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

Abstract

Improved capacity retention rate. [Solution] A positive electrode active material comprising primary particles and a coating, wherein the primary particles contain an olivine-type phosphate compound, the coating covers at least a portion of the surface of the primary particles, the coating contains carbon, and the filtrate obtained by a preparation method in which 0.5 g of the positive electrode active material is immersed in 10 g of pure water, subjected to ultrasonic treatment for 10 minutes, stirred for 6 hours, and then filtered, has a total concentration of transition metal elements detected by ICP-AES of 200 ppm or less.

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material, a battery, and a method for manufacturing a positive electrode active material. [Background technology]

[0002] Japanese Patent Publication No. 2021-9838 (Patent Document 1) discloses a positive electrode active material in which a carbon coating layer is formed on the surface of manganese iron lithium phosphate (hereinafter abbreviated as "LMFP") particles. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-9838 [Overview of the project] [Problems that the invention aims to solve]

[0004] To improve battery characteristics, olivine-type phosphate compounds such as LMFP, lithium manganese phosphate (LMP), and lithium iron phosphate (LFP) have been developed. In liquid-based batteries, trace amounts of water can react with fluorides such as LiPF6 in the electrolyte to generate hydrogen fluoride (HF). Contact between the olivine-type phosphate compound and HF can destroy the crystal structure of the olivine-type phosphate compound, potentially worsening its capacity retention rate.

[0005] By coating olivine-type phosphate compounds with a carbon coating layer as described in Patent Document 1, it is expected that the capacity retention rate will be improved. However, there is still room for improvement in the battery's capacity retention rate.

[0006] The purpose of this disclosure is to improve the capacity retention rate. [Means for solving the problem]

[0007] The technical configuration and effects of this disclosure are described below. However, the mechanism of action of this disclosure includes assumptions. The mechanism of action does not limit the technical scope of this disclosure.

[0008] [1] A positive electrode active material, Includes primary particles and coatings, The primary particles contain an olivine-type phosphate compound. The coating covers at least a portion of the surface of the primary particles. The aforementioned coating contains carbon, The filtrate obtained by a preparation method in which 0.5 g of the positive electrode active material is immersed in 10 g of pure water, subjected to ultrasonic treatment for 10 minutes, stirred for 6 hours, and then filtered, has a total concentration of transition metal elements detected by ICP-AES of 200 ppm or less. Cathode active material.

[0009] The inventors have found that the concentration of transition metal elements in the filtrate can serve as an indicator for estimating the degree of deterioration in capacity retention. It is expected that if the total concentration of transition metal elements in the filtrate is 200 ppm or less, the deterioration of the battery's capacity retention can be suppressed.

[0010] [2] The positive electrode active material according to [1], wherein the filtrate has a Gardner color number of 6 or less.

[0011] The inventors have found that the Gardner color number of the filtrate can serve as an indicator for estimating the degree of deterioration in capacity retention. It is expected that when the Gardner color number of the filtrate is 6 or less, the deterioration in the battery's capacity retention can be further suppressed.

[0012] [3] The positive electrode active material according to [1] or [2], wherein the rate of change in mass after raising the temperature of the positive electrode active material from 25°C to 300°C at 1°C / min and then leaving it at 300°C for 1 hour is 0.20% or less.

[0013] The inventors have found that the rate of mass change of the positive electrode active material can serve as an indicator for estimating the degree of deterioration in capacity retention. It is expected that a rate of mass change of 0.20% or less can suppress the deterioration of the battery's capacity retention.

[0014] [4] The primary particles form secondary particles The positive electrode active material described in any of [1] to [3].

[0015] [5] The olivine-type phosphate compound comprises at least one selected from the group consisting of lithium manganese iron phosphate, lithium manganese phosphate, and lithium iron phosphate. The positive electrode active material described in any of [1] to [4].

[0016] [6] The olivine-type phosphate compound is lithium iron manganese phosphate, The transition metal is manganese and iron, as described in any one of [1] to [4].

[0017] A battery comprising the positive electrode active material described in any of [1] through [6] [7].

