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

Abstract

The present disclosure relates to a positive electrode active material comprising primary particles and a coating, the primary particles comprising an olivine-type phosphate compound, the coating covering at least part of the surface of the primary particles, the coating containing carbon, a trifluoromethyl group being 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 the positive electrode active material. Background Technology

[0002] Japanese Patent Application Publication No. 2021-9838 discloses a positive electrode active material with a carbon coating formed on the surface of lithium manganese iron phosphate (hereinafter referred to as "LMFP") particles. Summary of the Invention

[0003] To improve battery performance, olivine-type phosphate compounds such as LMFP, lithium manganese phosphate (LMP), and lithium iron phosphate (LFP) have been developed. In liquid batteries, trace amounts of water mixed in react with fluorides such as LiPF6 in the electrolyte to generate hydrogen fluoride (HF). Moreover, the contact between olivine-type phosphate compounds and HF disrupts the crystal structure of the olivine-type phosphate compounds, potentially deteriorating capacity retention.

[0004] As described in Japanese Patent Application Publication No. 2021-9838, coating olivine-type phosphate compounds with a carbon coating is expected to improve capacity retention. However, there is still room for improvement in the capacity retention of the battery.

[0005] This disclosure provides a positive electrode active material with improved capacity retention, a battery, and a method for manufacturing the positive electrode active material.

[0006] The technical structure and effects of this disclosure are described below. However, the mechanism of action of this disclosure includes presumptions. The mechanism of action is not intended to limit the technical scope of this disclosure.

[0007] The positive electrode active material of the first aspect of this disclosure comprises primary particles and a coating, the primary particles comprising an olivine-type phosphate compound, the coating covering at least a portion of the surface of the primary particles, the coating comprising carbon, and being detected by X-ray photoelectron spectroscopy as trifluoromethyl.

[0008] X-ray photoelectron spectroscopy (XPS) is used to obtain information about the outermost surface of the target material (positive electrode active material). Specifically, the chemical bonding state of elements determined by XPS is considered to represent the chemical bonding state of elements on the surface of primary particles or within the coating. The detection of trifluoromethyl (CF3) groups by XPS indicates that the coating of the positive electrode active material contains CF3 groups. Coatings typically contain hydroxyl (OH) groups derived from the material. The presence of CF3 groups in the coating suggests a relatively low number of hydroxyl groups. Fewer hydroxyl groups reduce the amount of water adsorbed by the positive electrode active material, thus inhibiting its degradation. As a result, improved durability can be expected.

[0009] In the positive electrode active material of the first aspect of this disclosure, in the Cs1 spectrum obtained by X-ray photoelectron spectroscopy, when the peak intensity of trifluoromethyl is set to I(CF3) and the peak intensities corresponding to the C-C bond and the CH bond are set to I(C), the positive electrode active material can satisfy the following relationship (1):

[0010] 0.01≤I(CF3) / I(C) (1).

[0011] In coatings containing a certain amount or more of CF3 groups, improved durability can be expected.

[0012] In the positive electrode active material of the first aspect of this disclosure, the coating may have a trifluoromethyl group.

[0013] In the positive electrode active material of the first aspect of this disclosure, the amount of adsorbed water after being placed at a temperature of 23°C and a relative humidity of 50% for 24 hours can be less than 1900 ppm.

[0014] In the positive electrode active material of the first aspect of this disclosure, the secondary particles may be an aggregate of the primary particles.

[0015] In the positive electrode active material of the first aspect of this disclosure, the olivine-type phosphate compound may contain at least one selected from lithium manganese iron phosphate, lithium manganese phosphate, and lithium iron phosphate.

[0016] In the positive electrode active material of the first aspect of this disclosure, the I(CF3) / I(C) ratio can be 0.3 or less.

[0017] In the positive electrode active material of the first aspect of this disclosure, the I(CF3) / I(C) ratio can be 0.1 or less.

[0018] In the positive electrode active material of the first aspect of this disclosure, the amount of adsorbed water can be 1 ppm or more.

[0019] In the positive electrode active material of the first aspect of this disclosure, the amount of adsorbed water may be less than 700 ppm.

[0020] The battery of the second aspect of this disclosure may include the positive electrode active material of the first aspect.

[0021] The battery of the second embodiment of this disclosure may have a bipolar structure.

[0022] The method for manufacturing the positive electrode active material according to the third aspect of this disclosure may include preparing precursor particles and manufacturing the positive electrode active material by reacting the precursor particles with a trifluoromethyl source, wherein the positive electrode active material may be the positive electrode active material in the first aspect.

[0023] In the preparation method of the positive electrode active material according to the third aspect of this disclosure, the trifluoromethyl source can be trifluoroacetic acid.

[0024] In the following description, one embodiment (hereinafter referred to as "this embodiment") and one example (hereinafter referred to as "this example") of the present disclosure will be described. However, this embodiment and this example are not intended to limit the technical scope of the present disclosure. This embodiment and this example are merely illustrative in all respects. This embodiment and this example are non-limiting. The technical scope of the present disclosure includes all modifications made with changes equivalent in meaning and scope to the claims. For example, any structure extracted from this embodiment and combined in any way will result in a solution that is intended to fall within the scope of the present invention from the outset. Attached Figure Description

[0025] Figure 1 A conceptual diagram of the secondary particle in this embodiment is shown.

[0026] Figure 2 A schematic flowchart of the method for manufacturing the positive electrode active material in this embodiment is shown.

[0027] Figure 3 A schematic perspective view of the battery according to this embodiment is shown.

[0028] Figure 4 A schematic cross-sectional view along line IV-IV is shown.

[0029] Figure 5 This is a table showing the experimental results of Examples No.1 to No.4. Detailed Implementation

[0030] The features, advantages, and industrial and technical significance of embodiments of the present invention will now be described with reference to the accompanying drawings. Similar symbols denote similar elements. Terms and phrases...

[0031] Expressions such as "comprising", "including", "containing", "having" and their variant expressions are open-ended. In addition to the necessary elements, a composition expressed in an open-ended manner may or may not include additional elements. A description of "composition" is a closed-ended expression. However, even a composition expressed in a closed-ended manner may include impurities that are usually incidental or additional elements unrelated to the object technology. A description of "substantially consisting of..." is a semi-closed-ended expression. In a composition expressed in a semi-closed-ended manner, elements that do not substantially affect the novelty and basic characteristics of the object technology are allowed to be added.

