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

Abstract

A positive electrode active material including a plurality of secondary particles, each of the plurality of secondary particles including a plurality of primary particles, each of the plurality of primary particles including an olivine-type phosphate compound, carbon and lithium phosphate being adhered to at least a part of a surface of the secondary particles, in a cross section of the secondary particle, the secondary particle is configured from a central portion, an intermediate portion, and an outer peripheral portion, and satisfies the relationship 1.05 < = CLPO / XLPO, the CLPO representing the amount-of-substance concentration of the lithium phosphate in the outer peripheral portion, and the XLPO representing the average value of the amount-of-substance concentration of the lithium phosphate in the central portion, the intermediate portion, and the outer peripheral portion.

Description

Positive electrode active material, battery, and manufacturing method of positive electrode active material 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. 2019-175764 discloses a positive electrode material for lithium-ion secondary batteries made by covering the surface of an olivine-type phosphate compound with carbon. Summary of the Invention

[0003] Olivine-type phosphate compounds have been developed as positive electrode active materials. Previously, a scheme to improve electronic conductivity by coating olivine-type phosphate compounds with carbon was proposed. However, there is still room for improvement in durability.

[0004] The purpose of this disclosure is to improve durability.

[0005] The technical solution and effects of this disclosure are described below. However, the mechanism of action of this disclosure includes conjecture. The mechanism of action does not limit the technical scope of this disclosure.

[0006] [1] A positive electrode active material,

[0007] The positive electrode active material contains multiple secondary particles.

[0008] Each of the plurality of secondary particles comprises a plurality of primary particles.

[0009] Each of the plurality of said primary particles contains an olivine-type phosphate compound.

[0010] At least a portion of the surface of the secondary particles is coated with carbon and lithium phosphate.

[0011] In the cross-section of the secondary particle, the secondary particle is composed of a central part, a middle part, and an outer peripheral part.

[0012] Satisfying 1.05 ≤ C LPO / X LPO Relationship,

[0013] The C LPO This indicates the molar concentration of lithium phosphate in the outer periphery.

[0014] The X LPO This represents the average molar concentration of lithium phosphate in the central portion, the middle portion, and the outer periphery.

[0015] It is believed that when only carbon is attached to the surface of secondary particles, the olivine-type phosphate compounds contained in the secondary particles deteriorate with charge-discharge cycles, thereby promoting capacity degradation. That is, sufficient durability may not be obtained.

[0016] In addition to carbon, lithium phosphate (Li3PO4, hereinafter referred to as "LPO") is attached to the surface of the secondary particles of this disclosure. Furthermore, carbon and LPO are attached not only to the surface but also to the interior of the secondary particles. It is considered that the molar concentration of LPO on the surface of the secondary particles is greater than the molar concentration of LPO inside the secondary particles, especially when 1.05 ≤ C LPO / X LPO Under certain conditions, the degradation of olivine-type phosphate compounds contained in secondary particles can be suppressed. That is, an improvement in durability can be expected.

[0017] [2] According to the positive electrode active material recorded in [1],

[0018] Satisfying 1.5≤C LPO / X LPO The relationship.

[0019] By satisfying 1.5≤C LPO / X LPO Given this relationship, we can expect even greater improvements in durability.

[0020] [3] According to the positive electrode active material described in [1] or [2],

[0021] Satisfy C LPO / X LPO Relationships ≤7.0.

[0022] C LPO / X LPO The larger the value, the more likely improvements in durability can be expected. On the other hand, in C... LPO / X LPO In large cases, there is a tendency for the specific capacity to decrease. This can be addressed by satisfying C. LPO / X LPO A value of ≤7.0 allows for a balance between durability and specific capacity.

[0023] [4] Based on any of the positive electrode active materials described in [1] to [3],

[0024] Satisfy C LPO / X LPO A relationship of ≤4.5.

[0025] By satisfying C LPO / X LPO A value of ≤4.5 allows for a better balance between durability and specific capacity.

[0026] [5] According to any one of the positive electrode active materials recorded in [1]~[4],

[0027] Satisfy C LPO / X LPO Relationships ≤3.0.

[0028] [6] Based on any of the positive electrode active materials described in [1] to [5],

[0029] The surface of the secondary particle includes a first attachment portion and a second attachment portion.

[0030] Carbon is attached to the first attachment portion.

[0031] Carbon and lithium phosphate are attached to the second attachment portion.

[0032] [7] According to any one of the positive electrode active materials described in [1] to [6],

[0033] The olivine-type phosphate compound is lithium manganese iron phosphate.

[0034] [8] A battery comprising the positive electrode active material described in any one of [1] to [7].

[0035] [9] The battery described in [8] has a bipolar structure.

[0036]

[10] A method for manufacturing a positive electrode active material includes the following steps:

[0037] Step (a): The first slurry is formed by mixing a manganese compound, a first lithium compound, a first phosphate compound, a carbon material, and a first solvent;

[0038] Step (b): Precursor particles are formed by drying the first slurry;

[0039] Step (c): The first particle is formed by heat treatment of the precursor particles;

[0040] Step (d): forming a second slurry by mixing the first particle, the second lithium compound, the second phosphate compound, and the second solvent; and

[0041] Step (e): The second particle is produced by drying the second slurry.

[0042] By following the manufacturing process described in

[10] above, it is expected that the positive electrode active material described in [1] above can be manufactured.

[0043]

[11] According to the method for manufacturing the positive electrode active material described in

[10] ,

[0044] The concentration of the second lithium compound in the second slurry is greater than 0.1% and less than 0.5% by mass fraction.

[0045] The concentration of the second phosphate compound in the second slurry is greater than 0.3% and less than 1.5% by mass fraction.