[0018] [8] The battery according to [7], having a bipolar structure.

[0019] [9] The first step is to prepare precursor particles, The process includes a second step of producing a positive electrode active material by vacuum drying the aforementioned precursor particles at a temperature of 150°C or higher, The positive electrode active material is the positive electrode active material described in any of [1] to [6]. A method for manufacturing a positive electrode active material.

[0020]

[10] The vacuum drying process is carried out at a temperature of 180°C to 250°C. [9] A method for producing a positive electrode active material as described above.

[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 showing secondary particles in this embodiment. [Figure 2] This is a schematic flowchart illustrating the method for producing the positive electrode active material 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 table shows the experimental results for Examples No. 1 to 3. [Modes for carrying out the invention]

[0023] <Terms and 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] Unless otherwise specified, the order in which the various steps, actions, and operations included in each method are executed is not limited to the order in which they are described. For example, multiple steps may occur simultaneously. For example, multiple steps may occur one after the other.

[0026] Expressions such as "first," "second," etc., are used solely to distinguish between multiple elements. These expressions do not in any way limit the elements to which they are attached. These expressions are unrelated, for example, to the order, importance, etc., of the elements to which they are attached.

[0027] For example, the expression "at least one of A and B" includes both "A or B" and "A and B". "At least one of A and B" can also be written as "A and / or B".

[0028] 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.

[0029] 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.

[0030] Numerical ranges such as "m~n%" include upper and lower limits unless otherwise specified. That is, "m~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 equals sign inequality signs "<" 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.

[0031] 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.

[0032] The devices, software, etc., used to measure 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.

[0033] The chemical composition of a 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.

[0034] "D50" indicates the particle size at which the cumulative value in the volume-based particle size distribution (cumulative distribution) reaches 50%. D50 (excluding D50 for primary particles) is measured, for example, by a laser diffraction particle size distribution analyzer.

[0035] "Maximum Ferret diameter" indicates the length of the longer side of the circumscribing rectangle (rectangle or square) of the particle. If the circumscribing rectangle is a square, the length of the longer side refers to the length of one side.

[0036] 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.

[0037] 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.

[0038] <Cathode active material> Figure 1 is a conceptual diagram showing secondary particles in this embodiment. The positive electrode active material includes primary particles 1 and a coating 5. "Primary particles 1" are the smallest units of particles. Primary particles 1 may exist individually without agglomeration. Primary particles 1 existing individually are also called single particles. Primary particles 1 may form secondary particles 2. The positive electrode active material may be, for example, a powder of secondary particles 2. 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.

[0039] Secondary particles 2 are aggregates of primary particles 1. Secondary particles 2 can have any shape. For example, secondary particles 2 may be spherical, rod-shaped, angular, etc. If secondary particles 2 are spherical, for example, improved packing performance can be expected. The sphericity of secondary particles 2 may be, for example, 0.85 or higher, 0.90 or higher, or 0.95 or higher. The sphericity of secondary particles 2 may be, for example, 1 or less, 0.95, or 0.90 or less. "Sphericity" refers to the circularity in an SEM (Scanning Electron Microscope) image (two-dimensional image). Sphericity (circularity) is calculated by the following formula. ψ = 4πS / L 2 ψ: Sphericity (Circularity) π: Pi S: Cross-sectional area of ​​secondary particle 2 (area of ​​the region enclosed by the contour line of secondary particle 2) L: Circumference of secondary particle 2 (length of the outline of secondary particle 2) Sphericity is expressed as the arithmetic mean of 30 secondary particles.

[0040] The primary particle 1 may have any shape. For example, the primary particle 1 may be spherical, rod-shaped, angular, etc. The maximum Ferret diameter of the primary particle 1 may be, for example, 10 to 90 nm. The maximum Ferret diameter of the primary particle 1 may be, for example, 20 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, or 80 nm or more. The maximum Ferret diameter of the primary particle 1 may be, for example, 80 nm or less, or 60 nm or less. The maximum Ferret diameter of the primary particle 1 represents the arithmetic mean of 30 primary particles 1.