[0032] Expressions such as "may", "can" etc. do not mean obligation, that is, they do not mean "must do", but rather mean permission to do, that is, "the meaning of having the possibility of doing".

[0033] For multiple steps, actions, operations, etc. included in various methods, as long as there is no special indication, the order of their implementation is not limited to the described order. For example, multiple steps can be carried out simultaneously. For example, multiple steps can also be carried out successively.

[0034] Descriptions such as "first", "second", etc. are only used to distinguish multiple elements from each other. This description does not impose any limitations on the elements to which they are attached. This description has nothing to do with, for example, the order, importance, etc. of the elements to which they are attached.

[0035] For example, the description of "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 described as "A and / or B".

[0036] Geometric terms should not be strictly understood. As geometric terms, examples can be cited such as "parallel", "perpendicular", "orthogonal", etc. For example, directions, angles, distances, etc. can have relative displacements within the range where basically the same or similar functions can be obtained. Geometric terms can include tolerances, errors, etc. in, for example, design, operation, manufacturing, etc. The dimensional relationships in each figure are sometimes inconsistent with the actual dimensional relationships. In order to help readers understand, the dimensional relationships in each figure are sometimes changed. For example, there are cases where lengths, widths, thicknesses, etc. are changed. There are also cases where a part of the structure is omitted.

[0037] Unless otherwise specified, elements described in "singular form" may also include plural forms. For example, particles sometimes represent multiple particles, a collection of particles, and powders.

[0038] Unless otherwise specified, the numerical ranges such as "m~n%" include both upper and lower limits. That is, "m~n%" represents a numerical range of "m% and below n%". Furthermore, "m% and below n%" includes "greater than m% and less than n%". "Above" and "below" are indicated by inequality signs "≤" and "≥" with an equal sign. "Greater than" and "less than" are indicated by inequality signs "<" and ">" without an equal sign. Any value selected from the numerical range can also be used as a new upper or lower limit. For example, a new numerical range can be set by arbitrarily combining values ​​within the numerical range with values ​​described in other parts of this specification, tables, figures, etc.

[0039] All numerical values ​​are modified by the word "approximately." "Approximately" can mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​can be approximations that vary depending on the application of the technology. All numerical values ​​can be displayed with significant figures. Unless otherwise specified, the measured value can be the average of multiple measurements. The number of measurements can be 3 or more, 5 or more, or 10 or more. Generally, the more measurements, the higher the reliability of the average value can be expected. The measured value can be rounded to the nearest hundredth based on the number of significant figures. The measured value may include errors arising from factors such as the detection limits of the measuring device.

[0040] The apparatus and software used for measuring various values ​​are merely one example. Equivalent items, identical to those illustrated, may also be used. When using equivalent items, the measurement conditions may be adjusted accordingly based on the apparatus.

[0041] The analysis performed by XPS was carried out according to the following steps. The sample powder, consisting of the positive electrode active material, was placed on the XPS apparatus. The XPS analysis conditions were as follows:

[0042] Analytical apparatus: PHI5000 VersaProbeIII (manufactured by ULVAC-PHI)

[0043] X-ray source: AlKα rays

[0044] Accelerating voltage: 15kV

[0045] Beam diameter: 100μmφ

[0046] XPS analysis was used to obtain the analytical results of all elements contained in the positive electrode active material (X-ray photoelectron spectroscopy). In X-ray photoelectron spectroscopy, the horizontal axis represents the binding energy (eV), and the vertical axis represents the spectral intensity (the number of X-ray photoelectrons). In the Cs1 spectrum (280–296 eV) of X-ray photoelectron spectroscopy, 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 and COC bonds, and the peak near 285.0 eV corresponds to the CH and CC bonds.

[0047] The chemical composition of a compound can be determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). A sample solution is prepared by dissolving 0.1 g of the sample (e.g., a positive electrode active material) in a mixed acid solution (10 ml) of hydrochloric acid and sulfuric acid. The sample solution is then diluted to an appropriate concentration using a volumetric flask. After dilution, the composition is analyzed using an ICP-AES apparatus. For example, product names such as "PS3520UVDDII (manufactured by Hitachi High-Tech Science)" can also be used.

[0048] "D50" indicates the particle size at which the cumulative value in the volumetric particle size distribution (cumulative distribution) is 50%. D50 (excluding the D50 of primary particles) is measured, for example, by a laser diffraction particle size distribution measuring device.

[0049] The "maximum Ferrett diameter" refers to the length of the longer side of the circumscribed rectangle (rectangle or square) of the particle. When the circumscribed rectangle is a square, the length of the longer side represents the length of one side.

[0050] Stoichiometric composition indicates a representative example of a compound. Compounds can also have non-stoichiometric compositions. For example, "Al₂O₃" is not limited to compounds having 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, trace elements may be doped into the compound. A portion of Al and O may be replaced by another element.

[0051] A "derivative" is a compound that is altered from a parent compound through at least one of the following methods: introduction of a functional group, substitution of atoms, oxidation, reduction, or other chemical reactions. The altered position can be one or more positions. The "substituent" may contain at least one selected from, for example, alkyl, alkenyl, alkynyl, cycloalkyl, unsaturated cycloalkyl, aromatic, heterocyclic, halogen atom (F, Cl, Br, I, etc.), OH, SH, CN, SCN, OCN, nitro, alkoxy, unsaturated alkoxy, amino, alkylamino, dialkylamino, aryloxy, acyl, alkoxycarbonyl, acyloxy, aryloxycarbonyl, acylamino, alkoxycarbonylamino, aryloxycarbonylamino, sulfonylamino, aminosulfonyl, carbamoyl, alkylthio, arylthio, sulfonyl, sulfinyl, urea, phosphoramidyl, sulfonyl, carboxyl, hydroxamic acid, sulfinyl group, hydrazine, imino, and silyl. These substituents may also be substituted. When there are two or more substituents, the substituents may be the same or different. Multiple substituents may combine to form a ring.

