Positive electrode active material, electrode, and battery, and method for manufacturing a positive electrode active material.

Abstract

Achieving both flexibility and filling properties. [Solution] The positive electrode active material includes secondary particles. The secondary particles include a first particle group and a second particle group. The first particle group and the second particle group each consist of primary particles. The primary particles contain an olivine-type phosphate compound. The second particle group has a larger average particle size than the first particle group. The first particle group and the second particle group are dispersed amongst themselves within the secondary particles.

Description

Technical Field

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

Background Art

[0002] JP-A-2021-009838 discloses an agglomerate of manganese-rich lithium manganese iron phosphate particles (average particle size of 10 nm or more and 80 nm or less) and iron-rich lithium manganese iron phosphate particles (average particle size of 80 nm or more and 150 nm or less).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] From the viewpoints of energy density and cycle resistance, it has been proposed to form secondary particles (also referred to as "agglomerates", "aggregated particles", etc.) from two types of primary particles having different average particle sizes. However, there is room for improvement from the viewpoint of achieving both packing density and tortuosity. "Tortuosity" is one of the indexes of ionic conductivity in an electrode. It is considered that the smaller the tortuosity, the better the ionic conductivity.

[0005] An object of the present disclosure is to achieve both tortuosity and packing density.

Means for Solving the Problems

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

[0007] 1. One aspect of this disclosure is a positive electrode active material. The positive electrode active material includes secondary particles. The secondary particles include a first particle group and a second particle group. The first particle group and the second particle group each consist of primary particles. The primary particles contain an olivine-type phosphate compound. The second particle group has a larger average particle size than the first particle group. The first particle group and the second particle group are dispersed amongst themselves within the secondary particles.

[0008] Hereafter, "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."

[0009] Olivine-type phosphate compounds (hereinafter sometimes abbreviated as "olivine") tend to have high resistance. To achieve practical resistance, it is necessary to reduce the primary particles to the submicron to nanometer scale. Fine primary particles tend to aggregate very easily. Conventionally, it has been proposed to prepare small particles and large particles separately and form secondary particles from the small and large particles. However, as mentioned above, since primary particles aggregate very easily, it is thought that the small and large particles each form primary aggregates, and then the primary aggregates aggregate further to form secondary aggregates. When the electrode is compressed, it is thought that small particles have difficulty entering the gaps between large particles in the primary aggregates made up of large particles. Therefore, it is difficult to achieve both packing and flexibility.

[0010] In the secondary particles of this disclosure, small and large particles are dispersed amongst themselves. Therefore, when the electrode is compressed, it is thought that the small particles will fill the gaps between the large particles, resulting in dense packing of the primary particles. Thus, a balance between packing and flexibility can be expected.

[0011] 2. The positive electrode active material described in item "1" above may include, for example, the following configuration: The positive electrode active material satisfies the relationship "1.5 ≤ d2 / d1 ≤ 10". "d1" represents the average particle size of the first particle group. "d2" represents the average particle size of the second particle group.

[0012] The improvement of the degree of bending is expected because the average particle size ratio "d2 / d1" is from 1.5 to 10.

[0013] 3. The positive electrode active material described in item "1" or item "2" above may, for example, include the following configuration. The positive electrode active material satisfies the relationship of "3.0 ≤ d2 / d1".

[0014] The improvement of the degree of bending is expected because the average particle size ratio "d2 / d1" is 3.0 or more.

[0015] 4. The positive electrode active material described in any one of items "1" to "3" above may, for example, include the following configuration. The positive electrode active material satisfies the relationship of "5.0 ≤ d2 / d1".

[0016] The improvement of the degree of bending is expected because the average particle size ratio "d2 / d1" is 5.0 or more.

[0017] 5. The positive electrode active material described in any one of items "1" to "4" above may, for example, include the following configuration. The positive electrode active material satisfies the relationship of "200 nm ≤ d2 ≤ 500 nm".

[0018] The improvement of the degree of bending is expected because the average particle size of the large particles is 200 nm or more. The improvement of the ionic conductivity in the large particles is expected because the average particle size of the large particles is 500 nm or less.

[0019] 6. The positive electrode active material described in any one of items "1" to "5" above may, for example, include the following configuration. The positive electrode active material satisfies the relationship of "0.7000 < n1 / (n1 + n2) < 1.000". "n1" represents the number ratio of the primary particles belonging to the first particle group. "n2" represents the number ratio of the primary particles belonging to the second particle group.

[0020] The ratio "n1 / (n1 + n2)" represents the number ratio of the small particles to the total of the small particles and the large particles. The improvement of the degree of bending is expected because the number ratio of the small particles is more than 0.7000 and less than 1.000.

[0021] 7. The positive electrode active material described in any one of the above items "1" to "6" may include, for example, the following configuration: The positive electrode active material satisfies the relationship "0.4 ≤ m1 / (m1 + m2) ≤ 0.6". "m1" represents the total mass of primary particles belonging to the first particle group. "m2" represents the total mass of primary particles belonging to the second particle group.

[0022] The ratio "m1 / (m1+m2)" represents the mass ratio of small particles to the total mass of large particles. An improvement in curvature is expected when the mass ratio of small particles is between 0.4 and 0.6.

[0023] 8. The positive electrode active material described in any one of items "1" to "7" above may include, for example, the following composition: The olivine-type phosphate compound includes at least one selected from the group consisting of lithium iron phosphate (hereinafter also referred to as "LFP"), lithium manganese phosphate (hereinafter also referred to as "LMP"), and lithium iron manganese phosphate (hereinafter also referred to as "LMFP").

[0024] 9. One aspect of the present disclosure is an electrode. The electrode includes a positive electrode layer. The positive electrode layer includes a positive electrode active material as described in any one of the above sections "1" to "8".

[0025] The positive electrode layer can be referred to as the "positive electrode active material layer," "positive electrode composite material layer," etc. The "electrode" may be a "monopolar electrode (positive electrode)" or a "bipolar electrode," as long as it includes the positive electrode layer.

[0026] 10. One aspect of this disclosure is a battery, which includes the electrodes described in section 9 above.

[0027] 11. The battery described in item "10" above may include, for example, the following configuration: The battery has a bipolar structure.

[0028] A bipolar structure can be formed by stacking bipolar electrodes. A bipolar structure is expected to improve, for example, output characteristics. However, a thick cathode layer may be required in a bipolar structure. The thicker the cathode layer, the greater the impact of the packing density of the cathode active material and the curvature of the cathode layer on the rate characteristics. The cathode active material described in item "1" above is considered particularly suitable for a bipolar structure.

[0029] 12. One aspect of this disclosure is a method for producing a positive electrode active material. The production method includes (a) to (c) below. (a) Prepare a number of secondary particles containing an olivine-type phosphate compound, wherein the average particle size of the primary particles differs from one another. (b) A slurry is formed by wet grinding, which breaks down each of the multiple secondary particles to the scale of the primary particles. (c) New secondary particles are formed by spray-drying a slurry in which multiple primary particles with different average particle sizes are dispersed.

[0030] In this disclosure, secondary particles composed of small particles and secondary particles composed of large particles are prepared. Each secondary particle is first broken down to the scale of a primary particle. A slurry in which the small and large particles are dispersed at the scale of a primary particle is spray-dried to form secondary particles in which the large and small particles are dispersed amongst themselves.