[0041] The coating 5 contains carbon. The bonding state of the carbon element in the coating 5 is not limited. The coating 5 covers at least a portion of the surface of the primary particle 1. The coating 5 may cover the entire surface of the primary particle 1.

[0042] The thickness of the coating 5 may be, for example, 1 nm or more, 2 nm or more, 3 nm or more, 4 nm or more, or 5 nm or more. The thickness of the coating 5 may also be, for example, 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, or 5 nm or less.

[0043] The mass fraction of coating 5 may be 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, or 4% or more relative to the mass of the positive electrode active material (olivine-type phosphate compound). The mass fraction of coating 5 may be 5% or less, 4% or less, or 3% or less relative to the mass of the positive electrode active material.

[0044] Primary particle 1 contains an olivine-type phosphate compound. "Olivine-type" refers to a crystalline structure belonging to the space group Pnma. The space group is identified by powder X-ray diffraction (XRD) measurement. Primary particle 1 may be, for example, a single-phase compound. Primary particle 1 may further contain phases belonging to other space groups, as long as it contains an olivine-type crystalline phase. Primary particle 1 may further contain, for example, an amorphous phase.

[0045] The filtrate obtained by a preparation method in which 0.5 g of positive electrode active material is immersed in 10 g of pure water, subjected to ultrasonic treatment for 10 minutes, stirred for 6 hours, and then filtered, has a total concentration of transition metal elements of 200 ppm or less, but may be 150 ppm or less, 100 ppm or less, or 80 ppm or less. The total concentration of transition metal elements in the filtrate may be 1 ppm or more, 5 ppm or more, or 10 ppm or more.

[0046] The filtrate can be prepared, for example, at room temperature, or at a temperature within the range of 20-25°C. The ultrasound used in sonication is not limited and can be selected from, for example, the range of 30-2000 kHz or 40-1000 kHz. Stirring can be performed using a shaker. The shaking speed can be selected from, for example, the range of 20-200 r / min. The shaking method is not limited and can be appropriately selected from, for example, reciprocating shaking or swirling shaking. For filtration, a membrane filter with a pore size that does not allow the positive electrode active material to pass through can be used. For example, a membrane filter with a pore size that does not allow all of the positive electrode active material to pass through, does not allow positive electrode active material with a particle size of D10 or larger to pass through, or does not allow positive electrode active material with a particle size of D20 or larger to pass through can be used. As for the pore size, for example, membrane filters with 0.1 μm, 0.2 μm, or 0.3 μm can be used.

[0047] The concentration of transition metal elements in the filtrate can be measured by the ICP-AES method described above. The transition metal elements detected in the filtrate are those that constitute olivine-type phosphate compounds. The detected transition metal elements may include at least one selected from the group consisting of manganese (Mn) and iron (Fe).

[0048] The filtrate preferably has a Gardner color number of 6 or less, and more preferably 5 or less. The Gardner color number is one of the standards for the intensity of the color of a sample as defined in the Japanese Industrial Standards (JIS), and can be measured by the method specified in "JIS K0071-2:1998 Color Test Methods for Chemical Products - Part 2: Gardner Color Number". Specifically, it is measured as a color number expressed by a color number in the range of 1 to 18, by comparing the transmitted color (color number in the range of 1 to 18) of a Gardner color number standard solution prepared using potassium hexachloroplatinate(IV), iron(III) chloride, cobalt(II) chloride, and hydrochloric acid with the transmitted color of the sample. The filtrate may have a Gardner color number of, for example, 1 or more, or 2 or more.

[0049] The positive electrode active material preferably has a mass change rate of 0.20% or less, and more preferably 0.10% or less, after being heated from 25°C to 300°C at a rate of 1°C / min and then left at 300°C for 1 hour. The mass change rate may be 0.01% or more, or 0.02% or more.

