Positive electrode active material, battery, and method for manufacturing 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 comprise an olivine-type phosphate compound, and the coating covers at least a portion of the surface of the primary particles, and the coating comprises carbon, and wherein a preparation method is used in which 0.5 g of the positive electrode active material is immersed in 10 g of pure water to prepare an immersion solution, which is subjected to ultrasonic treatment for 10 minutes, stirred for 6 hours, and then filtered. The filtrate obtained by ICP-AES detection has a total concentration of transition metal elements of 200 ppm or less.

Description

[Technical Field]

[0001] The present 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 Application Laid-Open No. 2021-9838 (Patent Document 1) discloses a positive electrode active material in which a carbon coating layer is formed on the surface of lithium manganese iron phosphate (hereinafter abbreviated as "LMFP") particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-9838 Summary of the Invention [Problem to be solved by the invention]

[0004] Olivine-type phosphate compounds such as LMFP, lithium manganese phosphate (LMP), and lithium iron phosphate (LFP) have been developed to improve battery performance. In liquid electrolyte batteries, trace amounts of water can react with fluorides such as LiPF6 in the electrolyte to produce hydrogen fluoride (HF). When olivine-type phosphate compounds come into contact with HF, their crystal structure is destroyed, potentially resulting in a deterioration in capacity retention.

[0005] It is expected that the capacity retention rate can be improved by coating an olivine-type phosphate compound with a carbon coating layer as described in Patent Document 1. However, there is still room for improvement in the capacity retention rate of a battery.

[0006] An object of the present disclosure is to improve the capacity retention rate. [Means for solving the problem]

[0007] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action of the present disclosure includes speculation. The mechanism of action does not limit the technical scope of the present disclosure.

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

[0009] The present inventors have found that the concentration of transition metal elements in the filtrate can be used as an index for estimating the degree of deterioration in capacity retention. When the total concentration of transition metal elements in the filtrate is 200 ppm or less, it is expected that deterioration in the capacity retention of the battery can be suppressed.

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

[0011] The inventors have found that the Gardner color number of the filtrate can be used as an index for estimating the degree of deterioration in capacity retention. When the Gardner color number of the filtrate is 6 or less, it is expected that the deterioration in the capacity retention of the battery can be further suppressed.

[0012] [3] The positive electrode active material according to [1] or [2], wherein the positive electrode active material has a mass change rate of 0.20% 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.

[0013] The inventors have found that the mass change rate of the positive electrode active material can be used as an index for estimating the degree of deterioration in the capacity retention rate. By keeping the mass change rate at 0.20% or less, it is expected that deterioration in the capacity retention rate of the battery can be suppressed.

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

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

[0016] [6] The olivine-type phosphate compound is lithium iron manganese phosphate; The positive electrode active material according to any one of [1] to [4], wherein the transition metal is manganese and iron.

[0017] [7] A battery comprising the positive electrode active material according to any one of [1] to [6].

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

[0019] [9] A first step of preparing precursor particles; a second step of subjecting the precursor particles to a vacuum drying treatment at a temperature of 150°C or higher to produce a positive electrode active material; The positive electrode active material is the positive electrode active material according to any one of [1] to [6]. A method for producing a positive electrode active material.

[0020]

[10] The vacuum drying treatment is carried out at a temperature of 180°C or higher and 250°C or lower. [9] A method for producing a positive electrode active material according to [9].