[0046] The following describes one embodiment (hereinafter referred to as "this embodiment") and one example of this disclosure (hereinafter referred to as "this example"). However, this embodiment and this example do not limit the technical scope of this disclosure. This embodiment and this example are illustrative in all respects. This embodiment and this example are non-limiting. The technical scope of this disclosure includes all modifications within the meaning and scope equivalent to the claims. For example, it is intended from the outset to include any solutions extracted from this embodiment and to combine them arbitrarily.

[0047] The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the invention, which will be understood in conjunction with the accompanying drawings. Attached Figure Description

[0048] Figure 1 shows C LPO and X LPO A conceptual diagram of the determination method.

[0049] Figure 2 is a conceptual diagram of the area near the outermost surface of the secondary particle in this embodiment.

[0050] Figure 3 is a schematic flowchart illustrating the method for manufacturing the positive electrode active material according to this embodiment.

[0051] Figure 4 is a schematic perspective view of the battery according to this embodiment.

[0052] Figure 5 is a schematic cross-sectional view along line VI-VI in Figure 4.

[0053] Figure 6 is a table showing the manufacturing conditions and experimental results of the positive electrode active material in the embodiments.

[0054] Figure 7 shows the temperature curve during firing. Detailed Implementation

[0055] <Terminology and Phrases>

[0056] "Possessing," "Including," "Having," and their variations are open-ended expressions. Structures expressed in an open-ended manner may include additional elements besides the necessary ones, or they may not include additional elements. The statement "Composed of..." is a closed-ended expression. However, even structures expressed in a closed-ended manner may include usually accompanying impurities and additional elements unrelated to the target technology. The statement "Substantially composed of..." is a semi-closed-ended expression. In structures expressed in a semi-closed manner, it is permissible to add elements that do not substantially affect the basic and new characteristics of the target technology.

[0057] The expressions "maybe" and "can" are not used in an obligatory sense (meaning "must do this"), but rather in a permissive sense (meaning "this possibility exists").

[0058] Unless otherwise specified, the order in which the various steps, actions, and operations involved in a method are executed is not limited to the order in which they are recorded. For example, multiple steps can be performed simultaneously. Or, multiple steps can be performed sequentially.

[0059] The use of terms like "first," "second," etc., is solely for distinguishing multiple elements from one another. This use makes no distinction regarding the elements to which they are attached. For example, it is unrelated to the order or importance of the elements to which they are attached.

[0060] For example, the expression "at least one of A and B" includes "A or B" as well as "A and B". "At least one of A and B" can also be written as "A and / or B".

[0061] Geometric terms should not be interpreted strictly. Examples of geometric terms include "parallel," "perpendicular," and "orthogonal." For instance, directions, angles, and distances can also be relative displacements within a range where substantially the same or similar functions can be achieved. Geometric terms can also encompass tolerances and errors in design, operation, and manufacturing. Dimensional relationships in drawings sometimes differ from actual dimensional relationships. To aid understanding, dimensional relationships in drawings are sometimes altered. For example, length, width, and thickness may be changed. Sometimes, parts of the structure may be omitted.

[0062] Unless otherwise specified, elements described in the "singular form" may also include plural forms. For example, "particle" may sometimes refer to multiple particles, a collection of particles, or a powder or granular body.

[0063] Unless otherwise specified, the numerical range "m~n%" includes both an upper and lower limit. 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 represented by inequality signs "≤" and "≥" with an equal sign. "Greater than" and "less than" are represented by inequality signs "<" and ">" without an equal sign. Alternatively, a new upper or lower limit can be set by arbitrarily selecting a value from the numerical range. For example, a new numerical range can be set by arbitrarily combining values ​​from the numerical range with values ​​recorded in other parts of this specification, tables, and figures.

[0064] All numerical values ​​are modified by the term "approximately". The term "approximately" can mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​can be approximate values ​​that may vary depending on the application of the technology. All numerical values ​​can be expressed 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 are expected, the higher the reliability of the average value. The measured value can be rounded based on the number of significant figures. The measured value may include, for example, errors such as the detection limits of the accompanying measuring device.

[0065] The apparatus and software used in the determination of various values ​​are just one example. Equivalent products to the illustrated apparatus can also be used. When using equivalent products, the measurement conditions can be adjusted in conjunction with the apparatus.

[0066] C LPO and X LPO The determination is performed in the following order: Samples are prepared by embedding secondary particles (positive electrode active material) in resin. The samples are then sliced ​​using a FIB (Focused Ion Beam) or CP (Cross Section Polisher). The samples are observed using a transmission electron microscope (TEM). For ease of determination, secondary particles of a certain size can be screened out. For example, line analysis can be performed on secondary particles with a maximum Feretta diameter of 10 μm or more. Line analysis is performed using an EDS (Energy Dispersive X-ray Spectroscopy) instrument.

[0067] The magnification can be, for example, around 10,000 to 50,000 times. For example, in the case of secondary particles of about 10 μm, the magnification can be around 10,000 times. In this case, for example, it is possible to obtain a TEM image covering the range from the center to the outermost periphery of the secondary particle.

[0068] Figure 1 shows C LPO and X LPO A conceptual diagram of the measurement method. In the cross-sectional TEM image, the contour of secondary particle 1 is fitted with a minimum circumcircle. The radius of the minimum circumcircle is D. The circular portion within a distance of 1 / 3D from the center of the minimum circumcircle is considered the "center". The portion enclosed by the circle at a distance of 2 / 3D from the center of the minimum circumcircle and the minimum circumcircle is considered the "outer periphery". The portion enclosed by the center and the outer periphery is considered the "middle portion".

