", "0.00 ≤ b < 1.00", and "b < a" are satisfied.

[0013] In Formula 1, "a" represents the Mn composition ratio of small particles. In Formula 2, "b" represents the Mn composition ratio of large particles.

[0014] The positive electrode active material described in the above solution may also include the following composition. In Formulas 1 and 2, the relationship of "0.20 ≤ a ≤ 1.00" and "0.00 ≤ b ≤ 0.80" is satisfied.

[0015] The positive electrode active material described in the above solution may also include the following composition. In Formulas 1 and 2, the relationship of "0.60 ≤ a ≤ 0.90" and "0.10 ≤ b ≤ 0.50" is satisfied.

[0016] The positive electrode active material described in the above solution may also include the following composition. In Formulas 1 and 2, the relationship of "0.10 ≤ a - b ≤ 0.90" is further satisfied.

[0017] The positive electrode active material described in the above solution may also include the following composition. The relationship of "1.5 ≤ d2 / d1 ≤ 10" is satisfied. "d1" represents the average particle size of the first particle group. "d2" represents the average particle size of the second particle group. [[ID=二十一]] [[ID=二十二]]

[0018] [[ID=二十三]]By the average particle size ratio "d2 / d1" being 1.5 to 10, a reduction in battery resistance can be expected. [[ID=二十四]] [[ID=二十五]]

[0019] [[ID=二十六]]The positive electrode active material described in the above solution may also include the following composition. The relationship of "0.4 ≤ m1 / (m1 + m2) ≤ 0.6" is satisfied. "m1" represents the total mass of the primary particles belonging to the first particle group. "m2" represents the total mass of the primary particles belonging to the second particle group. [[ID=二十七]] [[ID=二十八]]

[0020] [[ID=二十九]]The ratio "m1 / (m1 + m2)" represents the mass ratio of small particles to the total of small particles and large particles. By the mass ratio of small particles being 0.4 to 0.6, an improvement in battery resistance can be expected. [[ID=三十]] [[ID=三十一]]

[0021] [[ID=三十二]]The second solution of the present disclosure is an electrode. The electrode includes a positive electrode layer. The positive electrode layer includes the positive electrode active material described in the above solution. [[ID=三十三]] [[ID=三十四]]

[0022] [[ID=三十五]]The positive electrode layer may also be referred to as a "positive electrode active material layer", a "positive electrode mixture layer", etc. As long as the "electrode" includes a positive electrode layer, it may be either a "single-pole electrode (positive electrode)" or a "bipolar electrode".

[0023] The third aspect of this disclosure is a battery. The battery includes the electrodes described in the above-described aspects.

[0024] The battery described in the above scheme may also include the following configuration: The battery has a bipolar structure.

[0025] Bipolar structures can be formed by stacking bipolar electrodes. Improvements in output characteristics, for example, can be expected through bipolar structures. However, a thick positive electrode layer is sometimes required in bipolar structures. The thicker the positive electrode layer, the greater the impact of the filling of the positive electrode active material and the tortuosity of the positive electrode layer on the battery resistance. The positive electrode active material described in the above scheme is considered particularly suitable for bipolar structures.

[0026] The following describes one embodiment (hereinafter referred to as "this embodiment") and one example of this disclosure (hereinafter referred to as "this example"). However, this embodiment and this example do not limit the technical scope of this disclosure. This embodiment and this example are illustrative in all respects. This embodiment and this example are non-limiting. The technical scope of this disclosure includes all modifications within the meaning and scope equivalent to the claims. For example, it is intended from the outset to include cases where any configuration extracted from this embodiment is arbitrarily combined. Attached Figure Description

[0027] The features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure are described below with reference to the accompanying drawings, wherein like reference numerals denote like elements.

[0028] Figure 1 is a conceptual diagram of a secondary particle in the reference mode.

[0029] Figure 2 This is a conceptual diagram of the secondary particle in this embodiment.

[0030] Figure 3 This is an example of the number distribution of particle size in primary particles.

[0031] Figure 4 This is a simplified flowchart of the method for manufacturing the positive electrode active material according to this embodiment.

[0032] Figure 5 This is a schematic perspective view of the battery according to this embodiment.

[0033] Figure 6 It is along Figure 5 A rough cross-sectional view of line VI-VI in the diagram.

[0034] Figure 7 This is a table representing the experimental results. Detailed Implementation

[0035] Terms and phrases

[0036] "Possessing," "including," "having," and their variations are open-ended expressions. A composition expressed in an open-ended manner may or may not include additional elements beyond the necessary elements. The statement "composed of..." is a closed-ended expression. However, even compositions expressed in a closed-ended manner can usually include incidental impurities or additional elements unrelated to the target technology. The statement "substantially composed of..." is a semi-closed-ended expression. In compositions expressed in a semi-closed-ended manner, it is permissible to add elements that do not substantially affect the basic or novel characteristics of the target technology.

[0037] Expressions like "maybe" and "can" do not strictly mean "must," but are used in the sense of "this possibility exists," implying that they are permitted.

[0038] Geometric terms should not be interpreted in a strict sense. As geometric terms, they may exemplify, for example, "parallel," "perpendicular," and "orthogonal." For instance, direction, angle, and distance can also represent relative displacement within a range where substantially the same or similar function can be achieved. Geometric terms may include, for example, tolerances and errors in design, operation, and manufacturing. Dimensional relationships in the drawings may sometimes differ from actual dimensional relationships. To aid understanding, dimensional relationships in the drawings may sometimes be altered. For example, length, width, and thickness may be changed. Some structural elements may also be omitted.

[0039] Unless otherwise specified, elements described in the "singular form" may also include those in the plural form. For example, "particle" sometimes also refers to multiple particles (particle swarms), collections of particles, and powders.

[0040] Unless otherwise specified, numerical ranges such as "m~n%" include both upper and lower limits. That is, "m~n%" represents a numerical range "above m% and below n%". Furthermore, "above m% and below n%" includes "greater than m% and less than n%". "Above" and "below" are indicated by inequality signs "≤" and "≥" with an equal sign. "Greater than" and "less than" are indicated by inequality signs "<" and ">" without an equal sign. Alternatively, a new upper or lower limit can be set by arbitrarily selecting values ​​from the numerical range. For example, a new numerical range can be set by arbitrarily combining values ​​from the numerical range with values ​​recorded in other parts of this specification, tables, figures, etc.

[0041] All numerical values ​​are modified by the term "approximately". The term "approximately" can mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​can be approximate values ​​that may vary depending on the application of the technology. All numerical values ​​can be expressed in significant figures. Unless otherwise specified, the measured value can be the average of multiple measurements. The number of measurements can be 3 or more, 5 or more, or 10 or more. Generally, the more measurements, the higher the reliability of the average value. The measured value can be rounded based on the number of significant figures. The measured value may include, for example, errors associated with the detection limits of the measuring device.

[0042] The apparatus and software used in the determination of various values ​​are just one example. Products equivalent to the illustrated apparatus can also be used. When using equivalent products, the measurement conditions can be adjusted in conjunction with the apparatus.

[0043] For example, size determination and shape analysis in various images can also be performed using image analysis software. For instance, image analysis software such as "ImageJ" can be used.

[0044] "Primary particles" refer to particles that do not appear to have grain boundaries in SEM images captured by FE-SEM at magnifications of 20,000 to 100,000 times.

[0045] "Particle size" is determined by image analysis (microscopy). Particle size is represented in an SEM image as the arithmetic mean of the long side (major axis diameter) and the short side (uniaxial diameter) within the minimum bounding rectangle (MBR) relative to the particle's outline.

[0046] "Average particle size" refers to the average particle size. The average particle size is determined in the following order: SEM images of the secondary particles (powder) are obtained using FE-SEM. The image magnification is from 20,000 to 100,000 times. From the SEM images, a total of 100 primary particles are randomly extracted from multiple secondary particles. The particle size of each primary particle is measured. The arithmetic mean of the particle sizes of the 100 primary particles is considered the average particle size of the primary particles. Similarly, the arithmetic mean of the particle sizes of the 100 secondary particles is considered the average particle size of the secondary particles.

[0047] In secondary particles, the state of "small particles and large particles being dispersed from each other" means that in the SEM image (20000x) of secondary particles captured by FE-SEM, one or more of the following conditions (1) to (6) are satisfied.

[0048] (1) It does not form a condensate of more than 5 large particles.

[0049] (2) In each of the 10 or more large particles extracted arbitrarily, more than 10% of the adjacent particles of that large particle are small particles.

[0050] (3) Among the 3 or more large particles in any 10 large particles extracted, more than 30% of the adjacent particles of the large particle are small particles.

[0051] (4) In each of the five or more large particles among the ten large particles extracted at random, more than 30% of the adjacent particles of that large particle are small particles.