[0021] Hereinafter, one embodiment of the present disclosure (hereinafter may be abbreviated as "this embodiment") and one example of the present disclosure (hereinafter may be abbreviated as "this example") will be described. However, this embodiment and this example do 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 non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is originally intended that any configurations may be extracted from this embodiment and arbitrarily combined. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 2 is a conceptual diagram showing secondary particles in the present embodiment. [Figure 2] 1 is a schematic flowchart showing a method for producing a positive electrode active material in the present embodiment. [Figure 3] 1 is a schematic perspective view of a battery according to an embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view taken along line IV-IV in FIG. [Figure 5] 1 is a table showing the experimental results of Nos. 1 to 3 in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0023] <Terms and phrases> "Comprises," "includes," "has," and variations thereof are open-ended expressions. An open-ended structure may or may not further include additional elements in addition to the required elements. "Consists of" is a closed expression. However, even a closed structure may include additional elements that are normally associated impurities or unrelated to the subject technology. "Consists essentially of..." is a semi-closed expression. A semi-closed structure allows the addition of elements that do not substantially affect the basic and novel characteristics of the subject technology.

[0024] Expressions such as "may" and "may" are used in the permissive sense, meaning "to have the possibility," rather than in the obligatory sense, meaning "to have to."

[0025] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0026] The terms "first," "second," etc. are used only to distinguish between multiple elements. Such terms do not limit the elements to which they are attached. Such terms have no bearing on, for example, the order or importance of the elements to which they are attached.

[0027] For example, the phrase "at least one of A and B" includes "A or B" as well as "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 in a strict sense. Examples of geometric terms include "parallel," "perpendicular," and "orthogonal." For example, directions, angles, distances, and the like may be displaced relative to one another as long as substantially the same or similar functions are obtained. Geometric terms may include, for example, tolerances, errors, and the like in design, work, and manufacturing. The dimensional relationships in each figure may not match the actual dimensional relationships. The dimensional relationships in each figure may be changed to aid the reader's understanding. For example, length, width, thickness, and the like may be changed. Some components may be omitted.

[0029] Elements described in the "singular" can also include the plural unless otherwise specified. For example, a particle can refer to a plurality of particles, a collection of particles, and granular matter.

[0030] Numerical ranges such as "m to n%" include the upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." "Equal to or more" and "equal to or less" are expressed by inequality signs with an equal sign "≦, ≧." "More than" and "less than" are expressed by inequality signs without an equal sign "<, >." A numerical value 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 numerical value within the numerical range with a numerical value described elsewhere in this specification, in a table, a figure, or the like.

[0031] All numerical values are modified by the term "about." The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values may be approximate values that may vary depending on the application of the subject technology. All numerical values may be expressed with significant figures. Unless otherwise specified, measured values may be average values of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, 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. Products equivalent to the devices, etc. exemplified may also be used. When equivalent products are used, the measurement conditions may be adjusted to suit the device.

[0033] The chemical composition of a compound can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). A sample solution is prepared by dissolving 0.1 g of a sample (e.g., a 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 using a measuring flask. After dilution, composition analysis is performed using an ICP-AES device. For example, a device with the product name "PS3520 UVDD II (manufactured by Hitachi High-Tech Science Corporation)" may be used.

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

[0035] The "maximum Feret diameter" refers to the length of the long side of the circumscribing rectangle (rectangle or square) of the particle. When the circumscribing rectangle is a square, the length of the long side refers to the length of one side.

[0036] The stoichiometric composition formula indicates a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to a compound having a molar ratio of "Al / O=2 / 3". Unless otherwise specified, "Al2O3" indicates a compound containing Al and O in any molar ratio. For example, the compound may be doped with a trace element. A portion of the Al and O may be substituted with another element.

[0037] The term "derivative" refers to a compound in which a part of a parent compound has been modified by at least one method selected from the group consisting of the introduction of a functional group, atomic substitution, oxidation, reduction, and other chemical reactions. The modification may be at one or more locations. The "substituent" 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 (e.g., F, Cl, Br, I), 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, phosphoric acid amide groups, sulfo groups, carboxy groups, hydroxamic acid groups, sulfino groups, hydrazino groups, imino groups, and silyl groups. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different. A plurality of substituents may be bonded to each other to form a ring.

