Positive electrode active material, electrode, and battery

Abstract

Balancing filling efficiency and battery resistance. [Solution] The positive electrode active material includes secondary particles. The secondary particles include a first particle group, a second particle group, and a carbon layer. The first particle group and the second particle group each consist of primary particles. The first particle group has a larger average particle size than the second particle group. The primary particles contain an olivine-type compound. The carbon layer covers at least a portion of the surface of the primary particles. The positive electrode active material is "T B <T A The relationship "T A " indicates the average thickness of the carbon layer in primary particles belonging to the first particle group. B This indicates the average thickness of the carbon layer in primary particles belonging to the second particle group.

Description

[Technical Field]

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

[0002] Japanese Patent Publication No. 2023-538479 discloses that the ratio H / D of the thickness H of the carbon coating layer to the average particle size D of carbon-coated lithium iron phosphate is between 0.01 and 0.04. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2023-538479 [Overview of the project] [Problems that the invention aims to solve]

[0004] Olivine-type compounds are being considered as positive electrode active materials. Olivine-type compounds tend to have high resistance. Conventionally, to reduce resistance, for example, miniaturization of primary particles and coating of primary particles with a carbon layer have been considered. Miniaturization of primary particles can reduce the ion diffusion distance within the primary particles. Coating of primary particles with a carbon layer can impart electronic conductivity to the primary particles. A reduction in battery resistance is expected due to the synergistic effect of these actions. However, there is room for improvement in terms of balancing packing efficiency and battery resistance.

[0005] The purpose of this disclosure is to achieve both filling performance and battery resistance. [Means for solving the problem]

[0006] The technical configuration and effects of this disclosure are described below. However, the mechanism of action includes assumptions. The mechanism of action does not limit the technical scope of this disclosure.

[0007] 1. One aspect of the present disclosure is a positive electrode active material. The positive electrode active material includes secondary particles. The secondary particles include a first particle group, a second particle group, and a carbon layer. The first particle group and the second particle group are each composed of primary particles. The first particle group has a larger average particle diameter than the second particle group. The primary particles include an olivine-type compound. The carbon layer covers at least a part of the surface of the primary particles. The positive electrode active material satisfies the relationship of "T B <T A ". "T A " represents the average thickness of the carbon layer in the primary particles belonging to the first particle group. "T B " represents the average thickness of the carbon layer in the primary particles belonging to the second particle group.

[0008] Due to the refinement of the primary particles, the packing density decreases. To increase the packing density, it is also conceivable to mix relatively large primary particles (large particles) and relatively small (small particles). However, since the electron conductivity of the large particles is low, the balance of electron conductivity between the large particles and the small particles deteriorates, which may increase the overall battery resistance. That is, it is difficult to achieve both high packing density and low battery resistance.

[0009] In the secondary particles of the present disclosure, the large particles and the small particles are each covered with a carbon layer. The carbon layer covering the large particles is thicker than the carbon layer covering the small particles. By improving the balance of electron conductivity between the large particles and the small particles, a reduction in battery resistance is expected. That is, it is expected to achieve both high packing density and low battery resistance.

[0010] 2. The positive electrode active material described in the above item "1" may include, for example, the following configuration. The positive electrode active material satisfies the relationship of "80 nm < d A " and "30 nm ≤ d B ≤ 80 nm". "d A " represents the average particle diameter of the primary particles belonging to the first particle group. "d B " represents the average particle diameter of the primary particles belonging to the second particle group.

[0011] "80 nm < d A " and "30 nm ≤ d BA reduction in battery resistance is expected when the relationship "≤80nm" is satisfied.

[0012] 3. The positive electrode active material described in item "1" or "2" above may include, for example, the following configuration: The positive electrode active material is "3.5 nm ≤ T A <8.0nm and 1.0nm <T B It satisfies the relationship "<3.5nm".

[0013] "3.5nm≦T A <8.0nm and 1.0nm <T B A reduction in battery resistance is expected when the "<3.5nm" relationship is satisfied.