[0052] <Positive Electrode Active Material>

[0053] Figure 1 This is a conceptual diagram representing secondary particles in this embodiment. The positive electrode active material includes primary particles 1 and a coating 5. "Primary particle 1" is the smallest unit of a particle. Primary particles 1 may also exist independently without aggregation. Independently existing primary particles 1 are also called primary particles. Primary particles 1 may also form secondary particles 2. The positive electrode active material may, for example, be a powder of secondary particles 2. The D50 of the positive electrode active material may, for example, be 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, for example, be 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0054] Secondary particles 2 are an aggregate of primary particles 1. Secondary particles 2 can have any shape. For example, secondary particles 2 can also be spherical, rod-shaped, angular, etc. By making secondary particles 2 spherical, for example, improved filling properties are expected. The sphericity of secondary particles 2 can be, for example, 0.85 or higher, 0.90 or higher, or 0.95 or higher. The sphericity of secondary particles 2 can be, for example, less than 1, less than 0.95, or less than 0.90. "Sphericity" refers to the roundness in a SEM (Scanning Electron Microscope) image (two-dimensional image). Sphericity (roundness) is calculated using the following formula.

[0055] ψ=4πS / L 2

[0056] ψ: Sphericity (Circularity)

[0057] π: Pi

[0058] S: Cross-sectional area of ​​secondary particle 2 (the area of ​​the region enclosed by the outline of secondary particle 2)

[0059] L: The perimeter of secondary particle 2 (the length of the outline of secondary particle 2)

[0060] Sphericity is represented by the arithmetic mean of 30 secondary particles.

[0061] Primary particle 1 can have any shape. For example, it can be spherical, rod-shaped, angular, etc. The maximum Feret diameter of primary particle 1 can be, for example, 10–90 nm. The maximum Feret diameter of primary particle 1 can be, for example, greater than 20 nm, greater than 30 nm, greater than 40 nm, greater than 50 nm, greater than 60 nm, greater than 70 nm, or greater than 80 nm. The maximum Feret diameter of primary particle 1 can be, for example, less than 80 nm or less than 60 nm. The maximum Feret diameter of primary particle 1 represents the arithmetic mean of 30 primary particles 1.

[0062] The coating 5 contains carbon. The bonding state of the carbon elements 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 also cover the entire surface of the primary particle 1.

[0063] The thickness of the coating 5 can 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 can be, for example, less than 10 nm, less than 9 nm, less than 8 nm, less than 7 nm, less than 6 nm or less.

[0064] The mass fraction of the coating 5 relative to the mass of the positive electrode active material (olivine-type phosphate compound) can be 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, or 4% or more. The mass fraction of the coating 5 relative to the mass of the positive electrode active material can be less than 5%, less than 4%, or less than 3%.

[0065] Primary particle 1 contains an olivine-type phosphate compound. "Olivine-type" indicates a crystal structure belonging to space group Pnma. The space group can be determined by powder X-ray diffraction (XRD) measurements. Primary particle 1 can also be a single-phase compound, for example. It is sufficient that primary particle 1 contains an olivine-type crystalline phase; it can also contain phases belonging to other space groups. Primary particle 1 can also contain, for example, an amorphous phase.

[0066] The CF3 group was detected by XPS of the positive electrode active material. That is, the coating 5 contains carbon, and the carbon exists at least as a CF3 group. In the coating 5, the carbon can exist in the form of C=O bond, COH bond, COC bond, CH bond, and CC bond. In the Cs1 spectrum obtained by XPS (binding energy 280-296 eV), when the intensity of the peak corresponding to trifluoromethyl (CF3 group) (binding energy around 292.0 eV) is set as I(CF3), and the intensity of the peaks corresponding to CH bond and CC bond (binding energy around 285.0 eV) is set as I(C), the following relationship is satisfied: 0.01≤I(CF3) / I(C) (1).

[0067] In the "I(CF3) / I(C)" of formula (1), the amount of carbon present in the coating 5 as CF3 groups is reflected in I(CF3), and the amount of carbon present as CH or CC bonds is reflected in I(C). That is, "I(CF3) / I(C)" can be used as an indicator of the proportion of carbon (C) present in the coating 5 as trifluoromethyl (CF3 groups). For example, if a portion of the COH group is modified to become a CO-CO-CF3 group, comparing the values ​​before and after modification, although there is no difference in the value of I(C), the value of I(CF3) increases, and "I(CF3) / I(C)" increases. In addition, for example, if a portion of the COH group is modified to become CO-CO-CF3, an increase in "I(CF3) / I(C)" means that the proportion of carbon present as COH is smaller. A smaller proportion of carbon present as COH means fewer OH groups. The OH group has the function of adsorbing water molecules, and the water molecules adsorbed on the OH group can be a cause of degradation of the positive electrode active material. "I(CF3) / I(C)" can be 0.02 or higher. In addition, "I(CF3) / I(C)" can be 0.3 or lower, 0.2 or lower, or 0.1 or lower.

[0068] By satisfying the relationship in equation (1), a portion of the carbon present in the coating 5 exists as CF3 groups, or a small proportion of carbon exists as COH, which can suppress the degradation of the positive electrode active material. By using such a positive electrode active material in the battery, an improvement in the battery's capacity retention rate can be expected.

[0069] After the positive electrode active material is fully dried, the amount of adsorbed water after being placed in an environment of 23°C and 50% relative humidity for 24 hours is preferably less than 1900 ppm. The amount of adsorbed water is a value calculated by the Karl Fischer method. Satisfying the relationship of the above formula (1) can be used as an indicator of the low number of OH groups present on the surface of the coating 5, and it is expected that the amount of adsorbed water in the positive electrode active material in the battery will be reduced, thereby suppressing the degradation of the positive electrode active material. The amount of adsorbed water can be, for example, less than 1000 ppm, less than 900 ppm, less than 800 ppm, or less than 700 ppm. The amount of adsorbed water can be, for example, more than 1 ppm, more than 10 ppm, or more than 100 ppm.

[0070] Olivine-type phosphate compounds may contain at least one selected from lithium manganese iron phosphate (LMFP), lithium manganese phosphate (LMP), and lithium iron phosphate (LFP). Olivine-type phosphate compounds may also have compositions represented by the following general formula, for example.