[0052] (5) In each of the five or more large particles among the ten large particles extracted at random, more than 50% of the adjacent particles of that large particle are small particles.

[0053] (6) Among the 10 large particles extracted at random, the total length of the grain boundaries of the large particles and the small particles is longer than the total length of the grain boundaries of the large particles.

[0054] The existence of two or more particle groups with different average particle sizes can also be confirmed by using a "number distribution (frequency distribution based on the number of particles)". The number distribution is prepared in the following order: Prepare SEM images taken at magnifications of 20,000x to 100,000x using FE-SEM. Randomly extract 10 secondary particles from the SEM images. Randomly extract 100 primary particles from each secondary particle. That is, randomly extract a total of 1000 primary particles. Measure the particle size of each primary particle. Prepare a number distribution based on the particle sizes of the 1000 primary particles. Identify the peak with the highest height (maximum peak) in the number distribution. A convex region with a height greater than 0.1 times that of the maximum peak is considered a peak. The number of peaks corresponds to the number of particle groups. The particle size at the apex of each peak is the "mode diameter". The mode diameter corresponds to the average particle size.

[0055] The detection intensity of Mn was determined using FE-SEM / EDX. In the number distribution of primary particles, the first and second peaks were identified. The second peak has a larger mode diameter than the first peak. The first peak was considered to originate from the first particle swarm. The second peak was considered to originate from the second particle swarm. The FWHM (Full Width at Half Maximum) of the first and second peaks was determined. From the observation images obtained by FE-SEM, 100 primary particles with a diameter within the range of "modal diameter of the first peak ± 0.5 FWHM" were randomly extracted. The observation magnification ranged from 50,000 to 200,000. The detection intensity of Mn was determined for each primary particle by performing point analysis using EDX. The arithmetic mean of the detection intensities of Mn for the 100 primary particles was considered the detection intensity "I1" of Mn belonging to the first particle swarm. Similarly, from the observation images obtained by FE-SEM, 100 primary particles with a diameter within the range of "modal diameter of the second peak ± 0.5 FWHM" were randomly extracted. Point analysis by EDX was performed near the center of each primary particle to determine the detection intensity of Mn. The arithmetic mean of the detection intensities of Mn for the 100 primary particles was taken as the detection intensity "I2" of Mn belonging to the second particle group.

[0056] "D50" indicates the particle size at which the cumulative value in the volumetric cumulative distribution reaches 50%. The volumetric particle size distribution is determined using a laser diffraction particle size distribution measuring device.

[0057] The "roundness" of the particles is determined in the SEM images. Roundness is calculated using the following formula. The arithmetic mean of the roundness of 10 particles is used.

[0058] ψ = 4πS / L 2

[0059] ψ: roundness

[0060] π: Pi

[0061] S: Cross-sectional area of ​​the particle (the area of ​​the region enclosed by the particle's outline)

[0062] L: The perimeter of the particle (the length of the particle's outline).

[0063] The chemical composition of a compound can be determined using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy). A sample solution is prepared by dissolving 0.1 g of the sample (e.g., a positive electrode active material) in a mixed acid solution (10 ml) of hydrochloric acid and sulfuric acid. The sample solution is then diluted to an appropriate concentration using a volumetric flask. After dilution, compositional analysis is performed using an ICP-AES apparatus. For example, an apparatus sold under the product name "PS3520UVDD II (manufactured by Hitachi High Technology Co., Ltd.)" can also be used.

[0064] A stoichiometric formula represents a representative example of a compound. Compounds can also have non-stoichiometric compositions. For example, "Al₂O₃" is not limited to compounds having a molar ratio of Al / O = 2 / 3. Unless otherwise specified, "Al₂O₃" refers to a compound containing Al and O in any molar ratio. For example, trace elements can be doped into the compound. A portion of Al and O can also be replaced by other elements.

[0065] "Derivative" refers to a compound that has been altered in part by at least one of the following chemical reactions: introduction of a functional group, substitution of an atom, oxidation, reduction, and others. The alteration may occur at one or more sites. "Substituents" may include, for example, at least one selected from alkyl, alkenyl, alkynyl, cycloalkyl, unsaturated cycloalkyl, aryl, heterocyclic, halogen (F, Cl, Br, I, etc.), OH, SH, CN, SCN, OCN, nitro, alkoxy, unsaturated alkoxy, amino, alkylamino, dialkylamino, aryloxy, acyl, alkoxycarbonyl, acyloxy, aryloxycarbonyl, acylamino, alkoxycarbonyl, aminoaryloxycarbonylamino, sulfonylamino, aminosulfonyl, carbamoyl, alkylthio, arylthio, sulfonyl, sulfinyl, urea, phosphoramidyl, sulfonyl, carboxyl, oxime, sulfinic acid, hydrazine, imino, and silyl. These substituents may also be further substituted. When there are two or more substituents, the substituents can be the same or different. Multiple substituents can combine with each other to form a ring.

[0066] Positive electrode active material

[0067] The positive electrode active material contains secondary particles. The positive electrode active material can also be an aggregate of secondary particles. The D50 of the positive electrode active material can be, for example, 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more. Alternatively, the D50 of the positive electrode active material can be, for example, less than 30 μm, less than 25 μm, less than 20 μm, less than 15 μm, or less than 10 μm.

[0068] Secondary particles

[0069] Secondary particles are condensations of primary particles. A condensation of primary particles comprises a first particle group and a second particle group. Both the first and second particle groups are composed of primary particles. The average particle size of the second particle group is larger than that of the first particle group. That is, primary particles belonging to the first particle group are small particles, while primary particles belonging to the second particle group are large particles.

[0070] Figure 1 This is a conceptual diagram of a secondary particle in the reference configuration. Secondary particle 2 contains primary particle 1. Primary particle 1 contains small particle 1a and large particle 1b. In the reference configuration, within secondary particle 2, small particle 1a and large particle 1b are not dispersed. Small particle 1a and large particle 1b each form a primary aggregate. Gaps are formed between the primary aggregates.

[0071] Figure 2 This is a conceptual diagram of the secondary particles in this embodiment. In this embodiment, small particles 1a and large particles 1b are dispersed within the secondary particle 2. Therefore, it is assumed that small particles 1a and large particles 1b are easily packed together. That is, in this embodiment ( Figure 2 ) and reference method ( Figure 1 Compared to [previous method], improved fillability can be expected. Furthermore, improved tortuosity can be expected through the dispersion of large 1b particles. Through the synergistic effect of these actions, a reduction in battery resistance can be anticipated.

[0072] Figure 2 The dispersion at the primary particle scale shown can be achieved, for example, by spray drying a slurry containing dispersed small and large particles using a wet bead mill. Furthermore, spray mills pulverize particles through the impact of these particles against each other. Therefore, compared to bead mills which use beads as the pulverizing medium, spray mills tend to have weaker pulverizing power. It is considered difficult to achieve a dispersion at the primary particle scale using spray mills.

[0073] In this embodiment, the secondary particles 2 can have any shape. For example, the secondary particles 2 can be spherical, rod-shaped, angular, block-shaped, etc. The roundness of the secondary particles 2 can be, for example, 0.50 or higher, 0.60 or higher, 0.70 or higher, 0.80 or higher, 0.90 or higher, or 0.95 or higher. The roundness of the secondary particles 2 can be, for example, 1.00 or lower, 0.95 or lower, 0.90 or lower, 0.80 or lower, 0.70 or lower, or 0.60 or lower. Higher roundness of the secondary particles 2 generally leads to improved filling performance.

[0074] The average particle size of the secondary particles 2 can be, for example, 1 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, or 15 μm or more. The average particle size of the secondary particles 2 can be, for example, less than 20 μm, less than 15 μm, less than 10 μm, less than 5 μm, or less than 3 μm.

[0075] Secondary particles 2, in addition to containing the first particle group (small particles 1a) and the second particle group (large particles 1b), may also include additional particle groups. The number of additional particle groups can be, for example, one or more, two or more, three or more, or four or more. The number of additional particle groups can be, for example, five or fewer, four or fewer, three or fewer, or two or fewer. The average particle size of the additional particle groups can, for example, be smaller than that of the first particle group (small particles 1a). For example, the average particle size of the additional particle groups can be between that of the first particle group (small particles 1a) and the second particle group (large particles 1b). For example, the average particle size of the additional particle groups can also be larger than that of the second particle group (large particles 1b). For example, even when secondary particles 2 contain three or more particle groups, the relationship that the larger the average particle size of the particle groups, the smaller the Mn composition ratio of the olivine-type compound can still be satisfied.