[0050] The olivine-type phosphate compound may comprise at least one selected from the group consisting of lithium manganese iron phosphate (LMFP), lithium manganese phosphate (LMP), and lithium iron phosphate (LFP). The olivine-type phosphate compound may have, for example, a composition represented by the following general formula. Li 1-a Mn 1-x Fe x PO4 For example, the relationship "-0.5 ≤ a ≤ 0.5" may be satisfied. x may be, for example, 0 or greater, 0.05 or greater, 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. x may be, for example, 1 or less, 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.

[0051] In LMFP, LMP, and LFP, elements other than lithium (Li), manganese (Mn), fe, phosphorus (P), and oxygen (O) may be doped (dopants). 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), sr, yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), lead (Pb), and bismuth (Bi). It may also contain at least one selected from the group consisting of 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.

[0052] The positive electrode active material may mainly consist of at least one selected from the group consisting of LMFP, LMP, and LFP, and may further contain other components. These other components may include, for example, lithium nickel composite oxide (LNO), lithium cobalt composite oxide (LCO), lithium manganese composite oxide (LMO), etc. When the positive electrode active material contains LMFP, the mixing ratio (mass ratio) of LMFP to the other components may be, for example, "LMFP / other components = 9 / 1 to 1 / 9", "LMFP / other components = 8 / 2 to 2 / 8", "LMFP / other components = 7 / 3 to 3 / 7", or "LMFP / other components = 6 / 4 to 4 / 6". The positive electrode active material may also be, for example, a mixture of LMFP powder and powder of the other components.

[0053] LMP is, for example, a general formula "Li 1-aIt may have a composition represented by "MnPO4 (-0.5 ≦ a ≦ 0.5)". LFP may have, for example, a composition represented by the general formula "Li 1-a FePO4 (-0.5 ≦ a ≦ 0.5)".

[0054] LNO may have, for example, a crystal structure belonging to the space group R-3m. LNO may have, for example, a composition represented by the following general formula. Li 1-a Ni x M 1-x O2 In the formula, the relationship of -0.5 ≦ a ≦ 0.5 and 0 ≦ x ≦ 1 is satisfied. M may contain, for example, at least one selected from the group consisting of Co, Mn, and Al. For example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x ≦ 1 may be satisfied. For example, the relationship of -0.4 ≦ a ≦ 0.4, -0.3 ≦ a ≦ 0.3, -0.2 ≦ a ≦ 0.2, or -0.1 ≦ a ≦ 0.1 may be satisfied.

[0055] LNO may contain, for example, at least one selected from the group consisting of LiNi 0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O2, and LiNiO2.

[0056] LNO may be represented by, for example, the following general formula. The compound represented by the following general formula may also be referred to as "NCM". Li 1-a Ni x Co y Mn z O2 In the formula, the relationships of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied. For example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1 may be satisfied. For example, the relationship of 0 < y ≦ 0.1, 0.1 ≦ y ≦ 0.2, 0.2 ≦ y ≦ 0.3, 0.3 ≦ y ≦ 0.4, 0.4 ≦ y ≦ 0.5, 0.5 ≦ y ≦ 0.6, 0.6 ≦ y ≦ 0.7, 0.7 ≦ y ≦ 0.8, 0.8 ≦ y ≦ 0.9, or 0.9 ≦ y < 1 may be satisfied. For example, the relationship of 0 < z ≦ 0.1, 0.1 ≦ z ≦ 0.2, 0.2 ≦ z ≦ 0.3, 0.3 ≦ z ≦ 0.4, 0.4 ≦ z ≦ 0.5, 0.5 ≦ z ≦ 0.6, 0.6 ≦ z ≦ 0.7, 0.7 ≦ z ≦ 0.8, 0.8 ≦ z ≦ 0.9, or 0.9 ≦ z < 1 may be satisfied.

[0057] NCM is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and LiNi 0.9 Co 0.05 Mn 0.05 It may contain at least one selected from the group consisting of O2.

[0058] LNO may be represented by, for example, the following general formula. The compound represented by the following general formula may also be referred to as "NCA". Li 1-a Ni x Co y Al z O2 In the formula, the relationships -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied. For example, the relationship 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x < 1 may be satisfied. For example, the relationship 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9, or 0.9 ≤ y < 1 may be satisfied. For example, the relationship 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1 may be satisfied.