[0031] Hereinafter, one embodiment of the present disclosure (which may be abbreviated as "this embodiment") and one example of the present disclosure (which may be abbreviated as "this example") will be described. However, this embodiment and this example will not limit the technical scope of the present disclosure. This embodiment and this example are illustrative in all respects. This embodiment and this example are not restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the claims. For example, it is intended from the outset that any configuration may be extracted from this embodiment and combined in any way. [Brief explanation of the drawing]

[0032] [Figure 1] This is a conceptual diagram of a secondary particle in a reference form. [Figure 2] This is a conceptual diagram of secondary particles in this embodiment. [Figure 3] This is an example of the number distribution of primary particle sizes. [Figure 4] This is a schematic flowchart of the method for manufacturing the positive electrode active material in this embodiment. [Figure 5] This is a schematic perspective view of the battery in this embodiment. [Figure 6] This is a schematic cross-sectional view along the line VI-VI in Figure 5. [Figure 7] This is a table showing the experimental results. [Modes for carrying out the invention]

[0033] Terms, phrases "To include," "to contain," "to possess," and variations thereof are open-ended phrases. Configurations expressed in open-ended phrases may or may not include additional elements in addition to the required elements. The statement "consists of" is a closed phrase. However, even configurations expressed in closed phrases may include additional elements that are usually incidental impurities or irrelevant to the subject technology. The statement "substantially consists of..." is a semi-closed phrase. Configurations expressed in semi-closed phrases may include elements that do not substantially affect the basic and novel characteristics of the subject technology.

[0034] Expressions such as "may do" and "may be" are used in a permissive sense, meaning "there is a possibility," rather than in an obligatory sense, meaning "it must be done."

[0035] Geometric terms should not be interpreted strictly. Examples of geometric terms include "parallel," "perpendicular," and "orthogonal." For example, direction, angle, distance, etc., may be relatively distorted within a range where substantially the same or similar function is obtained. Geometric terms may include tolerances, errors, etc., in design, operation, and manufacturing. Dimensional relationships in each figure may not match actual dimensional relationships. Dimensional relationships in each figure may be modified to aid the reader's understanding. For example, length, width, thickness, etc., may be changed. Some components may be omitted.

[0036] Elements described in the singular form may also include plural forms unless otherwise specified. For example, "particle" can refer to multiple particles (groups of particles), a collection of particles, or a powder.

[0037] Numerical ranges such as "m to n%" include upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less". Also, "m% or more and n% or less" includes "greater than m% and less than n%". "Greater than or equal to" and "less than or equal to" are represented by the equals sign inequality signs "≦" and "≧". "Greater than" and "less than" are represented by the inequality signs without an equals sign "<" and ">". A number 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 number within the numerical range with a number listed in another part of this specification, in a table, in a figure, etc.

[0038] All numerical values ​​are modified by the term "approximately." The term "approximately" can mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximations that can vary depending on the application of the technology in question. All numerical values ​​may be expressed with significant figures. Unless otherwise specified, measured values ​​may be the average of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. Generally, the more measurements taken, 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.

[0039] The devices, software, etc., used for measuring various values ​​are merely examples. Equivalent devices may be used. If equivalent devices are used, the measurement conditions may be adjusted to suit the device.

[0040] For example, dimensional measurement and shape analysis of various images may be performed using image analysis software. For instance, image analysis software such as "ImageJ" may be used.

[0041] "Primary particles" refer to particles that appear to lack grain boundaries in SEM images acquired by a Field Emission Scanning Electron Microscope (FE-SEM) at magnifications ranging from 20,000x to 100,000x.

[0042] "Particle size" is measured by image analysis (microscopy). In SEM images, particle size is the arithmetic mean of the long side (major axis diameter) and short side (uniaxial diameter) of the minimum bounding box (MBR) for the particle's contour line.

[0043] "Average particle size" refers to the average value of the particle size. The average particle size is measured using the following procedure: An SEM image of secondary particles (powder) is acquired using FE-SEM. The image magnification is between 20,000x and 100,000x. In the SEM image, a total of 100 primary particles are randomly selected 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 to be the average particle size of the primary particles. Similarly, the arithmetic mean of the particle sizes of the 100 secondary particles is considered to be the average particle size of the secondary particles.

[0044] In secondary particles, the state in which "small and large particles are dispersed amongst themselves" refers to a state in which one or more of the following conditions (1) to (6) are satisfied in the SEM image (20,000x magnification) of secondary particles acquired by FE-SEM. (1) No aggregates of five or more large particles have been formed. (2) Of the 10 large particles randomly selected, one or more of the large particles have small particles representing 10% or more of the adjacent particles. (3) Of the 10 large particles randomly selected, in three or more of the large particles, 30% or more of the adjacent particles are small particles. (4) Of the 10 large particles randomly selected, in five or more of the large particles, 30% or more of the adjacent particles are small particles. (5) Of the 10 large particles randomly selected, in five or more of the large particles, 50% or more of the adjacent particles are small particles. (6) In 10 arbitrarily selected large particles, the total length of the grain boundaries between the large particles and the small particles is longer than the total length of the grain boundaries between the large particles themselves.

[0045] The "number distribution (number-based frequency distribution)" may confirm the existence of two or more particle groups with different average particle sizes. The number distribution is created using the following procedure: An SEM image is prepared using FE-SEM at a magnification of 20,000x to 100,000x. Ten secondary particles are randomly selected from the SEM image. For each secondary particle, 100 primary particles are randomly selected. In other words, a total of 1,000 primary particles are randomly selected. The particle size of each primary particle is measured. A number distribution is created using the particle sizes of the 1,000 primary particles. The peak with the greatest height (highest peak) is identified in the number distribution. A convex region with a height of 0.1 times or more the height of the highest peak is considered a peak. The number of peaks may correspond to the number of particles in a group. The particle size at the peak top of each peak is the "mode diameter". The mode diameter may correspond to the average particle size.

[0046] "D50" indicates the particle size at which the cumulative value in the volume-based cumulative distribution reaches 50%. The volume-based particle size distribution is measured using a laser diffraction particle size analyzer.

[0047] "Circularity" is measured in SEM images of particles. Circularity is calculated using the following formula: The arithmetic mean of the circularity of 10 particles is used. ψ = 4πS / L 2 ψ: Circularity π: Pi S: Particle cross-section (area of ​​the region enclosed by the particle's outline) L: Particle circumference (length of the particle's outline)

[0048] The chemical composition of the compound can be measured by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy). A sample solution is prepared by dissolving 0.1 g of the sample (e.g., positive electrode active material) in a mixed acid (10 ml) of hydrochloric acid and sulfuric acid. The sample solution is diluted to an appropriate concentration in a volumetric flask. After dilution, compositional analysis is performed using an ICP-AES instrument. For example, a product name such as "PS3520 UVDD II (manufactured by Hitachi High-Tech Science Corporation)" may be used.

[0049] The stoichiometric composition formula shows a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to compounds with 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, the compound may be doped with trace elements. Some of the Al and O may be substituted with other elements.

[0050] A "derivative" refers to a compound in which a part of the parent compound has been modified by at least one of the following chemical reactions: introduction of a functional group, substitution of atoms, oxidation, reduction, and other chemical reactions. The modification may be at one location or multiple locations. The "substituents" 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 (F, Cl, Br, I, etc.), 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, phosphate amide groups, sulfo groups, carboxyl groups, hydroxamic acid groups, sulfino groups, hydrazino groups, imino groups, and silyl groups. These substituents may be further substituted. If 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.

[0051] positive electrode active material The positive electrode active material includes secondary particles. The positive electrode active material may also be an aggregate (powder) of secondary particles. The D50 of the positive electrode active material may be, for example, 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more. The D50 of the positive electrode active material may also be, for example, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0052] secondary particles Secondary particles are aggregates of primary particles. These aggregates of primary particles include a first particle group and a second particle group. Both the first and second particle groups consist of primary particles. The second particle group has a larger average particle size than 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.

