Positive electrode active material, electrode, and battery

Abstract

Reduced battery resistance. [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 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 among the secondary particles. 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. The second olivine-type compound has a lower Mn composition ratio than the first olivine-type compound.

Description

Technical Field

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

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2021-009838 discloses an agglomerate of particles of manganese-rich lithium manganese iron phosphate (average particle size of 10 nm or more and 80 nm or less) and particles of iron-rich lithium manganese iron phosphate (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] As positive electrode active materials, olivine-type compounds such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP) have been studied. For example, 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 in battery resistance.

[0005] An object of the present disclosure is to reduce battery resistance.

Means for Solving the Problems

[0006] Hereinafter, the technical configuration and operational 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 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. 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. The second olivine-type compound has a lower Mn composition ratio than the first olivine-type compound.

[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 compounds 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, because 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 aggregate 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. In other words, there is room for improvement in packing. Furthermore, it is thought that large particles have a longer ion conduction distance within the primary particles compared to small particles. It is thought that the formation of aggregates of large particles makes it easier for ions to stagnate, and the degree of bending increases. "Bend of bending" is one of the indicators of ion conductivity within the electrode. The smaller the degree of bending, the better the ion conductivity is thought to be. The combination of low packing and high degree of bending may result in insufficient battery resistance being obtained.

[0010] In the secondary particles of the present disclosure, small particles and large particles are dispersed in each other. Therefore, when the electrode is compressed, it is considered that small particles enter the gaps between large particles, making it easier for primary particles to be densely packed. Further, due to the dispersion of large particles, improvement in the degree of bending is expected. Moreover, large particles have a lower Mn composition ratio than small particles. The lower the Mn composition ratio, the lower the electrical resistance the primary particles can have. Due to large particles having a lower Mn composition ratio, further improvement in the degree of bending is expected. By the synergistic effect of these actions, reduction of battery resistance is expected.

[0011] 2. The positive electrode active material described in item “1” above may include, for example, the following configuration. In the FE-SEM / EDX (Field Emission-Scanning Electron Microscope Energy / Dispersive X-ray Spectroscopy) analysis of secondary particles, the relationship “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.

[0012] The difference in the Mn composition ratio between small particles and large particles can be specified, for example, by FE-SEM / EDX analysis.

[0013] 3. The positive electrode active material described in item “1” or “2” above may include, for example, the following configuration. The first olivine-type compound has a composition represented by the formula (1) “Li x Mn a Fe 1-a PO4”. The second olivine-type compound has a composition represented by the formula (2) “Li y Mn b Fe 1-b PO4”. In the formula (1) and the formula (2), the relationships “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.

[0014] In equation (1), "a" represents the Mn composition ratio of the small particles. In equation (2), "b" represents the Mn composition ratio of the large particles.

[0015] 4. The positive electrode active material described in item "3" above may include, for example, the following configuration: In equations (1) and (2), the relationships "0.20 ≤ a ≤ 1.00" and "0.00 ≤ b ≤ 0.80" are satisfied.

[0016] 5. The positive electrode active material described in item "4" above may include, for example, the following configuration: In equations (1) and (2), the relationships "0.60 ≤ a ≤ 0.90" and "0.10 ≤ b ≤ 0.50" are satisfied.

[0017] 6. The positive electrode active material described in any one of items "3" to "5" above may include, for example, the following configuration: In equations (1) and (2), the relationship "0.10 ≤ ab ≤ 0.90" is further satisfied.

[0018] 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 relationship "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.

[0019] A reduction in battery resistance is expected due to an average particle size ratio "d2 / d1" between 1.5 and 10.

[0020] 8. The positive electrode active material described in any one of the above items "1" to "7" may include, for example, the following configuration: The relationship "0.4 ≤ m1 / (m1 + m2) ≤ 0.6" is satisfied. "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.

[0021] The ratio "m1 / (m1+m2)" represents the mass ratio of small particles to the total mass of large particles. An improvement in battery resistance is expected when the mass ratio of small particles is between 0.4 and 0.6.