[0059] NCA is, for example, LiNi 0.7 Co 0.1 Al<​​​​​​​​​Al 0.1 O2, LiLiLi 0.8 Co 0.17 Al 0.03 O2, LiLiLi 0.8 Co 0.15 Al 0.05 O2 and LiNi 0.9 Co 0.05 Al 0.05 It may contain at least one selected from the group consisting of O2.

[0060] <Method for manufacturing positive electrode active material> Figure 2 is a schematic flowchart showing 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". The method for producing the positive electrode active material in this embodiment may include a first step and a second step. The first step may include, for example, "(a) slurry formation", "(b) granulation", and "(c) calcination".

[0061] (1st step) (a) Formation of slurry This method may include forming a slurry by mixing, for example, a lithium compound, a manganese compound, an iron compound, a phosphate compound, a carbon source, and a solvent. For example, a compound with the composition formula "Li 1-a Mn 1-x Fe x Lithium compounds, manganese compounds, phosphate compounds, and iron compounds may be weighed out to achieve the composition ratio (mole ratio) shown in PO4 (-0.5 ≤ a ≤ 0.5, 0 ≤ x ≤ 1). The lithium compound may include, for example, lithium carbonate, lithium hydroxide, etc. The manganese compound may include, for example, manganese carbonate, etc. The phosphate compound may include, for example, phosphoric acid, lithium dihydrogen phosphate, etc. The iron compound may include, for example, iron oxalate, ferric phosphate, etc.

[0062] The carbon source is a raw material for carbon that adheres to the surface of the primary particles. The carbon source may include, for example, sugars, organic acids, etc. The carbon source may include, for example, glucose, sucrose, fructose, citric acid, lactic acid, etc. The carbon source may include, for example, sugars. The amount of carbon source added may be, for example, 1 to 20% by mass fraction relative to the raw material mixture. The carbon source may also be added after forming a granule using a raw material mixture of other raw materials. In this case, the amount of carbon source added may be, for example, 1 to 20% by mass fraction relative to the granule.

[0063] The solvent may include, for example, water. The solid content concentration of the slurry may be, for example, 20 to 40% by mass fraction.

[0064] The particle size in the slurry may be adjusted by wet grinding. For example, wet grinding may be performed so that D50 is between 0.10 and 1 μm.

[0065] (b) Granulation This method may include, for example, granulating secondary particles by drying the slurry. For example, secondary particles may be granulated by spray drying. The secondary particles formed by the granulation operation are also called "granulated bodies." In other words, secondary particles may be referred to as granulated bodies.

[0066] (c) Firing This method may include generating an olivine-type phosphate compound by heat-treating secondary particles. Any heat treatment furnace (e.g., electric furnace, muffle furnace, etc.) can be used. The heat treatment atmosphere may be, for example, an inert atmosphere. The inert atmosphere may be, for example, a nitrogen atmosphere. The heat treatment temperature may be, for example, 400 to 700°C. The heat treatment time may be, for example, 1 to 6 hours.

[0067] The olivine-type phosphate compound obtained in this manner is used as a precursor particle. The precursor particle comprises a primary particle and a carbon layer. The primary particle contains the olivine-type phosphate compound. The carbon layer covers at least a portion of the surface of the primary particle. The carbon layer contains carbon.

[0068] (2nd process) The second step is to perform a vacuum drying treatment on the precursor particles prepared in the first step at a temperature of 150°C or higher. Vacuum drying is a drying treatment performed by placing a container containing the precursor particles inside a metal or glass chamber that can be opened and closed, and reducing the pressure of the atmosphere inside the chamber with a vacuum pump or the like. At this time, the temperature inside the chamber is preferably 150°C or higher, but may also be 160°C or higher, 170°C or higher, 180°C or higher, 190°C or higher, or 200°C or higher, and may be 250°C or lower, 240°C or lower, 230°C or lower, or 220°C or lower. The heating time may be, for example, 1 minute or more, 3 minutes or more, or 5 minutes or more, and may be 120 minutes or less, 90 minutes or less, or 60 minutes or less. As for the vacuum pump, rotary oil pumps, mechanical booster pumps, dry scroll pumps, dry roots pumps, turbomolecular pumps, etc. are usually used. The positive electrode active material is obtained by going through the second step.