[0014] 4. The positive electrode active material described in any one of the above items "1" to "3" may include, for example, the following components: The positive electrode active material is "0.5≦S A / (S A +S B The relationship "S ) ≤ 0.9" is satisfied. A " indicates the total area of ​​primary particles belonging to the first particle group in the electron microscope image of secondary particles. B This indicates the total area of ​​primary particles belonging to the second particle group in the electron microscope image of secondary particles.

[0015] Ratio “S” A / (S A +S B ) is thought to represent the ratio of large particles to the total amount of small particles. "0.5≦S A / (S A +S B The relationship ")≦0.9" is satisfied, which is expected to improve the packing performance.

[0016] 5. The positive electrode active material described in any one of items "1" to "4" above may include, for example, the following configuration: The mass fraction of the carbon layer in the secondary particles is 1.3% to 3.5%.

[0017] When the mass fraction of the carbon layer is between 1.3% and 3.5%, there tends to be a good balance between electronic conductivity and specific capacity.

[0018] 6. The positive electrode active material described in any one of the above items "1" to "5" may include, for example, the following configuration: A first particle group and a second particle group are dispersed among the secondary particles.

[0019] The dispersion of large and small particles at the primary particle scale is expected to improve packing efficiency.

[0020] 7. The positive electrode active material described in any one of the above items "1" to "6" may include, for example, the following composition: The olivine-type compound includes at least one selected from the group consisting of lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium iron manganese phosphate (LMFP).

[0021] 8. 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 "7".

[0022] 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.

[0023] 9. One aspect of this disclosure is a battery, which includes the electrodes described in section 8 above.

[0024] 10. The battery described in item "9" above may include, for example, the following configuration: The battery has a bipolar structure.

[0025] A bipolar structure can be formed by stacking bipolar electrodes. A bipolar structure is expected to improve, for example, output characteristics. However, a thicker positive electrode layer may be required in a bipolar structure. The thicker the positive electrode layer, the more important it is to balance packing performance with battery resistance. The positive electrode active material described in item "1" above is considered particularly suitable for a bipolar structure.

[0026] 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]

[0027] [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]

[0028] 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.

[0029] 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."

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] "Primary particles" are particles that appear to lack grain boundaries in electron microscope images taken at magnifications of 20,000 to 100,000 times. "Electron microscope images" can be acquired, for example, by FE-SEM (Field Emission Scanning Electron Microscope), SEM, TEM (Transmission Electron Microscope), etc.

[0037] "Particle size" is measured by image analysis (microscopy). Particle size indicates the diameter of the minimum circumscribed circle (MCC) relative to the particle's contour line in an electron microscope image.

[0038] "Average particle size" refers to the average value of the particle size. The average particle size is measured using the following procedure: Electron microscope images of secondary particles (powder) are acquired using FE-SEM. The image magnification is between 20,000x and 100,000x. In the electron microscope images, 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 the average particle size of the primary particles. The average particle size can be measured similarly for secondary particles.

[0039] 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: Electron microscope images are prepared at magnifications ranging from 20,000x to 100,000x. Ten secondary particles are randomly selected from the electron microscope images. 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.

[0040] The "average thickness" is measured using the following procedure. For example, in the number distribution of primary particles, the first and second peaks are identified. The first peak has a larger mode diameter than the second peak. The first peak is considered to originate from the first group of particles. The second peak is considered to originate from the second group of particles. The FWHM (Full Width at Half Maximum) of the first and second peaks is identified. Primary particles with a particle size of ±0.5 FWHM of the mode diameter of the first peak are considered large particles. Electron microscope images are acquired by TEM at magnifications from 50,000 to 100,000 times. The thickness of the carbon layer is measured in the region where the carbon layer is attached almost uniformly near the surface of the large particles. The thickness of the carbon layer is measured for five randomly selected primary particles. The arithmetic mean of the thicknesses of the five points is the average thickness "T A Similarly, primary particles with a particle size of ±0.5 FWHM for the mode diameter of the second peak are considered small particles, and the average thickness of the carbon layer in the small particles is "T B " is measured.