[0022] 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".

[0023] 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.

[0024] 10. One aspect of this disclosure is a battery, which includes the electrodes described in section 9 above.

[0025] 11. The battery described in item "10" above may include, for example, the following configuration: The battery has a bipolar structure.

[0026] A bipolar structure can be formed by stacking bipolar electrodes. A bipolar structure is expected to improve, for example, output characteristics. However, a thick positive electrode layer may be required in a bipolar structure. The thicker the positive electrode layer, the greater the impact on battery resistance due to the packing density of the positive electrode active material and the flexibility of the positive electrode layer. The positive electrode active material described in item "1" above is considered particularly suitable for a bipolar structure.

[0027] 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]

[0028] [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]

[0029] Terms, phrases "Equipped with," "includes," "possesses," and variations thereof are open-ended expressions. Configurations expressed in an open-ended manner may or may not include additional elements in addition to the essential elements. The statement "consists of" is a closed expression. However, even configurations expressed in a closed manner may include additional elements that are usually incidental impurities or irrelevant to the subject technology. The statement "substantially consists of..." is a semi-closed expression. In configurations expressed in a semi-closed manner, the addition of elements that do not substantially affect the basic and novel characteristics of the subject technology is permitted.

[0030] 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."

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] "Primary particles" refer to particles that appear to lack grain boundaries in SEM images acquired by FE-SEM at magnifications of 20,000x to 100,000x.

[0038] "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.

[0039] "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.

[0040] 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.

[0041] 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.

[0042] The detection intensity of Mn is measured by FE-SEM / EDX. In the number distribution of primary particles, a first peak and a second peak are identified. The second peak has a larger mode diameter than the first peak. The first peak is considered to originate from the first particle group. The second peak is considered to originate from the second particle group. The FWHM (Full Width at Half Maximum) of the first and second peaks is identified. In the FE-SEM observation image, 100 primary particles with particle sizes within the range of "mode diameter of the first peak ± 0.5 FWHM" are randomly selected. The observation magnification is 50,000 to 200,000 times. For each primary particle, point analysis by EDX is performed to measure the detection intensity of Mn. The arithmetic mean of the 100 primary particles is considered to be the detection intensity of Mn "I1" for primary particles belonging to the first particle group. Similarly, 100 primary particles with particle sizes within the range of "mode diameter of the second peak ±0.5FWHM" are randomly selected from the FE-SEM observation image. Point analysis by EDX is performed near the center of each primary particle to measure the detection intensity of Mn. The arithmetic mean of the 100 primary particles is considered to be the detection intensity "I2" of Mn in the primary particles belonging to the second particle group.

[0043] "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.

[0044] "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)

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 flexibility. The synergistic effect of these factors is expected to reduce battery resistance.

[0052] The dispersion state of primary particle scale shown in Figure 2 can be achieved, for example, by spray-drying a slurry in which small and large particles are dispersed using a wet bead mill. In contrast, jet mills pulverize materials through collisions between the materials themselves. Therefore, jet mills tend to have weaker pulverizing power compared to bead mills, which use beads as the grinding medium. It is considered difficult to achieve the dispersion state of primary particle scale with a jet mill.

[0053] 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.

[0054] 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.

[0055] Secondary particles 2 may further include additional particle groups, insofar as they include 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. Additional particle groups may have an average particle size smaller than that of the first particle group (small particles 1a). 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). Additional particle groups may have an average particle size larger than that of the second particle group (large particles 1b). For example, if secondary particles 2 includes three or more particle groups, the relationship that the Mn composition ratio of the olivine-type compound decreases as the average particle diameter of the particle groups increases may be satisfied.

[0056] 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.

[0057] 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, 2.5 or greater, 2.7 or greater, 3.0 or greater, 4.0 or greater, 5.0 or greater, 6.0 or greater, 7.0 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, 7.0 or less, 6.0 or less, 5.0 or less, 4.0 or less, 3.0 or less, 2.7 or less, 2.5 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.