[0038] <Cathode active material> FIG. 1 is a conceptual diagram showing secondary particles in this embodiment. The positive electrode active material includes a primary particle 1 and a coating 5. A "primary particle 1" is the smallest particle unit. The primary particle 1 may exist independently without agglomeration. A primary particle 1 existing independently is also referred to as a single particle. The primary particle 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] The secondary particles 2 are aggregates of the primary particles 1. The secondary particles 2 can have any shape. The secondary particles 2 may be, for example, spherical, rod-like, or angular. If the secondary particles 2 are spherical, for example, improved packing properties can be expected. The sphericity of the secondary particles 2 may be, for example, 0.85 or more, 0.90 or more, or 0.95 or more. The sphericity of the 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). The sphericity (circularity) is calculated using the following formula: ψ=4πS / L 2 ψ: Sphericity (circularity) π: Pi S: Cross-sectional area of secondary particle 2 (area of the region surrounded by the outline of secondary particle 2) L: Perimeter of secondary particle 2 (length of the outline of secondary particle 2) The sphericity indicates the arithmetic average of 30 secondary particles 2.

[0040] The primary particles 1 may have any shape. The primary particles 1 may be, for example, spherical, rod-like, angular, etc. The maximum Feret diameter of the primary particles 1 may be, for example, 10 to 90 nm. The maximum Feret diameter of the primary particles 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 Feret diameter of the primary particles 1 may be, for example, 80 nm or less, or 60 nm or less. The maximum Feret diameter of the primary particles 1 represents the arithmetic average 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 part 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 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 the 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 the 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] The primary particles 1 contain an olivine-type phosphate compound. "Olivine-type" refers to a crystal structure belonging to the space group Pnma. The space group is identified by powder X-ray diffraction (XRD) measurement. The primary particles 1 may be, for example, a single-phase compound. As long as the primary particles 1 contain an olivine-type crystal phase, they may further contain a phase belonging to another space group. The primary particles 1 may further contain, for example, an amorphous phase, etc.

[0045] The filtrate obtained by soaking 0.5 g of the positive electrode active material in 10 g of pure water for 10 minutes, subjecting the immersion solution to ultrasonic treatment, stirring for 6 hours, and then filtering the filtrate may have a total transition metal element concentration of 200 ppm or less, 150 ppm or less, 100 ppm or less, or 80 ppm or less. The total transition metal element concentration of 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, for example, at a temperature in the range of 20 to 25°C. The ultrasonic waves used in the ultrasonic treatment are not limited and can be selected from the range of 30 to 2000 kHz or 40 to 1000 kHz, for example. Stirring can be performed using a shaker. The shaking speed can be selected from the range of 20 to 200 r / min, for example. The shaking method is not limited and can be appropriately selected from, for example, reciprocal shaking, rotary shaking, etc. Filtration can be performed using a membrane filter with a pore size that does not allow the positive electrode active material to pass through. For example, a membrane filter with a pore size that does not allow the entire positive electrode active material to pass through, does not allow positive electrode active material with a particle size of D10 or more to pass through, or does not allow positive electrode active material with a particle size of D20 or more to pass through can be used. Pore sizes of membrane filters that can be used include, for example, 0.1 μm, 0.2 μm, or 0.3 μm.

[0047] The concentration of the transition metal element contained in the filtrate can be measured by the above-mentioned ICP-AES. The transition metal element detected in the filtrate is a transition metal element constituting the olivine-type phosphate compound. The detected transition metal element may include at least one selected from the group consisting of manganese (Mn) and iron (Fe).

[0048] The Gardner color scale of the filtrate is preferably 6 or less, and more preferably 5 or less. The Gardner color scale is one of the standards for the color intensity of a sample, as defined in the Japanese Industrial Standards (JIS), and can be measured by the method defined in "JISK0071-2:1998 Test Methods for Color of Chemical Products - Part 2: Gardner Color Scale." Specifically, the Gardner color scale is measured by comparing the transmitted color (color scale ranging from 1 to 18) of a Gardner color scale standard solution prepared using potassium hexachloroplatinate(IV), iron(III) chloride, cobalt(II) chloride, and hydrochloric acid with the transmitted color of the sample, and is expressed as a color scale ranging from 1 to 18. The Gardner color scale of the filtrate is, for example, 1 or more, and may be 2 or more.