[0041] The "total area of ​​primary particles belonging to each particle group" is measured by the following procedure. Similar to the above, the first and second peaks are identified in the number distribution. The sum of the MCC areas of primary particles with a particle size of ±0.5 FWHM of the mode diameter of the first peak is the total area of ​​primary particles belonging to the first particle group "S A The sum of the MCC areas of primary particles with a particle size of ±0.5 FWHM for the mode diameter of the second peak is considered to be the sum of the total area of ​​primary particles belonging to the second particle group "S B It is considered to be ".

[0042] 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.

[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 electron microscope 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 include a first particle group and a second particle group. Each of these groups consists of primary particles. The first particle group has a larger average particle size than the second particle group; that is, the primary particles belonging to the first particle group are large particles. The primary particles belonging to the second particle group are small particles. At least a portion of the surface of each primary particle is covered by a carbon layer; that is, secondary particles consist of the first particle group, the second particle group, and the carbon layer.

[0050] Figure 1 is a conceptual diagram of secondary particles in a reference configuration. Secondary particles 2 include primary particles 1. Primary particles 1 include large particles 1a and small particles 1b. Mixing large particles 1a and small particles 1b is expected to improve packing efficiency. Large particles 1a and small particles 1b are each coated with a carbon layer 1c. Typically, the carbon layer 1c is formed by adding a carbon material to a mixture of large particles 1a and small particles 1b. In large particles 1a, where the surface area per particle is relatively large, the carbon layer 1c may be formed relatively thinly. In small particles 1b, where the surface area per particle is relatively small, the carbon layer 1c may be formed relatively thickly. In large particles 1a, which inherently have low electronic conductivity, a thin carbon layer 1c may reduce the balance of electronic conductivity between large particles 1a and small particles 1b. As a result, battery resistance may increase.

[0051] Figure 2 is a conceptual diagram of secondary particles in this embodiment. Secondary particles 2 include primary particles 1. Primary particles 1 include large particles 1a and small particles 1b. Large particles 1a and small particles 1b are each coated with a carbon layer 1c. In this embodiment, the carbon layer 1c on large particles 1a is thicker than the carbon layer 1c on small particles 1b. By improving the balance of electronic conductivity between large particles 1a and small particles 1b, a reduction in battery resistance is expected.

[0052] Within the secondary particles 2, for example, large particles 1a and small particles 1b may each form a primary aggregate. Within the secondary particles 2, for example, large particles 1a and small particles 1b may be dispersed amongst themselves. For example, secondary particles 2 in which large particles 1a and small particles 1b are dispersed amongst themselves can be formed by spray-drying a slurry in which large particles 1a and small particles 1b are dispersed amongst themselves using a wet bead mill. In a jet mill, grinding is performed by collisions between the materials to be 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 in 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 particle 2 may further include additional particle groups, insofar as it includes the first particle group (large particles 1a) and the second particle group (small 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, for example, the second particle group (small particles 1b). Additional particle groups may have an average particle size between, for example, the second particle group (small particles 1b) and the first particle group (large particles 1a). Additional particle groups may have an average particle size larger than, for example, the first particle group (large particles 1a). For example, if secondary particle 2 includes three or more particle groups, the relationship that the average thickness of the carbon layer increases as the average particle size of the particle groups increases may be satisfied.