[0058] The average particle size "d2" of the second particle group (large particle 1b) may 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" may be, for example, 1000nm or less, 750nm or less, 500nm or less, 450nm or less, 400nm or less, 380nm or less, 360nm or less, 340nm or less, 320nm or less, 300nm 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, or 60nm or less. For example, relationships such as "200nm≦d2≦500nm", "300nm≦d2≦500nm", "200nm≦d2≦400nm", and "200nm≦d2≦300nm" may be satisfied.

[0059] The average particle size "d1" of the first particle group (small particle 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 also 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", "5 nm ≤ d1 ≤ 45 nm", "10 nm ≤ d1 ≤ 40 nm", and "20 nm ≤ d1 ≤ 40 nm" may be satisfied.

[0060] 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 of "0.5000 < n1 / (n1 + n2) < 1.000". The number ratio "n1 / (n1 + n2)" of the small particles 1a 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 "n1 / (n1 + n2)" of the small particles 1a 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, relationships such as "0.700 < n1 / (n1 + n2) < 1.00", "0.780 ≤ n1 / (n1 + n2) ≤ 0.999" may be satisfied.

[0061] 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 satisfy, for example, the relationship of "0.1 ≤ m1 / (m1 + m2) ≤ 0.9". The mass ratio "m1 / (m1 + m2)" of the small particles 1a 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 "m1 / (m1 + m2)" of the small particles 1a 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", "0.4 ≤ m1 / (m1 + m2) ≤ 0.6" may be satisfied.

[0062] FIG. 3 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 included in the secondary particles 2. The number distribution may be bimodal. That is, the number distribution may include at least the first peak P1 and the second peak P2.

[0063] The first peak P1 has a mode diameter "dm1". The second peak P2 has a mode diameter "dm2". The mode diameter "dm2" is larger than the mode diameter "dm1". 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). In some embodiments of this invention, the mode diameter of each peak may be considered as the average particle size of each particle group. In some embodiments, the integral value (area) of each peak may be considered as the number ratio of primary particles belonging to each peak.

[0064] 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, the shoulder peaks of the first peak P1. The additional peaks may be, for example, the shoulder peaks of the second peak P2.

[0065] composition The primary particles contain olivine-type compounds. The olivine-type compounds have a crystal structure assigned to the space group Pnma. The space group to which the crystal structure belongs can be identified by the XRD (X-Ray Diffraction) pattern. Primary particles (small particles) belonging to the first particle group contain the first olivine-type compound. 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 compared to the first olivine-type compound. The first olivine-type compound may contain, for example, at least one selected from the group consisting of LMP and LMFP. The second olivine-type compound may contain, for example, at least one selected from the group consisting of LFP and LMFP.

[0066] For example, in the FE-SEM / EDX analysis of secondary particles, the detection intensity of Mn in small particles, "I1", and the detection intensity of Mn in large particles, "I2", may satisfy the relationship "I2 < I1". The detection intensity ratio "I1 / I2" may 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" may 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.

[0067] The first olivine-type compound may have, for example, a composition represented by the formula (1) "Li x Mn a Fe 1-a PO4". The second olivine-type compound may have, for example, a composition represented by the formula (2) "Li y Mn b Fe 1-b PO4".

[0068] In the formula (1) and the formula (2), "a" and "b" represent the Mn composition ratio. Therefore, the relationship "b < a" is satisfied. The difference in the Mn composition ratio, "a - b", may be, for example, more 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 be, for example, 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, relationships such as "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.

[0069] In Formula (1) and Formula (2), the ratio "a / b" of the Mn composition ratio may 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 ratio "a / b" may 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.

[0070] In Formula (1), the Mn composition ratio "a" may be, for example, more than 0.00, 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 more than 0.90. The Mn composition ratio "a" may be, for example, 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, 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", "0.82 ≤ a ≤ 0.92", etc. may be satisfied.