[0069] By going through the second step, a positive electrode active material can be obtained in which the total concentration of transition metal elements detected by ICP-AES in the filtrate is 200 ppm or less. Furthermore, by going through the second step, a positive electrode active material can be obtained in which the Gardner color number of the filtrate is 6 or less. This is thought to be because the concentration of transition metal elements that dissolve when the positive electrode active material is immersed in pure water can be reduced by going through the second step. In other words, it is expected that a positive electrode active material that can suppress deterioration of capacity retention rate can be manufactured by going through the second step.

[0070] In the second step, the positive electrode active material may be impregnated and mixed with toluene before the vacuum drying process. By impregnating and mixing with toluene, the concentration of transition metal elements in the filtrate can be further reduced, and the number of Gardner colors can be further reduced.

[0071] <Battery> In some embodiments of this invention, the battery has a monopolar structure. In some embodiments of this invention, the battery has a bipolar structure. As an example, a battery having a bipolar structure (a bipolar battery) will be described.

[0072] 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 Figure 4, the Z-axis direction corresponds to the orthoplane direction. The X-axis and Y-axis directions are examples of in-plane directions.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] (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 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.

[0079] The positive electrode layer 11 may further contain, in addition to the positive electrode active material, a conductive material and a binder, for example. 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).

[0080] 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 ether, and derivatives thereof.

[0081] 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 11 may also contain, for example, polyoxyethylene allylphenyl ether phosphate, zeolite, silane coupling agents, MoS2, WO3, etc.

[0082] (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.

[0083] 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.

[0084] 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.

[0085] 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".

[0086] 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 dissimilar material. The dissimilar material may include, for example, at least one selected from the group consisting of P, W, Al, and O. Examples of dissimilar materials include Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO3. 3、 It may also include at least one selected from the group consisting of Li3PO4.

[0087] The alloy-based active material may contain 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.

[0088] SiO may be represented, for example, by the following general formula. SiO x In the formula, the relationship 0 < x < 2 is satisfied. For example, the relationship 0.5 ≦ x ≦ 1.5 or 0.8 ≦ x ≦ 1.2 may be satisfied.

[0089] The "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).

[0090] (Separator) The separator 20 can separate the positive electrode layer 11 from the negative electrode layer 12. The separator 20 has electrical insulation. The separator 20 may contain at least one selected from the group consisting of, for example, a resin film (polymer film), an inorganic particle layer, and an organic particle layer. The separator 20 may contain, for example, a resin film and an inorganic particle layer.

[0091] The resin film is porous. The resin film may contain, for example, a microporous membrane, a non-woven fabric, etc. The resin film contains a resin skeleton. The resin skeleton may be continuously reticulated, for example. Pores are formed in the gaps of the resin skeleton. The resin film can permeate an electrolyte. The resin film may have an average pore diameter of 1 μm or less, for example. The average pore diameter of the resin film may be, for example, 0.01 - 1 μm or 0.1 - 0.5 μm. The "average pore diameter" can be measured by the mercury intrusion method. The Gurley value of the resin film may be, for example, 50 - 250 s / 100 cm 3 and so on. The "Gurley value" can be measured by the Gurley test method.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] The inorganic particle layer is porous. The inorganic particle layer contains inorganic particles. 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.

[0096] 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.

[0097] 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.

[0098] The separator 20 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0099] (electrolyte) The electrolyte is a liquid electrolyte. The electrolyte contains a solute and a solvent. The concentration of the solute may be, for example, 0.5-1 mole / L, 1-1.5 mole / L, 1.5-2 mole / L, 2-2.5 mole / L, or 2.5-3 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.

[0100] 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.