[0056] primary particle Primary particle 1 can have any shape. That is, large particle 1a and small particle 1b can each have any shape independently. Large particle 1a and small particle 1b can each be independently, for example, spherical, rod-shaped, angular, or lumpy. The circularity of large particle 1a and small 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 large particle 1a and small 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 of the first particle group (large particle 1a) is "d A " may be, for example, greater than 80nm. That is, "80nm" <d A The relationship "d" may also be satisfied. A" may be, for example, 90nm or more, 100nm or more, 110nm or more, 120nm or more, 130nm or more, 140nm or more, 150nm or more, 160nm or more, 170nm or more, 180nm or more, 190nm or more, 200nm or more, 240nm or more, 280nm or more, 320nm or more, 360nm or more, 400nm or more, 440nm or more, 480nm or more, or 520nm or more. Average particle size "d A For example, "125nm≦d" could be 1000nm or less, 900nm or less, 800nm ​​or less, 700nm or less, 600nm or less, 520nm or less, 480nm or less, 440nm or less, 400nm or less, 360nm or less, 320nm or less, 280nm or less, 240nm or less, 200nm or less, 190nm or less, 180nm or less, 170nm or less, 160nm or less, 150nm or less, 140nm or less, 130nm or less, 120nm or less, 110nm or less, 100nm or less, or 90nm or less. For example, "125nm≦d A ≤320nm, 130nm ≤d A ≤159nm", "159nm ≤d A Relationships such as "≤320nm" may also be satisfied.

[0058] The average particle size of the second particle group (small particle 1b) is "d B " may be, for example, 80 nm or less. Average particle size "d B " may be, for example, 70 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, or 20 nm or less. Average particle size "d B " may be, for example, 10nm or more, 15nm or more, 20nm or more, 25nm or more, 30nm or more, 40nm or more, 50nm or more, 60nm or more, or 70nm or more. For example, "30nm≦d B ≤80nm, 42nm ≤d B ≤52nm, 42nm ≤d B ≤48nm, 42nm ≤d B Relationships such as "≤46nm" may also be satisfied.

[0059] The average particle size ratio of large particles to small particles "d A / d B" may be, for example, greater than 1, 1.1 or more, 1.2 or more, 1.5 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, 5.5 or more, 6.0 or more, 6.5 or more, or 7.0 or more. Average particle size ratio "d A / d B For example, "20 or less, 15 or less, 12 or less, 10 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.5 or less, 6.0 or less, 5.5 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, 1.5 or less, 1.2 or less, or 1.1 or less.

[0060] The abundance ratio of large particle 1a "S" A / (S A +S B The "S" value may be, for example, greater than 0, 0.1 or greater, 0.2 or greater, 0.3 or greater, 0.4 or greater, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.8 or greater, or 0.9 or greater. Abundance ratio of large particle 1a "S A / (S A +S B )" 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. For example, "0.5≦S A / (S A +S B )≦0.9", "0.5≦S A / (S A +S B )≦0.8", "0.8≦S A / (S A +S B Relationships such as ")≦0.9" may also be satisfied.

[0061] Figure 3 shows an example of the particle size 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 particle size distribution corresponds to the number of particles in the secondary particle 2. The particle size distribution may also be bimodal. That is, the particle size distribution may have at least the first peak P A and the second peak P B It may include.

[0062] First peak P A The mode diameter is "dm A It has the second peak P. B The mode diameter is "dm B It has a mode diameter "dm A " is the mode diameter "dm B It is larger than the first peak P. A It is composed of the first group of particles (large particle 1a). Second peak P B This is composed of a second group of particles (small 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.

[0063] The count distribution may be multimodal. That is, the first peak P A and the second peak P B In addition, there may be additional peaks. These additional peaks could be, for example, a second peak P. B In comparison, it may have a smaller mode diameter. Additional peaks may be, for example, a second peak P. B and the first peak P A It may have a mode diameter between and . Additional peaks may be, for example, the first peak P A It may have a larger mode diameter compared to the first peak P. Additional peaks may be, for example, the first peak P. A It could also be a shoulder peak. An additional peak could be, for example, a second peak P. B It could also be a shoulder peak.

[0064] composition Primary particle 1 contains an olivine-type compound. The olivine-type compound has 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. Large particle 1a and small particle 1b may have substantially the same composition as long as they contain an olivine-type compound, or they may have different compositions.