[0049] The positive electrode active material preferably has a mass change rate of 0.20% or less, more preferably 0.10% or less, after the temperature of the positive electrode active material is raised 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 may be 0.02% or more.

[0050] The olivine-type phosphate compound may contain 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 a composition represented by the following general formula, for example: 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 more, 0.05 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. 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] LMFP, LMP, and LFP may be doped with an element (dopant) other than lithium (Li), Mn, Fe, phosphorus (P), and oxygen (O). The doping amount (substance amount fraction relative to the substance amount of Li) may be, for example, 0.01 to 0.1. The dopant may be, for example, boron (B), nitrogen (N), halogen, silicon (Si), sodium (Na), 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), bismuth (Bi), or the like. ), 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 at least one selected from the group consisting of actinides.

[0052] The positive electrode active material may contain at least one selected from the group consisting of LMFP, LMP, and LFP as a main component, and may further contain other components. The 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 be, for example, a mixture of LMFP powder and powders of the other components.

[0053] LMP can be, for example, a compound represented by the 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, for example, by 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 -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.

[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 Mn0000038O2, 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, for example, by 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 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.

[0059] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O2, LiNi 0.7 Co 0.2 Al 0.1 O2, LiNi 0.8 Co 0.1Al 0.1 O2, LiNi 0.8 Co 0.17 Al 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and LiNi 0.9 Co 0.05 Al 0.05 O2.

[0060] <Method of manufacturing positive electrode active material> FIG. 2 is a schematic flowchart showing a method for producing a positive electrode active material according to this embodiment. Hereinafter, the "method for producing a positive electrode active material according to this embodiment" may be abbreviated as "this method." The method for producing a positive electrode active material according to this embodiment may include a first step and a second step. The first step may include, for example, "(a) forming a slurry," "(b) granulation," and "(c) firing."

[0061] (1st step) (a) Slurry formation The method may include, for example, forming a slurry by mixing a lithium compound, a manganese compound, an iron compound, a phosphate compound, a carbon source, a solvent, and the like. 1-a Mn 1-x Fe x The lithium compound, manganese compound, phosphate compound, and iron compound may be weighed out so as to satisfy the composition ratio (ratio of amounts of substances) 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 source of carbon that adheres to the surfaces 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 the 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 granules using a raw material mixture of other raw materials. In this case, the amount of the carbon source added may be, for example, 1 to 20% by mass fraction relative to the granules.

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

[0064] The particle size in the slurry may be adjusted by wet milling, for example, so that the D50 is 0.10 to 1 μm.

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

[0066] (c) Firing The method may include producing an olivine-type phosphate compound by subjecting the secondary particles to a heat treatment. Any heat treatment furnace (e.g., an electric furnace, a muffle furnace, etc.) may 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 thus obtained is used as precursor particles. The precursor particles include primary particles and a carbon layer. The primary particles include the olivine-type phosphate compound. The carbon layer covers at least a portion of the surface of the primary particles. The carbon layer includes carbon.

[0068] (2nd process) The second step involves vacuum drying the precursor particles prepared in the first step at a temperature of 150°C or higher. Vacuum drying involves placing a container containing the precursor particles in an openable metal or glass chamber and reducing the pressure in the chamber using a vacuum pump or similar. The temperature in the chamber is preferably 150°C or higher, and may be 160°C or higher, 170°C or higher, 180°C or higher, 190°C or higher, or 200°C or higher, or 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 longer, 3 minutes or longer, or 5 minutes or longer, or 120 minutes or shorter, 90 minutes or shorter, or 60 minutes or shorter. Vacuum pumps typically include rotary oil pumps, mechanical booster pumps, dry scroll pumps, dry roots pumps, and turbomolecular pumps. The positive electrode active material is obtained through the second step.

