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 trifluoromethyl groups are detected by X-ray photoelectron spectroscopy.

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). When olivine-type phosphate compounds come into contact with HF, the crystal structure of the olivine-type phosphate compounds may be destroyed, potentially worsening the 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] comprising 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, A trifluoromethyl group is detected by X-ray photoelectron spectroscopy. Cathode active material.

[0009] X-ray photoelectron spectroscopy (XPS) is used to obtain information about the outermost surface of the material being measured (positive electrode active material). In other words, the chemical bonding state of elements measured by XPS is considered to represent the chemical bonding state of elements on the surface of the primary particles or in the coating. The detection of trifluoromethyl groups (CF3 groups) by XPS indicates that the coating of the positive electrode active material has CF3 groups. Coatings usually have hydroxyl groups derived from the material. The presence of CF3 groups in the coating indicates that there are relatively few hydroxyl groups (OH groups) present in the coating. Fewer hydroxyl groups reduce the amount of water adsorbed on the positive electrode active material, which can suppress the degradation of the positive electrode active material. As a result, improved durability is expected.

[0010] [2] In the Cs1 spectrum obtained by X-ray photoelectron spectroscopy, when the peak intensity of the trifluoromethyl group is denoted as I(CF3) and the peak intensities corresponding to the CC bond and CH bond are taken as follows: (1) 0.01 ≤ I(CF3) / I(C) (1) Satisfying the relationship, The positive electrode active material described in [1].

[0011] In coatings, it is expected that durability will be improved by including a certain amount or more of CF3 units.

[0012] [3] The coating has a trifluoromethyl group, The positive electrode active material described in [1] or [2].

[0013] [4] The positive electrode active material described in any of [1] to [3], wherein the amount of adsorbed water after being left for 24 hours in an environment with a temperature of 23°C and a relative humidity of 50% is 1900 ppm or less.

[0014] [5] The primary particles form secondary particles The positive electrode active material described in any of [1] to [4].

[0015] [6] 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 [5].

[0016] [7] A positive electrode active material comprising any of the materials described in [1] to [6], battery.

[0017] [8] Having a bipolar structure, The battery described in [7].

[0018] [9] The first step is to prepare precursor particles, The process includes a second step of producing a positive electrode active material by reacting the aforementioned precursor particles with a trifluoromethyl source, The positive electrode active material is the positive electrode active material described in any one of items [1] to [6]. A method for manufacturing a positive electrode active material.

[0019]

[10] The trifluoromethyl source is trifluoroacetic acid. [9] A method for producing a positive electrode active material as described above.

[0020] 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]

[0021] [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 4. [Modes for carrying out the invention]

[0022] <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.

[0023] 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."

[0024] 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.

[0025] Expressions such as "first," "second," etc., are used solely to distinguish between multiple elements. These expressions do not limit the elements to which they are attached. They are unrelated, for example, to the order or importance of the elements to which they are attached.

[0026] 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".

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] XPS analysis is performed using the following procedure: A sample powder consisting of the positive electrode active material is placed in the XPS instrument. The XPS analysis conditions are, for example, as follows: Analytical instrument: PHI 5000 VersaProbe III (manufactured by ULVAC-PHI) X-ray source: AlKα radiation Acceleration voltage: 15kV Beam diameter: 100 μmφ

[0033] XPS analysis provides analytical results (X-ray photoelectron spectroscopy spectra) for all elements contained in the positive electrode active material. In the X-ray photoelectron spectroscopy spectrum, the horizontal axis shows the binding energy (eV), and the vertical axis shows the spectral intensity (number of X-ray photoelectrons). In the Cs1 spectrum (280-296 eV), which is an X-ray photoelectron spectroscopy spectrum, the peak near 292.0 eV corresponds to the CF3 group, the peak near 288.0 eV corresponds to the C=O bond, the peak near 286.5 eV corresponds to the COH bond and COC bond, and the peak near 285.0 eV corresponds to the CH bond and CC bond.

[0034] 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.

[0035] "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.

[0036] "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.

[0037] 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.

[0038] 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.

[0039] <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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] XPS of the positive electrode active material detects CF3 groups. That is, coating 5 contains carbon, and the carbon exists as at least CF3 groups. In coating 5, carbon may exist in the form of C=O bonds, COH bonds, COC bonds, CH bonds, and CC bonds. In the Cs1 spectrum obtained by XPS (bond energy 280~296 eV), if the intensity of the peak corresponding to the trifluoromethyl group (CF3 group) (bond energy around 292.0 eV) is denoted as I(CF3), and the intensity of the peaks corresponding to the CH bond and CC bond (bond energy around 285.0 eV) is denoted as I(C), then the following equation (1): 0.01 ≤ I(CF3) / I(C) (1) It is preferable that the relationship is satisfied.