[0071] Li 1-a Mn 1-x Fe x PO4

[0072] For example, the relationship "-0.5 ≤ a ≤ 0.5" can also be satisfied. x can be greater than 0, greater than 0.05, greater than 0.1, greater than 0.2, greater than 0.3, greater than 0.4, greater than 0.5, greater than 0.6, greater than 0.7, greater than 0.8, or greater than 0.9. x can also be less than 1, less than 1, less than 0.9, less than 0.8, less than 0.7, less than 0.6, less than 0.5, less than 0.4, less than 0.3, less than 0.2, or less than 0.1.

[0073] Elements other than lithium (Li), Mn, Fe, phosphorus (P), and oxygen (O) (dopants) can be doped into LMFP, LMP, and LFP. The doping amount (mass fraction relative to the amount of Li) can be, for example, 0.01 to 0.1. The dopant may include, for example, at least one selected from boron (B), nitrogen (N), halogen, silicon (Si), sodium (Na), magnesium (Mg), aluminum (Al), chromium (Cr), scandium (Sc), titanium (Ti), vanadium (V), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), selenium (Se), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), lead (Pb), bismuth (Bi), antimony (Sb), tin (Sn), tungsten (W), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and actinides.

[0074] The positive electrode active material may contain at least one selected from LMFP, LMP, and LFP as a main component, and may further contain other components. As the other components, for example, lithium nickel composite oxide (LNO), lithium cobalt composite oxide (LCO), lithium manganese composite oxide (LMO), etc. may be contained. When the positive electrode active material contains LMFP, the mixing ratio (mass ratio) of LMFP to 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 powders of LMFP and other components.

[0075] LMP may have a composition represented by, for example, the general formula "Li 1-a MnPO4 (-0.5 ≤ a ≤ 0.5)". LFP may have a composition represented by, for example, the general formula "Li 1-a FePO4 (-0.5 ≤ a ≤ 0.5)".

[0076] LNO may have a crystal structure belonging to the space group R-3m. For example, LNO may have a composition represented by the following general formula.

[0077] Li 1-a Ni x M 1-x O2

[0078] In the formula, the relationship of -0.5 ≤ a ≤ 0.5 and 0 ≤ x ≤ 1 is satisfied. For example, M may contain at least one selected from 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 ≤​​​​​​​​​​​​​​​​​​Ni x Co y Mn z O2

[0082] 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 relationships 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 can be satisfied. For example, the relationships 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 can be satisfied. For example, the relationships 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 can be satisfied.

[0083] NCM may include, for example, selected from LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co0.1 Mn 0.3 O2, 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 at least one of O2.

[0084] LNO can be represented, for example, by the following general formula. The compound represented by the following general formula may also be referred to as "NCA".

[0085] Li 1-a Ni x Co y Al z O2

[0086] 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 relationships 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 can be satisfied. For example, the relationships 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 can be satisfied. For example, the relationships 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 can be satisfied.

[0087] NCA may contain, for example, selected from LiNi 0.7 Co 0.1 Al 0.2 O2, LiNi 0.7 Co 0.2 Al 0.1 O2, LiNi 0.8 ]>Co 0.1 Al 0.1 O2, LiNi 0.8 sion Co 0.17 Al0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and LiNi 0.9 Co 0.05 Al 0.05 At least one of O2.

[0088] <Methods for Manufacturing Positive Electrode Active Materials>

[0089] Figure 2 This is a simplified flowchart illustrating the method for manufacturing the positive electrode active material in this embodiment. Hereinafter, "the method for manufacturing the positive electrode active material in this embodiment" will sometimes be simply referred to as "this method". The method for manufacturing the positive electrode active material in this embodiment may also include a first step and a second step. The first step may include, for example, steps such as "(a) slurry formation", "(b) granulation", and "(c) calcination".

[0090] Process 1

[0091] (a) Formation of slurry

[0092] This method may involve forming a slurry, for example, by mixing lithium compounds, manganese compounds, iron compounds, phosphoric acid compounds, carbon sources, and solvents. For example, it may be possible to form a slurry with the composition "Li". 1-a Mn 1-x Fe x The lithium compound, manganese compound, phosphoric acid compound, and iron compound are weighed according to the composition ratio (mass ratio) shown in "PO4(-0.5≤a≤0.5、0≤x≤1)". Examples of lithium compounds include lithium carbonate and lithium hydroxide. Examples of manganese compounds include manganese carbonate. Examples of phosphoric acid compounds include phosphoric acid and lithium dihydrogen phosphate. Examples of iron compounds include ferric oxalate and ferric (III) phosphate.

[0093] A carbon source is a raw material containing carbon that adheres to the surface of primary particles. Carbon sources can include, for example, sugars and organic acids. Examples of carbon sources include glucose, sucrose, fructose, citric acid, and lactic acid. The amount of carbon source added relative to the raw material mixture, by mass fraction, is, for example, 1 to 20%. The carbon source can also be added after the raw material mixture using other raw materials has been formed into granules. In this case, the amount of carbon source added relative to the granules, by mass fraction, is also, for example, 1 to 20%.

[0094] Solvents may include, for example, water. The concentration of solids in the slurry, expressed as a mass fraction, may be, for example, 20-40%.

[0095] The particle size in the slurry can also be adjusted by performing wet milling. For example, wet milling can be performed with a D50 of 0.10~1μm.

[0096] (b) Granulation

[0097] This method may also include, for example, the step of granulating a dried slurry to form secondary particles. For instance, secondary particles can also be formed by spray drying. The secondary particles formed through the granulation operation are also referred to as "granules." In other words, secondary particles can also be called granules.

[0098] (c) Firing

[0099] This method can also involve generating olivine-type phosphate compounds by heat treatment of secondary particles. Any heat treatment furnace (e.g., electric furnace, muffle furnace, etc.) can be used. The heat treatment atmosphere can be, for example, an inactive atmosphere, such as a nitrogen atmosphere. The heat treatment temperature can be, for example, 400–700°C. The heat treatment time can be, for example, 1–6 hours.

[0100] The resulting olivine-type phosphate compound is used as a precursor particle. The precursor particle comprises a primary particle and a carbon layer. The primary particle comprises 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 to contain carbon that has formed a COH bond. That is, the carbon layer preferably has hydroxyl groups.

