Positive electrode active material, electrode, and battery

Abstract

Improved rate characteristics. [Solution] The positive electrode active material contains flaky primary particles. The primary particles contain an olivine-type phosphate compound.

Description

[Technical Field]

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

[0002] Japanese Patent Publication No. 2021-009838 discloses a granulated material made of manganese-rich lithium manganese iron phosphate particles and iron-rich lithium manganese iron phosphate particles. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-009838 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The purpose of this disclosure is to improve the rate characteristics of the battery. [Means for solving the problem]

[0005] 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.

[0006] 1. One aspect of this disclosure is a positive electrode active material. The positive electrode active material comprises primary particles. The primary particles comprise an olivine-type phosphate compound. The primary particles have a circularity of 0.60 or less.

[0007] Traditionally, primary particles of olivine-type phosphate compounds have been synthesized to approximate a spherical shape. This is thought to be because spherical primary particles are expected to improve packing efficiency, i.e., increase energy density. Spherical particles have a high degree of circularity. Hereafter, primary particles with a circularity of 0.80 or higher will also be referred to as "spherical particles."

[0008] The primary particles of this disclosure have a circularity of 0.60 or less. Hereinafter, primary particles having a circularity of 0.60 or less will also be referred to as "non-spherical particles." Non-spherical particles have an irregular shape. Non-spherical particles may, for example, have angular portions. In the electrode (positive electrode layer), non-spherical particles tend to be oriented so that the angular portions are aligned along the thickness direction of the electrode. The inclusion of non-spherical particles in the electrode is expected to straighten the penetration path of the electrolyte in the thickness direction of the electrode. By improving the diffusivity of the electrolyte in the thickness direction of the electrode, an improvement in rate characteristics is expected.

[0009] 2. The positive electrode active material described in "1" above may include, for example, the following components: The positive electrode active material includes secondary particles. The secondary particles include first primary particles and second primary particles. Each of the first primary particles and the second primary particles contains an olivine-type phosphate compound. The first primary particles have a circularity of 0.80 or more. The second primary particles have a circularity of 0.60 or less.

[0010] Spherical and non-spherical particles may form secondary particles. Combining spherical and non-spherical particles is expected to improve, for example, the balance between rate characteristics and packing properties.

[0011] 3. The positive electrode active material described in "2" above may include, for example, the following components: Secondary particles are "0.05 B / (S A +S B The relationship ") < 0.30" is satisfied. A " indicates the total area of ​​the first primary particles in the cross-section of the secondary particles. B This indicates the total area of ​​the second primary particles in the cross-section of the secondary particle.

[0012] The inclusion of non-spherical particles in a specific ratio within the secondary particles is expected to improve rate characteristics.

[0013] ​4. The positive electrode active material described in "3" above may include, for example, the following configuration: The first primary particles have a circularity of 0.87 to 0.91. The second primary particles have a circularity of 0.40 to 0.60. The secondary particles have a circularity of 0.14 ≤ S B / (S A +S B The relationship )≦0.20 is satisfied.

[0014] When these conditions are met, an improvement in rate characteristics can be expected.

[0015] 5. The positive electrode active material described in any one of items "1" to "4" above may include, for example, the following composition: The olivine-type phosphate compound includes at least one selected from the group consisting of lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium iron manganese phosphate (LMFP).

[0016] 6. 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 items "1" to "5".

[0017] 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.

[0018] 7. One aspect of this disclosure is a battery, which includes the electrodes described in "6" above.

[0019] 8. The battery described in "7" above may include, for example, the following configuration: The battery has a bipolar structure.

[0020] A bipolar structure can be formed by stacking bipolar electrodes. A bipolar structure is expected to improve, for example, output characteristics. However, a thick cathode layer may be required in a bipolar structure. In a thick cathode layer, the diffusivity of the electrolyte in the thickness direction of the cathode layer can affect the rate characteristics. The cathode active material described in "1" above is considered particularly suitable for a bipolar structure.

[0021] 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]

[0022] [Figure 1] This is a conceptual diagram of a primary particle in this embodiment. [Figure 2] This is a conceptual diagram of secondary particles in this embodiment. [Figure 3] This is a schematic perspective view of the battery in this embodiment. [Figure 4] This is a schematic cross-sectional view along the line IV-IV in Figure 3. [Figure 5] This is a table showing the experimental results. [Modes for carrying out the invention]

[0023] 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.