[0047] In the above formula (1), in "I(CF3) / I(C)", the amount of carbon present in the coating 5 that exists as a CF3 group is reflected in I(CF3), and the amount of carbon present as a CH bond or CC bond is reflected in I(C). In other words, "I(CF3) / I(C)" can be used as an indicator representing the proportion of carbon present in the coating 5 that exists as a trifluoromethyl group (CF3 group). For example, if a portion of the COH group is modified to become a CO-CO-CF3 group, comparing the pre-modification and post-modification states that there is no difference in the value of I(C), but the value of I(CF3) increases, and "I(CF3) / I(C)" becomes larger. Also, for example, if a portion of the COH is modified to become CO-CO-CF3, a larger "I(CF3) / I(C)" may mean that the proportion of carbon present as COH is smaller. A smaller proportion of carbon present as COH means that there are fewer OH groups. The OH group has the ability to adsorb water molecules, and water molecules adsorbed on the OH group can cause degradation of the positive electrode active material. "I(CF3) / I(C)" may be 0.02 or greater. Also, "I(CF3) / I(C)" may be 0.3 or less, 0.2 or less, or 0.1 or less.

[0048] By satisfying the relationship in equation (1) above, some of the carbon present in the coating 5 exists as CF3 groups, or the proportion of carbon existing as COH is small, which can suppress the degradation of the positive electrode active material. By using such a positive electrode active material in a battery, an improvement in the battery's capacity retention rate can be expected.

[0049] It is preferable that the amount of adsorbed moisture obtained by thoroughly drying the positive electrode active material and then leaving it in an environment of 23°C and 50% relative humidity for 24 hours is 1900 ppm or less. The amount of adsorbed moisture shall be the value calculated by measuring it using the Karl Fischer method. Satisfying the relationship in formula (1) above can be used as an indicator that there are few OH groups present on the surface of the coating portion 5, and it is expected that the amount of adsorbed moisture in the positive electrode active material in the battery will be reduced, and furthermore, the degradation of the positive electrode active material will be suppressed. The amount of adsorbed moisture may be, for example, 1000 ppm or less, 900 ppm or less, 800 ppm or less, or 700 ppm or less. The amount of adsorbed moisture may be, for example, 1 ppm or more, 10 ppm or more, or 100 ppm 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, 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 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<...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 0.2 O2, LiNi 0.7 [[ID=5​​​​​​​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. The bonding state of the carbon in the carbon layer with other elements is not limited, but it is preferable that it contains carbon that forms COH bonds. That is, it is preferable that the carbon layer has hydroxyl groups.

[0068] (2nd process) The second step involves producing a positive electrode active material by reacting the precursor particles prepared in the first step with a trifluoromethyl source. This step involves a reaction in which the hydroxyl groups contained in the carbon layer of the precursor particles are modified by the trifluoromethyl source. The trifluoromethyl source is not limited to those containing trifluoromethyl groups, and may also contain trifluoroacetyl groups. Examples of trifluoromethyl sources include trifluoroacetic acid and trifluoroacetic anhydride. The second step may involve, for example, exposing the precursor particles and trifluoroacetic acid to a heated environment and reacting the volatile trifluoroacetic acid with the precursor particles.

[0069] The second step may introduce trifluoromethyl groups into the carbon layer. Furthermore, the second step may reduce the amount of hydroxyl groups in the carbon layer. If the carbon layer contains hydroxyl groups as COH groups, at least a portion of them may be modified with trifluoromethyl groups, and at least a portion of them may be modified to become CO-CO-CF3 groups.

[0070] After the second step, the obtained positive electrode active material may be subjected to a drying step. The drying step can evaporate and remove any excess trifluoromethyl source. The drying temperature can be any temperature at which the trifluoromethyl source used evaporates, for example, 70°C or higher, 80°C or higher, 90°C or higher, or 100°C or higher, and can be 200°C or lower, 150°C or lower, or 120°C or lower. When trifluoroacetic acid (boiling point: 72.4°C) is used as the trifluoromethyl source, it is preferable that the temperature be 72.4°C or higher. The drying step may be carried out by vacuum drying. In this way, a positive electrode active material containing primary particles and a coating is produced. The coating has trifluoromethyl groups.

[0071] In the above manufacturing method, the amount of trifluoromethyl groups contained in the coating of the positive electrode active material obtained in the second step is greater than the amount of trifluoromethyl groups contained in the carbon layer of the precursor particles obtained in the first step.

[0072] <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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] (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.

[0080] 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).

[0081] 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.

[0082] 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.

[0083] (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.

[0084] 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.

[0085] 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.

[0086] The carbon-based active material may include at least one selected from the group consisting of, for example, graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. 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".

[0087] The surface of the graphite may be coated with, for example, amorphous carbon. The surface of the graphite may be coated with, for example, a different material. The different material may include at least one selected from the group consisting of, for example, P, W, Al, and O. The different material may include at least one selected from the group consisting of, for example, Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO 3、 and, for example, at least one selected from the group consisting of Li3PO4.

[0088] The alloy-based active material may include at least one selected from the group consisting of, for example, Si, Li silicate, SiO, Si-based alloy, tin (Sn), SnO, and Sn-based alloy.