[0101] (Step 2)

[0102] The second step manufactures the positive electrode active material by reacting the precursor particles prepared in the first step with a trifluoromethyl source. In this step, a reaction occurs where the hydroxyl groups contained in the carbon layer of the precursor particles are modified by the trifluoromethyl source. The trifluoromethyl source is not limited as long as it contains a trifluoromethyl group, and may also contain a trifluoroacetyl group. Examples of trifluoromethyl sources include trifluoroacetic acid and trifluoroacetic anhydride. Examples of the second step include, for instance, exposing the precursor particles and trifluoroacetic acid to a heating environment, causing the volatile trifluoroacetic acid to react with the precursor particles.

[0103] The second step allows the introduction of trifluoromethyl groups into the carbon layer. Furthermore, the second step reduces the number of hydroxyl groups in the carbon layer. When the carbon layer contains hydroxyl groups as COH groups, at least a portion of them can be modified by trifluoromethyl groups to become CO-CO-CF3 groups.

[0104] Following the second step, a drying process can be performed on the obtained positive electrode active material. This drying process evaporates and removes any remaining 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, or 200°C or lower, 150°C or lower, or 120°C or lower. When using trifluoroacetic acid (boiling point: 72.4°C) as the trifluoromethyl source, 72.4°C or higher is preferred. The drying process can also be performed by vacuum drying. This produces a positive electrode active material containing primary particles and a coating. The coating has trifluoromethyl groups.

[0105] In the manufacturing method, the content of trifluoromethyl groups in the coating of the positive electrode active material obtained in the second step is greater than the content of trifluoromethyl groups in the carbon layer of the precursor particles obtained in the first step.

[0106] <Battery>

[0107] In some embodiments, the battery has a unipolar structure. In some embodiments, the battery has a bipolar structure. As an example, a battery with a bipolar structure (bipolar battery) is described.

[0108] Figure 3 This is a schematic perspective view of the battery according to this embodiment. Figure 4 It is along Figure 3 A schematic cross-sectional view of line IV-IV in the diagram. Hereinafter, "direction in plane" refers to the normal direction relative to the surface of the sheet-like component (e.g., foil, electrode, etc.). "In-plane direction" refers to any direction orthogonal to the direct direction in plane. Figure 4 In this context, the Z-axis direction corresponds to the plane's perpendicular direction. The X-axis and Y-axis directions are examples of in-plane directions.

[0109] The battery 100 includes a casing 90 and a power generation element. The power generation element is housed within the casing 90. The casing 90 may, for example, include a first current collector 91, a first laminate 92, a second laminate 93, and a second current collector 94. The ends of the first laminate 92 and the second laminate 93 are joined together in the in-plane direction. A sealing material (not shown) may also be sandwiched between the first laminate 92 and the second laminate 93 at the joint.

[0110] The first current collector plate 91 and the second current collector plate 94 are joined to the power generation element at their ends in the lamination direction (Z-axis direction). A first laminate 92 is joined to the first current collector plate 91. A second laminate 93 is joined to the second current collector plate 94. A sealing material (not shown) may also be sandwiched between the current collector plate and the laminate at the joint.

[0111] The power generation element comprises multiple bipolar electrodes. These multiple bipolar electrodes are stacked in the plane (Z-axis direction). Each of the multiple bipolar electrodes sequentially comprises a positive electrode layer 11, a current collector foil 13, and a negative electrode layer 12 in the plane. In the in-plane direction (e.g., the X-axis direction), the current collector foil 13 extends outward compared to the positive electrode layer 11 and the negative electrode layer 12. For example, the current collector foil 13 may extend outward compared to the positive electrode layer 11 and the negative electrode layer 12 throughout the entire in-plane direction.

[0112] The current collector foil 13 is a conductor. The current collector foil 13 may also contain, 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. A carbon material may also be coated on the surface of the current collector foil 13. The carbon material may include, for example, carbon black.

[0113] The power generation element includes a sealing material 30. At its in-plane end, the sealing material 30 is bonded to the current collector foil 13. The sealing material 30 may also be thermally fused to the current collector foil 13. Alternatively, the sealing material 30 may be disposed along the entire periphery in the in-plane direction. The sealing material may also contain, for example, a resin material. The sealing material 30 seals adjacent current collector foils 13 in the vertical direction. By sealing the current collector foils 13 with the sealing material 30, battery cells are defined. A battery cell is the smallest unit of the power generation element. Since the battery 100 contains multiple battery cells, it can also be called a "bipolar module." The multiple battery cells are individually sealed. The multiple battery cells are isolated from each other. Each of the multiple battery cells includes a positive electrode layer 11, a separator 20, a negative electrode layer 12, and an electrolyte.

[0114] Positive electrode layer

[0115] The positive electrode layer 11 is attached to one side of the current collector foil 13. For example, a groove may be formed on the positive electrode layer 11. The positive electrode layer 11 may also be formed in a stripe shape, for example. The positive electrode layer 11 contains a positive electrode active material. That is, the electrode contains a positive electrode active material. Details of the positive electrode active material are as described above.

[0116] In addition to the positive electrode active material, the positive electrode layer 11 may further include, for example, conductive materials and binders. The amount of conductive material relative to 100 parts by mass of the positive electrode active material may be, for example, 0.1 to 10 parts by mass. The conductive material may contain any components. The conductive material may contain at least one selected from, for example, graphite, acetylene black (AB), Ketjen black (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene sheets (GF).

[0117] The amount of binder relative to 100 parts by weight of the positive electrode active material can be, for example, 0.1 to 10 parts by weight. The binder can contain any components. The binder may contain at least one selected from, for example, polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ethers, and their derivatives.

[0118] The positive electrode layer 11 may further include, for example, inorganic fillers, organic fillers, solid electrolytes, surface modifiers, dispersants, lubricants, flame retardants, protective agents, fluxes, coupling agents, adsorbents, etc. The positive electrode layer may also include, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, silane coupling agents, MoS2, WO3, etc.

[0119] negative electrode layer

[0120] The negative electrode layer 12 is attached to one side 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 contains a negative electrode active material.