[0053] Figure 1 is a conceptual diagram of secondary particles 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, small particle 1a and large particle 1b are not dispersed within secondary particle 2. Small particle 1a and large particle 1b each form primary aggregates. Gaps are formed between the primary aggregates.

[0054] Figure 2 is a conceptual diagram of secondary particles in this embodiment. In this embodiment, small particles 1a and large particles 1b are dispersed amongst themselves within the secondary particle 2. Therefore, it is considered that the small particles 1a and large particles 1b are easily packed tightly together. In other words, this embodiment (Figure 2) is expected to show improved packing compared to the reference embodiment (Figure 1). Furthermore, the dispersion of large particles 1b is also expected to improve the degree of flexibility.

[0055] In this embodiment, the secondary particles 2 may have any shape. The secondary particles 2 may be, for example, spherical, rod-shaped, angular, or lumpy. The circularity of the secondary particles 2 may be, for example, 0.50 or more, 0.60 or more, 0.70 or more, 0.80 or more, 0.90 or more, or 0.95 or more. The circularity of the secondary particles 2 may be, for example, 1.00 or less, 0.95 or less, 0.90 or less, 0.80 or less, 0.70 or less, or 0.60 or less. The higher the circularity of the secondary particles 2, the better the packing performance can be expected to be.

[0056] The average particle size of secondary particles 2 may 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 secondary particles 2 may also be, for example, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less.

[0057] The secondary particle 2 may further include additional particle groups, insofar as it includes the first particle group (small particles 1a) and the second particle group (large particles 1b). The number of additional particle groups may be, for example, one or more, two or more, three or more, or four or more. The number of additional particle groups may be, for example, five or fewer, four or fewer, three or fewer, or two or fewer. The additional particle groups may have an average particle size smaller than that of the first particle group (small particles 1a). The additional particle groups may have an average particle size between that of the first particle group (small particles 1a) and the second particle group (large particles 1b). The additional particle groups may have an average particle size larger than that of the second particle group (large particles 1b).

[0058] primary particle Primary particle 1 can have any shape. That is, small particle 1a and large particle 1b can each have any shape independently. Small particle 1a and large particle 1b can each be independently, for example, spherical, rod-shaped, angular, or lumpy. The circularity of small particle 1a and large particle 1b can each be independently, for example, 0.50 or more, 0.60 or more, 0.70 or more, 0.80 or more, 0.90 or more, or 0.95 or more. The circularity of small particle 1a and large particle 1b can each be independently, for example, 1.00 or less, 0.95 or less, 0.90 or less, 0.80 or less, 0.70 or less, or 0.60 or less. The higher the circularity of primary particle 1, the better the packing performance can be expected to be.

[0059] The average particle size ratio "d2 / d1" between the first particle group (small particles 1a) and the second particle group (large particles 1b) may be, for example, 2.0 or greater, 3.0 or greater, 4.0 or greater, 5.0 or greater, 6.0 or greater, 7.0 or greater, 7.5 or greater, 8.0 or greater, 9.0 or greater, or 10 or greater. The average particle size ratio "d2 / d1" may also be, for example, 15 or less, 12 or less, 10 or less, 9.0 or less, 8.0 or less, 7.5 or less, 7.0 or less, 6.0 or less, 5.0 or less, 4.0 or less, 3.0 or less, or 2.0 or less. For example, relationships such as "1.5≦d2 / d1≦10", "3.0≦d2 / d1≦10", and "5.0≦d2 / d1≦10" may be satisfied.

[0060] The average particle size "d2" of the second particle group (large particle 1b) may be, for example, 50 nm or larger, 60 nm or larger, 61 nm or larger, 70 nm or larger, 80 nm or larger, 90 nm or larger, 100 nm or larger, 120 nm or larger, 140 nm or larger, 160 nm or larger, 180 nm or larger, 200 nm or larger, 220 nm or larger, 240 nm or larger, 260 nm or larger, 280 nm or larger, 298 nm or larger, 300 nm or larger, 320 nm or larger, 340 nm or larger, 360 nm or larger, 380 nm or larger, 400 nm or larger, or 401 nm or larger. The average particle size "d2" may be, for example, 1000nm or less, 750nm or less, 500nm or less, 450nm or less, 401nm or less, 400nm or less, 380nm or less, 360nm or less, 340nm or less, 320nm or less, 300nm or less, 298nm or less, 280nm or less, 260nm or less, 240nm or less, 220nm or less, 200nm or less, 180nm or less, 160nm or less, 140nm or less, 120nm or less, 100nm or less, 90nm or less, 80nm or less, 70nm or less, 61nm or less, or 60nm or less. For example, relationships such as "200nm≦d2≦500nm", "298nm≦d2≦500nm", "200nm≦d2≦401nm", and "200nm≦d2≦298nm" may be satisfied.

[0061] The average particle size “d1” of the first particle group (small particles 1a) may be, for example, less than 50 nm, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, or 10 nm or less. The average particle size “d1” may be, for example, 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, or 45 nm or more. For example, relationships such as “5 nm ≦ d1 < 50 nm”, “10 nm ≦ d1 ≦ 40 nm”, “20 nm ≦ d1 ≦ 40 nm” may be satisfied.

[0062] 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 satisfy, for example, the relationship “0.5000 < n1 / (n1 + n2) < 1.000”. The number ratio of small particles 1a “n1 / (n1 + n2)” may be, for example, 0.7500 or more, 0.7801 or more, 0.8000 or more, 0.8500 or more, 0.8889 or more, 0.9000 or more, 0.9500 or more, 0.9643 or more, 0.9921 or more, or 0.9976 or more. The number ratio of small particles 1a “n1 / (n1 + n2)” may be, for example, 0.9990 or less, 0.9976 or less, 0.9921 or less, 0.9643 or less, 0.9500 or less, 0.9000 or less, 0.8889 or less, 0.8500 or less, 0.8000 or less, 0.7801 or less, or 0.7500 or less. For example, relationships such as “0.7000 < n1 / (n1 + n2) < 1.000”, “0.7801 ≦ n1 / (n1 + n2) ≦ 0.9990” may be satisfied.

[0063] The total mass "m1" of primary particle 1 (small particle 1a) belonging to the first particle group and the total mass "m2" of primary particle 1 (large particle 1b) belonging to the second particle group may satisfy the relationship, for example, "0.1 ≤ m1 / (m1+m2) ≤ 0.9". The mass ratio of small particle 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 small particle 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, 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" may also be satisfied.

[0064] Figure 3 shows an example of the particle size number distribution of primary particles. The horizontal axis of the histogram represents particle size, and the vertical axis represents particle frequency. The number of peaks in the number distribution corresponds to the number of particles in the secondary particle 2 group. The number distribution may also be bimodal; that is, the number distribution may include at least a first peak P1 and a second peak P2.

[0065] The first peak P1 has a mode diameter "d1". The second peak P2 has a mode diameter "d2". The mode diameter "d2" is larger than the mode diameter "d1". That is, the first peak P1 is composed of the first group of particles (small particles 1a). The second peak P2 is composed of the second group of particles (large particles 1b). The mode diameter of each peak may be considered as the average particle size of each particle group. The integral value (area) of each peak may correspond to the number ratio of primary particles belonging to each peak. For example, the integral value of the first peak P1 may be considered as the number ratio "n1" of small particles 1a.