[0024] 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."

[0025] 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.

[0026] Elements described in the singular form may also include plural forms unless otherwise specified. For example, "particle" may refer to multiple particles, a collection of particles, or a granular material. Note that "multiple particles" can be rephrased as "group of particles."

[0027] 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.

[0028] 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.

[0029] 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.

[0030] "Primary particles" refer to particles that appear to lack grain boundaries in a Scanning Electron Microscope (SEM) image of a powder. The magnification of the SEM image may be, for example, 10,000x to 30,000x.

[0031] The shapes of the primary particles and secondary particles are evaluated by the following procedure. For example, a dispersion is formed by dispersing 1 g of a positive electrode active material (powder) in 10 g of an epoxy resin (product name "EPOTEX JP", manufactured by Nisshin EM Co., Ltd.). The dispersion is stirred and mixed for 1 minute using a mixer (product name "Awatori Renk太郎", manufactured by Shinchi Co., Ltd.). The stirring speed may be, for example, about 2000 rpm. The dispersion is degassed under vacuum. After vacuum degassing, a plate-like cured product is obtained by curing the epoxy resin inside a silicon mold. A cross-section sample having a smooth cross-section is prepared by performing cross-section processing on the plate-like cured product using a cross-section polisher (registered trademark). A cross-section SEM image is acquired by performing SEM observation of the smooth cross-section.

[0032] In the cross-section SEM image, 50 primary particles whose entire circumference of the particles is observable are extracted. For each of the 50 primary particles, the circularity is measured. The "circularity" is obtained by the following calculation formula. ψ = 4πS / L 2 ψ: Circularity π: Pi S: Cross-sectional area of the particle (area of the region surrounded by the contour line of the particle) L: Perimeter of the particle (length of the contour line of the particle)

[0033] Particles having a circularity of 0.8 or more are classified as spherical particles (first primary particles). The average value of the circularity in the collection of spherical particles is the "average circularity of spherical particles". Particles having a circularity of 0.6 or less are classified as non-spherical particles (second primary particles). The average value of the circularity in the collection of non-spherical particles is the "average circularity of non-spherical particles".

[0034] In the cross-section SEM image of the secondary particles, the total area "S A " of the spherical particles and the total area "S B " of the non-spherical particles are measured. By dividing the sum of "S A " and "S B " by "S B ", the area ratio "S B / (S A+S B )" is required.

[0035] Furthermore, various dimensional measurements and shape analyses in cross-sectional SEM images can be performed using, for example, image analysis software such as "ImageJ".

[0036] "Maximum Ferret diameter" refers to the length of the longer side of the minimum bounding rectangle (MBR) relative to the particle's contour line in a cross-sectional SEM image.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] "D50" indicates the particle size at which the cumulative value in the volume-based particle size distribution (cumulative distribution) reaches 50%. The volume-based particle size distribution is measured using a laser diffraction particle size analyzer.

[0041] positive electrode active material The positive electrode active material may, for example, be in the form of a powder. 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 be, for example, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0042] primary particle Figure 1 is a conceptual diagram of primary particles in this embodiment. The positive electrode active material contains primary particles (non-spherical particles 1b). The non-spherical particles 1b have a circularity of 0.60 or less. By incorporating irregularly shaped primary particles into the electrode, an improvement in rate characteristics is expected.

[0043] The average circularity of the non-spherical particle 1b may be, for example, 0.55 or less, 0.50 or less, 0.45 or less, 0.40 or less, or 0.35 or less. The average circularity of the non-spherical particle 1b may be 0.30 or more, 0.35 or more, 0.40 or more, 0.45 or more, 0.50 or more, or 0.55 or more. The average circularity of the non-spherical particle 1b may be, for example, between 0.40 and 0.60.

[0044] Non-spherical particles 1b may be, for example, angular particles. "Angular particles" refer to particles having the sharpest angle "θ" of 60° or less. "Sharpest angle" refers to the smallest sharpest angle among the interior angles formed by the particle's contour line in a cross-sectional SEM image. The sharpest angle may be, for example, 55° or less, 50° or less, 45° or less, 40° or less, 35° or less, 30° or less, 25° or less, 20° or less, or 15° or less. The sharpest angle may also be, for example, 10° or more, 15° or more, 20° or more, 25° or more, 30° or more, 35° or more, 40° or more, 45° or more, 50° or more, or 55° or more.