[0121] The negative electrode active material can be in particulate or sheet form. The D50 of the negative electrode active material can be, for example, 1 μm or more, 5 μm or more, or 10 μm or more. The D50 of the negative electrode active material can also be, for example, less than 30 μm, less than 20 μm, less than 15 μm, or less than 10 μm.

[0122] The negative electrode active material can contain any components. For example, it can contain at least one selected from carbon-based active materials, alloy-based active materials, Si-C composite materials, Li metal, Li-based alloys, and lithium titanate. In some embodiments, the battery can be a Li metal negative electrode battery.

[0123] Carbon-based active materials may contain at least one of, for example, graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. Graphite can 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".

[0124] The surface of graphite can be covered, for example, with amorphous carbon. The surface of graphite can also be covered, for example, with a dissimilar material. The dissimilar material can include, for example, at least one selected from P, W, Al, and O. The dissimilar material can also include, for example, at least one selected from Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO3, and Li3PO4.

[0125] The alloy-based active material may contain at least one selected from, for example, Si, lithium silicate, SiO, Si-based alloy, tin (Sn), SnO, and Sn-based alloy.

[0126] SiO may have, for example, a composition represented by the following general formula.

[0127] SiOx

[0128] In the formula, the relationship of "0 < x < 2" is satisfied, for example, and the relationship of "0.5 ≤ x ≤ 1.5" or "0.8 ≤ x ≤ 1.2" may be satisfied.

[0129] "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 also be dispersed in carbon particles. For example, Si fine particles may also be dispersed in graphite particles. For example, lithium silicate particles may be covered with a carbon material (such as amorphous carbon).

[0130] Separator

[0131] 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, for example, at least one selected from a resin film (polymer film), an inorganic particle layer, and an organic particle layer. The separator 20 may also contain, for example, a resin film and an inorganic particle layer.

[0132] The resin film is porous. The resin film may also contain, for example, a microporous membrane, non-woven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may also be continuously reticulated, for example. Fine pores are formed in the gaps of the resin skeleton. The resin film can allow the electrolyte to pass through. The resin film has an average pore diameter of 1 μm or less, for example. The average pore diameter of the resin film may also be 0.01 - 1 μm or 0.1 - 0.5 μm. The "average pore diameter" can be measured by the mercury intrusion method. The Gray Value of the resin film may be 50 - 250 s / 100 cm 3 . The "Gray Value" can be measured by the Gray test method.

[0133] The resin film may contain at least one selected from, for example, olefin-based resins, polyurethane-based resins, polyamide-based resins, cellulose-based resins, polyether-based resins, acrylic-based resins, and polyester-based resins, etc. The resin film may include at least one selected from, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and their derivatives. The resin film can be formed by, for example, a stretching method, a phase separation method, etc. The thickness of the resin film may also be 5 - 50 μm or 10 - 25 μm.

[0134] The resin membrane can also have a single-layer structure, for example. The resin membrane can also be composed of a PE layer. The framework of the PE layer is formed of PE. The PE layer can have a sealing function. The resin membrane can also have a multi-layer structure, for example. The resin membrane can include a PP layer and a PE layer. The framework of the PP layer is formed of PP. The resin membrane can also have a three-layer structure, for example. The resin membrane can also be formed by sequentially stacking a PP layer, a PE layer, and another PP layer. The thickness of the PE layer can also be, for example, 5~20 μm. The thickness of the PP layer can also be, for example, 3~10 μm.

[0135] Inorganic particle layers can also be formed on the surface of the resin membrane. The inorganic particle layer can be formed on only one side of the resin membrane or on both sides. The inorganic particle layer can be formed on the surface opposite to the positive electrode layer 11 or on the surface opposite to the negative electrode layer 12. Furthermore, the inorganic particle layer can be formed on the surface of the positive electrode layer 11 or on the surface of the negative electrode layer 12.

[0136] The inorganic particle layer is porous. It contains inorganic particles, which can also be called "inorganic fillers." Fine pores are formed between the inorganic particles. The thickness of the inorganic particle layer can be, for example, 0.5–10 μm or 1–5 μm. The inorganic particles may contain heat-resistant materials. An inorganic particle layer containing heat-resistant materials is also called a "HRL (Heat Resistance Layer)." The inorganic particles may contain at least one selected from boehmite, alumina, zirconium oxide, titanium dioxide, magnesium oxide, and silicon dioxide. The inorganic particles can have any shape. For example, they can be spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the inorganic particles can be, for example, 0.1–10 μm or 0.5–3 μm. The inorganic particle layer may also contain a binder. The binder may contain at least one selected from, for example, acrylic resins, polyamide resins, fluorinated resins, aromatic polyether resins, and liquid crystal polyester resins.

[0137] The diaphragm 20 may, for example, contain an organic particle layer. The diaphragm 20 may, for example, contain an organic particle layer instead of a resin membrane. The diaphragm 20 may, for example, contain an organic particle layer instead of an inorganic particle layer. The diaphragm 20 may simultaneously contain a resin membrane and an organic particle layer. The diaphragm 20 may simultaneously contain an inorganic particle layer and an organic particle layer. The diaphragm 20 may also contain a resin membrane, an inorganic particle layer, and an organic particle layer.

[0138] The thickness of the organic particle layer can be, for example, 0.1~50 μm, 0.5~20 μm, 0.5~10 μm, or 1~5 μm. The organic particle layer contains organic particles. Organic particles can also be referred to as "organic fillers." Organic particles can contain heat-resistant materials. Organic particles can contain at least one material selected from, for example, PE, PP, PTFE, PI, PAI, PA, and aromatic polyamides. Organic particles can be, for example, spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the organic particles can also be, for example, 0.1~10 μm or 0.5~3 μm.

[0139] The membrane 20 may also include a hybrid layer, for example. The hybrid layer contains both inorganic and organic particles.

[0140] electrolyte

[0141] The electrolyte is a liquid electrolyte. It contains a solute and a solvent. The concentration of the solute is, for example, 0.5–1 mol / L, 1–1.5 mol / L, 1.5–2 mol / L, 2–2.5 mol / L, or 2.5–3 mol / L. Sometimes "mol / L" is also designated as "M". The solute contains a supporting salt (supporting electrolyte, Li salt). Solutes can include, for example, inorganic acid salts, imide salts, oxalate complexes, halides, etc. The solute may also contain at least one of, for example, selected from 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 their derivatives.