[0069] Line analysis is performed along the radial direction R. For example, line analysis can also be performed near the center of the smallest circumference. Alternatively, it can be performed near the outermost periphery of the smallest circumference. For example, line analysis can also be performed transversely across secondary particle 1. Line analysis can also be performed at multiple locations. For example, it can be performed at two locations. Based on the results of the line analysis, the molar concentration of LPO in each region of the central region 1a, the middle region 1b, and the outer periphery 1c is determined. The molar concentration of LPO in the central region 1a is "A". LPO The molar concentration of LPO in the middle section 1b is B. LPO The molar concentration of LPO in the peripheral region 1c is C. LPO ", A LPO B LPO and C LPO The arithmetic mean is "X LPO A LPO B LPO and C LPO It can also be the arithmetic mean of two parts.

[0070] "Maximum Feret 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 the side.

[0071] "D50" indicates the particle size at which the cumulative value in the volumetric particle size distribution (cumulative distribution) reaches 50%. The volumetric particle size distribution is determined using a laser diffraction particle size distribution measuring device.

[0072] A stoichiometric formula represents 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 can be doped into the compound. A portion of Al and O can also be replaced by other elements.

[0073] The chemical composition of a compound can be determined using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy). 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, compositional analysis is performed using an ICP-AES apparatus. For example, product names such as "PS3520UVDD II (manufactured by Hitachi High Technology Co., Ltd.)" can also be used.

[0074] "Derivative" refers to a compound that has been altered in part by at least one of the following chemical reactions: introduction of a functional group, substitution of an atom, oxidation, reduction, and others. The alteration may occur at one or more sites. "Substituents" may include, for example, at least one of the following: alkyl, alkenyl, alkynyl, cycloalkyl, unsaturated cycloalkyl, aryl, heterocyclic, halogen (F, Cl, Br, I, etc.), OH, SH, CN, SCN, OCN, nitro, alkoxy, unsaturated alkoxy, amino, alkylamino, dialkylamino, aryloxy, acyl, alkoxycarbonyl, acyloxy, aryloxycarbonyl, acylamino, alkoxycarbonyl, aminoaryloxycarbonylamino, sulfonylamino, aminosulfonyl, carbamoyl, alkylthio, arylthio, sulfonyl, sulfinyl group, urea, phosphoramide, sulfonyl, carboxyl, oxime, sulfino group, hydrazine, imino, and silyl. These substituents can be further substituted. When there are two or more substituents, the substituents can be the same or different. Multiple substituents can combine to form a ring.

[0075] <Positive Active Material>

[0076] The positive electrode active material can have any morphology. For example, it can also be in powder or granular form. The D50 of the positive electrode active material can be, for example, 1 μm or more, 2.5 μm or more, 5 μm or more, 7.5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more. Alternatively, the D50 of the positive electrode active material can be, for example, less than 50 μm, less than 40 μm, less than 30 μm, less than 20 μm, or less than 15 μm.

[0077] The positive electrode active material contains multiple secondary particles 1. Secondary particles 1 are an aggregate of primary particles. That is, secondary particles 1 contain multiple primary particles.

[0078] The maximum Ferete diameter of the secondary particle 1 can be, for example, 1 μm or more, 2.5 μm or more, 5 μm or more, 7.5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more. The maximum Ferete diameter of the secondary particle 1 can be, for example, less than 50 μm, less than 40 μm, less than 30 μm, less than 20 μm, or less than 15 μm.

[0079] Secondary particle 1 can have any shape. For example, secondary particle 1 can be spherical, rod-shaped, angular, etc. Secondary particle 1 can also have a spherical shape. By making secondary particle 1 spherical, for example, improved filling performance can be expected. The sphericity of secondary particle 1 can be 0.85 or higher, 0.90 or higher, or 0.95 or higher. The sphericity of secondary particle 1 can, for example, be less than 1, less than 0.95, or less than 0.90. "Sphericity" refers to the roundness in a TEM image or SEM (Scanning Electron Microscope) image (two-dimensional image). Sphericity (roundness) is calculated using the following formula.

[0080] ψ = 4πS / L 2

[0081] ψ: Sphericity (roundness)

[0082] π: Pi

[0083] S: Cross-sectional area of ​​secondary particle 1 (the area of ​​the region enclosed by the outline of secondary particle 1)

[0084] L: The perimeter of secondary particle 1 (the length of the outline of secondary particle 1).

[0085] Sphericity is represented by the arithmetic mean of 30 secondary particles.

[0086] Primary particles can have any shape. For example, they can be spherical, rod-shaped, angular, etc. The maximum Feret diameter of a primary particle can be, for example, 10–90 nm. The maximum Feret diameter of a primary particle 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 a primary particle can be, for example, less than 80 nm or less than 60 nm. The maximum Feret diameter of a primary particle represents the arithmetic mean of 30 primary particles.

[0087] Figure 2 is a conceptual diagram of the vicinity of the outermost surface of the secondary particle in this embodiment. Carbon and LPO are attached to at least a portion of the surface of the secondary particle 1. Alternatively, a carbon layer 2 and a lithium phosphate layer 3 may be formed independently on at least a portion of the surface of the secondary particle 1. In this case, a carbon layer 2 may be formed on at least a portion of the surface of the secondary particle 1, and a lithium phosphate layer 3 may be formed on at least a portion of the surface of the carbon layer 2. The carbon layer 2 may be formed on the entire surface of the secondary particle 1, and the lithium phosphate layer 3 may be formed on the entire surface of the carbon layer 2.

[0088] When a carbon layer 2 is formed, the thickness of the carbon layer 2 can be, for example, 1 nm or more, 5 nm or more, 10 nm or more, or 20 nm or more. The thickness of the carbon layer 2 can be, for example, less than 100 nm, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, or 50 nm or less. When a lithium phosphate layer 3 is formed, the thickness of the lithium phosphate layer 3 can be, for example, 1 nm or more, 5 nm or more, 10 nm or more, or 20 nm or more. The thickness of the lithium phosphate layer 3 can be, for example, less than 100 nm, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, or 50 nm or less. The thicknesses of the carbon layer 2 and the lithium phosphate layer 3 can be determined based on TEM images.