[0045] The non-spherical particles 1b may be, for example, flake-like particles. The "flake-like particles" are plate-like particles and angular particles. The "plate-like particles" have a planar direction (plate surface direction) and a thickness direction. The "first aspect ratio" represents the ratio of the maximum Ferret diameter "d1" in the plate surface direction to the thickness "t" of the plate-like particles. The first aspect ratio "d1 / t" may be, for example, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, or 9 or more. The first aspect ratio "d1 / t" may be, for example, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, or 3 or less.

[0046] In plate-like particles, the plate surface can have any shape. "Plate surface" refers to the surface that has the largest apparent area. The plate surface may be, for example, a polygon, hexagon, pentagon, quadrilateral, parallelogram, rectangle, etc. "Second aspect ratio" refers to the ratio of the long side "d1" to the short side "d2" in the MBR relative to the plate surface. The second aspect ratio "d1 / d2" may be, for example, 1.2 or more, 1.5 or more, 1.8 or more, 2.1 or more, 2.4 or more, 2.7 or more, 3.0 or more, 4.0 or more, or 5.0 or more. The second aspect ratio "d1 / d2" may also be, for example, 10.0 or less, 5.0 or less, 4.0 or less, 3.0 or less, or 2.0 or less.

[0047] secondary particles Figure 2 is a conceptual diagram of secondary particles in this embodiment. Non-spherical particles 1b may exist individually without agglomerating. Non-spherical particles 1b may form aggregates. That is, the positive electrode active material may contain secondary particles 2. Secondary particles 2 may consist of non-spherical particles 1b. Secondary particles 2 may have any shape as long as they contain non-spherical particles 1b. Secondary particles may be spherical, rod-shaped, angular, lumpy, etc. The circularity of the secondary particles may be, for example, 0.50 or more, 0.60 or more, 0.70 or more, 0.80 or more, or 0.90 or more. The circularity of the secondary particles may be, for example, 0.90 or less, 0.80 or less, 0.70 or less, or 0.60 or less.

[0048] The secondary particle 2 may further contain spherical particles 1a in addition to non-spherical particles 1b. That is, the secondary particle 2 may contain a first primary particle (spherical particle 1a) and a second primary particle (non-spherical particle 1b). The spherical particle 1a has a circularity of 0.80 or more. The average circularity of the spherical particle 1a may be, for example, 0.85 or more, 0.87 or more, 0.89 or more, 0.90 or more, 0.91 or more, or 0.93 or more. The average circularity of the spherical particle 1a may be, for example, 0.95 or less, 0.93 or less, 0.91 or less, 0.89 or less, 0.87 or less, or 0.85 or less. The average circularity of the spherical particle 1a may be, for example, between 0.87 and 0.91.

[0049] Secondary particles 2 may contain non-spherical particles 1b in a specific ratio. For example, secondary particles 2 may contain "0.05 B / (S A +S B By satisfying the relationship ")<0.30", an improvement in rate characteristics can be expected. Area ratio "S B / (S A +S B )" may be, for example, 0.07 or higher, 0.09 or higher, 0.11 or higher, 0.13 or higher, 0.14 or higher, 0.15 or higher, 0.17 or higher, 0.19 or higher, 0.20 or higher, 0.21 or higher, 0.23 or higher, 0.25 or higher, 0.27 or higher, or 0.29 or higher. Area ratio "S B / (S A +S B )" may be, for example, 0.29 or less, 0.27 or less, 0.25 or less, 0.23 or less, 0.21 or less, 0.20 or less, 0.19 or less, 0.17 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.11 or less, 0.09 or less, or 0.07 or less. Secondary particle 2 may be, for example, "0.14≦S B / (S A +S B The relationship ")≦0.20" may also be satisfied.