[0142] The electrolyte may contain, for example, carbonate solvents. The solvent may contain, for example, cyclic carbonates, chain carbonates, fluorinated carbonates, etc. The solvent may contain at least one selected from, for example, ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene monofluorocarbonate (FEC), difluoroethylene carbonate, 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene carbonate, monofluoropropylene carbonate, difluoropropylene carbonate, and their derivatives.

[0143] The solvent can contain cyclic carbonates (EC, PC, FEC, etc.) and chain carbonates (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates to chain carbonates can 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".

[0144] The solvent may contain cyclic carbonates (EC, PC, etc.) and fluorinated cyclic carbonates (FEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates to fluorinated cyclic carbonates may be, for example, "cyclic carbonate / fluorinated cyclic carbonate = 99 / 1 to 90 / 10", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 1 / 9", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 7 / 3" or "cyclic carbonate / fluorinated cyclic carbonate = 3 / 7 to 1 / 9".

[0145] Solvents may include, for example, EC, FEC, EMC, DMC, and DEC. The volume ratios of the components may satisfy, for example, the relationship shown in the following formula.

[0146] V EC +V FEC +V EMC +V DMC +V DEC =10

[0147] In the formula V EC V FEC V EMC V DMC V DEC Let V represent the volume ratios of EC, FEC, EMC, DMC, and DEC, respectively. These must satisfy the condition 1 ≤ V. EC ≤4”, 0≤V FEC ≤3”, V EC +V FEC ≤4”、

[0148] “0≤V EMC ≤9”, 0≤V DMC ≤9”, 0≤V DEC ≤9” and “6≤V” EMC +V DMC +V DEC The relationship is ≤9".

[0149] For example, satisfying "1≤V" EC ≤2” or “2≤V” EC The relationship is ≤3".

[0150] For example, satisfying "1≤V" FEC ≤2” or “2≤V” FEC The relationship is ≤4".

[0151] For example, satisfying "3≤V" EMC ≤4” or “6≤V” EMC The relationship is ≤8".

[0152] For example, satisfying "3≤V" DMC ≤4” or “6≤V” DMC The relationship is ≤8".

[0153] For example, satisfying "3≤V" DEC ≤4” or “6≤V” DEC The relationship is ≤8".

[0154] The solvent, for example, has a composition in volume ratios 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".

[0155] The electrolyte may also contain ether-based solvents. The electrolyte may contain at least one selected from, for example, tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), hydrofluoroether (HFE), ethylene glycol diethyl ether, triethylene glycol dimethyl ether (triglyme), tetraethylene glycol dimethyl ether (trtraglyme), and their derivatives.

[0156] The electrolyte may contain any additives. The amount added (as a percentage of the total mass of the electrolyte) may be, for example, 0.01–5%, 0.05–3%, or 0.1–1%. 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.

[0157] As an additive, it may contain, for example, those selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propanesulfonate lactone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), vinyl sulfate (ES), propanesulfonate lactone (PS), vinyl sulfite (DTD), γ-butyrolactone, phosphazene compounds, and carboxylic acid esters [e.g., methyl formate (MF), methyl acetate (MA), etc.]. Methyl malonate (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.), benzene-chloroform (e.g., benzene-chloroform, 2-fluorobenzene-chloroform, 3-fluorobenzene-chloroform, 4-fluorobenzene-chloroform, 2-methylbenzene-chloroform, 3-methylbenzene-chloroform, 4-methylbenzene-chloroform, etc.), fluoroxylenes (e.g., 3-fluoroo-xylene, 4-fluoroo-xylene, 2-fluorom-xylene, 5-fluorom-xylene). The following are included in the following categories: benzene, sulfur-containing heterocyclic compounds (e.g., benzothiazole, 2-methylbenzothiazole, tetrathiofulvalene, etc.), nitrile compounds (e.g., adiponitrile, succinate, etc.), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate, etc.), carboxylic anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, etc.), alcohols (e.g., methanol, ethanol, n-propanol, ethylene glycol, diethylene glycol monomethyl ether, etc.), and at least one of their derivatives.

[0158] The aforementioned components described as solutes and solvents can be used as trace components (additives). As additives, they may include at least one selected from, for example, LiBF4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO2F2, FSO3Li, LiI, LiBr, HFE, DOX, PC, FEC, and their derivatives.

[0159] The electrolyte may contain ionic liquids. Ionic liquids may contain at least one selected from, for example, sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidineium salts, morpholinium salts, phosphonium salts, imidazoline salts, and their derivatives.

[0160] In some embodiments of this invention, the battery may comprise a gel electrolyte. That is, the battery may also be a polymer battery. The gel electrolyte may comprise an electrolyte and a polymeric material. The polymeric material may form a polymeric matrix. The polymeric material may comprise at least one selected from, for example, PVdF, PVdF-HFP, polyacrylonitrile (PAN), PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0161] <Manufacturing of Positive Electrode Active Materials>

[0162] (No.1)

[0163] Process 1

[0164] The first step is the precursor particle manufacturing process. Lithium carbonate, manganese carbonate, ferric oxalate, and phosphoric acid are weighed to achieve the composition "Li1Mn". 0.8 Fe 0.2 The composition ratio is shown in "PO4". These raw materials were dispersed in water and slurried. The mixture was then pulverized for 30 minutes using a bead mill with beads of 0.3 mm diameter at a circumferential speed of 10 m / s, followed by calcination to obtain granules. Fructose at a mass fraction of 10% was added relative to the granules for formulation. This formulation was heated to a calcination temperature of 600°C at a heating rate of 5°C / min in a dried, inert atmosphere, held for 1 hour, and then cooled to room temperature to obtain precursor particles.

[0165] Process 2

[0166] The second step is the trifluoroacetic acid (TFA) treatment. The precursor particles obtained in the first step are spread in a petri dish, and trifluoroacetic acid (TFA) is placed in a small container (made of fluoropolymer (PFA)). The petri dish and the container containing TFA are then placed in the same jar (made of fluoropolymer (PFA)) and sealed. The temperature inside the jar is then set to 80°C and maintained for 24 hours. Through this treatment, at least a portion of the hydroxyl groups on the surface of the precursor particles are replaced with CF3 groups by the volatilized TFA. The treated precursor particles are then recovered and dried at 100°C to obtain the positive electrode active material.