[0065] The olivine-type compound may include, for example, at least one selected from the group consisting of LFP, LMP, and LMFP. LMP and LMFP tend to have lower electronic conductivity than LFP. Therefore, this embodiment is considered particularly suitable for LMP and LMFP. In addition, LMP and LMFP tend to have larger crystal volume changes with charging and discharging compared to LFP. Due to the volume change of primary particles, the carbon layer may peel off, potentially reducing electronic conductivity. This tendency is particularly pronounced in large particles. In this embodiment, since the carbon layer is thicker in large particles, it is expected that the carbon layer will be less likely to peel off. As a result, for example, the cycle durability of LMP and LMFP may be improved.

[0066] Olivine-type compounds include, for example, those with the general formula "Li a Mn 1-x Fe x It 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, relationships such as "0.2 ≤ x ≤ 0.5" may also be satisfied.

[0067] A dopant may be added to the olivine-type compound. The dopant represents an element 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. The dopant may be interstitial or substitutional. 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.

[0068] Carbon layer The carbon layer 1c covers at least a part of the surface of the primary particles. The entire surface of the primary particles may be covered, or a part of the surface of the primary particles may be covered. The carbon layer 1c is a layer containing a carbon material. The carbon material may be derived from, for example, saccharides or the like. The mass fraction of the carbon layer 1c in the secondary particles 2 (the amount of the carbon material adhered to the secondary particles 2) is, for example, 0.5% or more, 0.8% or more, 1.0% or more, 1.1% or more, 1.2% or more, 1.3% or more, 1.4% or more, 1.5% or more, 1.6% or more, 1.7% or more, 1.8% or more, 1.9% or more, 2.0% or more, 2.1% or more, 2.2% or more, 2.3% or more, 2.4% or more, 2.5% or more, 2.6% or more, 2.7% or more, 2.8% or more, 2.9% or more, 3.0% or more, 3.1% or more, 3.2% or more, 3.3% or more, 3.4% or more, 3.5% or more, 3.6% or more, 3.7% or more, 3.8% or more, 3.9% or more, or 4.0% or more. The mass fraction of the carbon layer 1c in the secondary particles 2 is, for example, 5.0% or less, 4.5% or less, 4.0% or less, 3.9% or less, 3.8% or less, 3.7% or less, 3.6% or less, 3.5% or less, 3.4% or less, 3.3% or less, 3.2% or less, 3.1% or less, 3.0% or less, 2.9% or less, 2.8% or less, 2.7% or less, 2.6% or less, 2.5% or less, 2.4% or less, 2.3% or less, 2.2% or less, 2.1% or less, 2.0% or less, 1.9% or less, 1.8% or less, 1.7% or less, 1.6% or less, 1.5% or less, 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, or 1.0% or less. The mass fraction of the carbon layer 1c in the secondary particles 2 is, for example, from 1.3% to 3.5%, or from 2.0% to 3.1%.

[0069] The average thickness "T A " of the carbon layer 1c in the large particles 1a is larger than the average thickness "T B " of the carbon layer 1c in the small particles 1b. That is, the relationship of "T B < T A " is satisfied. The average thickness ratio "T A / T B" may be, for example, 1.1 or more, 1.2 or more, 1.5 or more, 1.8 or more, 2.1 or more, 2.4 or more, 2.7 or more, or 3.0 or more. The average thickness ratio "T A / T B " may be, for example, 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, 2.4 or less, 2.1 or less, 1.8 or less, 1.5 or less, 1.2 or less, or 1.1 or less.