[0089] The amount of carbon adhering, for example, relative to secondary particle 1, can be 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, or 4% or more by mass fraction. The amount of carbon adhering, for example, relative to secondary particle 1, can be less than 5%, less than 4%, or less than 3% by mass fraction. The amount of LPO adhering, for example, relative to secondary particle 1, can be 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, or 4% or more by mass fraction. The amount of LPO adhering, for example, relative to secondary particle 1, can be less than 5%, less than 4%, or less than 3% by mass fraction.

[0090] The surface of the secondary particle 1 may also include a first attachment portion 4 and a second attachment portion 5. Carbon is attached to the first attachment portion 4, and carbon and LPO are attached to the second attachment portion 5. Alternatively, only carbon may be attached to the first attachment portion 4. The first attachment portion 4 may be composed of a carbon layer 2, and the second attachment portion 5 may be composed of a carbon layer 2 and a lithium phosphate layer 3. The second attachment portion 5 may also have a carbon layer 2 formed on the surface of the secondary particle 1, and a lithium phosphate layer 3 formed on the surface of the carbon layer 2.

[0091] In the cross-section of secondary particle 1, secondary particle 1 is composed of a central part 1a, a middle part 1b, and an outer peripheral part 1c. LPO This indicates the molar concentration of LPO in the peripheral region 1c. X LPO This represents the average molar concentration of LPO in the central portion 1a, the middle portion 1b, and the outer peripheral portion 1c. That is, satisfying X... LPO = (ALPO +B LPO +C LPO The relationship is 1.05 / 3. This is achieved by satisfying "1.05≤C". LPO / X LPO The relationship between these factors allows us to expect improvements in durability.

[0092] C LPO / X LPO For example, it can be 1.25 or higher, 1.5 or higher, 1.75 or higher, or 2.0 or higher. C LPO / X LPO For example, it can be below 7.0, below 6.5, below 6.0, below 5.5, below 5.0, below 4.5, below 4.0, below 3.5, below 3.0, or below 2.7. C LPO / X LPO The larger the value, the more likely improvements in durability can be expected. On the other hand, in C... LPO / X LPO In large cases, there is a tendency for the specific capacity to decrease. This can be addressed by satisfying C. LPO / X LPO A value of ≤7.0 allows for a balance between durability and specific capacity.

[0093] Each of the multiple primary particles contains an olivine-type phosphate compound. "Olivine-type" indicates a crystal structure belonging to space group Pnma. Space groups are identified by powder X-ray diffraction (XRD). Primary particles can also be single-phase compounds. As long as a primary particle contains an olivine-type crystalline phase, it can also contain phases belonging to other space groups. Primary particles can also contain amorphous phases, for example.

[0094] Olivine-type phosphate compounds may include, for example, lithium iron phosphate (LFP) and lithium manganese phosphate (LMP). In LMP, a portion of the manganese (Mn) can be replaced by iron (Fe). The Fe-substituted LMP is also referred to as lithium manganese iron phosphate (LMFP). LMP may, for example, have a composition represented by the following general formula.

[0095] Li 1-a Mn 1-x Fe x PO4

[0096] For example, the relationship -0.5 ≤ a ≤ 0.5 can be satisfied. The amount of Fe substitution (x) can be, for example, 0 or more, 0.05 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. The amount of Fe substitution (x) can be, for example, 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.

[0097] LMFPs can also be doped with elements other than lithium (Li), Mn, Fe, phosphorus (P), and oxygen (O) (dopants). The doping amount (the mole fraction relative to the amount of Li) can be, for example, 0.01 to 0.1. The dopant may include at least one element selected from boron (B), nitrogen (N), halogens, silicon (Si), sodium (Na), magnesium (Mg), aluminum (Al), chromium (Cr), scandium (Sc), titanium (Ti), vanadium (V), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), selenium (Se), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), 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.

[0098] The positive electrode active material can contain olivine-type phosphate compounds, and may also contain other components. These other components may include, for example, lithium nickel oxide (LNO), lithium cobalt oxide (LCO), and lithium manganese oxide (LMO). The mixing ratio (mass ratio) of the olivine-type phosphate compound and other components can be, for example, "olivine-type phosphate compound / other components = 9 / 1 to 1 / 9", "olivine-type phosphate compound / other components = 8 / 2 to 2 / 8", "olivine-type phosphate compound / other components = 7 / 3 to 3 / 7", or "olivine-type phosphate compound / other components = 6 / 4 to 4 / 6".

[0099] LNO can have, for example, a crystal structure belonging to space group R-3m. LNO can have, for example, a composition represented by the following general formula.

[0100] Li 1-a Ni x M 1-x O2

[0101] In the formula, the relationships of -0.5 ≤ a ≤ 0.5 and 0 ≤ x ≤ 1 are satisfied. M can include, for example, at least one selected from Co, Mn, and Al. 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 -0.4 ≤ a ≤ 0.4, -0.3 ≤ a ≤ 0.3, -0.2 ≤ a ≤ 0.2, or -0.1 ≤ a ≤ 0.1 can be satisfied.

[0102] LNO can include, for example, at least one selected from 0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O2, and LiNiO2.

[0103] LNO can be represented, for example, by the following general formula. The compound represented by the following general formula can also be referred to as "NCM".

[0104] Li 1-a Ni x Co y Mn z O2

[0105] 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.

[0106] NCM can include, for example, at least one selected from LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn0.3 O2, LiNi 0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 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.