[0050] The maximum Ferret diameter of the primary particles may be, for example, between 20 nm and 300 nm. The maximum Ferret diameter of the primary particles may be, for example, 25 nm or more, 50 nm or more, 75 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, or 250 nm or more. The maximum Ferret diameter of the primary particles may be, for example, 250 nm or less, 200 nm or less, 150 nm or less, 100 nm or less, 75 nm or less, or 50 nm or less. The maximum Ferret diameter of the primary particles represents the arithmetic mean of 30 primary particles. The maximum Ferret diameters between spherical particles 1a and non-spherical particles 1b may be the same or different from each other.

[0051] ​Carbon may coat the surface of the primary particles. That is, a carbon layer may be formed on the surface of the primary particles. The carbon may coat a part of the surface of the primary particles or the entire surface of the primary particles. The carbon may be derived from sugars, for example. The amount of carbon 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 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.

[0052] The maximum Ferret diameter of secondary particle 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 maximum Ferret diameter of secondary particle 2 may be, for example, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less.

[0053] composition The primary particles contain an olivine-type phosphate compound. That is, the positive electrode active material contains an olivine-type phosphate compound. Hereinafter, the olivine-type phosphate compound may be abbreviated as "olivine". Olivine has a crystal structure that belongs to the space group Pnma. The space group to which the crystal structure belongs can be determined by the XRD (X-Ray Diffraction) pattern.

[0054] Olivine may further contain, for example, a glass phase, a crystallized glass phase, etc., in addition to the crystalline phase. For example, non-spherical particles 1b may be formed by appropriately grinding a glassy material. For example, a crystallized glass phase, etc., may be formed by vitrification and then crystallization of the raw materials during synthesis.

[0055] The olivine may include, for example, at least one selected from the group consisting of LFP, LMP, and LMFP. LMP and LMFP tend to have lower rate characteristics compared to LFP. This embodiment is considered particularly suitable for LMP and LMFP.

[0056] Olivine, for example, has 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, for example, the relationship "0.2 ≤ x ≤ 0.5" may be satisfied.

[0057] Olivine may contain dopants. The dopants represent elements other than lithium (Li), manganese (Mn), iron (Fe), phosphorus (P), and oxygen (O). The doping amount (molecular fraction relative to the amount of Li) may be, for example, 0.01 to 0.1. Examples of dopants include boron (B), nitrogen (N), halogens, silicon (Si), sodium (Na), magnesium (Mg), aluminum (Al), chromium (Cr), scandium (Sc), titanium (Ti), vanadium (V), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), selenium (Se), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), and lead (Pb). It may also contain at least one selected from the group consisting of bismuth (Bi), antimony (Sb), tin (Sn), tungsten (W), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and actinides.

[0058] The positive electrode active material may further contain other components as long as it contains olivine. The mixing ratio (mass ratio) of olivine to other components may be, for example, "olivine / other components = 9 / 1 to 1 / 9", "olivine / other components = 8 / 2 to 2 / 8", "olivine / other components = 7 / 3 to 3 / 7", or "olivine / other components = 6 / 4 to 4 / 6". The positive electrode active material may be, for example, a mixture of olivine powder and other component powder. The other components may include, for example, at least one selected from the group consisting of Li[NiCoMn]O2 (layered structure), Li[NiCoAl]O2 (layered structure), LiMnO2 (rock salt structure), and Li[NiMn]2O4 (spinel structure). Note that the notation [NiCoMn] etc. indicates that the sum of the composition ratios in [] is 1. As long as the sum is 1, each component in [] can take on any composition ratio.

[0059] 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.

[0060] Figure 3 is a schematic perspective view of the battery in this embodiment. Figure 4 is a schematic cross-sectional view along the line IV-IV in Figure 3. 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 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 multiple cells 40 and may also be called a "bipolar module". Each of the multiple cells 40 is sealed. The multiple cells 40 are isolated from each other. Each of the multiple cells 40 includes a positive electrode layer 11, a separator 20, a negative electrode layer 12, and an electrolyte.

[0066] Positive electrode layer The positive electrode layer 11 is attached to one side of the current collector foil 13. The thickness of the positive electrode layer 11 may be, for example, 50 μm to 1000 μm. The thickness of the positive electrode layer 11 may be, for example, 100 μm or more, 200 μm or more, 300 μm or more, 400 μm or more, or 500 μm or more. The thickness of the positive electrode layer 11 may be, for example, 750 μm or less, 500 μm or less, or 400 μm or less. For example, grooves may be formed in the positive electrode layer 11. The positive electrode layer 11 may be formed in a stripe shape, for example. The positive electrode layer 11 contains a positive electrode active material. That is, the electrode contains a positive electrode active material. Details of the positive electrode active material are as described above.