[0076] Primary particle

[0077] Primary particles 1 can have any shape. That is, small particles 1a and large particles 1b can each independently have any shape. Small particles 1a and large particles 1b can each independently be, for example, spherical, rod-shaped, angular, block-shaped, etc. The roundness of small particles 1a and large particles 1b can each independently be, for example, 0.50 or higher, 0.60 or higher, 0.70 or higher, 0.80 or higher, 0.90 or higher, or 0.95 or higher. The roundness of small particles 1a and large particles 1b can each independently be, for example, 1.00 or lower, 0.95 or lower, 0.90 or lower, 0.80 or lower, 0.70 or lower, or 0.60 or lower. The higher the roundness of primary particles 1, the more likely an improvement in filling performance can be expected.

[0078] The average particle size ratio "d2 / d1" of the first particle group (small particles 1a) and the second particle group (large particles 1b) can be, for example, 2.0 or higher, 2.5 or higher, 2.7 or higher, 3.0 or higher, 4.0 or higher, 5.0 or higher, 6.0 or higher, 7.0 or higher, 8.0 or higher, 9.0 or higher, or 10 or higher. The average particle size ratio "d2 / d1" can be, for example, less than 15, less than 12, less than 10, less than 9.0, less than 8.0, less than 7.0, less than 6.0, less than 5.0, less than 4.0, less than 3.0, less than 2.7, less than 2.5, or less than 2.0. For example, it can also satisfy relationships such as "1.5 ≤ d2 / d1 ≤ 10", "3.0 ≤ d2 / d1 ≤ 10", and "5.0 ≤ d2 / d1 ≤ 10".

[0079] The average particle size "d2" of the second particle group (large particle 1b) can be, for example, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 120 nm or more, 140 nm or more, 160 nm or more, 180 nm or more, 200 nm or more, 220 nm or more, 240 nm or more, 260 nm or more, 280 nm or more, 300 nm or more, 320 nm or more, 340 nm or more, 360 nm or more, 380 nm or more, or 400 nm or more. The average particle size "d2" can be, for example, below 1000nm, below 750nm, below 500nm, below 450nm, below 400nm, below 380nm, below 360nm, below 340nm, below 320nm, below 300nm, below 280nm, below 260nm, below 240nm, below 220nm, below 200nm, below 180nm, below 160nm, below 140nm, below 120nm, below 100nm, below 90nm, below 80nm, below 70nm, or below 60nm. For example, it can also satisfy relationships such as "200nm≤d2≤500nm", "300nm≤d2≤500nm", "200nm≤d2≤400nm", and "200nm≤d2≤300nm".

[0080] The average particle size "d1" of the first particle swarm (small particles 1a) can be, for example, less than 50 nm, less than 45 nm, less than 40 nm, less than 35 nm, less than 30 nm, less than 25 nm, less than 20 nm, less than 15 nm, or less than 10 nm. The average particle size "d1" can be, for example, greater than 5 nm, greater than 10 nm, greater than 15 nm, greater than 20 nm, greater than 25 nm, greater than 30 nm, greater than 35 nm, greater than 40 nm, or greater than 45 nm. For example, it can also satisfy relationships such as "5 nm ≤ d1 < 50 nm", "5 nm ≤ d1 ≤ 45 nm", "10 nm ≤ d1 ≤ 40 nm", and "20 nm ≤ d1 ≤ 40 nm".

[0081] The number ratio "n1" of the primary particles 1 (small particles 1a) belonging to the first particle group and the number ratio "n2" of the primary particles 1 (large particles 1b) belonging to the second particle group may, for example, satisfy the relationship of "0.5000 < n1 / (n1 + n2) < 1.000". The number ratio of the small particles 1a, "n1 / (n1 + n2)", may be, for example, 0.750 or more, 0.780 or more, 0.800 or more, 0.850 or more, 0.900 or more, 0.950 or more, 0.975 or more, 0.990 or more, or 0.995 or more. The number ratio of the small particles 1a, "n1 / (n1 + n2)", may be, for example, 0.999 or less, 0.995 or less, 0.975 or less, 0.950 or less, 0.900 or less, 0.850 or less, 0.800 or less, 0.780 or less, or 0.750 or less. For example, it may also satisfy relationships such as "0.700 < n1 / (n1 + n2) < 1.00" and "0.780 ≤ n1 / (n1 + n2) ≤ 0.999".

[0082] The total mass "m1" of the primary particles 1 (small particles 1a) belonging to the first particle group and the total mass "m2" of the primary particles 1 (large particles 1b) belonging to the second particle group may, for example, satisfy the relationship of "0.1 ≤ m1 / (m1 + m2) ≤ 0.9". The mass ratio of the small particles 1a, "m1 / (m1 + m2)", may be, for example, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. The mass ratio of the small particles 1a, "m1 / (m1 + m2)", may be, for example, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less. For example, it may also satisfy relationships such as "0.2 ≤ m1 / (m1 + m2) ≤ 0.8", "0.3 ≤ m1 / (m1 + m2) ≤ 0.7", and "0.4 ≤ m1 / (m1 + m2) ≤ 0.6".

[0083] Figure 3 It is an example of the number distribution of the particle diameters of the primary particles. The horizontal axis of the histogram is the particle diameter, and the vertical axis is the number frequency. The number of peaks in the number distribution corresponds to the number of particle groups contained in the secondary particles 2. The number distribution may also be bimodal. That is, the number distribution may at least include the first peak P1 and the second peak P2.

[0084] The first peak P1 has a modal diameter "dm1". The second peak P2 has a modal diameter "dm2". The modal diameter "dm2" is greater than the modal diameter "dm1". That is, the first peak P1 is composed of the first particle group (small particles 1a). The second peak P2 is composed of the second particle group (large particles 1b). In some embodiments of the present disclosure, the modal diameter of each peak can be regarded as the average particle size of each particle group. In some embodiments, the integral value (area) of each peak can be regarded as the number ratio of primary particles belonging to each peak.

[0085] The number distribution can also be multimodal. That is, in addition to the first peak P1 and the second peak P2, there can be additional peaks. For example, the additional peak can have a modal diameter smaller than the first peak P1. For example, the additional peak can have a modal diameter between the first peak P1 and the second peak P2. For example, the additional peak can have a modal diameter larger than the second peak P2. For example, the additional peak can be a shoulder peak of the first peak P1. For example, the additional peak can also be a shoulder peak of the second peak P2.

[0086] Composition

[0087] The primary particles contain an olivine-type compound. The olivine-type compound has a crystal structure belonging to the space group Pnma. The space group to which the crystal structure belongs can be determined by an XRD (X-Ray Diffraction) pattern. The primary particles (small particles) belonging to the first particle group contain the first olivine-type compound. The primary particles (large particles) belonging to the second particle group contain the second olivine-type compound. The second olivine-type compound has a lower Mn composition ratio than the first olivine-type compound. The first olivine-type compound can, for example, contain at least one selected from LMP and LMFP. The second olivine-type compound can, for example, contain at least one selected from LFP and LMFP.

[0088] For example, in the FE-SEM / EDX analysis of secondary particles, the detection intensity "I1" of Mn in small particles and the detection intensity "I2" of Mn in large particles can satisfy the relationship "I2 < I1". The detection intensity ratio "I1 / I2" can be, for example, 1.2 or more, 1.5 or more, 1.8 or more, 2.0 or more, 2.5 or more, 3.0 or more, 3.5 or more, 4.0 or more, 4.5 or more, 5.0 or more, 6.0 or more, 7.0 or more, 8.0 or more, 9.0 or more, or 10 or more. The detection intensity ratio "I1 / I2" can be, for example, 100 or less, 50 or less, 20 or less, 10 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.5 or less, 2.0 or less, 1.8 or less, 1.5 or less, or 1.2 or less.

[0089] The first olivine-type compound may, for example, have a composition represented by the formula (1) "Li x Mn a Fe 1-a PO4". The second olivine-type compound may, for example, have a composition represented by the formula (2) "Li y Mn b Fe 1-b PO4".

[0090] In the formula (1) and the formula (2), "a" and "b" represent the Mn composition ratio. Therefore, the relationship of "b < a" is satisfied. The difference in the Mn composition ratio "a - b" may, for example, be greater than 0, 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, 0.60 or more, 0.70 or more, 0.80 or more, or 0.90 or more. The difference "a - b" may, for example, be 1.00 or less, 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, 0.20 or less, or 0.10 or less. For example, the relationships of "0.10 ≤ a - b ≤ 0.90", "0.11 ≤ a - b ≤ 0.82", "0.33 ≤ a - b ≤ 0.82", "0.40 ≤ a - b ≤ 0.82", "0.33 ≤ a - b ≤ 0.60", "0.33 ≤ a - b ≤ 0.50", "0.33 ≤ a - b ≤ 0.40", etc. may be satisfied.