[0069] By performing the second step, a positive electrode active material can be obtained in which the total concentration of transition metal elements in the filtrate, as detected by ICP-AES, is 200 ppm or less. Furthermore, by performing the second step, a positive electrode active material can be obtained in which the Gardner color index of the filtrate is 6 or less. This is thought to be because performing the second step reduces the concentration of transition metal elements that leach out when the positive electrode active material is immersed in pure water. In other words, performing the second step is expected to produce a positive electrode active material that can suppress deterioration in capacity retention.

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

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

[0072] Fig. 3 is a schematic perspective view of a battery according to this embodiment. Fig. 4 is a schematic cross-sectional view taken along line IV-IV in Fig. 3. Hereinafter, "plane-perpendicular direction" refers to the normal direction to the surface of a sheet-like member (e.g., foil, electrode, etc.). "In-plane direction" refers to any direction perpendicular to the plane-perpendicular direction. In Fig. 4, the Z-axis direction corresponds to the plane-perpendicular direction. The X-axis direction and the Y-axis direction are examples of in-plane directions.

[0073] The battery 100 includes an exterior body 90 and a power generating element 50. The exterior body 90 houses the power generating element 50. The exterior body 90 may include, for example, a first current collecting plate 91, a first laminate film 92, a second laminate film 93, and a second current collecting plate 94. The first laminate film 92 and the second laminate film 93 are joined to each other at their in-plane end portions. At the joint between the first laminate film 92 and the second laminate film 93, a sealant (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 generating element 50 at their ends in the stacking direction (Z-axis direction). A first laminate film 92 is joined to the first current collector plate 91. A second laminate film 93 is joined to the second current collector plate 94. A sealant (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 generating 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 a positive electrode layer 11, a current collecting foil 13, and a negative electrode layer 12, in this order, in the direction perpendicular to the plane. In the in-plane direction (e.g., the X-axis direction), the current collecting foil 13 extends outward relative to the positive electrode layer 11 and the negative electrode layer 12. For example, the current collecting foil 13 may extend outward relative to the positive electrode layer 11 and the negative electrode layer 12 over the entire periphery in the in-plane direction.

[0076] The current collecting foil 13 is a conductor. The current collecting foil 13 may include, for example, a metal foil, a conductive resin layer, or the like. For example, the current collecting foil 13 may be formed by laminating an Al foil and a Cu foil together. A carbon material may be applied to the surface of the current collecting foil 13. The carbon material may include, for example, carbon black, or the like.

[0077] The power generating element 50 includes a sealing material 30. The sealing material 30 is bonded to the current collecting foil 13 at an end in the in-plane direction. The sealing material 30 may be, for example, heat-welded to the current collecting foil 13. For example, the sealing material 30 may be disposed around the entire periphery in the in-plane direction. The sealing material 30 may include, for example, a resin material. The sealing material 30 seals between adjacent current collecting foils 13 in the direction perpendicular to the plane. The sealing material 30 seals between the current collecting foils 13, thereby dividing them into cells 40. A cell 40 is the smallest unit of the power generating element 50. The battery 100 includes multiple cells 40, and may therefore also be referred to as a "bipolar module." Each of the multiple cells 40 is sealed. The multiple cells 40 are isolated from one another. Each of the multiple 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 surface of the current collector foil 13. For example, grooves may be formed in the positive electrode layer 11. For example, the positive electrode layer 11 may be formed in a striped pattern. 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, for example, a conductive material and a binder in addition to the positive electrode active material. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material. The conductive material may contain any component. For example, the conductive material may contain at least one material selected from the group consisting of graphite, acetylene black (AB), Ketjen Black (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 the positive electrode active material. The binder may contain any component. 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), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, and derivatives thereof.