[0066] The number distribution may be multimodal. That is, in addition to the first peak P1 and the second peak P2, there may be additional peaks. The additional peaks may have, for example, smaller mode diameters than the first peak P1. The additional peaks may have, for example, mode diameters between the first peak P1 and the second peak P2. The additional peaks may have, for example, larger mode diameters than the second peak P2. The additional peaks may be, for example, shoulder peaks of the first peak. The additional peaks may be, for example, shoulder peaks of the second peak.

[0067] composition Primary particle 1 contains olivine. Olivine has a crystal structure assigned to the space group Pnma. The space group to which the crystal structure belongs can be determined by the XRD (X-Ray Diffraction) pattern. Small particle 1a and large particle 1b may have substantially the same composition as long as they contain olivine, or they may have different compositions.

[0068] The olivine may include, for example, at least one selected from the group consisting of LFP, LMP, and LMFP. LMP and LMFP tend to have lower rate characteristics compared to LFP. Therefore, LMP and LMFP require even smaller primary particles 1 compared to LFP. This embodiment is considered particularly suitable for LMP and LMFP.

[0069] Olivine, for example, has the general formula "Li a Mn 1-x Fe xIt may have a composition represented by "PO4". In the general formula, the Li composition ratio "a" may 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. In the general formula, the Li composition ratio "a" may be, for example, 2.0 or less, 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, 1.1 or less, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, or 0.6 or less. In the general formula, for example, the relationship "0.5 ≤ a ≤ 1.5" may be satisfied. In the general formula, the Fe composition ratio "x" may 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. In the general formula, the Fe composition ratio "x" may be, for example, 1.0 or less, 0.9 or less, 0.8 or less, 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. In the general formula, for example, the relationship "0.2 ≤ x ≤ 0.5" may be satisfied.

[0070] Olivine may contain dopants. The dopants represent elements other than lithium (Li), manganese (Mn), iron (Fe), phosphorus (P), and oxygen (O). The doping amount (molecular fraction relative to the amount of Li) may be, for example, 0.01 to 0.1. Examples of dopants include boron (B), nitrogen (N), halogens, 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), and lead (Pb). It may also contain at least one selected from the group consisting of 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.

[0071] The primary particle 1 may be coated with a carbon material (not shown). Part of the surface of the primary particle 1 may be coated, or the entire surface of the primary particle 1 may be coated. The amount of coating may differ between the small particle 1a and the large particle 1b. The carbon material may be derived from, for example, sugars. The amount of carbon material attached may 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 relative to the secondary particle 2. The amount of carbon material attached may be, for example, 20% or less, 15% or less, 10% or less, 5% or less, 4% or less, or 3% or less by mass fraction relative to the secondary particle 2.

[0072] The positive electrode active material may further contain other components as long as it contains olivine. The mixing ratio (mass ratio) of olivine to other components may be, for example, "olivine / other components = 9 / 1 to 1 / 9", "olivine / other components = 8 / 2 to 2 / 8", "olivine / other components = 7 / 3 to 3 / 7", or "olivine / other components = 6 / 4 to 4 / 6". The positive electrode active material may be, for example, a mixture of olivine powder and other component powder. The other components may include, for example, at least one selected from the group consisting of Li[NiCoMn]O2 (layered structure), Li[NiCoAl]O2 (layered structure), LiMnO2 (rock salt structure), and Li[NiMn]2O4 (spinel structure). Note that the notation [NiCoMn] etc. indicates that the sum of the composition ratios in [] is 1. As long as the sum is 1, each component in [] can take on any composition ratio.

[0073] Method for manufacturing positive electrode active material Figure 4 is a schematic flowchart of the method for producing the positive electrode active material in this embodiment. Hereinafter, "the method for producing the positive electrode active material in this embodiment" may be abbreviated as "this method". This method includes "(a) preparation of a plurality of secondary particles", "(b) wet grinding", and "(c) reforming of secondary particles". This method may further include "(d) calcination".

[0074] (a) Preparation of multiple secondary particles This method involves preparing multiple secondary particles, each containing olivine. The secondary particles have different average particle sizes from the primary particles. Each secondary particle can be prepared independently. As an example, a method for synthesizing secondary particles of LMFP is described.

[0075] (a1) Mixing For example, a slurry may be formed by mixing a lithium compound, a manganese compound, an iron compound, a phosphate compound, and a dispersion medium. For example, the general formula "Li a Mn 1-x Fe xEach raw material may be weighed so that the composition ratio (molar ratio) is as shown in "PO4 (0.5 ≦ a ≦ 1.5, 0 < x < 1)". The lithium compound may contain, for example, lithium hydroxide or the like. The manganese compound may contain, for example, manganese carbonate or the like. The iron compound may contain, for example, ferric phosphate or the like. The phosphate compound may contain, for example, lithium dihydrogen phosphate or the like.

[0076] A carbon material may be mixed into the slurry. The carbon material can coat the surface of the primary particles. The carbon material may contain, for example, saccharides, organic acids, or the like. The carbon material may contain, for example, glucose, sucrose, fructose, citric acid, or the like. The addition amount of the carbon material may be, for example, 1% to 20% in mass fraction with respect to the total solid content.

[0077] The dispersion medium may contain, for example, water or the like. The solid content concentration of the slurry may be, for example, 30% ± 20% in mass fraction.

[0078] (a2) Wet grinding For example, by wet grinding the slurry using a bead mill, the average particle size of the primary particles can be adjusted. That is, wet grinding can be carried out so that the primary particles have a desired average particle size. For example, wet grinding may be carried out so that D50 becomes about 0.30 μm.

[0079] (a3) Granulation For example, by spray drying the slurry, secondary particles may be formed. The primary particles contained in the secondary particles include the precursor of LMFP.

[0080] (a4) Firing By subjecting the secondary particles to heat treatment, the precursor can be converted into LMFP. In this method, any heat treatment furnace (for example, an electric furnace, a muffler furnace, etc.) can be used. The heat treatment atmosphere may be, for example, a nitrogen atmosphere. The heat treatment temperature may be, for example, 400°C to 700°C. The heat treatment time may be, for example, 4 hours to 6 hours.

[0081] For example, by changing the conditions of "(a2) wet grinding" and repeating the steps from "(a1) mixing" to "(a4) calcination," two or more types of secondary particles are prepared. The two or more types of secondary particles are prepared such that the average particle size of the primary particles differs from one another.

[0082] (b) Wet grinding (disintegration of secondary particles, dispersion of primary particles) This method involves forming a slurry in which primary particles are dispersed by wet grinding, which grinds each of several secondary particles down to the scale of primary particles. For example, several slurries may be formed by individually wet grinding each secondary particle. These several slurries may then be mixed. Alternatively, a single slurry may be formed by wet grinding several secondary particles simultaneously. In either case, several primary particles with different average particle sizes can be dispersed amongst themselves in the slurry. The solid content concentration of the slurry may be, for example, 5% to 50% by mass fraction.

[0083] Wet grinding is performed so that secondary particles are broken down to the scale of primary particles and the primary particles are dispersed. Wet grinding can be performed, for example, by a bead mill. The bead diameter is selected according to the size of the primary particles. The grinding time is adjusted so that secondary particles are broken down to the scale of primary particles and the primary particles are dispersed. However, the grinding time is adjusted to be as short as possible so that the primary particles are not ground. For example, if the primary particles are ground and overdispersion occurs, the difference in average particle size between multiple primary particles may not be adjusted to the desired range. Jet mills perform grinding by collision of materials being ground. Therefore, jet mills tend to have weaker grinding power compared to bead mills that use beads as a grinding medium. It is considered difficult to achieve a dispersed state of primary particle scale with a jet mill.