[0071] It should be noted that there seems to be a possible error in the original text where "[0.92]" is likely a typo and should be "0.92" in the English translation for the sake of correct numerical expression.In formula (2), the Mn composition ratio "b" may 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 Mn composition ratio "b" may also be, for example, less than 1.00, 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, 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" may also be satisfied.

[0072] In equation (1), the Li composition ratio "x" 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. The Li composition ratio "x" may also 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. For example, the relationship "0.5 ≤ x ≤ 1.5" may be satisfied.

[0073] In equation (2), the Li composition ratio "y" 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. The Li composition ratio "y" may also 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. For example, the relationship "0.5 ≤ y ≤ 1.5" may be satisfied.

[0074] The first olivine-type compound and the second olivine-type compound may each independently contain a dopant. The dopant represents an element other than lithium (Li), manganese (Mn), iron (Fe), phosphorus (P), and oxygen (O). The dopant may be substitutional or interstitial. The doping amount (molecular fraction relative to the amount of Li) may be, for example, 0.01 to 0.1. Dopants include, for example, 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.

[0075] 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.

[0076] The positive electrode active material may further contain other components, as long as it contains a first olivine-type compound and a second olivine-type compound. The mixing ratio (mass ratio) of the olivine-type compound to the 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 be, for example, a mixture of powder of the olivine-type compound and powder of the other components. 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 within [] can take on any compositional ratio.

[0077] 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".

[0078] (a) Preparation of multiple secondary particles This method involves preparing multiple secondary particles, each containing an olivine-type compound. The secondary particles differ from each other in the average particle size and Mn composition ratio of the primary particles. Each secondary particle can be prepared independently.

[0079] (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, formula (1) "Li x Mn a Fe 1-a"PO4" or formula (2) "Li y Mn b Fe 1-b Each raw material may be weighed to achieve the composition ratio (mole ratio) shown in "PO4". The lithium compound may include, for example, lithium hydroxide. The manganese compound may include, for example, manganese carbonate. The iron compound may include, for example, ferric phosphate. The phosphate compound may include, for example, lithium dihydrogen phosphate.

[0080] A carbon material may be mixed into the slurry. The carbon material may coat the surface of the primary particles. The carbon material may contain, for example, sugars, organic acids, etc. The carbon material may contain, for example, glucose, sucrose, fructose, citric acid, etc. The amount of carbon material added may be, for example, 1% to 20% by mass fraction relative to the total solid content.

[0081] The dispersion medium may contain, for example, water. The solid content concentration of the slurry may be, for example, 30% ± 20% by mass fraction.

[0082] (a2) Wet grinding For example, the average particle size of primary particles can be adjusted by wet grinding of the slurry using a bead mill. That is, wet grinding can be performed so that the primary particles have a desired average particle size. For example, wet grinding may be performed so that D50 is approximately 0.30 μm.

[0083] (a3) Granulation For example, secondary particles may be formed by spray-drying the slurry. The primary particles contained in the secondary particles include precursors of olivine-type compounds.

[0084] (a4) Firing By heat-treating the secondary particles, the precursor can be converted into an olivine-type compound. In this method, any heat treatment furnace (e.g., electric furnace, muffle 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 to 6 hours.

[0085] For example, by repeating the process from "(a1) preparation" to "(a4) calcination" while changing the Mn composition ratio in "(a1) preparation" and changing the grinding conditions in "(a2) wet grinding," 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. The two or more types of secondary particles are prepared such that the larger the average particle size of the primary particles, the lower the Mn composition ratio.

[0086] (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.

[0087] Wet grinding is carried out so that secondary particles are broken down to the scale of primary particles and the primary particles are dispersed. Wet grinding can be carried out, for example, by a bead mill. The bead diameter is selected to match 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.

[0088] (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".

[0089] (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".

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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).

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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".

[0105] 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.

[0106] 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.

[0107] SiO may have, for example, a composition represented by 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.

[0108] "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).

[0109] 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.