[0091] In the formula (1) and the formula (2), the ratio of the Mn composition ratio "a / b" may, for example, be 1.2 or more, 1.5 or more, 1.8 or more, 2.0 or more, 2.5 or more, 3.0 or more, 3.5 or more, 4.0 or more, 4.5 or more, 5.0 or more, 6.0 or more, 7.0 or more, 8.0 or more, 9.0 or more, or 10 or more. The ratio "a / b" may, for example, be 100 or less, 50 or less, 20 or less, 10 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.5 or less, 2.0 or less, 1.8 or less, 1.5 or less, or 1.2 or less.

[0092] In formula (1), the composition ratio "a" of Mn can be greater than 0.00, greater than 0.10, greater than 0.20, greater than 0.30, greater than 0.40, greater than 0.50, greater than 0.60, greater than 0.70, greater than 0.80, or greater than 0.90. The composition ratio "a" of Mn can be less than 1.00, less than 0.90, less than 0.80, less than 0.70, less than 0.60, less than 0.50, less than 0.40, less than 0.30, less than 0.20, or less than 0.10. For example, it can also satisfy relationships such as "0.00<a≤1.00", "0.20≤a≤1.00", "0.60≤a≤0.90", "0.17≤a≤0.92", "0.24≤a≤0.92", "0.42≤a≤0.92", "0.53≤a≤0.92", "0.61≤a≤0.92", "0.75≤a≤0.92", and "0.82≤a≤0.92".

[0093] In formula (2), the composition ratio "b" of Mn can be, for example, 0.00 or more, 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, 0.60 or more, 0.70 or more, 0.80 or more, or 0.90 or more. The composition ratio "b" of Mn can be, for example, less than 1.00, less than 0.90, less than 0.80, less than 0.70, less than 0.60, less than 0.50, less than 0.40, less than 0.30, less than 0.20, or less than 0.10. For example, it can also satisfy relationships such as "0.00≤b<1.00", "0.00≤b≤0.80", "0.10≤b≤0.50", "0.13≤b≤0.92", "0.13≤b≤0.82", "0.13≤b≤0.75", "0.13≤b≤0.61", "0.13≤b≤0.42", "0.13≤b≤0.24", and "0.13≤b≤0.21".

[0094] In formula (1), the Li composition ratio "x" can be, for example, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.1 or more, 1.2 or more, 1.3 or more, or 1.4 or more. The Li composition ratio "x" can be, for example, less than 2.0, less than 1.5, less than 1.4, less than 1.3, less than 1.2, less than 1.1, less than 1.0, less than 0.9, less than 0.8, less than 0.7, or less than 0.6. For example, it can also satisfy the relationship "0.5≤x≤1.5".

[0095] In formula (2), the Li composition ratio "y" can be, for example, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.1 or more, 1.2 or more, 1.3 or more, or 1.4 or more. The Li composition ratio "y" can be, for example, less than 2.0, less than 1.5, less than 1.4, less than 1.3, less than 1.2, less than 1.1, less than 1.0, less than 0.9, less than 0.8, less than 0.7, or less than 0.6. For example, it can also satisfy the relationship "0.5≤y≤1.5".

[0096] The first and second olivine-type compounds may also contain dopants independently. Dopants are elements other than lithium (Li), manganese (Mn), iron (Fe), phosphorus (P), and oxygen (O). Dopants can be substitutional or interstitial. The doping amount (molar fraction relative to the amount of Li) can be, for example, 0.01 to 0.1. Dopant may include, for example, at least one element selected from boron (B), nitrogen (N), halogen, silicon (Si), sodium (Na), magnesium (Mg), aluminum (Al), chromium (Cr), scandium (Sc), titanium (Ti), vanadium (V), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), selenium (Se), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), lead (Pb), bismuth (Bi), antimony (Sb), tin (Sn), tungsten (W), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and actinides.

[0097] Primary particles 1 can also be covered by carbon material (not shown). This coverage can be partial or complete. The amount of coverage can also differ between small particles 1a and large particles 1b. The carbon material can be derived from, for example, sugars. The amount of carbon material attached, relative to secondary particles 2, can be, for example, 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, or 10% or more by mass fraction. The amount of carbon material attached, relative to secondary particles 2, can be, for example, less than 20%, less than 15%, less than 10%, less than 5%, less than 4%, or less than 3% by mass fraction.

[0098] The positive electrode active material may contain other components as long as it includes the first olivine-type compound and the second olivine-type compound. The mixing ratio (mass ratio) of the olivine-type compound and other components may be, for example, "olivine-type compound / other components = 9 / 1 to 1 / 9", "olivine-type compound / other components = 8 / 2 to 2 / 8", "olivine-type compound / other components = 7 / 3 to 3 / 7", or "olivine-type compound / other components = 6 / 4 to 4 / 6". The positive electrode active material may also be, for example, a mixture of powder of the olivine-type compound and powder of other components. Other components may include, for example, at least one selected from Li[NiCoMn]O2 (layered structure), Li[NiCoAl]O2 (layered structure), LiMnO2 (rock salt structure), and Li[NiMn]2O4 (spinel structure). Furthermore, the description of [NiCoMn], etc., indicates that the total composition ratio within [] is 1. As long as the total is 1, the composition ratio of each component within [] can be any.

[0099] Method for manufacturing positive electrode active material

[0100] Figure 4 This is a simplified flowchart of the method for manufacturing the positive electrode active material according to this embodiment. Hereinafter, "the method for manufacturing the positive electrode active material according to this embodiment" may be simply referred to as "this method". This method includes "(a) preparation of various secondary particles", "(b) wet pulverization", and "(c) recombination of secondary particles". This method may also include "(d) calcination".

[0101] (a) Preparation of various secondary particles

[0102] This method involves preparing multiple secondary particles. Each of these secondary particles contains an olivine-type compound. The average particle size and Mn composition ratio of the primary particles in each of the secondary particles are different. The various secondary particles can be prepared independently.

[0103] (a1) harmonization

[0104] For example, a slurry can be formed by mixing lithium compounds, manganese compounds, iron compounds, phosphoric acid compounds, and a dispersion medium. For example, it can be in the form of formula (1) "Li x Mn a Fe 1-a PO4" or formula (2) "Li y Mn b Fe 1-b Weigh each ingredient according to the composition ratio (molar ratio) shown in "PO4". Lithium compounds may include, for example, lithium hydroxide. Manganese compounds may include, for example, manganese carbonate. Iron compounds may include, for example, iron phosphate. Phosphoric acid compounds may include, for example, lithium dihydrogen phosphate.

[0105] Carbon materials can also be mixed into the slurry. These carbon materials can coat the surface of the primary particles. Examples of carbon materials include sugars and organic acids. Examples of carbon materials include glucose, sucrose, fructose, and citric acid. The amount of carbon material added relative to the total solid components, by mass fraction, can be, for example, 1% to 20%.

[0106] The dispersion medium may include, for example, water. The concentration of the solids in the slurry, expressed as a mass fraction, may be, for example, 30% ± 20%.

[0107] (a2) Wet grinding

[0108] For example, by using a bead mill to wet-mill the slurry, the average particle size of the primary particles can be adjusted. That is, wet milling can be performed to give the primary particles a desired average particle size. For example, wet milling can also be performed to make the D50 approximately 0.30 μm.

[0109] (a3) Granulation

[0110] For example, secondary particles can be formed by spray drying the slurry. The primary particles contained in the secondary particles contain precursors of olivine-type compounds.

[0111] (a4) Firing

[0112] The precursor can be converted into an olivine-type compound by heat treatment of the secondary particles. In this method, any heat treatment furnace (e.g., electric furnace, muffle furnace, etc.) can be used. The heat treatment atmosphere can be, for example, a nitrogen atmosphere. The heat treatment temperature can be, for example, 400°C to 700°C. The heat treatment time can be, for example, 4 hours to 6 hours.

[0113] For example, by repeatedly performing "(a1) blending" to "(a4) calcination" while changing the Mn composition ratio in "(a1) blending" and changing the pulverization conditions in "(a2) wet pulverization", two or more types of secondary particles can be prepared. Two or more types of secondary particles can be prepared in a manner where the average particle size of the primary particles is different from each other. Two or more types of secondary particles can be prepared in a manner where the larger the average particle size of the primary particles, the lower the Mn composition ratio.

[0114] (b) Wet grinding (crushing of secondary particles and dispersion of primary particles)

[0115] This method involves wet crushing various secondary particles to the scale of primary particles, thereby forming a slurry in which primary particles are dispersed. For example, multiple slurries can be formed by individually wet crushing various secondary particles. These slurries can then be mixed. Alternatively, a single slurry can be formed by simultaneously wet crushing multiple secondary particles. In either case, multiple primary particles with different average particle sizes are dispersed within the slurry. The solids concentration of the slurry, by mass fraction, can be, for example, 5% to 50%.