[0084] (c) Reformation of secondary particles This method involves forming secondary particles by spray-drying the slurry. The spray-drying procedure may be the same as, for example, "(a3) Granulation".

[0085] (d) firing This method may include heat treatment of the secondary particles. The heat treatment procedure may be the same as, for example, "(a4) firing".

[0086] liquid battery In some embodiments, the battery may be an electrolyte battery. An "electrolyte battery" refers to a battery that contains an electrolyte. For example, polymer batteries, which contain an electrolyte, belong to the category of electrolyte batteries. In some embodiments, the battery has a monopolar structure. In a monopolar structure, the power generation element may be wound or stacked. In some embodiments, the battery has a bipolar structure. As an example, a battery having a bipolar structure (bipolar battery) is described.

[0087] Figure 5 is a schematic perspective view of the battery in this embodiment. Figure 6 is a schematic cross-sectional view along the line VI-VI in Figure 5. Hereinafter, "orthoplane direction" refers to the direction normal to the surface of a sheet-like member (e.g., foil, electrode, etc.). "In-plane direction" refers to any direction perpendicular to the orthoplane direction. In the figures of this embodiment, the Z-axis direction corresponds to the orthoplane direction. The X-axis and Y-axis directions are examples of in-plane directions.

[0088] 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 include, for example, a first current collector plate 91, a first laminate film 92, a second laminate film 93, and a second current collector plate 94. The first laminate film 92 and the second laminate film 93 are joined to each other at their in-plane edges. At the joint between the first laminate film 92 and the second laminate film 93, a sealing material (not shown) may be interposed between the first laminate film 92 and the second laminate film 93.

[0089] The first current collector plate 91 and the second current collector plate 94 are joined to the power generation element 50 at their ends in the stacking direction (Z-axis direction). The first laminate film 92 is joined to the first current collector plate 91. The second laminate film 93 is joined to the second current collector plate 94. A sealing material (not shown) may be interposed between the current collector plate and the laminate film at the joint between the current collector plate and the laminate film.

[0090] The power generation element 50 includes a plurality of bipolar electrodes 10. The plurality of bipolar electrodes 10 are stacked in the direction perpendicular to the plane (Z-axis direction). Each of the plurality of bipolar electrodes 10 includes, in the direction perpendicular to the plane, a positive electrode layer 11, a current collector foil 13, and a negative electrode layer 12 in this order. In the in-plane direction (for example, in the X-axis direction), the current collector foil 13 extends outward relative to the positive electrode layer 11 and the negative electrode layer 12. For example, the current collector foil 13 may extend outward relative to the positive electrode layer 11 and the negative electrode layer 12 over the entire circumference in the in-plane direction.

[0091] 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 may be formed by bonding an Al foil and a Cu foil together. A carbon material may be coated on the surface of the current collector foil 13. The carbon material may include, for example, carbon black.

[0092] The power generation element 50 includes a sealing material 30. At its in-plane end, the sealing material 30 is joined to the current collector foil 13. The sealing material 30 may, for example, be heat-welded to the current collector foil 13. For example, the sealing material 30 may be arranged around the entire circumference of the in-plane periphery. The sealing material 30 may include, for example, a resin material. The sealing material 30 seals between adjacent current collector foils 13 in the direction perpendicular to the plane. The sealing material 30 between the current collector foils 13 partitions the cells 40. A cell 40 is the smallest unit of the power generation element 50. The battery 100 includes a plurality of cells 40 and may therefore also be called a "bipolar module". Each of the plurality of cells 40 is sealed. The plurality of cells 40 are isolated from each other. Each of the plurality of cells 40 includes a positive electrode layer 11, a separator 20, a negative electrode layer 12, and an electrolyte.

[0093] Positive electrode layer The positive electrode layer 11 is attached to one side of the current collector foil 13. For example, grooves may be formed in the positive electrode layer 11. The positive electrode layer 11 may be formed in a striped pattern, 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, 1000 μm or less, 900 μm or less, 800 μm or less, 700 μm or less, 600 μm or less, 500 μm or less, 400 μm or less, 300 μm or less, or 200 μm or less.

[0094] 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 further contain, for example, a conductive material and a binder. The amount of conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of positive electrode active material. The conductive material may contain any components. For example, the conductive material may contain at least one selected from the group consisting of graphite, acetylene black (AB), Ketjenblack (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF).

[0095] The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of positive electrode active material. The binder may contain any components. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ethers, and derivatives thereof.

[0096] The positive electrode layer 11 may further 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 also contain, for example, polyoxyethylene allylphenyl ether phosphate, zeolite, silane coupling agents, MoS2, WO3, etc.

[0097] Negative electrode layer The negative electrode layer 12 is attached to one side of the current collector foil 13. The negative electrode layer 12 is located 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, 1000 μm or less, 900 μm or less, 800 μm or less, 700 μm or less, 600 μm or less, 500 μm or less, 400 μm or less, 300 μm or less, or 200 μm or less.

[0098] The negative electrode layer 12 contains a negative electrode active material. The negative electrode active material may be, for example, particulate or in sheet form. The D50 of the negative electrode active material may be, for example, 1 μm or more, 5 μm or more, or 10 μm or more. The D50 of the negative electrode active material may be, for example, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0099] The negative electrode active material may contain any components. For example, the negative electrode active material may include at least one selected from the group consisting of 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 invention, the battery may be a Li metal negative electrode battery.

[0100] 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. 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".

[0101] 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 contain, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may contain, for example, at least one selected from the group consisting of Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO3, and Li3PO4.

[0102] The alloy-based active material may contain, for example, at least one selected from the group consisting of Si, Li silicate, SiO, Si-based alloy, tin (Sn), SnO, and Sn-based alloy.

[0103] SiO may have a composition represented by, for example, the general formula "SiO x ". In the general formula, for example, the relationship of "0 < x < 2", "0.5 ≤ x ≤ 1.5" or "0.8 ≤ x ≤ 1.2" may be satisfied.

[0104] "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 be coated with a carbon material (such as amorphous carbon).

[0105] Separator 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 contain, for example, at least one selected from the group consisting of a resin film (polymer film), an inorganic particle layer, and an organic particle layer. The separator 20 may contain, for example, a resin film and an inorganic particle layer.

[0106] The resin film is porous. The resin film may include, for example, a microporous membrane, a non-woven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may be continuously connected, for example, in a network. Pores are formed in the gaps of the resin skeleton. The resin film can permeate an electrolyte. The resin film may have, for example, an average pore diameter of 1 μm or less. The average pore diameter of the resin film may be, for example, from 0.01 to 1 μm, or from 0.1 to 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, from 50 to 250 s / 100 cm 3 and may be. The "Gurley value" can be measured by the Gurley test method.

[0107] The resin film may include at least one selected from the group consisting of, for example, olefin resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, acrylic resins, and polyester resins. The resin film may include 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 can be formed, for example, by a stretching method, a phase separation method, etc. The thickness of the resin film may be, for example, from 5 to 50 μm, or from 10 to 25 μm.

[0108] 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 by PE. The PE layer can 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 by PP. The resin film may have, for example, a three-layer structure. The resin film may be formed, for example, by laminating a PP layer, a PE layer, and a PP layer in this order. The thickness of the PE layer may be, for example, from 5 to 20 μm. The thickness of the PP layer may be, for example, from 3 to 10 μm.