[0070] "T B <T A " As long as the relationship is satisfied, the average thickness "T A " of the carbon layer 1c in the large particle 1a can take any value. The average thickness "T A " may be, for example, 1.5 nm or more, 2.0 nm or more, 2.5 nm or more, 3.0 nm or more, 3.5 nm or more, 4.0 nm or more, 4.5 nm or more, 5.0 nm or more, 5.5 nm or more, 6.0 nm or more, 6.5 nm or more, 7.0 nm or more, 7.5 nm or more, 8.0 nm or more, 8.5 nm or more, 9.0 nm or more, or 9.5 nm or more. The average thickness "T A " may be, for example, 10 nm or less, 9.5 nm or less, 9. nm or less, 8.5 nm or less, 8.0 nm or less, 7.5 nm or less, 7.0 nm or less, 6.5 nm or less, 6.0 nm or less, 5.5 nm or less, 5.0 nm or less, 4.5 nm or less, 4.0 nm or less, 3.5 nm or less, 3.0 nm or less, 2.5 nm or less, or 2.0 nm or less. For example, "3.5 nm ≤ T A < 8.0 nm", "4.2 nm ≤ T A ≤ 6.2 nm" and other relationships may be satisfied.

[0071] "T B <T A " As long as the relationship is satisfied, the average thickness "T B " of the carbon layer 1c in the small particle 1b can take any value. The average thickness "T B " may be, for example, more than 1.0 nm, 1.2 nm or more, 1.5 nm or more, 2.0 nm or more, 2.5 nm or more, 3.0 nm or more, or 3.5 nm or more. The average thickness "T B" may be, for example, 4.0nm or less, 3.5nm or less, 3.0nm or less, 2.5nm or less, 2.0nm or less, 1.5nm or less, or 1.2nm or less. For example, "1.0nm" <T B <3.5nm", "1.5nm≦T B ≤3.3nm, 2.0nm ≤T B ≤3.3nm, 1.5nm ≤T B Relationships such as "≤2.0nm" may also be satisfied.

[0072] 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 slurry" and "(b) granulation".

[0073] (a) Preparation of slurry In this method, for example, a slurry containing a first particle group (olivine-type compound) and a second particle group (precursor of olivine-type compound) may be prepared.

[0074] For example, a first slurry is formed by mixing lithium compounds, manganese compounds, iron compounds, phosphate compounds, and a dispersion medium. For example, the general formula is "Li a Mn 1-x Fe x 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.

[0075] Furthermore, the carbon material is weighed. The carbon material coats 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 carbon material is mixed into the first slurry. The amount of carbon material added is one of the control factors for the average thickness of the carbon layer. The amount of carbon material added may be, for example, 1% to 20% by mass fraction relative to the total solid content.

[0076] The dispersion medium may contain, for example, water. The solid content concentration of the first slurry may be, for example, 30% ± 20% by mass fraction.

[0077] For example, the particle size of the dispersion (precursor of primary particles) is adjusted by wet grinding the first slurry using a bead mill. For example, wet grinding may be performed so that the primary particles become large. For example, wet grinding may be performed so that the D50 is approximately 0.30 μm.

[0078] The first slurry is dried to recover the precursor powder. The precursor can be converted into an olivine-type compound by heat treatment. Furthermore, the carbon material can be converted into a carbon layer. Any heat treatment furnace (e.g., electric furnace, muffle furnace, etc.) can be used in this method. 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. From the above, the first group of particles (olivine-type compound) is prepared.

[0079] For example, a second slurry is formed by mixing lithium compounds, manganese compounds, iron compounds, phosphate compounds, carbon materials, and a dispersion medium. Details of each material are as described above. The particle size of the dispersion (precursor of primary particles) is adjusted by subjecting the second slurry to wet grinding. For example, wet grinding may be performed so that the primary particles become small particles.

[0080] Furthermore, the first particle group obtained earlier is mixed into the second slurry. The solid content of the second slurry is adjusted. The solid content concentration of the second slurry may be, for example, 30% ± 20% by mass fraction. The second slurry may contain, for example, the first particle group (olivine-type compound, large particles) and the second particle group (precursor of olivine-type compound, small particles).

[0081] (b) Granulation Secondary particles are formed when the second slurry is spray-dried. The secondary particles may include, for example, a first particle group (olivine-type compound, large particles) and a second particle group (precursor of olivine-type compound, small particles). Prior to spray-drying, the second slurry may be subjected to wet grinding using a bead mill so that the large and small particles are dispersed on the scale of the primary particles.