[0107] LNO can be represented by the following general formula. Compounds represented by the following general formula can also be called "NCA".

[0108] Li 1-a Ni x Co y Al z O2

[0109] 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.

[0110] NCA may, for example, contain at least one 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 Co 0.17 Al 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, and LiNi 0.9 Co 0.05 Al 0.05 O2.

[0111] <Method for manufacturing a positive electrode active material>

[0112] Figure 3 is a schematic flowchart showing the method for manufacturing the positive electrode active material of the present embodiment. Hereinafter, "the method for manufacturing the positive electrode active material of the present embodiment" may be abbreviated as "this method". This method may, for example, include "(a) the first mixing step", "(b) the granulation step", "(c) the firing step", "(d) the second mixing step", and "(e) the drying step".

[0113] (a)The first mixing step

[0114] This process involves forming a first slurry by mixing a manganese compound, a first lithium compound, a first phosphate compound, a carbon material, and a first solvent. The following explanation uses the manufacture of LMFP as the positive electrode active material as an example. However, the positive electrode active material disclosed herein is not limited to LMFP.

[0115] For example, to become the composition "Li 1-a Mn 1-x Fe x The composition ratio (molar ratio) shown in "PO4 (-0.5≤a≤0.5, 0≤x<1)" is used to weigh manganese compound, lithium compound 1, phosphate compound 1, carbon material, and iron compound. Manganese compound 1 may include, for example, manganese carbonate. Lithium compound 1 may include, for example, lithium hydroxide. Phosphate compound 1 may include, for example, lithium dihydrogen phosphate. Iron compound 1 may include, for example, iron phosphate.

[0116] Carbon-based raw materials may include, for example, sugars and organic acids. Examples of carbon-based raw materials include glucose, sucrose, fructose, and citric acid. The amount of carbon-based raw materials added relative to the mixture of raw materials other than carbon materials, by mass fraction, may be, for example, 1 to 20%.

[0117] The first solvent may include, for example, water. The concentration of the solids in the first slurry, by mass fraction, may be, for example, 20 to 40%.

[0118] By performing wet milling, the particle size in the first slurry can be adjusted. For example, wet milling can be performed to achieve a D50 of 0.10~1μm.

[0119] (b) Granulation process

[0120] This process involves drying the first slurry to form precursor particles.

[0121] For example, precursor particles can be granulated using spray drying. The inlet temperature can be, for example, 230–270°C. The outlet temperature can be, for example, 100–130°C. The spray rate can be, for example, 5–20 mL / min. The inlet pressure can be, for example, approximately 1.8–2.2 MPa. The nozzle pressure of the spray nozzle can be, for example, 0.1–0.3 MPa.

[0122] (c) Firing process

[0123] This process involves heat-treating the precursor particles to form the first particle. The first particle is a carbon-coated particle on the surface of the LMFP.

[0124] 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℃. The heat treatment time can be, for example, 4~6 hours. During the heating process in firing, the heating can be not continuous, but can be temporarily stopped around 200℃ and maintained at 200℃ for about 1 hour.

[0125] (d) Second mixing process

[0126] This process involves mixing the first particle, the second lithium compound, the second phosphate compound, and the second solvent to form the second slurry.

[0127] The second lithium compound may include, for example, lithium hydroxide. The second phosphoric acid compound may include, for example, orthophosphoric acid. The concentration of the second lithium compound in the second slurry, by mass fraction, may be greater than 0.1% and less than 0.5%. The concentration of the second lithium compound in the second slurry, by mass fraction, may be greater than 0.11%, greater than 0.15%, or greater than 0.2%. The concentration of the second lithium compound in the second slurry, by mass fraction, may be less than 0.4%, less than 0.35%, or less than 0.3%. The concentration of the second phosphoric acid compound in the second slurry, by mass fraction, may be greater than 0.3% and less than 1.5%. The concentration of the second phosphoric acid compound in the second slurry, by mass fraction, may be greater than 0.33%, greater than 0.45%, or greater than 0.6%. The concentration of the second phosphoric acid compound in the second slurry, by mass fraction, may be less than 1.2%, less than 1.05%, or less than 0.9%.

[0128] The second solvent may include, for example, water.

[0129] (e) Drying process

[0130] This process involves producing a second particle by drying a second slurry. The second particle is a particle on which LPO is further attached to the surface of the first particle.

[0131] In this process, the second slurry can also be dried using the same method as in the granulation process (spray drying). In this process, the dried material can also be further dried after the spray drying process, for example.

[0132] Liquid batteries

[0133] In some embodiments, the battery is a liquid-based battery. A liquid-based battery contains an electrolyte. 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) will be described.

[0134] Figure 4 is a schematic perspective view of the battery according to this embodiment. Figure 5 is a schematic cross-sectional view along line VI-VI in Figure 4. Hereinafter, "plane-perpendicular direction" refers to the normal direction relative to the surface of the sheet-like member (e.g., foil, electrode, etc.). "In-plane direction" refers to any direction orthogonal to the plane-perpendicular direction. In the figures of this embodiment, the Z-axis direction corresponds to the plane-perpendicular direction. The X-axis direction and Y-axis direction are examples of in-plane directions.

[0135] 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 also include, for example, 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) can be inserted between the first laminate 92 and the second laminate 93 at the joint.

[0136] The first collector plate 91 and the second collector plate 94 are joined to the power generation element 50 at their ends in the lamination direction (Z-axis direction). A first laminate 92 is joined to the first collector plate 91. A second laminate 93 is joined to the second collector plate 94. A sealing material (not shown) may also be inserted between the collector plate and the laminate at the joint.