[0109] The inorganic particle layer may be formed on the surface of the resin film. The inorganic particle layer may be formed on only one side of the resin film or on both sides. The inorganic particle layer may be formed on the surface facing the positive electrode layer 11 or on the surface facing the negative electrode layer 12. The inorganic particle layer may be formed on the surface of the positive electrode layer 11 or on the surface of the negative electrode layer 12.

[0110] The inorganic particle layer is porous. The inorganic particle layer contains inorganic particles. The inorganic particles may also be called "inorganic fillers." Pores are formed in the gaps between the inorganic particles. The thickness of the inorganic particle layer may be, for example, 0.5 to 10 μm or 1 to 5 μm. The inorganic particles may contain, for example, a heat-resistant material. An inorganic particle layer containing a heat-resistant material is also called an "HRL (Heat Resistance Layer)." The inorganic particles may contain at least one selected from the group consisting of boehmite, alumina, zirconia, titania, magnesia, and silica. The inorganic particles may have any shape. For example, the inorganic particles may be spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the inorganic particles may be, for example, 0.1 to 10 μm or 0.5 to 3 μm. The inorganic particle layer may further contain a binder. The binder may include, for example, at least one selected from the group consisting of acrylic resins, polyamide resins, fluororesins, aromatic polyether resins, and liquid crystal polyester resins.

[0111] The separator 20 may include, for example, an organic particle layer. The separator 20 may include, for example, an organic particle layer instead of a resin film. The separator 20 may include, for example, an organic particle layer instead of an inorganic particle layer. The separator 20 may include both a resin film and an organic particle layer. The separator 20 may include both an inorganic particle layer and an organic particle layer. The separator 20 may include a resin film, an inorganic particle layer, and an organic particle layer.

[0112] The thickness of the organic particle layer may be, for example, 0.1 to 50 μm, 0.5 to 20 μm, 0.5 to 10 μm, or 1 to 5 μm. The organic particle layer contains organic particles. The organic particles may also be called "organic fillers". The organic particles may contain heat-resistant materials. The organic particles may contain at least one selected from the group consisting of, for example, PE, PP, PTFE, PI, PAI, PA, and aramid. The organic particles may be spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the organic particles may be, for example, 0.1 to 10 μm, or 0.5 to 3 μm.

[0113] The separator 20 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0114] electrolyte The electrolyte is a liquid electrolyte. The electrolyte contains a solute and a solvent. The concentration of the solute may be, for example, 0.5 to 1 mole / L, 1 to 1.5 mole / L, 1.5 to 2 mole / L, 2 to 2.5 mole / L, or 2.5 to 3 mole / L. "mol / L" may also be written as "M". The solute contains a supporting salt (Li salt). The solute may also contain, for example, inorganic acid salts, imide salts, oxalate complexes, halides, etc. The solute may include, for example, at least one selected from the group consisting of 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.

[0115] The electrolyte may contain, for example, a carbonate-based solvent (carbonate ester-based solvent). The solvent may contain, for example, cyclic carbonates, linear carbonates, fluorinated carbonates, etc. 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.

[0116] The solvent may contain cyclic carbonates (EC, PC, FEC, etc.) and linear carbonates (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates to linear carbonates may be, for example, "cyclic carbonate / linear carbonate = 1 / 9 to 4 / 6", "cyclic carbonate / linear carbonate = 2 / 8 to 3 / 7", or "cyclic carbonate / linear carbonate = 3 / 7 to 4 / 6".

[0117] The solvent may contain cyclic carbonates (EC, PC, etc.) and fluorinated cyclic carbonates (FEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates to fluorinated cyclic carbonates 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".

[0118] The solvent may include, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component can be expressed, for example, by the relationship "V EC +V FEC +V EMC +VDMC +V DEC The relationship expressed by "=10" may also be satisfied. In the relationship, "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 The relationship "≤9" is satisfied. For example, "1 ≤ V" EC ≤2" or "2 ≤ V" EC The relationship "≤3" may also be satisfied. For example, "1 ≤ V" FEC ≤2" or "2 ≤ V" FEC The relationship "≤4" may also be satisfied. For example, "3 ≤ V" EMC ≤4" or "6 ≤ V" EMC The relationship "≤8" may also be satisfied. For example, "3 ≤ V" DMC ≤4" or "6 ≤ V" DMC The relationship "≤8" may also be satisfied. For example, "3 ≤ V" DEC ≤4" or "6 ≤ V" DEC The relationship "≤8" may also be satisfied.

[0119] The solvent may have compositions 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", and "EC / FEC / DMC / EMC=1 / 2 / 3 / 4" in volume ratio.

[0120] The electrolyte may contain an ether-based solvent. The electrolyte may contain, for example, 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), ethylglycyle, triglycyle, tetraglycyle, and derivatives thereof.

[0121] The electrolyte may contain any additives. The amount of additive (mass fraction of the total electrolyte) may be, for example, 0.01 to 5%, 0.05 to 3%, or 0.1 to 1%. The additives may include, for example, SEI (Solid Electrolyte Interphase) formation promoters, SEI formation inhibitors, gas generators, overcharge inhibitors, flame retardants, antioxidants, electrode protectants, surfactants, etc.

[0122] Additives include, for example, vinylene carbonate (VC), vinylethylene carbonate (VEC), 1,3-propanesaltone (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.], and fluorobenzenes [e.g., monofluorobenzene (FB), 1,2-di-butylbenzene]. 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.), fluorotoluene (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-methyl benzothiazole) It may contain at least one selected from the group consisting of (e.g., nzothiazole, tetrathiafulvalene), nitrile compounds (e.g., adiponitrile, succinonitrile), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate), carboxylic acid anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride), alcohols (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, diethylene glycol monomethyl ether), and derivatives thereof.

[0123] The components mentioned above may be used as solutes and solvents, or as trace components (additives). The additives may include, for example, at least one selected from the group consisting of LiBF4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO2F2, FSO3Li, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0124] The electrolyte may contain an ionic liquid. The ionic liquid may contain, 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.

[0125] In some embodiments of this invention, the battery may include a gel electrolyte; that is, the battery may be a polymer battery. The gel electrolyte may include an electrolyte solution and a polymer material. 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, polyacrylonitrile (PAN), PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0126] All solid state battery In some embodiments of this invention, the battery may be an all-solid-state battery. The all-solid-state battery may have a bipolar structure. The all-solid-state battery includes a solid electrolyte instead of an electrolyte and a separator 20. The solid electrolyte may also be included in the positive electrode layer 11 and the negative electrode layer 12. Instead of a separator 20, the solid electrolyte layer separates the negative electrode layer 12 from the positive electrode layer 11. The solid electrolyte layer includes, for example, a solid electrolyte and a binder.

[0127] The solid electrolyte may be, for example, a powder. The D50 of the solid electrolyte may 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 the solid electrolyte may be, for example, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less.

[0128] The solid electrolyte may include, for example, at least one selected from the group consisting of sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, hydride solid electrolytes, and nitride solid electrolytes.

[0129] The sulfide solid electrolyte may contain at least one selected from the group consisting of an amorphous phase, a crystalline phase, and a glass ceramic (crystallized glass) phase. The crystalline phase may be, for example, an argyrodite type or an LGPS type. The sulfide solid electrolyte contains Li and sulfur (S). In addition to Li and S, the sulfide solid electrolyte may further contain any other components.

[0130] 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, Li 10 GeP2S 12 Li4P2S6, Li7P3S 11 It may include at least one selected from the group consisting of Li3PS4 and Li7PS6.