[0116] Wet milling is performed to break secondary particles down to the size of primary particles and disperse the primary particles. Wet milling can be performed, for example, using a bead mill. The diameter of the beads is selected to match the size of the primary particles. The milling time is adjusted to break secondary particles down to the size of primary particles and disperse the primary particles. However, the milling time is adjusted to be as short as possible to avoid further pulverizing the primary particles. For example, if the primary particles are over-dispersed due to pulverization, the difference in average particle size between various primary particles may not be able to be adjusted to the desired range.

[0117] (c) Re-formation of secondary particles

[0118] This method includes forming secondary particles by spray drying the slurry. The spray drying sequence can be, for example, the same as "(a3) granulation".

[0119] (d) Firing

[0120] This method may also include heat treatment of secondary particles. The order of heat treatment may be the same as that of "(a4) firing".

[0121] Liquid batteries

[0122] In some embodiments of this disclosure, the battery may be a liquid-based battery. "Liquid-based battery" refers to a battery containing an electrolyte. For example, polymer batteries contain an electrolyte and are therefore liquid-based batteries. In some embodiments of this disclosure, the battery has a unipolar structure. In a unipolar structure, the power generation element may be wound or stacked. In some embodiments of this disclosure, the battery has a bipolar structure. As an example, a battery with a bipolar structure (bipolar battery) will be described.

[0123] Figure 5 This is a schematic perspective view of the battery according to this embodiment. Figure 6 It is along Figure 5A schematic cross-sectional view of line VI-VI in the diagram. Hereinafter, "plane-perpendicular direction" refers to the normal direction relative to the surface of the sheet-like member (e.g., foil, electrode, etc.). "In-plane direction" refers to any direction orthogonal to the plane-perpendicular direction. In the figures of this embodiment, the Z-axis direction corresponds to the plane-perpendicular direction. The X-axis and Y-axis directions are examples of in-plane directions.

[0124] The battery 100 includes an outer casing 90 and a power generation element 50. The outer casing 90 houses the power generation element 50. The outer casing 90 may also include, for example, a first current collector 91, a first laminate 92, a second laminate 93, and a second current collector 94. The ends of the first laminate 92 and the second laminate 93 are joined together in the in-plane direction. At the joint between the first laminate 92 and the second laminate 93, a sealing material (not shown) may also be placed between the first laminate 92 and the second laminate 93.

[0125] The first collector plate 91 and the second collector plate 94 are joined to the power generation element 50 at their ends in the lamination direction (Z-axis direction). A first laminate 92 is joined to the first collector plate 91. A second laminate 93 is joined to the second collector plate 94. At the junction of the collector plate and the laminate, a sealing material (not shown) may also be placed between the collector plate and the laminate.

[0126] The power generation element 50 includes a plurality of bipolar electrodes 10. The plurality of bipolar electrodes 10 are stacked in a plane-perpendicular direction (Z-axis direction). Each of the plurality of bipolar electrodes 10 sequentially includes a positive electrode layer 11, a current collector foil 13, and a negative electrode layer 12 in the plane-perpendicular direction. In the in-plane direction (e.g., the X-axis direction), the current collector foil 13 extends outward compared to the positive electrode layer 11 and the negative electrode layer 12. For example, the current collector foil 13 may extend outward throughout the entire in-plane direction compared to the positive electrode layer 11 and the negative electrode layer 12.

[0127] The current collector foil 13 is a conductor. The current collector foil 13 may include, for example, a metal foil, a conductive resin layer, etc. For example, the current collector foil 13 can be formed by laminating an Al foil and a Cu foil. A carbon material may also be coated on the surface of the current collector foil 13. The carbon material may include, for example, carbon black.

[0128] The power generation element 50 includes a sealing material 30. At its in-plane end, the sealing material 30 is bonded to the current collector foil 13. The sealing material 30 may also be thermally welded to the current collector foil 13, for example. Alternatively, the sealing material 30 may be disposed along the entire periphery in the in-plane direction. The sealing material 30 may also contain, for example, a resin material. The sealing material 30 seals adjacent current collector foils 13 in the perpendicular direction between the planes. By sealing the current collector foils 13 with the sealing material 30, units 40 are defined. Unit 40 is the smallest unit of the power generation element 50. The battery 100 includes multiple units 40 and is therefore also referred to as a "bipolar module." The multiple units 40 are individually sealed. The multiple units 40 are isolated from each other. Each of the multiple units 40 includes a positive electrode layer 11, a separator 20, a negative electrode layer 12, and an electrolyte.

[0129] Positive electrode layer

[0130] The positive electrode layer 11 is attached to one side of the current collector foil 13. For example, a groove may be formed in the positive electrode layer 11. The positive electrode layer 11 may be formed in a strip shape, for example. The thickness of the positive electrode layer 11 may be, for example, 50 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, 300 μm or more, 400 μm or more, 500 μm or more, 600 μm or more, 700 μm or more, 800 μm or more, or 900 μm or more. The thickness of the positive electrode layer 11 may be, for example, less than 1000 μm, less than 900 μm, less than 800 μm, less than 700 μm, less than 600 μm, less than 500 μm, less than 400 μm, less than 300 μm, or less than 200 μm.

[0131] The positive electrode layer 11 contains a positive electrode active material. That is, the battery 100 contains a positive electrode active material. Details of the positive electrode active material are as described above. In addition to the positive electrode active material, the positive electrode layer 11 may also contain, for example, conductive materials and binders. The amount of conductive material relative to 100 parts by mass of the positive electrode active material may be, for example, 0.1 to 10 parts by mass. The conductive material may contain optional components. For example, the conductive material may contain at least one selected from graphite, acetylene black (AB), Ketjen black (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene sheets (GF).

[0132] The amount of binder relative to 100 parts by weight of the positive electrode active material can be, for example, 0.1 to 10 parts by weight. The binder may contain optional components. For example, the binder may contain at least one selected from polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ethers, and derivatives thereof.

[0133] The positive electrode layer 11 may also contain, for example, inorganic fillers, organic fillers, solid electrolytes, surface modifiers, dispersants, lubricants, flame retardants, protective agents, fluxes, coupling agents, adsorbents, etc. The positive electrode layer may contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, silane coupling agents, MoS2, WO3, etc.

[0134] negative electrode layer

[0135] The negative electrode layer 12 is attached to one side of the current collector foil 13. The negative electrode layer 12 is disposed on the back side of the positive electrode layer 11. The negative electrode layer 12 may have a larger area than the positive electrode layer 11. The thickness of the negative electrode layer 12 may be, for example, 50 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, 300 μm or more, 400 μm or more, 500 μm or more, 600 μm or more, 700 μm or more, 800 μm or more, or 900 μm or more. The thickness of the negative electrode layer 12 may be, for example, less than 1000 μm, less than 900 μm, less than 800 μm, less than 700 μm, less than 600 μm, less than 500 μm, less than 400 μm, less than 300 μm, or less than 200 μm.

[0136] The negative electrode layer 12 contains a negative electrode active material. The negative electrode active material can be, for example, in particulate or sheet form. The D50 of the negative electrode active material can be, for example, 1 μm or more, 5 μm or more, or 10 μm or more. The D50 of the negative electrode active material can be, for example, less than 30 μm, less than 20 μm, less than 15 μm, or less than 10 μm.

[0137] The negative electrode active material may contain optional components. For example, the negative electrode active material may contain at least one selected from carbon-based active materials, alloy-based active materials, Si-C composite materials, Li metal, Li-based alloys, and lithium titanate. In some embodiments of this disclosure, the battery may also be a Li metal negative electrode battery.

[0138] Carbon-based active materials may include at least one selected from graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. Graphite may also 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".

[0139] The surface of graphite can be covered, for example, with amorphous carbon. The surface of graphite can also be covered with a dissimilar material. The dissimilar material can, for example, contain at least one selected from P, W, Al, and O. The dissimilar material can also, for example, contain at least one selected from Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO3, and Li3PO4.

[0140] The alloy-based active material may, for example, contain at least one selected from Si, Li silicate, SiO, Si-based alloy, tin (Sn), SnO, and Sn-based alloy.

[0141] SiO may have, for example, a composition represented by the general formula "SiO x ". In the general formula, the relationship of "0 < x < 2", "0.5 ≤ x ≤ 1.5", or "0.8 ≤ x ≤ 1.2" may also be satisfied, for example.

[0142] "Si-C composite material" refers to a composite material of a carbon-based active material (such as graphite) and an alloy-based active material (such as Si). For example, Si fine particles may be dispersed in carbon particles. For example, Si fine particles may be dispersed in graphite particles. For example, Li silicate particles may also be covered with a carbon material (such as amorphous carbon).

[0143] Separator

[0144] The separator 20 can separate the positive electrode layer 11 from the negative electrode layer 12. The separator 20 has electrical insulation. The separator 20 may, for example, contain at least one selected from a resin film (polymer film), an inorganic particle layer, and an organic particle layer. The separator 20 may, for example, contain a resin film and an inorganic particle layer.