[0137] The power generation element 50 includes a plurality of bipolar electrodes 10. The plurality of bipolar electrodes 10 are stacked in a plane-perpendicular direction (Z-axis direction). Each of the plurality of bipolar electrodes 10 sequentially includes a positive electrode layer 11, a current collector foil 13, and a negative electrode layer 12 in the plane-perpendicular direction. 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 along a full circumference in the in-plane direction compared to the positive electrode layer 11 and the negative electrode layer 12. Details of the positive electrode layer 11 are as previously described.

[0138] 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 can also be formed by laminating 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.

[0139] The power generation element 50 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 heat-fused onto the current collector foil 13, for example. Alternatively, the sealing material 30 may be disposed along the entire periphery in the in-plane direction. The sealing material 30 may also contain, for example, a resin material. The sealing material 30 seals adjacent current collector foils 13 in the perpendicular direction between the planes. Sealing the current collector foils 13 with the sealing material 30 divides the space into units 40. Unit 40 is the smallest unit of the power generation element 50. The battery 100 includes multiple units 40 and can therefore be referred to as a "bipolar module." The multiple units 40 are individually sealed. The multiple units 40 are isolated from each other. Each of the multiple units 40 includes a positive electrode layer 11, a separator 20, a negative electrode layer 12, and an electrolyte.

[0140] (Negative electrode layer)

[0141] 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.

[0142] 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. Alternatively, the D50 of the negative electrode active material can be, for example, less than 30 μm, less than 20 μm, less than 15 μm, or less than 10 μm.

[0143] The negative electrode active material may contain optional components. The negative electrode active material may contain at least one selected from, for example, 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 may be a Li metal negative electrode battery.

[0144] Carbon-based active materials may include at least one selected from graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. Graphite may also be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1", "natural graphite / artificial graphite = 2 / 8 to 8 / 2", or "natural graphite / artificial graphite = 3 / 7 to 7 / 3".

[0145] The surface of graphite can be covered, for example, with amorphous carbon. The surface of graphite can also be covered 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 include, for example, at least one selected from Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO3, and Li3PO4.

[0146] The alloy-based active material may contain at least one selected from, for example, Si, Li silicates, SiO, Si-based alloys, tin (Sn), SnO, and Sn-based alloys.

[0147] SiO can be represented by, for example, the following general formula.

[0148] SiO x

[0149] In the formula, the relationship 0 < x < 2 must be satisfied. For example, the relationship 0.5 ≤ x ≤ 1.5 or 0.8 ≤ x ≤ 1.2 can also be satisfied.

[0150] "Si-C composite material" refers to a composite material of carbon-based active materials (such as graphite) and alloy-based active materials (such as Si). For example, Si particles may be dispersed within carbon particles. For example, Si particles may be dispersed within graphite particles. For example, Li silicate particles may be covered by carbon materials (such as amorphous carbon).

[0151] (Diaphragm)

[0152] The separator 20 is capable of separating the positive electrode layer 11 from the negative electrode layer 12. The separator 20 is electrically insulating. The separator 20 may contain at least one selected from, for example, a resin membrane (polymer membrane), an inorganic particle layer, and an organic particle layer. The separator 20 may contain, for example, a resin membrane and an inorganic particle layer.

[0153] The resin membrane is porous. It can include, for example, microporous membranes or nonwoven fabrics. The resin membrane comprises a resin backbone, which can be, for example, a continuous network. Fine pores are formed in the gaps between the resin backbone. The resin membrane allows electrolyte to permeate. The average pore size of the resin membrane can be, for example, less than 1 μm. The average pore size of the resin membrane can be, for example, 0.01~1 μm or 0.1~0.5 μm. The "average pore size" can be determined by mercury porosimetry. The Gurley value of the resin membrane can be, for example, 50~250 s / 100 cm⁻¹. 3 The "Gerley value" can be determined using the Gerley test method.

[0154] The resin membrane 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 resins, and polyester-based resins. The resin membrane may also contain at least one selected from, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamide-imide (PAI), polyimide (PI), aromatic polyamides, polyphenylene ether (PPE), and their derivatives. The resin membrane can be formed by, for example, stretching or phase separation. The thickness of the resin membrane may be, for example, 5-50 μm or 10-25 μm.

[0155] The resin membrane can have, for example, a single-layer structure. The resin membrane can be composed of, for example, 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, for example, a multi-layer structure. The resin membrane can include, for example, a PP layer and a PE layer. The framework of the PP layer is formed of PP. The resin membrane can also have, for example, a three-layer structure. The resin membrane can be formed by, for example, sequentially stacking a PP layer, a PE layer, and another PP layer. The thickness of the PE layer can, for example, be 5~20 μm. The thickness of the PP layer can, for example, be 3~10 μm.

[0156] The inorganic particle layer can 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.

[0157] The inorganic particle layer is porous. It contains inorganic particles, which can also be referred to as "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, for example, 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 oxide, magnesium oxide, and silicon oxide. The inorganic particles can have any shape. They can be, for example, 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 an adhesive. The adhesive may contain, for example, at least one selected from acrylic resins, polyamide resins, fluorinated resins, aromatic polyether resins, and liquid crystal polyester resins.

[0158] The membrane 20 may include, for example, an organic particle layer. The membrane 20 may also include, for example, an organic particle layer instead of a resin membrane. The membrane 20 may include, for example, an organic particle layer instead of an inorganic particle layer. The membrane 20 may also simultaneously include a resin membrane and an organic particle layer. The membrane 20 may simultaneously include an inorganic particle layer and an organic particle layer. The membrane 20 may also include a resin membrane, an inorganic particle layer, and an organic particle layer.

[0159] 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. These organic particles can also be referred to as "organic fillers." The organic particles may contain heat-resistant materials. The organic particles may contain at least one material selected from, for example, PE, PP, PTFE, PI, PAI, PA, and aromatic polyamides. The organic particles can be, for example, spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the organic particles can be, for example, 0.1~10 μm or 0.5~3 μm.