[0082] By heat-treating the secondary particles, the precursor can be converted into an olivine-type compound, and the carbon material can be converted into a carbon layer. The heat treatment conditions are as described above. Thus, secondary particles can be synthesized that include a first particle group (olivine-type compound, large particles) and a second particle group (olivine-type compound, small particles).

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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).

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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".

[0098] The surface of the graphite may be coated with, for example, amorphous carbon. The surface of the graphite may be coated with, for example, a different material. The different material may include, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may include, for example, at least one selected from the group consisting of Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO3, and Li3PO4.

[0099] The alloy-based active material may include, 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.

[0100] 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.

[0101] "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).

[0102] Separator The separator 20 can separate the positive electrode layer 11 from the negative electrode layer 12. The separator 20 has electrical insulation properties. The separator 20 may include, 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 may include, for example, a resin film and an inorganic particle layer.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] The separator 20 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0111] 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.

[0112] 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.

[0113] 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".

[0114] 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".

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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)".

[0129] 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.

[0130] 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.

[0131] 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).

[0132] 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.

[0133] The sulfide solid electrolyte may have, for example, a composition represented by 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.

[0134] The halide solid electrolyte may have, for example, a composition represented by 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 “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.

[0135] The halide solid electrolyte may have, for example, a composition represented by 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.

[0136] 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.

[0137] 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]

[0138] Sample preparation Figure 7 is a table showing the experimental results. Cathode active materials No. 1 to No. 11 were manufactured according to the following procedure.

[0139] No.1, No.2 In No. 1 and No. 2, secondary particles are formed in which the particle size distribution (number distribution) of the primary particles is monomodal.

[0140] "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". Glucose is weighed out to form a carbon layer with the desired average thickness. The weighed materials are mixed with water to form a slurry. The solid content concentration of the slurry is 30% by mass fraction.

[0141] The average particle size of the dispersion (primary particles) is adjusted by wet grinding of the slurry using a bead mill.

[0142] 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 ± 1 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

[0143] 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.

[0144] No. 3 to No. 11 In particles No. 3 through No. 11, secondary particles are formed in which the particle size distribution (number distribution) of the primary particles is bimodal.

[0145] "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". Glucose is weighed out to form a carbon layer with the desired average thickness. The weighed materials are mixed with water to form the first slurry. The solid content concentration of the first slurry is 30% by mass fraction.

[0146] The first slurry is wet-milled using a bead mill, which adjusts the average particle size of the dispersion (primary particles). The precursor powder is recovered by drying the first slurry.

[0147] The precursor powder is placed in the calcination 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. Furthermore, the furnace temperature is cooled to room temperature at a cooling rate of 15°C / min. This converts the precursor into an olivine-type compound. Thus, the first group of particles is prepared.

[0148] "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". Glucose is weighed out to form a carbon layer with the desired average thickness. The weighed materials, the previously obtained first particle group, and water are mixed to form a second slurry. The solid content concentration of the second slurry is 30% by mass fraction.

[0149] Secondary particles are formed by spray drying the second slurry using a spray dryer. The secondary particles consist of a first particle group (olivine-type compound) and a second particle group (precursor of the olivine-type compound). The target D50 value for the secondary particles (powder) is 9 μm ± 1 μm. The settings for the spray dryer 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

[0150] 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 remaining precursor into an olivine-type compound.

[0151] evaluation 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.