[0167] (No.2)

[0168] Except for setting the firing temperature in the precursor particle manufacturing process (step 1) to 650°C, the positive electrode active material is obtained under the same conditions as No.1.

[0169] (No.3)

[0170] Instead of performing the TFA processing step No. 1 (Step 2), the precursor particles obtained under the same conditions as the precursor particle manufacturing step No. 1 (Step 1) will be used as the positive electrode active material.

[0171] (No.4)

[0172] Instead of performing the TFA processing step No.2 (Step 2), the precursor particles obtained under the same conditions as the precursor particle manufacturing step No.2 (Step 1) will be used as the positive electrode active material.

[0173] <Measurement>

[0174] (XPS measurement)

[0175] After fixing the positive electrode active materials No.1 to No.4 with carbon tape, XPS analysis was performed using the aforementioned method to obtain Cs1 spectra. Based on the obtained Cs1 spectra, the "I(CF3) / I(C)" ratio of each sample was calculated. Figure 5 The calculation results are shown.

[0176] (Measurement of adsorbed water content)

[0177] The positive electrode active materials No.1 to No.4 were spread thinly in a petri dish and placed in a standard atmosphere (temperature 23°C and relative humidity 50%) for 24 hours. The amount of adsorbed water was then measured using a Karl Fischer moisture meter. Figure 5 The measurement results are shown.

[0178] (Battery characteristics)

[0179] A lithium-ion secondary battery (button cell) was manufactured. The battery structure is as follows.

[0180] A mixture is formed by combining the positive electrode active material, conductive material (acetylene black), and binder (PVdF). The mixing ratio (mass ratio) is "positive electrode active material / conductive material / binder = 92 / 5 / 3". A paste is formed by dispersing the mixture in a solvent (N-methyl-2-pyrrolidone). The solids concentration of the paste is 50% by mass fraction. The positive electrode layer is formed by coating the paste onto the surface of an Al foil and drying it. The density of the positive electrode layer is adjusted to 1.8 g / cm³ using a rolling mill. 3 This process forms the positive electrode plate. The positive electrode plate material is then subjected to vacuum drying at 120°C for 12 hours. After drying, a disc sample (diameter: 14mm) is removed from the positive electrode plate through punching.

[0181] Button batteries were assembled inside the glove box. The battery configuration is as follows.

[0182] Working electrode: Disk-shaped sample (positive electrode)

[0183] Counter electrode: Li foil

[0184] Diaphragm: Porous polymer membrane

[0185] Electrolyte: "EC / DMC = 3 / 7 (volume ratio)", LiPF6 (1 mol / L)

[0186] The 1C capacity of the obtained button cell was calculated based on the discharge capacity estimated from the coating weight. "C" is the symbol for the rate of current flow (time rate). At a 1C rate, the theoretical capacity is achieved over 1 hour. After CCCV charging at 25°C with a charging rate of 0.1C, an upper limit voltage of 4.3V, and a charging termination condition of 0.01C, the 0.1C discharge capacity at a discharge termination potential of 3V was calculated (as the "first discharge capacity"). The cell was then fully charged again, and then kept at 60°C for 14 days. The 0.1C discharge capacity was calculated again (as the "second discharge capacity"). The capacity retention rate was calculated as (second discharge capacity / first discharge capacity) × 100%. Figure 5 The capacity retention rate is shown. It is assumed that a higher capacity retention rate indicates better durability.

[0187] <Results>

[0188] like Figure 5 As shown, under the conditions of this disclosure, a tendency for high capacity maintenance can be observed. Furthermore, as... Figure 5 As shown, under the conditions of this disclosure, it can be seen that the amount of water in the atmosphere tends to decrease after exposure.

Claims

1. A positive electrode active material, characterized in that, Includes primary particles and coating. The primary particles contain olivine-type phosphate compounds. The coating covers at least a portion of the surface of the primary particles. The coating contains carbon. Trifluoromethyl was detected by X-ray photoelectron spectroscopy.

2. The positive electrode active material as described in claim 1, characterized in that, In the Cs1 spectrum obtained by X-ray photoelectron spectroscopy, when the intensity of the peak corresponding to the trifluoromethyl group is set as I(CF3) and the intensity of the peaks corresponding to the C-C and CH bonds is set as I(C), the following relationship (1) is satisfied: 0.01≤I(CF3) / I(C) (1).

3. The positive electrode active material as described in claim 1, characterized in that, The coating has trifluoromethyl groups.

4. The positive electrode active material as described in claim 1, characterized in that, After being placed in an environment with a temperature of 23°C and a relative humidity of 50% for 24 hours, the amount of water adsorbed is less than 1900 ppm.

5. The positive electrode active material as described in claim 1, characterized in that, Secondary particles are a collection of primary particles.

6. The positive electrode active material as described in claim 1, characterized in that, The olivine-type phosphate compound contains at least one selected from lithium manganese iron phosphate, lithium manganese phosphate, and lithium iron phosphate.

7. The positive electrode active material as described in claim 2, characterized in that, The ratio of I(CF3) / I(C) is below 0.

3.

8. The positive electrode active material as described in claim 7, characterized in that, The I(CF3) / I(C) ratio is below 0.

1.

9. The positive electrode active material as described in claim 4, characterized in that, The amount of water adsorbed is above 1 ppm.

10. The positive electrode active material as described in claim 9, characterized in that, The amount of adsorbed water is below 700 ppm.

11. A battery, characterized in that, It contains the positive electrode active material as described in any one of claims 1 to 10.

12. The battery as claimed in claim 11, characterized in that, It has a bipolar structure.

13. A method for manufacturing a positive electrode active material, characterized in that, It includes the following processes: Prepare precursor particles, and The positive electrode active material is manufactured by reacting the precursor particles with a trifluoromethyl source. The positive electrode active material is any one of claims 1 to 10.

14. The method for manufacturing the positive electrode active material as described in claim 13, characterized in that, The trifluoromethyl source is trifluoroacetic acid.

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