[0110] The resin film is porous. The resin film may include, for example, a microporous membrane, a nonwoven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may be continuous, for example, in a mesh-like manner. Pores are formed in the gaps of the resin skeleton. The resin film can permeate the 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, 0.01 to 1 μm, or 0.1 to 0.5 μm. The "average pore diameter" can be measured by the mercury intrusion method. The Gaurle value of the resin film is, for example, 50 to 250 s / 100 cm. 3 It may also be the case that the "Gehré value" can be measured by the Gehré test method.

[0111] The resin film may contain 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 also contain at least one selected from the group consisting of, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamide-imide (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, or the like. The thickness of the resin film may be, for example, 5 to 50 μm or 10 to 25 μm.

[0112] The resin film may have, for example, a single-layer structure. The resin film may consist of, for example, a PE layer. The framework of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multilayer structure. The resin film may include, for example, a PP layer and a PE layer. The framework of the PP layer is formed of PP. The resin film may have, for example, a three-layer structure. The resin film may be formed by laminating a PP layer, a PE layer and a PP layer in this order. The thickness of the PE layer may be, for example, 5 to 20 μm. The thickness of the PP layer may be, for example, 3 to 10 μm.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] The separator 20 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0118] 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.

[0119] 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.

[0120] 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".

[0121] 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".

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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)".

[0136] 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.

[0137] 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.

[0138] 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).

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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]

[0145] Sample preparation Figure 7 is a table showing the experimental results. The positive electrode active materials No. 1 to No. 7 were manufactured according to the following procedure.

[0146] (a) Preparation of multiple secondary particles (a1) Mixing Equation (1) "Li x Mn a Fe 1-a Lithium hydroxide monohydrate, manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate are weighed out to match the composition ratio shown in "PO4". The Mn composition ratio "a" for each sample is shown in Figure 7. In this example, "x = 1.04". 8% glucose is weighed out by mass fraction relative to the total mass of the raw materials. A slurry is formed by mixing the weighed materials with water. The solid content concentration of the slurry is 30% ± 20% by mass fraction.

[0147] (a2) Wet grinding The average particle size of the dispersion (primary particles) is adjusted by wet grinding of the slurry using a bead mill.

[0148] (a3) Granulation Secondary particles are formed by spray drying the slurry using a spray dryer. 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: Air intake temperature: 250℃ Exhaust vent temperature: 115℃±15℃ Intake pressure: 2.0 MPa Spray nozzle pressure: 0.2 ± 0.1 MPa

[0149] (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 an olivine-type compound.

[0150] As a result, 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) preparation" 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.

[0151] (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 for No. 1 and No. 3 are as follows: Slurry processing capacity: 1.5 kg Bead diameter: 2.0mm Grinding time: 10 min Mil peripheral speed: 8 m / s

[0152] The grinding conditions for No. 2, and for Nos. 4 through 7, are as follows: Slurry processing capacity: 1.5 kg Bead diameter: 3.0 to 0.1 mm Grinding time: 30 to 240 min Mil peripheral speed: 8 to 12 m / s

[0153] (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.

[0154] (d) firing The secondary particles are subjected to heat treatment. The heat treatment conditions are the same as those for "(a4) Firing" described above.

[0155] evaluation Each sample was evaluated according to the following procedure.

[0156] 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. The density of the positive electrode layer is 1.8 g / cm³ by roll pressing. 3 The raw material sheet is formed by adjusting the material. The raw material sheet is subjected to a vacuum drying process at 120°C for 12 hours. After drying, electrodes (diameter: 14 mm) are removed from the raw material sheet by die-cutting.

[0157] Measurement 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

[0158] 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

[0159] The porosity "ε" is calculated from the electrode design values. The degree of flexibility "τ" is calculated using the following formula. τ=(Κ·ε) / κeff pos Κ: Conductivity of the bulk electrolyte

[0160] The normalized degree of bending shown in FIG. 7 is a value normalized with the degree of bending in No. 1 being 1.00.