[0131] For example, "LiI-LiBr-Li3PS4" indicates 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. The mixing ratio may be specified by prefixing each raw material with a number. For example, "10LiI-15LiBr-75Li3PS4" indicates that the mixing ratio is "LiI / LiBr / Li3PS4 = 10 / 15 / 75 (molar ratio)".

[0132] A sulfide solid electrolyte may have a composition represented by the general formula "xLi2S-(1-x)P2S5". In the general formula, "x" may be, for example, greater than 0, 0.1 or greater, 0.2 or greater, 0.25 or greater, 0.3 or greater, 0.4 or greater, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.75 or greater, 0.8 or greater, or 0.9 or greater. "x" may also be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.75 or less, 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. For example, when "x = 0.75", "xLi2S-(1-x)P2S5" may have the composition of Li3PS4.

[0133] The sulfide solid electrolyte may have a composition represented by the general formula "yLiI-zLiBr-(100-yz)[xLi2S-(1-x)P2S5]". In the general formula, "x" may 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" may 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" may be, for example, 0 or more, 5 or more, 10 or more, 15 or more, 20 or more, or 25 or more. "y" may be, for example, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, or 5 or less. "z" may be, for example, 0 or more, 5 or more, 10 or more, 15 or more, 20 or more, or 25 or more. "z" could be, for example, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, or 5 or less.

[0134] Sulfide solid electrolytes are, for example, those with the general formula "Li 7-x-2y PS 6-x-y X y It may have a composition 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 include, for example, at least one selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0135] Sulfide solid electrolytes are, for example, those with the general formula "Li4-x M 1-x P x It may have a composition represented by "S4". In the general formula, "x" may be, for example, greater than 0, 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. "x" may be, for example, less than 1, 0.9 or less, 0.8 or less, 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. "M" may contain, for example, at least one selected from the group consisting of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0136] The sulfide solid electrolyte may have a composition represented by, for example, the general formula "Li 10+x Ge 1+x P 2-x S 12 ". In the general formula, "x" may 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" may 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 may contain, for example, a LGPS-type crystal phase.

[0137] The halide solid electrolyte may have a composition represented by, for example, the general formula "Li 6-na M a X6". In the general formula, "n" indicates the oxidation number of "M". "M" may contain, for example, an atom having an oxidation number of +3. "M" may contain, for example, an atom having an oxidation number of +4. "M" may contain, for example, at least one selected from the group consisting of Y, Al, Ti, Zr, Ca, and Mg. For example, the relationship of "0 < a < 2" may be satisfied. "X" may contain, for example, at least one selected from the group consisting of F, Cl, Br, and I.

[0138] The halide solid electrolyte may have a composition represented by, for example, the general formula "Li 3-a Tia Al 1-a It may have a composition represented by "F6". In the general formula, "a" may 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" may be, for example, 1 or less, 0.9 or less, 0.8 or less, 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.

[0139] Halide solid electrolytes include, for example, those with the general formula "Li3YCl a Br b I 6-a-b It may have a composition represented by ". In the general formula, for example, the relationship "0 ≤ a + b ≤ 6" may be satisfied. "a" may be, for example, 0 or more, 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. "a" may be, for example, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1 or less. "b" may be, for example, 0 or more, 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. "b" may be, for example, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1 or less.

[0140] Oxide solid electrolytes include, for example, LiNbO3, Li 1.5 Al 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 the following. The hydride solid electrolyte may include, for example, LiBH4. The nitride solid electrolyte may include, for example, Li3N, Li3BN2, etc. [Examples]

[0141] Sample preparation No.1 The positive electrode active material No. 1 was manufactured using the following procedure.

[0142] (a) Preparation of multiple secondary particles (a1) Mixing Compositional formula “Li 1.04 Mn 0.6 Fe 0.4 Lithium hydroxide monohydrate, manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate are weighed out to match the composition ratio shown in "PO4". 8% glucose is weighed out by mass fraction relative to the total mass of the raw materials. The weighed materials are mixed with water to form a slurry. The solid content concentration of the slurry is 30% ± 20% by mass fraction.

[0143] (a2) Wet grinding The average particle size of the dispersion (primary particles) is adjusted by wet grinding of the slurry using a bead mill.

[0144] (a3) Granulation Secondary particles are formed by spray drying the slurry using a spray dryer. These secondary particles contain LMFP precursors. The target D50 value for the secondary particles (powder) is 9 μm ± 5 μm. The spray dryer settings are as follows. Air intake temperature: 250℃ Exhaust vent temperature: 115℃±15℃ Intake pressure: 2.0 MPa Spray nozzle pressure: 0.2 ± 0.1 MPa

[0145] (a4) Firing Secondary particles are placed inside the firing furnace. The furnace atmosphere is nitrogen. The furnace temperature is raised to 200°C at a heating rate of 3°C / min. The furnace temperature is maintained at 200°C for 1 hour. Next, the furnace temperature is raised to 650°C at a heating rate of 5°C / min. The furnace temperature is maintained at 650°C for 5 hours. After that, the furnace temperature is cooled to 400°C at a cooling rate of 2°C / min. The furnace temperature is further cooled to room temperature at a cooling rate of 15°C / min. This converts the precursor into LMFP.

[0146] Two types of secondary particles are prepared using the above procedure. The average particle size of the primary particles is measured for each type of secondary particle. In one type of secondary particle (Particle Group 1), the average particle size of the primary particles is 40 nm. In the other type of secondary particle (Particle Group 2), the average particle size of the primary particles is 61 nm.

[0147] (b) Wet grinding (disintegration of secondary particles, dispersion of primary particles) A slurry is formed by mixing two types of secondary particles with water. The solid content of the slurry is 5% to 50% by mass fraction. The slurry is wet-milled using a bead mill. The milling conditions are, for example, as follows: Slurry processing capacity: 1.5 kg Bead diameter: 0.1mm Grinding time: 10 min Mil peripheral speed: 13 m / s

[0148] (c) Reformation of secondary particles Secondary particles are formed when the slurry is spray-dried using a spray dryer. The settings for the spray dryer are the same as those for "(a3) Granulation" described above.

[0149] (d) firing The secondary particles are subjected to heat treatment. The heat treatment conditions are the same as those for "(a4) Firing" described above.

[0150] No. 2 to No. 6 Figure 7 is a table showing the experimental results. As shown in Figure 7, the positive electrode active material was manufactured in the same manner as in No. 1, except that the average particle size of the primary particles in one of the secondary particles was changed. The grinding conditions were adjusted within the following range. Bead diameter: 3mm to 0.1mm Grinding time: 10 minutes or more, and for an extremely short time such that the particle size of the primary particles does not change. Mil peripheral speed: 8 m / s to 14 m / s

[0151] For samples No. 3 through No. 6, which have a large average particle size ratio, wet grinding was performed individually before the two types of slurries were mixed.

[0152] No. 7 to No. 13 As shown in Figure 7, the two particles of one type prepared in "(a) Preparation of multiple secondary particles" were used as the positive electrode active material.

[0153] evaluation Each sample was evaluated according to the following procedure.

[0154] Electrode fabrication A mixture is formed by mixing the positive electrode active material, conductive material (acetylene black), and 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 solid content concentration of the paste is 50% by mass fraction. The positive electrode layer is formed by applying the paste to the surface of an aluminum foil and drying it. A raw material sheet is formed by compressing the positive electrode layer with a roll press. The raw material sheet is subjected to a vacuum drying treatment at 120°C for 12 hours. After drying, electrodes (diameter: 14 mm) are removed from the raw material sheet by punching.