[0145] The resin film is porous. The resin film may contain, for example, a microporous membrane, non-woven fabric, etc. The resin film contains a resin skeleton. The resin skeleton may, for example, be continuously reticulated. Fine pores are formed in the gaps of the resin skeleton. The resin film can allow the electrolyte to permeate. The average pore diameter of the resin film may be, for example, 1 μm or less. The average pore diameter of the resin film may be, for example, 0.01 - 1 μm or 0.1 - 0.5 μm. The "average pore diameter" can be measured by the mercury intrusion method. The Gurley value of the resin film may be, for example, 50 - 250 s / 100 cm 3 . The "Gurley value" can be measured by the Gurley test method.

[0146] The resin film may contain, for example, at least one selected from olefin-based resins, polyurethane-based resins, polyamide-based resins, cellulose-based resins, polyether-based resins, acrylic-based resins, polyester-based resins, etc. The resin film may contain, for example, at least one selected from polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and their derivatives. The resin film can be formed by, for example, the stretching method, the phase separation method, etc. The thickness of the resin film may be, for example, 5 - 50 μm or 10 - 25 μm.

[0147] The resin membrane can have, for example, a single-layer structure. The resin membrane can be composed of, for example, a PE layer. The framework of the PE layer is formed of PE. The PE layer can have a sealing function. The resin membrane can also have, for example, a multi-layer structure. The resin membrane can include, for example, a PP layer and a PE layer. The framework of the PP layer is formed of PP. The resin membrane can also have, for example, a three-layer structure. The resin membrane can be formed by, for example, sequentially stacking a PP layer, a PE layer, and another PP layer. The thickness of the PE layer can, for example, be 5~20 μm. The thickness of the PP layer can, for example, be 3~10 μm.

[0148] The inorganic particle layer can be formed on the surface of the resin membrane. The inorganic particle layer can be formed on only one side of the resin membrane or on both sides. The inorganic particle layer can be formed on the surface opposite to the positive electrode layer 11 or on the surface opposite to the negative electrode layer 12. Furthermore, the inorganic particle layer can be formed on the surface of the positive electrode layer 11 or on the surface of the negative electrode layer 12.

[0149] The inorganic particle layer is porous. It contains inorganic particles, which can also be referred to as "inorganic fillers." Fine pores are formed between the inorganic particles. The thickness of the inorganic particle layer can be, for example, 0.5–10 μm or 1–5 μm. The inorganic particles may contain, for example, heat-resistant materials. An inorganic particle layer containing heat-resistant materials is also called a "HRL (Heat Resistance Layer)." The inorganic particles may contain at least one selected from boehmite, alumina, zirconium oxide, titanium oxide, magnesium oxide, and silicon oxide. The inorganic particles can have any shape. They can be, for example, spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the inorganic particles can be, for example, 0.1–10 μm or 0.5–3 μm. The inorganic particle layer may also contain an adhesive. The adhesive may contain, for example, at least one selected from acrylic resins, polyamide resins, fluorinated resins, aromatic polyether resins, and liquid crystal polyester resins.

[0150] The membrane 20 may include, for example, an organic particle layer. The membrane 20 may also include, for example, an organic particle layer instead of a resin membrane. The membrane 20 may include, for example, an organic particle layer instead of an inorganic particle layer. The membrane 20 may also simultaneously include a resin membrane and an organic particle layer. The membrane 20 may simultaneously include an inorganic particle layer and an organic particle layer. The membrane 20 may also include a resin membrane, an inorganic particle layer, and an organic particle layer.

[0151] The thickness of the organic particle layer can be, for example, 0.1~50 μm, 0.5~20 μm, 0.5~10 μm, or 1~5 μm. The organic particle layer contains organic particles. These organic particles can also be referred to as "organic fillers." The organic particles may contain heat-resistant materials. The organic particles may contain at least one material selected from, for example, PE, PP, PTFE, PI, PAI, PA, and aromatic polyamides. The organic particles can be, for example, spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the organic particles can be, for example, 0.1~10 μm or 0.5~3 μm.

[0152] The membrane 20 may also include a hybrid layer, for example. The hybrid layer contains both inorganic and organic particles.

[0153] electrolyte

[0154] The electrolyte is a liquid electrolyte. The electrolyte contains a solute and a solvent. The concentration of the solute can be, for example, 0.5–1 mol / L, 1–1.5 mol / L, 1.5–2 mol / L, 2–2.5 mol / L, or 2.5–3 mol / L. "mol / L" is sometimes expressed as "M". The solute contains a supporting electrolyte (Li salt). The solute can contain, for example, inorganic acid salts, imide salts, oxalate complexes, halides, etc. The solute can contain, for example, at least one selected from 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 their derivatives.

[0155] The electrolyte may contain, for example, a carbonate-based solvent or a carbonate-ester-based solvent. The solvent may contain, for example, cyclic carbonates, chain carbonates, fluorinated carbonates, etc. The solvent may contain, for example, at least one selected from ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene monofluorocarbonate (FEC), difluoroethylene carbonate, 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene carbonate, fluoropropylene carbonate, difluoropropylene carbonate, and their derivatives.

[0156] The solvent may contain cyclic carbonates (EC, PC, FEC, etc.) and chain carbonates (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates and chain carbonates 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".

[0157] The solvent may contain cyclic carbonates (EC, PC, etc.) and fluorinated cyclic carbonates (FEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates and fluorinated cyclic carbonates may be, for example, "cyclic carbonate / fluorinated cyclic carbonate = 99 / 1~90 / 10", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1~1 / 9", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1~7 / 3" or "cyclic carbonate / fluorinated cyclic carbonate = 3 / 7~1 / 9".

[0158] Solvents may include, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component can satisfy, for example, the relationship "V EC +V FEC +V EMC +V DMC +V DEC =10" represents a relation. In the relation expression, "V" represents a relationship. EC V FEC V EMC V DMC V DEC "Represent the volume ratios of EC, FEC, EMC, DMC, and DEC, respectively. Satisfying "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 The relationship ≤ 9. For example, it can also satisfy "1 ≤ V". EC ≤2" or "2≤V" EC The relationship is "≤3". For example, it can also satisfy "1≤V". FEC ≤2" or "2≤V" FEC The relationship ≤ 4. For example, it can also satisfy "3 ≤ V". EMC ≤4" or "6≤V" EMC The relationship is ≤8. For example, it can also satisfy "3≤V". DMC ≤4" or "6≤V" DMCThe relationship is ≤8. For example, it can also satisfy "3≤V". DEC ≤4" or "6≤V" DEC The relationship is ≤8".

[0159] The solvent may have, for example, a composition in volume ratios such as "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", "EC / FEC / DMC / EMC=1 / 2 / 3 / 4", etc.

[0160] The electrolyte may contain ether-based solvents. The electrolyte may contain, for example, solvents selected from tetrahydrofuran (THF), 1,4-dihydrofuran, etc. At least one of the following: alkylene (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), hydrofluoroether (HFE), ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and their derivatives.

[0161] The electrolyte may contain optional additives. The amount added (relative to the total mass fraction of the electrolyte) may be, for example, 0.01~5%, 0.05~3%, or 0.1~1%. Additives may include, for example, SEI (solid electrolyte interface) formation promoters, SEI formation inhibitors, gas generators, overcharge preventers, flame retardants, antioxidants, electrode protectants, surfactants, etc.

[0162] Additives may include, for example, those selected from vinylene carbonate (VC), ethylene ethylene carbonate (VEC), 1,3-propanesulfonate lactone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfide (ES), ethylene sulfide (DTD), γ-butyrolactone, phosphazene compounds, and carboxylic acid esters (e.g., methyl formate (MF), methyl acetate (MA), methyl propionate (MP), diethyl malonate (DE)). fluorobenzenes (e.g., monofluorobenzene (FB), 1,2-difluorobenzene, 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.), and fluorotoluenes (e.g., 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, etc.). 1,5-Difluorotoluene, 2,6-Difluorotoluene, 3,4-Difluorotoluene, octafluorotoluene, etc.), trifluorotoluene (e.g., trifluorotoluene, 2-fluorotrifluorotoluene, 3-fluorotrifluorotoluene, 4-fluorotrifluorotoluene, 2-methyltrifluorotoluene, 3-methyltrifluorotoluene, 4-methyltrifluorotoluene, etc.), fluoroxylene (e.g., 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m-xylene, etc.), The following are included in the list of sulfur-containing heterocyclic compounds (e.g., benzothiazole, 2-methylbenzothiazole, tetrathiofulvalene, etc.), nitrile compounds (e.g., adiponitrile, succinate, etc.), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate, etc.), carboxylic anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, etc.), alcohols (e.g., methanol, ethanol, n-propanol, ethylene glycol, diethylene glycol monomethyl ether, etc.), and their derivatives.