[0081] The positive electrode layer 11 may further include, for example, an inorganic filler, an organic filler, a solid electrolyte, a surface modifier, a dispersant, a lubricant, a flame retardant, a protective agent, a flux, a coupling agent, an adsorbent, etc. The positive electrode layer 11 may also include, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, a silane coupling agent, MoS2, WO3, etc.

[0082] (negative electrode layer) The negative electrode layer 12 is attached to one surface of the current collector foil 13. The negative electrode layer 12 is disposed 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 includes a negative electrode active material.

[0083] The negative electrode active material may be, for example, in the form of particles or a sheet. 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 include any component. For example, the negative electrode active material may include at least one selected from the group consisting of a carbon-based active material, an alloy-based active material, a Si-C composite material, Li metal, a Li-based alloy, and lithium titanate. In some embodiments of the present invention, the battery may be a Li metal negative electrode battery.

[0085] The carbon-based active material may contain, 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. 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."

[0086] The surface of graphite may be coated with, for example, amorphous carbon. The surface of graphite may be coated with, for example, a different material. The different material may contain, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may be, for example, Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO 3、 and 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 connected, for example, in a network. Pores are formed in the gaps of the resin skeleton. The resin film can permeate an electrolyte. The resin film may have, for example, an average pore diameter of 1 μm or less. The average pore diameter of the resin film may be, for example, 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 may be. The "Gurley value" can be measured by the Gurley test method.

[0092] The resin film may contain, for example, at least one selected from the group consisting of olefin-based resins, polyurethane-based resins, polyamide-based resins, cellulose-based resins, polyether-based resins, acrylic-based resins, and polyester-based resins. The resin film may contain, for example, at least one selected from the group consisting of polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and derivatives thereof. The resin film may 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 be composed of, for example, a PE layer. The skeleton of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multi-layer structure. The resin film may include, for example, a PP layer and a PE layer. The skeleton of the PP layer is formed of PP. The resin film may have, for example, a three-layer structure. The resin film may be formed by laminating, for example, 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. The inorganic particles may also be referred to as "inorganic filler." 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 referred to as an "HRL (Heat Resistance Layer)." The inorganic particles may contain at least one type selected from the group consisting of boehmite, alumina, zirconia, titania, magnesia, silica, and the like. The inorganic particles may have any shape. The inorganic particles may be, for example, spherical, rod-like, plate-like, fibrous, or the like. 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 contain, for example, at least one selected from the group consisting of acrylic resins, polyamide resins, fluorine resins, 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 referred to as "organic filler." The organic particles may contain a heat-resistant material. The organic particles may contain, for example, at least one selected from the group consisting of PE, PP, PTFE, PI, PAI, PA, and aramid. The organic particles may be, for example, spherical, rod-like, plate-like, fibrous, or the like. The D50 of the organic particles may be, for example, 0.1 to 10 μm, or 0.5 to 3 μm.

[0098] Separator 20 may include, for example, a mixed layer, which includes 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 to 1 mol / L, 1 to 1.5 mol / L, 1.5 to 2 mol / L, 2 to 2.5 mol / L, or 2.5 to 3 mol / L. "mol / L" may also be written as "M." The solute contains a supporting salt (Li salt). The solute may contain, for example, an inorganic acid salt, an imide salt, an oxalate complex, a halide, 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 electrolytic solution may contain, for example, a carbonate-based solvent (carbonate ester-based solvent). The solvent may contain, for example, a cyclic carbonate, a chain carbonate, a fluorinated carbonate, or the like. 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 a cyclic carbonate (EC, PC, FEC, etc.) and a chain carbonate (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate to 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 a cyclic carbonate (EC, PC, etc.) and a fluorinated cyclic carbonate (FEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate to 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 include, 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 indicates the volume ratio of EC, FEC, EMC, DMC, and DEC, respectively. 1≦V EC ≦4, 0≦V FEC ≦3, V EC +V FEC ≦4, 0≦V EMC ≦9, 0≦V DMC ≦9, 0≦V DEC ≦9, 6≦V EMC +V DMC +V DEC ≦9 The relationship is satisfied. For example, 1 ≤ V EC ≦2, or 2≦V EC The relationship ≦3 may be satisfied. For example, 1 ≤ V FEC ≦2, or 2≦V FEC The relationship ≦4 may be satisfied. For example, 3≦V EMC ≦4, or 6≦V EMC The relationship ≦8 may be satisfied. For example, 3≦V DMC ≦4, or 6≦V DMC The relationship ≦8 may be satisfied. For example, 3≦V DEC ≦4, or 6≦V DEC The relationship ≦8 may be satisfied.