[0161] Fabrication of the battery In a glove box, a coin cell was assembled. The cell configuration is as follows. Working electrode: Electrode (positive electrode) Counter electrode: Li foil Separator: Polymer porous membrane Electrolyte: "EC / DMC = 3 / 7 (volume ratio)", LiPF6 (1 mol / L)

[0162] Measurement of the initial IV resistance In a coin cell, charging from 3.0 V to 4.3 V is regarded as 100% SOC (State Of Charge). The SOC of the coin cell is adjusted to 50%. In a temperature environment of 0°C, at a rate of 0.1C, the coin cell is discharged for 10 seconds. The voltage drop amount (unit: V) after 10 seconds from the start of discharge is measured. Similarly, the voltage drop amount is measured at each rate of 0.3C, 0.5C, 0.7C, and 1C. The relationship between the voltage drop amount and the current is plotted on a two-dimensional coordinate. An approximate straight line (linear function) of the point group is drawn. The slope of the approximate straight line is regarded as the initial IV resistance. The normalized initial IV resistance shown in FIG. 7 is a value normalized with the initial IV resistance in No. 1 being 1.00. Note that "C" is a symbol indicating the rate of current. At a rate of 1C, the rated capacity of the battery flows in 1 hour. [[ID='28']]

[0163] Results In FIG. 7, when the relationship of "b < a" is satisfied, the IV resistance tends to decrease. Furthermore, due to the dispersion of small particles and large particles with each other, the IV resistance tends to be significantly improved.

[0164] Supplementary Note This disclosure also provides the following positive electrode active materials. Contains secondary particles, The secondary particles include primary particles, The number distribution of particle sizes of the primary particles includes a first peak and a second peak. The second peak has a larger mode diameter compared to 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 amongst themselves. The primary particles belonging to the first peak contain a first olivine-type compound. The primary particles belonging to the second peak contain a second olivine-type compound, and The second olivine-type compound has a lower Mn composition ratio compared to the first olivine-type compound. Cathode active material. [Explanation of Symbols]

[0165] 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 second group of particles has a larger average particle size compared to the first group of particles. Within the secondary particles, the first particle group and the second particle group are dispersed amongst themselves. The primary particles belonging to the first group of particles contain a first olivine-type compound, The primary particles belonging to the second group of particles contain a second olivine-type compound, and The second olivine-type compound has a lower Mn composition ratio compared to the first olivine-type compound. Cathode active material.

2. In the FE-SEM / EDX analysis of the aforementioned secondary particles, I 2 <I 1 The relationship is satisfied, The above I 1 This indicates the detection intensity of Mn in the primary particles belonging to the first particle group, and, The above I 2 This indicates the detection intensity of Mn in the primary particles belonging to the second particle group. The positive electrode active material according to claim 1.

3. The first olivine-type compound is defined by formula (1): Li x Mn a Fe 1-a PO 4 It has a composition represented by, The second olivine-type compound has a composition represented by the formula (2): Li y Mn b Fe 1-b PO 4 and has the composition represented thereby. In the above formulas (1) and (2), 0.5 ≤ x ≤ 1.5, 0.00 < a ≤ 1.00, 0.5 ≤ y ≤ 1.5, 0.00 ≤ b < 1.00, and, b < a The relationship is satisfied, The positive electrode active material according to claim 1.

4. In the above formulas (1) and (2), 0.20 ≤ a ≤ 1.00 and 0.00 ≤ b ≤ 0.80 The relationship is further satisfied, The positive electrode active material according to claim 3.

5. In the above formulas (1) and (2), 0.60 ≤ a ≤ 0.90 and 0.10 ≤ b ≤ 0.50 The relationship is further satisfied, The positive electrode active material according to claim 4.

6. In the above formulas (1) and (2), 0.10 ≤ a - b ≤ 0.90 The relationship is further satisfied, The positive electrode active material according to claim 3.

7. 1.5≦d 2 / d 1 ≦10 The relationship is satisfied, 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 any one of claims 1 to 6.

8. 0.4≦m 1 / (m 1 +m 2 )≦0.6 The relationship is satisfied, 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 6.

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 6. electrode.

10. The electrode included in claim 9, battery.

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

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