[0152] Battery manufacturing The coin cell was assembled inside the glove compartment. The cell configuration is as follows: Working electrode: Electrode (positive electrode) Opposite pole: Li foil Separator: Polymer porous membrane Electrolyte: "EC / DMC=3 / 7 (volume ratio)", LiPF6 (1mol / L)

[0153] Measurement of IV resistance In a coin cell, a charge from 3.0V to 4.3V is considered to be 100% SOC (State of Charge). The SOC of the coin cell is adjusted to 50%. Under a temperature environment of 0°C, the coin cell is discharged for 10 seconds at a rate of 0.1C. The voltage drop (in V) after 10 seconds from the start of discharge is measured. Similarly, the voltage drop is measured at rates of 0.3C, 0.5C, 0.7C, and 1C. The relationship between the voltage drop and the current is plotted on a two-dimensional coordinate system. An approximate straight line (linear function) of the point cloud is drawn. The slope of the approximate straight line is considered to be the IV resistance. The "normalized IV resistance" in Figure 7 is the value normalized with the IV resistance in No. 1 set to 1.00. "C" is a symbol indicating the current rate. At a rate of 1C, the rated capacity of the battery is supplied over 1 hour.

[0154] result In the results for No. 1 to No. 5, compared to No. 1 and No. 2, which included either large or small particles, No. 3 to No. 5, which included both large and small particles, tended to show a reduction in IV resistance.

[0155] In No. 3 to No. 5, the average thickness of the carbon layer in the large particles is "T A " is changing. In the results from No. 3 to No. 5, "T B <T A When the following relationship is satisfied, the IV resistance tends to decrease even further.

[0156] In Nos. 6 to 8, the average thickness of the carbon layer in small particles is "T B" has changed. In the results from No. 6 to No. 8, "T B <T A When the following relationship is satisfied, the IV resistance tends to decrease even further.

[0157] Note This disclosure also provides the following cathode active materials. Contains secondary particles, The secondary particles include primary particles and a carbon layer. The number distribution of particle sizes of the primary particles includes a first peak and a second peak. The first peak has a larger mode diameter compared to the second peak. The carbon layer covers at least a portion of the surface of the primary particles, T B <T A Satisfying the relationship, Said T A This indicates the average thickness of the carbon layer in the primary particles belonging to the first peak, and, Said T B This indicates the average thickness of the carbon layer in the primary particles belonging to the second peak. Cathode active material. [Explanation of Symbols]

[0158] 1 Primary particles, 1a Large particles, 1b Small particles, 1c Carbon layer, 2 Secondary particles, 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, P A First peak, P B Second peak.

Claims

1. Contains secondary particles, The secondary particles include a first particle group, a second particle group, and a carbon layer. The first particle group and the second particle group each consist of primary particles, The first group of particles has a larger average particle size compared to the second group of particles. The primary particles contain an olivine-type compound, The carbon layer covers at least a portion of the surface of the primary particles, T B <T A Satisfying the relationship, Said T A This indicates the average thickness of the carbon layer in the primary particles belonging to the first particle group, and, Said T B This indicates the average thickness of the carbon layer in the primary particles belonging to the second particle group. Cathode active material.

2. 80 nm < d A ,and, 30nm≦d B ≦80nm Satisfying the relationship, The aforementioned d A This represents the average particle size of the primary particles belonging to the first particle group, and, The aforementioned d B This indicates the average particle size of the primary particles belonging to the second particle group. The positive electrode active material according to claim 1.

3. 3.5 nm ≤ T A <8.0 nm, and 1.0nm<T B <3.5nm、 Satisfying the relationship, The positive electrode active material according to claim 1.

4. 0.5≦S A / (S A +S B )≦0.9 Satisfying the relationship, The aforementioned S A This indicates the total area of ​​the primary particles belonging to the first particle group in the electron microscope image of the secondary particles, and, The aforementioned S B This indicates the total area of ​​the primary particles belonging to the second particle group in the electron microscope image of the secondary particles. The positive electrode active material according to any one of claims 1 to 3.

5. The mass fraction of the carbon layer in the secondary particles is 1.3% to 3.5%. The positive electrode active material according to any one of claims 1 to 3.

6. Within the secondary particles, the first particle group and the second particle group are dispersed amongst themselves. The positive electrode active material according to any one of claims 1 to 3.

7. The olivine-type 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 3.

8. 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 3. electrode.

9. The electrode included in claim 8, battery.

10. Having a bipolar structure, The battery according to claim 9.

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