[0089] 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.

[0090] "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).

[0091] (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 include 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 include, for example, a resin film and an inorganic particle layer.

[0092] The resin film is porous. The resin film may include, for example, a microporous membrane, a non-woven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may be continuously connected, for example, in a network form. Pores are formed in the gaps of the resin skeleton. The resin film can permeate the electrolyte. The resin film may have, for example, an average pore diameter of 1 μm or less. The average pore diameter of the resin film may be, for example, 0.01 - 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.

[0093] The resin film may include at least one selected from the group consisting of, for example, an olefin-based resin, a polyurethane-based resin, a polyamide-based resin, a cellulose-based resin, a polyether-based resin, an acrylic-based resin, and a polyester-based resin. The resin film may include at least one selected from the group consisting of, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (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, etc. The thickness of the resin film may be, for example, 5 - 50 μm, or 10 - 25 μm.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] The separator 20 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0100] (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.

[0101] 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.

[0102] 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".

[0103] 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".

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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]

[0112] <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.

[0113] (Trifluoroacetic acid treatment process (second process)) The precursor particles obtained in the first step were spread in a petri dish, trifluoroacetic acid (TFA) was placed in a small container (made of fluoropolymer (PFA)), and the petri dish and the container with TFA were placed in the same jar (made of fluoropolymer (PFA)) and sealed. The temperature inside the jar was then maintained at 80°C for 24 hours. Through this treatment, at least some of the hydroxyl groups on the surface of the precursor particles were replaced with CF3 groups by the volatilized TFA. The treated precursor particles were recovered and dried at 100°C to obtain the cathode active material.

[0114] (No.2) The positive electrode active material was obtained under the same conditions as in No. 1, except that the calcination temperature in the precursor particle manufacturing process (first step) was set to 650°C.

[0115] (No.3) The TFA treatment process (second step) of No. 1 was omitted, and precursor particles obtained under the same conditions as the precursor particle manufacturing process (first step) of No. 1 were used as the cathode active material.

[0116] (No.4) The TFA treatment process (second step) of No. 2 was omitted, and precursor particles obtained under the same conditions as the precursor particle manufacturing process (first step) of No. 2 were used as the cathode active material.

[0117] <Measurement> (XPS measurement) After fixing each of the positive electrode active materials from No. 1 to No. 4 with carbon tape, XPS analysis was performed using the method described above to obtain Cs1 spectra. Based on the obtained Cs1 spectra, the "I(CF3) / I(C)" ratio for each sample was calculated. The calculation results are shown in Figure 5.

[0118] (Measurement of adsorbed water content) Each of the positive electrode active materials from No. 1 to No. 4 was spread thinly in a petri dish and left for 24 hours in a standard atmosphere (temperature 23°C and relative humidity 50%). The amount of adsorbed water was then measured using a Karl Fischer moisture meter. Figure 5 shows the measurement results.

[0119] (Battery characteristics) A lithium-ion secondary battery (coin cell) has been manufactured. The cell configuration is as follows:

[0120] 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 By adjusting the material, a cathode base was formed. The cathode base was subjected to vacuum drying at 120°C for 12 hours. After drying, a disc sample (diameter: 14 mm) was removed from the cathode base by punching.

[0121] 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)

[0122] The discharge capacity of the obtained coin cells was determined based on the discharge capacity estimated from the coated 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 charging 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. After that, the battery was fully charged again and held at a temperature of 60°C for 14 days, and the discharge capacity at 0.1C (referred to as the "second discharge capacity") was determined again. The capacity retention rate was calculated as (second discharge capacity / first discharge capacity) × 100%. Figure 5 shows the capacity retention rate. A higher capacity retention rate indicates better durability.

[0123] <Result> As shown in Figure 5, when the conditions of this disclosure are met, there is a tendency for a high capacity retention rate. Also, as shown in Figure 5, when the conditions of this disclosure are met, there is a tendency for a low moisture content after exposure to air. [Explanation of symbols]

[0124] 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. 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, A trifluoromethyl group is detected by X-ray photoelectron spectroscopy. Cathode active material.

2. In the Cs1 spectrum obtained by X-ray photoelectron spectroscopy, the intensity of the peak corresponding to the trifluoromethyl group is I(CF ３ ) and when the intensity of the peaks corresponding to the C-C bond and C-H bond is denoted as I(C), then the following equation (1): 0.01≦I(CF ３ ) / I(C) (1) Satisfying the relationship, The positive electrode active material according to claim 1.

3. The coating material is a positive electrode active material according to claim 1, wherein the coating material has a trifluoromethyl group.

4. The positive electrode active material according to claim 1, wherein the amount of adsorbed moisture after being left for 24 hours in an environment with a temperature of 23°C and a relative humidity of 50% is 1900 ppm or less.

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

6. 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.

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 reacting the aforementioned precursor particles with a trifluoromethyl source, 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 method for producing a positive electrode active material according to claim 9, wherein the trifluoromethyl source is trifluoroacetic acid.

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