[0101] The solvent may contain cyclic carbonates (such as EC, PC, FEC, etc.) and chain carbonates (such as EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate and the chain carbonate may be, for example, "cyclic carbonate / chain carbonate = 1 / 9 to 4 / 6", "cyclic carbonate / chain carbonate = 2 / 8 to 3 / 7", or "cyclic carbonate / chain carbonate = 3 / 7 to 4 / 6".

[0102] The solvent may contain cyclic carbonates (such as EC, PC, etc.) and fluorinated cyclic carbonates (such as FEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate and the fluorinated cyclic carbonate 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".

[0103] The solvent may contain, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy, for example, the relationship represented by the following formula. V EC +V FEC +V EMC +V DMC +V DEC =10 In the above formula, V EC 、V FEC 、V EMC 、V DMC 、V DEC respectively represent the volume ratios of EC, FEC, EMC, DMC, and DEC. 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 ≦9 The relationship is satisfied. For example, 1 ≤ V EC ≤ 2, or 2 ≤ V EC The condition ≤ 3 may also be satisfied. For example, 1 ≤ V FEC ≤ 2, or 2 ≤ V FEC The condition ≤ 4 may also be satisfied. For example, 3 ≤ V EMC ≤4, or 6 ≤V EMC The condition ≤ 8 may also be satisfied. For example, 3 ≤ V DMC ≤4, or 6 ≤V DMC The condition ≤ 8 may also be satisfied. For example, 3 ≤ V DEC ≤4, or 6 ≤V DEC The condition ≤ 8 may also be satisfied.

[0104] 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.

[0105] 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.

[0106] The electrolyte may contain any additives. The amount of additive (mass fraction of the total electrolyte) may be, for example, 0.01-5%, 0.05-3%, or 0.1-1%. 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.

[0107] Additives include, for example, vinylene carbonate (VC), vinylethylene carbonate (VEC), 1,3-propanesultone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfite (ES), propanesultone (PS), 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.], fluorobenzenes [e.g., monofluorobenzene (FB), 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, etc.), 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.

[0108] 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.

[0109] 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.

[0110] 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. [Examples]

[0111] <Manufacturing of positive electrode active material> (No.1) (Precursor particle manufacturing process (Step 1)) Compositional formula “Li1Mn 0.8 Fe 0.2 Lithium carbonate, manganese carbonate, iron oxalate, and phosphoric acid were weighed to match the composition ratio shown in "PO4". Each of these raw materials was dispersed in water to form a slurry, which was then ground in a bead mill using 0.3 mm diameter beads at a peripheral speed of 10 m / s for 30 minutes, and then calcined to obtain granules. 10% fructose by mass fraction was added to the granules. After drying this mixture, it was heated in an inert atmosphere to a calcination temperature of 600°C at a heating rate of 5°C / min, held for 1 hour, and then cooled to room temperature to obtain precursor particles.

[0112] (Vacuum drying process (second process)) The precursor particles obtained in the first step were impregnated and mixed with toluene, and then vacuum-dried at a temperature of 200°C.

[0113] (No.2) The positive electrode active material was obtained under the same conditions as in No. 1, except that the vacuum drying process (second step) was performed without impregnation and mixing with toluene.

[0114] (No.3) Without performing the vacuum drying process (second step) of No. 1, precursor particles obtained under the same conditions as the precursor particle manufacturing process (first step) of No. 1 were used as the positive electrode active material.

[0115] <Measurement> (ICP-AES measurement) A filtrate was obtained by immersing 0.5 g each of the positive electrode active materials No. 1 to No. 3 in 10 g of pure water, subjecting the immersion solution to sonication for 10 minutes, stirring for 6 hours, and then filtering it using a membrane filter with a pore size of 0.2 μm. The preparation process was carried out at room temperature (25°C). The concentration of transition metal elements in the filtrate was measured by ICP-AES. The concentration of transition metal elements was defined as the sum of the concentrations of Fe and Mg. The measurement results are shown in Figure 5.

[0116] (Gardner color depth measurement) The filtrate obtained above was placed in a quartz cell and evaluated using a colorimeter with the Gardner color scale for petroleum observation. Figure 5 shows the evaluation results.