[0163] The components described above as solutes and solvents can be used as trace components (additives). Additives may contain at least one selected from, for example, LiBF4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO2F2, FSO3Li, LiI, LiBr, HFE, DOX, PC, FEC, and their derivatives.

[0164] The electrolyte may contain ionic liquids. Ionic liquids may contain, for example, salts selected from sulfonium salts, ammonium salts, pyridinium salts, piperidine salts, pyrrolidine salts, morpholine salts, etc. Salt, imidazole At least one of salts and their derivatives.

[0165] In some embodiments of this disclosure, the battery may comprise a gel electrolyte. That is, the battery may be a polymer battery. The gel electrolyte may comprise an electrolyte and a polymeric material. The polymeric material may form a polymeric matrix. The polymeric material may comprise, for example, at least one selected from PVdF, PVdF-HFP, polyacrylonitrile (PAN), PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0166] All-solid-state batteries

[0167] In some embodiments of this disclosure, the battery may be an all-solid-state battery. An all-solid-state battery may have a bipolar structure. An all-solid-state battery includes a solid electrolyte in place of the electrolyte and separator 20. The solid electrolyte may also be included in the positive electrode layer 11 and the negative electrode layer 12. The solid electrolyte layer separates the negative electrode layer 12 from the positive electrode layer 11 in place of the separator 20. The solid electrolyte layer includes, for example, a solid electrolyte and a binder.

[0168] Solid electrolytes can also be, for example, powders. The D50 of a solid electrolyte can be, for example, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, 0.4 μm or more, 0.5 μm or more, 0.6 μm or more, 0.7 μm or more, 0.8 μm or more, 0.9 μm or more, or 1 μm or more. The D50 of a solid electrolyte can also be, for example, less than 5 μm, less than 4 μm, less than 3 μm, less than 2 μm, or less than 1 μm.

[0169] Solid electrolytes may include at least one selected from, for example, sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, hydride solid electrolytes and nitride solid electrolytes.

[0170] The sulfide solid electrolyte may contain at least one selected from amorphous phases, crystalline phases, and glass-ceramic (crystalline glass) phases. The crystalline phase may be, for example, argillite-germanium sulfide or LGPS type. The sulfide solid electrolyte contains Li and sulfur (S). In addition to Li and S, the sulfide solid electrolyte may also contain optional components.

[0171] Sulfide solid electrolytes may contain, for example, compounds selected from 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, Li 10 GeP2S 12 Li4P2S6, Li7P3S 11 At least one of Li3PS4 and Li7PS6.

[0172] For example, "LiI-LiBr-Li3PS4" indicates a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li3PS4 in any molar ratio. Sulfide solid electrolytes can also be produced by mechanochemical methods. The mixing ratio can also be determined by adding numbers before each raw material. For example, "10LiI-15LiBr-75Li3PS4" indicates a mixing ratio of "LiI / LiBr / Li3PS4 = 10 / 15 / 75 (molar ratio)".

[0173] Sulfide solid electrolytes can have compositions, for example, represented by the general formula "xLi₂S-(1-x)P₂S₅". In this formula, x can be greater than 0, or greater than 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.75, 0.8, or 0.9. x can also be less than 1, less than 0.9, less than 0.8, less than 0.75, less than 0.7, less than 0.6, less than 0.5, less than 0.4, less than 0.3, less than 0.2, or less than 0.1. For example, when x = 0.75, "xLi₂S-(1-x)P₂S₅" can have a composition of Li₃PS₄.

[0174] The sulfide solid electrolyte can have a composition, for example, represented by the general formula "yLiI-zLiBr-(100-yz)[xLi2S-(1-x)P2S5]". In this formula, x can be, for example, 0.5 or more, 0.6 or more, 0.7 or more, 0.75 or more, 0.8 or more, or 0.9 or more. x can be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.75 or less, 0.7 or less, or 0.6 or less. y can be, for example, 0 or more, 5 or more, 10 or more, 15 or more, 20 or more, or 25 or more. y can be, for example, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, or 5 or less. z can be, for example, 0 or more, 5 or more, 10 or more, 15 or more, 20 or more, or 25 or more. z can be, for example, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, or 5 or less.

[0175] Sulfide solid electrolytes can have, for example, properties derived from the general formula "Li". 7-x-2y PS 6-x-y X y The composition is represented by the formula. In the general formula, the relationships "0 < 7-x-2y", "0 < 6-xy", "0 ≤ x", and "0 ≤ y" are satisfied. X may contain at least one of, for example, fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0176] Sulfide solid electrolytes can have, for example, properties derived from the general formula "Li".4-x M 1-x P x The composition represented by "S4". In the general formula, x can be greater than 0, greater than 0.1, greater than 0.2, greater than 0.3, greater than 0.4, greater than 0.5, greater than 0.6, greater than 0.7, greater than 0.8, or greater than 0.9. x can be less than 1, less than 0.9, less than 0.8, less than 0.7, less than 0.6, less than 0.5, less than 0.4, less than 0.3, less than 0.2, or less than 0.1. M can contain at least one of, for example, selected from Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0177] Sulfide solid electrolytes can have, for example, properties derived from the general formula "Li". 10+x Ge 1+x P 2-x S 12 The composition is indicated by the formula. In the general formula, x can be, for example, 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, or 0.6 or more. x can be, for example, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. The sulfide solid electrolyte represented by the above general formula can contain, for example, a crystalline phase of the LGPS type.

[0178] Halogenated solid electrolytes can have, for example, properties derived from the general formula "Li". 6-na M a The composition represented by "X6" is as follows. In the general formula, "n" represents the oxidation number of "M". For example, "M" may contain atoms with an oxidation number of +3. For example, "M" may contain atoms with an oxidation number of +4. For example, "M" may contain at least one selected from Y, Al, Ti, Zr, Ca, and Mg. For example, the relationship "0 < a < 2" may also be satisfied. "X" may contain at least one selected from, for example, F, Cl, Br, and I.

[0179] Halogenated solid electrolytes can have, for example, properties derived from the general formula "Li". 3-a Ti a Al 1-a F6 represents the composition. In the general formula, "a" can be, for example, 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. "a" can be, for example, less than 1, less than 0.9, less than 0.8, less than 0.7, less than 0.6, less than 0.5, less than 0.4, less than 0.3, less than 0.2, or less than 0.1.

[0180] Halogen solid electrolytes can have, for example, properties derived from the general formula "Li3YCl". a Br b I6-a-b The formula represents the composition. In the general formula, it can also satisfy relationships such as "0 ≤ a + b ≤ 6". "a" can be, for example, 0 or higher, 1 or higher, 2 or higher, 3 or higher, 4 or higher, or 5 or higher. "a" can also be, for example, less than 6, less than 5, less than 4, less than 3, less than 2, or less than 1. "b" can also be, for example, 0 or higher, 1 or higher, 2 or higher, 3 or higher, 4 or higher, or 5 or higher. "b" can also be, for example, less than 6, less than 5, less than 4, less than 3, less than 2, or less than 1.

[0181] Oxide solid electrolytes may contain, for example, those selected from LiNbO3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, La 2 / 3-x Li 3x TiO3 and Li7La3Zr2O 12 At least one of the following. Hydride solid electrolytes may contain, for example, LiBH4. Nitride solid electrolytes may contain, for example, Li3N, Li3BN2, etc.

[0182] Sample preparation

[0183] Figure 7 This is a table showing the experimental results. Positive electrode active materials No. 1 through No. 7 were manufactured in the following order.

[0184] (a) Preparation of two types of secondary particles

[0185] (a1) harmonization

[0186] To become formula (1) "Li x Mn a Fe 1-a Weigh lithium hydroxide monohydrate, manganese carbonate, iron phosphate, and lithium dihydrogen phosphate according to the composition ratio shown in "PO4". The Mn composition ratio "a" in each sample is as follows: Figure 7 As shown. In this embodiment, "x=1.04". Glucose is weighed to a mass fraction of 8% relative to the total mass of the raw materials. The weighed material is mixed with water to form a slurry. The solids concentration of the slurry is 30% ± 20% by mass fraction.

[0187] (a2) Wet grinding

[0188] The average particle size of the dispersion (primary particles) is adjusted by wet grinding of the slurry using a bead mill.

[0189] (a3) Granulation

[0190] The slurry is spray-dried using a spray dryer to form secondary particles. These secondary particles contain precursors of olivine-type compounds. The target D50 value for the secondary particles (powder) is 9 μm ± 5 μm. The spray dryer settings are as follows.