[0067] The positive electrode layer 11 may further contain, for example, a conductive material and a binder, in addition to the positive electrode active material. 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).

[0068] 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.

[0069] 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.

[0070] 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 negative electrode layer 12 contains a negative electrode active material.

[0071] The negative electrode active material may be in the form of parts or sheets, for example. 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.

[0072] 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.

[0073] The carbon-based active material may include at least one selected from the group consisting of, for example, graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. The graphite may be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1", "natural graphite / artificial graphite = 2 / 8 to 8 / 2", or "natural graphite / artificial graphite = 3 / 7 to 7 / 3".

[0074] 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 at least one selected from the group consisting of, for example, P, W, Al, and O. The different material may include at least one selected from the group consisting of, for example, Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO 3、 and at least one selected from the group consisting of Li3PO4.

[0075] The alloy-based active material may include at least one selected from the group consisting of, for example, Si, Li silicate, SiO, Si-based alloy, tin (Sn), SnO, and Sn-based alloy.

[0076] 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.

[0077] "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).

[0078] Separator The separator 20 can separate the positive electrode layer 11 from the negative electrode layer 12. The separator 20 has electrical insulating 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 20 may include, for example, a resin film and an inorganic particle layer.

[0079] 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.

[0080] 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 stretching, phase separation, or the like. The thickness of the resin film may be, for example, 5 to 50 μm or 10 to 25 μm.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] The separator 20 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0087] 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.

[0088] 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.

[0089] 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".

[0090] 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".

[0091] 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 +V DMC +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" and "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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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. In the electrodes (positive electrode layer) of the all-solid-state battery, it is expected that the non-spherical particles 1b will promote ion conduction in the thickness direction.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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)".

[0105] 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, 0.7 or less, 0.75 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.

[0106] 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.

[0107] 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).

[0108] 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.

[0109] 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.

[0110] 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 "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.

[0111] 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.

[0112] The halide solid electrolyte may have a composition represented by, for example, the general formula "Li3YCl a Br b I 6-a-b ". In the general formula, for example, the relationship of "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.

[0113] The oxide solid electrolyte may contain, for example, at least one selected from the group consisting of LiNbO3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, La 2 / 3-x Li 3x TiO3, and Li7La3Zr2O 12 . The hydride solid electrolyte may contain, for example, LiBH4 or the like. The nitride solid electrolyte may contain, for example, Li3N, Li3BN2 or the like.

Examples

[0114] Preparation of Samples Figure 5 is a table showing experimental results. The positive electrode active materials of No. 1 to No. 3 were produced by the following procedure.

[0115] [[ID=4 Preparation of glass precursors Compositional formula “Li1Mn 0.8 Fe 0.2 The raw materials, lithium carbonate, manganese carbonate, iron oxalate, and phosphoric acid, are weighed out to match the composition ratio shown in "PO4". A powder mixture is formed by mixing the powder materials other than phosphoric acid. The powder mixture is then crushed and mixed in a mortar while phosphoric acid is added until the reaction stops, forming the first precursor powder. At this time, gas generation can be suppressed by gradually adding phosphoric acid. The first precursor powder is placed in a graphite crucible. The graphite crucible is placed in a firing furnace. Firing is carried out in an inert atmosphere in the following procedure. First, the furnace temperature is increased at a heating rate of 5°C / min until it reaches 1100°C. The furnace temperature of 1100°C is maintained for 1 hour. After 1 hour, the furnace temperature is cooled at a cooling rate of 5°C / min until it reaches 600°C. Then, the furnace temperature is cooled at a cooling rate of 15°C / min until it reaches room temperature. This yields a glassy active material mass. The active material mass is crushed by a mechanical crushing device, thereby forming a second precursor.

[0116] Wet grinding A third precursor is formed by adding 10% fructose by mass fraction to the second precursor. A fourth precursor is formed by grinding the third precursor in an aqueous solvent using a bead mill. Beads (grinding media) with a diameter (φ) of 0.5 mm are used during grinding. The peripheral speed is 10 m / s. The grinding time is 30 min.