[0117] (Mass change rate) 0.5 g (mass before drying) of each positive electrode active material from No. 1 to No. 3 was heated from room temperature (25°C) to 300°C at a heating rate of 1°C / min in an inert atmosphere, and then left at 300°C for 1 hour. The mass (mass after drying) was measured, and the rate of mass change was calculated using the following formula. The calculation results are shown in Figure 5. Mass change rate (%) = {(Mass before drying - Mass after drying) / Mass before drying} × 100

[0118] <Rating> (Battery characteristics) A lithium-ion secondary battery (coin cell) has been manufactured. The cell configuration is as follows:

[0119] A mixture was formed by mixing the positive electrode active material, conductive material (acetylene black), and binder (PVdF). The mixing ratio (mass ratio) was "positive electrode active material / conductive material / binder = 92 / 5 / 3". A paste was formed by dispersing the mixture in a solvent (N-methyl-2-pyrrolidone). The solid content concentration of the paste was 50% by mass fraction. The positive electrode layer was formed by applying the paste to the surface of an Al foil and drying it. The density of the positive electrode layer was 1.8 g / cm³ by roll pressing. 3 The cathode material was formed by adjusting the material. The cathode material was subjected to vacuum drying at 120°C for 12 hours. After drying, a disc sample (diameter: 14 mm) was removed from the cathode material by punching.

[0120] The coin cell was 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)

[0121] The discharge capacity of the obtained coin cells was determined based on the discharge capacity estimated from the coating weight. "C" is a symbol indicating the current rate (time rate). At a rate of 1C, the theoretical capacity is supplied over one hour. Under conditions of 25°C, the discharge capacity at 0.1C (referred to as the "first discharge capacity") was determined after CCCV quasi-charge with a charge rate of 0.1C, an upper voltage limit of 4.3V, and a charge termination condition of 0.01C, followed by a discharge termination potential of 3V. Subsequently, the 0.1C rate was reset based on the obtained discharge capacity, and the discharge capacity after 50 cycles (referred to as the "discharge capacity after 50 cycles") was determined. The capacity retention rate was calculated as (discharge capacity after 50 cycles / first discharge capacity) × 100%. Figure 5 shows the capacity retention rate. A higher capacity retention rate indicates better durability.

[0122] <Result> As shown in Figure 5, when the conditions of this disclosure are met, a high capacity retention rate tends to be observed. [Explanation of Symbols]

[0123] 1 Primary particle, 2 Secondary particle, 5 Coating, 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.

Claims

1. It is a positive electrode active material, Includes primary particles and coatings, The primary particles contain an olivine-type phosphate compound. The coating covers at least a portion of the surface of the primary particles. The aforementioned coating contains carbon, The filtrate obtained by a preparation method in which 0.5 g of the positive electrode active material is immersed in 10 g of pure water, subjected to ultrasonic treatment for 10 minutes, stirred for 6 hours, and then filtered, has a total concentration of transition metal elements detected by ICP-AES of 200 ppm or less. Cathode active material.

2. The positive electrode active material according to claim 1, wherein the filtrate has a Gardner color number of 6 or less.

3. The positive electrode active material according to claim 1, wherein the rate of mass change after raising the temperature of the positive electrode active material from 25°C to 300°C at a rate of 1°C / min and then leaving it at 300°C for 1 hour is 0.20% or less.

4. The primary particles form secondary particles. The positive electrode active material according to claim 1.

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

6. The olivine-type phosphate compound is manganese iron lithium phosphate, The positive electrode active material according to claim 1, wherein the transition metal element comprises at least one selected from the group consisting of manganese and iron.

7. A battery comprising the positive electrode active material according to any one of claims 1 to 6.

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

9. The first step involves preparing precursor particles, The process includes a second step of producing a positive electrode active material by vacuum drying the precursor particles at a temperature of 150°C or higher, The positive electrode active material is the positive electrode active material described in any one of claims 1 to 6. A method for manufacturing a positive electrode active material.

10. The vacuum drying process is carried out at a temperature of 180°C to 250°C. A method for producing a positive electrode active material according to claim 9.

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