[0160] The membrane 20 may also include, for example, a hybrid layer. This hybrid layer contains both inorganic and organic particles.

[0161] (Electrolyte)

[0162] The electrolyte is a liquid electrolyte. The electrolyte contains a solute and a solvent. The concentration of the solute can be, 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. "mol / L" is sometimes expressed as "M". The solute contains a supporting electrolyte (Li salt). The solute can contain, for example, inorganic acid salts, imide salts, oxalate complexes, halides, etc. The solute can contain, for example, at least one 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.

[0163] The electrolyte may contain, for example, a carbonate-based solvent or a carbonate-ester-based solvent. The solvent may contain, for example, cyclic carbonates, chain carbonates, fluorinated carbonates, etc. The solvent may contain, for example, at least one selected from 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, fluoropropylene carbonate, difluoropropylene carbonate, and their derivatives.

[0164] The solvent may contain cyclic carbonates (EC, PC, FEC, etc.) and chain carbonates (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates and chain carbonates 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".

[0165] The solvent may contain cyclic carbonates (EC, PC, etc.) and fluorinated cyclic carbonates (FEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates and fluorinated cyclic carbonates may be, for example, "cyclic carbonate / fluorinated cyclic carbonate = 99 / 1~90 / 10", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1~1 / 9", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1~7 / 3" or "cyclic carbonate / fluorinated cyclic carbonate = 3 / 7~1 / 9".

[0166] Solvents may include, for example, EC, FEC, EMC, DMC, and DEC. The volume ratios of the components may also satisfy, for example, the relationship expressed by the following formula.

[0167] V EC +V FEC +V EMC +V DMC +V DEC =10

[0168] In the above formula, V EC V FEC V EMC V DMC V DEC These represent the volume ratios of EC, FEC, EMC, DMC, and DEC, respectively.

[0169] The following relationship must be satisfied:

[0170] 1≤V EC ≤4、0≤V FEC ≤3、V EC +V FEC ≤4、

[0171] 0≤V EMC ≤9、0≤V DMC ≤9、0≤V DEC ≤9、6≤V EMC +V DMC +V DEC ≤9.

[0172] For example, it can satisfy 1≤V EC ≤2 or 2≤V EC Relationships ≤3.

[0173] For example, it can satisfy 1≤V FEC ≤2 or 2≤V FEC Relationships ≤4.

[0174] For example, it can satisfy 3≤V EMC ≤4 or 6≤V EMC The relationship is ≤8.

[0175] For example, it can satisfy 3≤V DMC ≤4 or 6≤V DMC The relationship is ≤8.

[0176] For example, it can satisfy 3≤V DEC ≤4 or 6≤V DEC The relationship is ≤8.

[0177] The solvent may have, for example, 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", "EC / FEC / DMC / EMC=1 / 2 / 3 / 4", etc.

[0178] The electrolyte may contain ether-based solvents. The electrolyte may contain, for example, solvents selected from tetrahydrofuran (THF), 1,4-dihydrofuran, etc. At least one of the following: alkylene (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), hydrofluoroether (HFE), ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and their derivatives.

[0179] The electrolyte may contain optional additives. The amount added (relative to the total mass fraction 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 interface) formation promoters, SEI formation inhibitors, gas generators, overcharge preventers, flame retardants, antioxidants, electrode protectants, surfactants, etc.

[0180] Additives may include, for example, those selected from vinylene carbonate (VC), ethylene ethylene carbonate (VEC), 1,3-propanesulfonyl lactone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfide (ES), propanesulfonyl lactone (PS), ethylene sulfide (DTD), γ-butyrolactone, phosphazene compounds, and carboxylic acid esters (e.g., methyl formate (MF), methyl acetate (MA), methyl propionate (MP), propylene glycol). Diethyl ester (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-difluoromethyl... Benzene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene, 3,4-difluorotoluene, octafluorotoluene, etc.), trifluorotoluene (e.g., trifluorotoluene, 2-fluorotrifluorotoluene, 3-fluorotrifluorotoluene, 4-fluorotrifluorotoluene, 2-methyltrifluorotoluene, 3-methyltrifluorotoluene, 4-methyltrifluorotoluene, etc.), fluoroxylene (e.g., 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m-xylene). The following are included in the list of at least one of the following: 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.).

[0181] The components described above as solutes and solvents can be used as trace components (additives). Additives may contain at least one selected from, for example, LiBF4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO2F2, FSO3Li, LiI, LiBr, HFE, DOX, PC, FEC, and their derivatives.

[0182] The electrolyte may contain ionic liquids. Ionic liquids may contain, for example, salts selected from sulfonium salts, ammonium salts, pyridinium salts, piperidine salts, pyrrolidine salts, morpholine salts, etc. Salt, imidazole At least one of salts and their derivatives.

[0183] In some embodiments of this invention, the battery may comprise a gel electrolyte. That is, the battery may 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, for example, at least one selected from PVdF, PVdF-HFP, polyacrylonitrile (PAN), PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0184] All-solid-state batteries

[0185] In some embodiments of this invention, the battery is an all-solid-state battery. An all-solid-state battery may also have a bipolar structure. The all-solid-state battery contains a solid electrolyte in place of the electrolyte and separator 20. That is, a solid electrolyte layer separates the negative electrode layer 12 from the positive electrode layer 11, instead of the separator 20. The solid electrolyte layer may contain, for example, a solid electrolyte and a binder. Both the positive electrode layer 11 and the negative electrode layer 12 may also contain a solid electrolyte.