[0104] The solvent may have a composition, for example, in volume ratios of "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," or "EC / FEC / DMC / EMC=1 / 2 / 3 / 4."

[0105] The electrolyte may contain an ether-based solvent, such as 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), ethylglyme, triglyme, tetraglyme, and derivatives thereof.

[0106] The electrolyte may contain any additive. The amount of additive (mass fraction relative to the total amount of the electrolyte) may be, for example, 0.01 to 5%, 0.05 to 3%, or 0.1 to 1%. The additive may include, for example, an SEI (Solid Electrolyte Interphase) formation accelerator, an SEI formation inhibitor, a gas generator, an overcharge inhibitor, a flame retardant, an antioxidant, an electrode protectant, a surfactant, etc.

[0107] Examples of the additives include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfite (ES), propane sultone (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.), fluorotoluenes (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-methylbenzotrifluoride, The solvent may contain at least one selected from the group consisting of benzotriazole, benzotriazole, tetrathiafulvalene, etc.), nitrile compounds (e.g., adiponitrile, succinonitrile, etc.), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate, etc.), carboxylic acid anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, etc.), alcohols (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, diethylene glycol monomethyl ether, etc.), and derivatives thereof.

[0108] The components described above as solutes and solvents may be used as minor components (additives). The additives may include, for example, at least one selected from the group consisting of LiBF, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPOF, FSOLi, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0109] The electrolyte solution may contain an ionic liquid, which may include, 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 the present 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. [Example]

[0111] <Production of positive electrode active material> (No.1) (Precursor particle manufacturing process (first process)) Compositional formula “Li1Mn 0.8 Fe 0.2 Lithium carbonate, manganese carbonate, iron oxalate, and phosphoric acid were weighed out to achieve the composition ratio shown in "PO4". These raw materials were dispersed in water to form a slurry, which was then pulverized in a bead mill using 0.3 mm diameter beads at a peripheral speed of 10 m / s for 30 minutes and then fired to obtain granules. 10% by mass of fructose was added to the granules. After drying, this mixture was heated to a firing temperature of 600°C at a heating rate of 5°C / min in an inert atmosphere, held at that temperature 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) A positive electrode active material was obtained under the same conditions as in No. 1, except that in the vacuum drying treatment step (second step), the vacuum drying treatment was carried out without immersion and mixing in toluene.

[0114] (No.3) The precursor particles obtained under the same conditions as in the precursor particle production step (first step) of No. 1, without carrying out the vacuum drying treatment (second step) of No. 1, were used as the positive electrode active material.

[0115] <Measurement> (ICP-AES measurement) 0.5 g of each of the positive electrode active materials No. 1 to No. 3 was immersed in 10 g of pure water, and the resulting immersion solution was subjected to ultrasonic treatment for 10 minutes, stirred for 6 hours, and then filtered using a membrane filter with a pore size of 0.2 μm to obtain a filtrate. 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 determined by the following methods: Fe and Mn The measurement results are shown in Figure 5.

[0116] (Gardner color scale measurement) The filtrate obtained above was placed in a quartz cell and evaluated using a colorimeter with the Gardner color scale, which is used to measure petroleum. The evaluation results are shown in Figure 5.