[0117] firing The fourth precursor is dried. After drying, the fourth precursor is placed in a graphite crucible. The graphite crucible is placed in a firing furnace. The furnace temperature is increased at a heating rate of 5°C / min until it reaches 650°C. The furnace temperature of 650°C is maintained for 1 hour. After that, the furnace is cooled until it reaches room temperature. Thus, the cathode active material (LMFP) is produced. A cross-sectional SEM image of the cathode active material is obtained. The circularity of the primary particles is evaluated in the cross-sectional SEM image.

[0118] No.2 In the wet grinding process, the positive electrode active material is produced in the same manner as in No. 1, except that the grinding time is changed to 60 min.

[0119] No.3 In the wet grinding process, the positive electrode active material is manufactured in the same manner as in No. 2, except that beads with a diameter (φ) of 0.1 mm are used.

[0120] evaluation Coin cell production 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 solvent (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 cathode raw material is formed by adjusting the temperature. The cathode raw material is subjected to a vacuum drying treatment at 120°C for 12 hours. After drying, a disc sample (diameter: 14 mm) is removed from the cathode raw material by punching.

[0121] The coin cell is assembled inside the glove compartment. The cell configuration is as follows: Working electrode: Disc sample (positive electrode) Opposite pole: Li foil Separator: Polymer porous membrane Electrolyte: "EC / DMC=3 / 7 (volume ratio)", LiPF6 (1mol / L)

[0122] Evaluation of Rate Characteristics Based on the discharge capacity (theoretical capacity) obtained from the coating mass of the positive electrode layer, the rate equivalent to 1C is determined. "C" is a symbol indicating the rate (time rate) of current. At a rate of 1C, the theoretical capacity is discharged over 1 hour. At 25°C, the coin cell is charged by constant current-constant voltage (CCCV) charging under the following conditions. Rate during CC charging: 0.1C Charging upper limit voltage: 4.3V Rate of cut-off current during CV charging: 0.01C

[0123] After charging, at 25°C, CC discharge is performed at a rate of 0.1C until 3.0V, whereby the discharge capacity "A" at 0.1C discharge is measured. Again, the coin cell is charged by the above CCCV charging. After charging, at 25°C, CC discharge is performed at a rate of 1C until 3.0V, whereby the discharge capacity "B" at 1C discharge is measured. By the calculation formula "B / A", the ratio "1C capacity / 0.1C capacity" is obtained. The larger the ratio "1C capacity / 0.1C capacity", the better the rate characteristics are considered to be.

[0124] Experimental results As shown in FIG. 5, by including non-spherical particles (primary particles) having a circularity of 0.60 or less in the positive electrode active material, there is a tendency for the rate characteristics to improve.

[0125] Even when secondary particles including spherical particles and non-spherical particles are formed, there is a tendency for the rate characteristics to improve.

[0126] In samples with good rate characteristics, the secondary particles have a tendency to satisfy the relationship of "0.05 < S B / (S A +S B ) < 0.30".

Explanation of symbols

[0127] 1a Spherical particles, 1b Non-spherical particles, 2 Secondary particles, 10 Bipolar electrodes, 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.

Claims

1. It contains flaky primary particles, The primary particles contain an olivine-type phosphate compound. Cathode active material.

2. The primary particle has an acute angle of 10° or more and 60° or less, The aforementioned acute angle represents the smallest acute angle among the interior angles formed by the contour line of the primary particle. The positive electrode active material according to claim 1.

3. The primary particle has a plate surface, The aforementioned plate surface represents the surface having the largest area among the outer surfaces of the primary particles. The primary particle has a first aspect ratio of 2 to 10, and The first aspect ratio represents the ratio of the maximum Ferret diameter of the plate surface to the thickness of the primary particles. The positive electrode active material according to claim 1.

4. The primary particle has a second aspect ratio of 1.2 or more and 10.0 or less, The second aspect ratio represents the ratio of the longer side to the shorter side in the smallest circumscribing rectangle of the board surface. The positive electrode active material according to claim 3.

5. The olivine-type phosphate compound comprises at least one selected from the group consisting of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate. The positive electrode active material according to any one of claims 1 to 4.

6. 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 4. electrode.

7. The electrode included in claim 6, battery.

8. Having a bipolar structure, The battery according to claim 7.

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