[0155] Fillability The roll pressing conditions were the same for each sample. The attainment density of the positive electrode layer in No. 7 was 1.8 g / cm³. 3 The "packing density" in Figure 7 indicates the density of each sample. The densities in Figure 7 are relative values, with the density of No. 7 set to 1.

[0156] degree of curvature Two uncharged electrodes are prepared. The electrodes are stacked so that the positive electrode layers face each other, forming a laminate. The laminate and electrolyte are placed in a coin-shaped case to create a coin cell. The impedance of the coin cell is measured under the following conditions. SOC: 50% Frequency range: 100,000 to 0.01 Hz Temperature: 25℃ Voltage amplitude "ΔV": ±5mV

[0157] The impedance measurement results are analyzed using the analysis software "ZView (registered trademark)" to determine the liquid resistance "R ion The effective conductivity of the electrolyte "κ" is calculated using the following formula. eff pos The result is calculated as follows. κ eff pos =L / (S·R ion ) L: Film thickness S: Product of the electrode area and the electrode porosity

[0158] The porosity "ε" is calculated from the electrode design values. The degree of flexibility "τ" is calculated using the following formula. τ=(Κ·ε) / κ eff pos K: Conductivity of bulk electrolyte

[0159] The curvature shown in Figure 7 is a relative value with the value of No. 7 set to 100.

[0160] result In Figure 7, the results for No. 7 to No. 13 show that when the primary particles constituting the secondary particles are monomodal, the curvature tends to improve as the size of the primary particles increases. However, on the other hand, the density decreases as the size of the primary particles increases.

[0161] In Figure 7, results No. 1 to No. 6 show that when the primary particles constituting the secondary particles are bimodal, the curvature tends to improve as the average particle size ratio "d2 / d1" increases. The density is maintained even when the large particles (primary particles) become larger.

[0162] In Figure 7, the results for No. 1 to No. 6 show a tendency for the curvature to improve when the relationship "1.5 ≤ d2 / d1 ≤ 10" is satisfied.

[0163] In Fig. 7, in the results of No. 1 to No. 6, when the relationship of "3.0 ≦ d2 / d1" is satisfied, the degree of bending tends to be improved.

[0164] In Fig. 7, in the results of No. 1 to No. 6, when the relationship of "5.0 ≦ d2 / d1" is satisfied, the degree of bending tends to be improved.

[0165] In Fig. 7, in the results of No. 1 to No. 6, when the relationship of "200 nm ≦ d2" is satisfied, the degree of bending tends to be improved.

[0166] In Fig. 7, in the results of No. 1 to No. 6, when the relationship of "0.7000 < n1 / (n1 + n2) < 1.000" is satisfied, the degree of bending tends to be improved.

[0167] In Fig. 7, in the results of No. 1 to No. 6, when the relationship of "0.4 ≦ m1 / (m1 + m2) ≦ 0.6" is satisfied, the degree of bending tends to be improved.

[0168] From the results of No. 7 to No. 13 in Fig. 7, even if the primary particles constituting the secondary particles are bimodal, when large particles form primary aggregates within the secondary particles, it is considered that the density decreases and it is difficult to achieve both the degree of bending and the filling property.

[0169] Supplementary Note The present disclosure also provides the following positive electrode active material.

[0170] Supplementary Note 1 including secondary particles, the secondary particles include primary particles, the primary particles include an olivine-type phosphate compound, the number distribution of the particle diameters of the primary particles includes a first peak and a second peak, the second peak has a larger mode diameter than the first peak, within the secondary particles, the primary particles belonging to the first peak and the primary particles belonging to the second peak are dispersed in each other. Cathode active material.

[0171] Note 2 The aforementioned distribution of the number of items is 1.5 ≤ d2 / d1 ≤ 10 Satisfying the relationship, The aforementioned d1 represents the mode diameter of the first peak, and, The aforementioned d2 indicates the mode diameter of the second peak. The positive electrode active material as described in Appendix 1.

[0172] Note 3 The aforementioned distribution of the number of items is 3.0 ≤ d² / d1 Satisfying the relationship, The positive electrode active material as described in Appendix 2.

[0173] Note 4 The aforementioned distribution of numbers is 5.0 ≤ d² / d1 Satisfying the relationship, The positive electrode active material as described in Appendix 3.

[0174] Note 5 The aforementioned distribution of numbers is 200nm ≤ d2 ≤ 500nm Satisfying the relationship, The positive electrode active material as described in Appendix 2.

[0175] Note 6 The aforementioned distribution of numbers is 0.7000 <n1 / (n1+n2)<1.000 Satisfying the relationship, The aforementioned n1 represents the integral value of the first peak, and, n2 represents the integral value of the second peak. The positive electrode active material described in any one of the items from Appendix 1 to Appendix 5. [Explanation of Symbols]

[0176] 1 Primary particle, 1a Small particle, 1b Large particle, 2 Secondary particle, 10 Bipolar electrode, 11 Positive electrode layer, 12 Negative electrode layer, 13 Current collector foil, 20 Separator, 30 Sealing material, 40 Cell, 50 Power generation element, 90 Outer casing, 91 First current collector plate, 92 First laminate film, 93 Second laminate film, 94 Second current collector plate, 100 Battery, P1 First peak, P2 Second peak.

Claims

1. Contains secondary particles, The secondary particles include a first particle group and a second particle group, The first particle group and the second particle group each consist of primary particles, The primary particles contain an olivine-type phosphate compound. The second group of particles has a larger average particle size than the first group of particles, and Within the secondary particles, the first particle group and the second particle group are dispersed amongst themselves. Cathode active material.

2. 1.5≦d 2 / d 1 ≦10 Satisfying the relationship, The aforementioned d 1 This represents the average particle size of the first particle group, and, The aforementioned d 2 This represents the average particle size of the second group of particles. The positive electrode active material according to claim 1.

3. 3.0≦d 2 / d 1 Satisfying the relationship, The positive electrode active material according to claim 2.

4. 5.0≦d 2 / d 1 Satisfying the relationship, The positive electrode active material according to claim 3.

5. 200nm≦d 2 ≦500nm Satisfying the relationship, The positive electrode active material according to claim 2.

6. 0.7000<n 1 / (n 1 +n 2 )<1.000 Satisfying the relationship, The aforementioned n 1 This indicates the number ratio of the primary particles belonging to the first particle group, and, The aforementioned n 2 This indicates the number ratio of the primary particles belonging to the second particle group. The positive electrode active material according to any one of claims 1 to 5.

7. 0.4≦m 1 / (m 1 +m 2 )≦0.6 Satisfying the relationship, Said m 1 This indicates the total mass of the primary particles belonging to the first particle group, and, Said m 2 This indicates the total mass of the primary particles belonging to the second particle group. The positive electrode active material according to any one of claims 1 to 5.

8. The olivine-type phosphate compound comprises at least one selected from the group consisting of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate. The positive electrode active material according to any one of claims 1 to 5.

9. It includes a positive electrode layer, and The positive electrode layer comprises the positive electrode active material described in any one of claims 1 to 5. electrode.

10. The electrode included in claim 9, battery.

11. Having a bipolar structure, The battery according to claim 10.

12. (a) Prepare a plurality of secondary particles containing an olivine-type phosphate compound, wherein the average particle size of the primary particles differs from one another. (b) By wet grinding, each of the multiple secondary particles is broken down to the scale of the primary particles, thereby forming a slurry in which the primary particles are dispersed, and (c) Forming new secondary particles by spray-drying a slurry in which a plurality of primary particles having different average particle sizes are dispersed. including, A method for manufacturing a positive electrode active material.

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