[0117] (Mass change rate) 0.5 g (mass before drying) of each of the positive electrode active materials Nos. 1 to 3 was heated from room temperature (25°C) to 300°C at a 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 mass change rate 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} x 100

[0118] <Evaluation> (Battery characteristics) A lithium-ion secondary battery (coin cell) was 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". The mixture was dispersed in a solvent (N-methyl-2-pyrrolidone) to form a paste. The solid concentration of the paste was 50% by mass. The paste was applied to the surface of Al foil and dried to form a positive electrode layer. The density of the positive electrode layer was reduced to 1.8 g / cm by roll pressing. 3 The positive electrode blank was then subjected to a vacuum drying treatment at 120°C for 12 hours. After drying, a disk sample (diameter: 14 mm) was cut out from the positive electrode blank by punching.

[0120] A coin cell was assembled in a glove box. The cell configuration is as follows: Working electrode: disk sample (positive electrode) Counter electrode: Li foil Separator: Porous polymer membrane Electrolyte: "EC / DMC=3 / 7 (volume ratio)", LiPF6 (1mol / L)

[0121] The 1C discharge capacity of the resulting coin cell was calculated based on the estimated discharge capacity from the coating weight. "C" represents the current rate (time rate). At a rate of 1C, the theoretical capacity flows over one hour. Under a 25°C environment, the charge rate was set to 0.1C, the upper voltage limit was 4.3V, and the charge termination condition was 0.01C. After the CCCV charging, the discharge termination potential was set to 3V. The 0.1C discharge capacity (referred to as the "first discharge capacity") was calculated. The discharge capacity after 50 cycles (referred to as the "discharge capacity after 50 cycles") was then calculated. The capacity retention was calculated as (discharge capacity after 50 cycles / first discharge capacity) x 100%. Figure 5 shows the capacity retention. It is believed that a higher capacity retention indicates better durability.

[0122] <Result> As shown in FIG. 5, when the conditions of the present disclosure are met, the capacity retention rate tends to be high. [Explanation of symbols]

[0123] 1 primary particles, 2 secondary particles, 5 coating, 10 bipolar electrode, 11 positive electrode layer, 12 negative electrode layer, 13 current collecting foil, 20 separator, 30 sealing material, 40 cell, 50 power generating element, 90 exterior body, 91 first current collecting plate, 92 first laminate film, 93 second laminate film, 94 second current collecting plate, 100 battery.

Claims

1. A positive electrode active material, comprising primary particles and a coating, the primary particles include an olivine-type phosphate compound; the olivine-type phosphate compound is lithium manganese iron phosphate; the coating covers at least a portion of the surface of the primary particles, the coating comprises carbon; a preparation method in which 0.5 g of the positive electrode active material is immersed in 10 g of pure water, the immersion liquid is subjected to ultrasonic treatment for 10 minutes, stirred for 6 hours, and then filtered, and the filtrate obtained by this preparation method has a total concentration of transition metal elements detected by ICP-AES of 200 ppm or less; the concentration of the transition metal element is the sum of the concentrations of iron and manganese, The filtrate has a Gardner color score of 6 or less.

2. 2. The positive electrode active material according to claim 1, wherein the positive electrode active material has a mass change rate of 0.20% 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.

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

4. A battery comprising the positive electrode active material according to any one of claims 1 to 3.

5. having a bipolar structure, The battery of claim 4.

6. A first step of preparing precursor particles; a second step of subjecting the precursor particles to a vacuum drying treatment at a temperature of 150°C or higher to produce a positive electrode active material; The positive electrode active material is the positive electrode active material according to any one of claims 1 to 3. A method for producing a positive electrode active material.

7. The vacuum drying treatment is carried out at a temperature of 180°C or higher and 250°C or lower. The method for producing a positive electrode active material according to claim 6 .

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