[0191] Inlet temperature: 250℃

[0192] Exhaust port temperature: 115℃±15℃

[0193] Inhalation pressure: 2.0 MPa

[0194] Nozzle pressure of the spray nozzle: 0.2±0.1MPa

[0195] (a4) Firing

[0196] The secondary particles were placed in a calcination furnace under a nitrogen atmosphere. The furnace temperature was increased to 200°C at a rate of 3°C / min and maintained at 200°C for 1 hour. Then, the temperature was increased to 650°C at a rate of 5°C / min and maintained at 650°C for 5 hours. Subsequently, the furnace temperature was decreased to 400°C at a rate of 2°C / min, and then decreased to room temperature at a rate of 15°C / min. Thus, the precursor was converted into an olivine-type compound.

[0197] Thus, secondary particles containing the first particle group (average particle size "d1=45nm", Mn composition ratio "a") are formed. By changing the Mn composition ratio in "(a1) blending" and the average particle size of the primary particles in "(a2) wet grinding", secondary particles containing the second particle group (average particle size "d2=120nm", Mn composition ratio "b") are formed.

[0198] (b) Wet grinding (crushing of secondary particles and dispersion of primary particles)

[0199] A slurry is formed by mixing two types of secondary particles and water. The solids concentration of the slurry is 5% to 50% by mass fraction. The slurry is wet-milled using a bead mill. The milling conditions for No.1 and No.3 are as follows.

[0200] Slurry processing capacity: 1.5 kg

[0201] Bead diameter: 2.0mm

[0202] Grinding time: 10 minutes

[0203] Mill circumferential speed: 8m / s

[0204] The pulverization conditions for No. 2 and No. 4~7 are as follows.

[0205] Slurry processing capacity: 1.5 kg

[0206] Bead diameter: 3.0~0.1mm

[0207] Grinding time: 30~240 minutes

[0208] Mill circumferential speed: 8~12m / s

[0209] (c) Re-formation of secondary particles

[0210] The slurry is spray-dried using a spray dryer to form secondary particles. The settings of the spray dryer are the same as those in "(a3) Granulation" above.

[0211] (d) Firing

[0212] The secondary particles were subjected to heat treatment. The heat treatment conditions were the same as those described in "(a4) firing".

[0213] evaluate

[0214] The samples were evaluated in the following order.

[0215] Electrode fabrication

[0216] A mixture is formed by combining a positive electrode active material, a conductive material (acetylene black), and a binder (PVdF). The mixing ratio (mass ratio) is "positive electrode active material / conductive material / binder = 92 / 5 / 3". A paste is formed by dispersing the mixture in a dispersion medium (N-methyl-2-pyrrolidone). The solids concentration of the paste is 50% by mass fraction. The paste is coated onto the surface of an Al foil and dried, thereby forming the positive electrode layer. The density of the positive electrode layer is adjusted to 1.8 g / cm³ by rolling. 3 This process forms the raw material sheet. The raw material sheet is then subjected to vacuum drying at 120°C for 12 hours. After drying, the electrode (diameter: 14mm) is removed from the raw material sheet by stamping.

[0217] Determination of curvature

[0218] Prepare two uncharged electrodes. Form a laminate by stacking the electrodes with the positive electrode layers facing each other. Fabricate a button cell by housing the laminate and electrolyte in a button-shaped casing. Perform impedance measurement of the button cell under the following conditions.

[0219] SOC: 50%

[0220] Frequency range: 100,000~0.01Hz

[0221] Temperature: 25℃

[0222] Voltage amplitude “ΔV”: ±5mV

[0223] The impedance measurement results were analyzed using the analysis software "ZView (registered trademark)," from which the liquid resistance "R" was calculated. ion Furthermore, the effective conductivity of the electrolyte can be calculated using the following formula: κ eff pos ".

[0224] κ eff pos =L / (S·R ion )

[0225] L: Film thickness

[0226] S: The product of electrode area and electrode porosity

[0227] Calculate the porosity "ε" based on the electrode design values. Calculate the tortuosity "τ" using the following formula.

[0228] τ=(Κ·ε) / κ eff pos

[0229] K: Conductivity of the bulk electrolyte

[0230] Figure 7 The normalized curvature shown is the value after normalizing the curvature in No.1 to 1.00.

[0231] Battery manufacturing

[0232] Assemble the button unit inside the glove box. The unit structure is described below.

[0233] Working electrode: Electrode (positive electrode)

[0234] Counter electrode: Li foil

[0235] Separator: Polymer porous membrane

[0236] Electrolyte: EC / DMC = 3 / 7 (volume ratio), LiPF6 (1 mol / L)

[0237] Measurement of initial IV resistance

[0238] In the button cell, charging from 3.0V to 4.3V is considered 100% SOC (State of Charge). The button cell's SOC was adjusted to 50%. At 0°C, the button cell was discharged at a rate of 0.1C for 10 seconds. The voltage drop (in V) was measured 10 seconds after the start of discharge. Similarly, the voltage drop was measured at rates of 0.3C, 0.5C, 0.7C, and 1C. The relationship between voltage drop and current was plotted on a two-dimensional coordinate system. An approximate straight line (linear function) was drawn representing the group of points. The slope of the approximate straight line was considered the initial IV resistance. Figure 7 The standardized initial IV resistance shown is the value standardized by setting the initial IV resistance in No.1 to 1.00. Further, "C" is a symbol representing the current rate. At a rate of 1C, the rated capacity of the battery is circulated in 1 hour.

[0239] Result

[0240] In Figure 7 , when the relationship of "b < a" is satisfied, a tendency for the IV resistance to decrease can be seen. In addition, by dispersing small particles and large particles with each other, a tendency for a significant improvement in the IV resistance can be seen.

[0241] Supplementary note

[0242] The present disclosure also provides the following positive electrode active material.

[0243] A positive electrode active material,

[0244] comprising secondary particles,

[0245] the secondary particles comprising primary particles,

[0246] the number distribution of the particle diameters of the primary particles includes a first peak and a second peak,

[0247] the mode diameter of the second peak is larger than that of the first peak,

[0248] inside the secondary particles, the primary particles belonging to the first peak and the primary particles belonging to the second peak are dispersed with each other,

[0249] the primary particles belonging to the first peak contain a first olivine-type compound,

[0250] the primary particles belonging to the second peak contain a second olivine-type compound, and, )

[0251] the Mn composition ratio of the second olivine-type compound is lower than that of the first olivine-type compound.

Claims

1. A positive electrode active material, characterized in that, Includes secondary particles, The secondary particles include a first particle group and a second particle group. Both the first particle group and the second particle group are composed of primary particles. The average particle size of the second particle swarm is larger than that of the first particle swarm. Within the secondary particles, the first particle group and the second particle group are dispersed from each other. The primary particles belonging to the first particle group contain a first olivine-type compound. The primary particles belonging to the second particle group contain a second olivine-type compound, and, The Mn composition ratio of the second olivine-type compound is lower than that of the first olivine-type compound.

2. The positive electrode active material according to claim 1, characterized in that, In the field emission scanning electron microscopy / energy dispersive X-ray spectroscopy (FE-SEM / EDX) analysis of the secondary particles, the following relationship is satisfied: I2 < I1, Wherein, I1 represents the detection intensity of Mn of the primary particle belonging to the first particle group, and, I2 represents the detection intensity of Mn of the primary particle belonging to the second particle group.

3. The positive electrode active material according to claim 1, characterized in that, The composition of the first olivine-type compound is given by formula 1: Li x Mn a Fe 1-a PO4 indicates that, The composition of the second olivine-type compound is given by formula 2: Li y Mn b Fe 1-b PO4 indicates that, In Equations 1 and 2, the following relationship is satisfied: 0.5≤x≤1.5、0.00 <a≤1.00、 0.5≤y≤1.5, 0.00≤b<1.00, and, b < a.

4. The positive electrode active material according to claim 3, characterized in that, In Equations 1 and 2, the following relationship is also satisfied: 0.20≤a≤1.00, and 0.00≤b≤0.

80.

5. The positive electrode active material according to claim 4, characterized in that, In Equations 1 and 2, the following relationship is also satisfied: 0.60≤a≤0.90, and 0.10≤b≤0.

50.

6. The positive electrode active material according to claim 3, characterized in that, In Equations 1 and 2, the following relationship is also satisfied: 0.10≤ab≤0.

90.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that, The following relationship must be satisfied: 1.5≤d2 / d1≤10, Where d1 represents the average particle size of the first particle swarm, and, d2 represents the average particle size of the second particle group.

8. The positive electrode active material according to any one of claims 1 to 6, characterized in that, The following relationship must be satisfied: 0.4≤m1 / (m1+m2)≤0.6 Where m1 represents the total mass of the primary particles belonging to the first particle swarm, and, m2 represents the total mass of the primary particles belonging to the second particle group.

9. An electrode comprising a positive electrode layer, characterized in that, The positive electrode layer comprises the positive electrode active material according to any one of claims 1 to 6.

10. A battery, characterized in that, It includes the electrode as described in claim 9.

11. The battery according to claim 10, characterized in that, The battery has a bipolar structure.

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