[0186] Solid electrolytes can also be, for example, powders. The D50 of a solid electrolyte can be, for example, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, 0.4 μm or more, 0.5 μm or more, 0.6 μm or more, 0.7 μm or more, 0.8 μm or more, 0.9 μm or more, or 1 μm or more. The D50 of a solid electrolyte can also be less than 5 μm, less than 4 μm, less than 3 μm, less than 2 μm, or less than 1 μm.

[0187] Solid electrolytes may include at least one selected from, for example, sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, hydride solid electrolytes and nitride solid electrolytes.

[0188] The sulfide solid electrolyte may contain at least one selected from amorphous phases, crystalline phases, and glass-ceramic (crystalline glass) phases. The crystalline phase may be, for example, argillite-germanium sulfide or LGPS type. The sulfide solid electrolyte contains Li and sulfur (S). In addition to Li and S, the sulfide solid electrolyte may also contain optional components.

[0189] Sulfide solid electrolytes may contain, for example, compounds selected from LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-GeS2-P2S5, Li2S-P2S5, Li 10 GeP2S 12 Li4P2S6, Li7P3S 11 At least one of Li3PS4 and Li7PS6.

[0190] For example, "LiI-LiBr-Li3PS4" indicates a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li3PS4 in any molar ratio. Sulfide solid electrolytes can be produced, for example, by a mechanochemical method. The mixing ratio can also be determined by adding numbers before each raw material. For example, "10LiI-15LiBr-75Li3PS4" indicates a mixing ratio of "LiI / LiBr / Li3PS4 = 10 / 15 / 75 (molar ratio)".

[0191] Sulfide solid electrolytes can have compositions, for example, represented by the following general formula.

[0192] xLi2S-(1-x)P2S5

[0193] In the formula, x can be greater than 0, greater than 0.1, greater than 0.2, greater than 0.25, greater than 0.3, greater than 0.4, greater than 0.5, greater than 0.6, greater than 0.7, greater than 0.75, greater than 0.8, or greater than 0.9. x can also be less than 1, less than 0.9, less than 0.8, less than 0.7, less than 0.75, 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. For example, when x = 0.75, "xLi2S-(1-x)P2S5" can have the composition of Li3PS4.

[0194] Sulfide solid electrolytes can have compositions, for example, represented by the following general formula.

[0195] yLiI-zLiBr-(100-yz)[xLi2S-(1-x)P2S5]

[0196] In the formula, x can be, for example, 0.5 or higher, 0.6 or higher, 0.7 or higher, 0.75 or higher, 0.8 or higher, or 0.9 or higher. x can also be, for example, less than 1, less than 0.9, less than 0.8, less than 0.75, less than 0.7, or less than 0.6. y can be, for example, 0 or higher, 5 or higher, 10 or higher, 15 or higher, 20 or higher, or 25 or higher. y can also be, for example, less than 30, less than 25, less than 20, less than 15, less than 10, or less than 5. z can be, for example, 0 or higher, 5 or higher, 10 or higher, 15 or higher, or 20 or higher. z can also be, for example, less than 30, less than 25, less than 20, less than 15, less than 10, or less than 5.

[0197] Sulfide solid electrolytes can have compositions, for example, represented by the following general formula.

[0198] Li 7-x-2y PS 6-x-y Xy

[0199] In the formula, the relationships “0 < 7-x-2y”, “0 < 6-xy”, “0 ≤ x” and “0 ≤ y” are satisfied. X may contain at least one of, for example, fluorine (F), chlorine (Cl), bromine (Br) and iodine (I).

[0200] Sulfide solid electrolytes can have compositions, for example, represented by the following general formula.

[0201] Li 4-x M 1-x P x S4

[0202] In the formula, x can be greater than 0, greater than or equal to 0.1, greater than or equal to 0.2, greater than or equal to 0.3, greater than or equal to 0.4, greater than or equal to 0.5, greater than or equal to 0.6, greater than or equal to 0.7, greater than or equal to 0.8, or greater than or equal to 0.9. x can be less than 1, less than or equal to 0.9, less than or equal to 0.8, less than or equal to 0.7, less than or equal to 0.6, less than or equal to 0.5, less than or equal to 0.4, less than or equal to 0.3, less than or equal to 0.2, or less than or equal to 0.1. M can contain at least one of, for example, selected from Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0203] Sulfide solid electrolytes can have compositions, for example, represented by the following general formula.

[0204] Li 10+x Ge 1+x P 2-x S 12

[0205] In the formula, x can be, for example, 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, or 0.6 or more. x can be, for example, 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. The sulfide solid electrolyte represented by the above general formula may contain, for example, a crystalline phase of the LGPS type.

[0206] Halogenated solid electrolytes can have compositions, for example, represented by the following general formula.

[0207] Li 6-na M a X6

[0208] In the formula, n represents the oxidation number of M. For example, M may contain atoms with an oxidation number of +3. For example, M may contain atoms with an oxidation number of +4. For example, M may contain at least one selected from Y, Al, Ti, Zr, Ca, and Mg. For example, the relationship "0 < a < 2" may also be satisfied. X may contain at least one selected from, for example, F, Cl, Br, and I.

[0209] Halogenated solid electrolytes can have compositions, for example, represented by the following general formula.

[0210] Li 3-a Ti a Al 1-a F6

[0211] In the formula, 'a' can be, for example, 0 or above, 0.1 or above, 0.2 or above, 0.3 or above, 0.4 or above, 0.5 or above, 0.6 or above, 0.7 or above, 0.8 or above, or 0.9 or above. 'a' can be, for example, below 1, below 0.9, below 0.8, below 0.7, below 0.6, below 0.5, below 0.4, below 0.3, below 0.2, or below 0.1.

[0212] Halogenated solid electrolytes can have compositions, for example, represented by the following general formula.

[0213] Li3YCl a Br b I 6-a-b

[0214] In the formula, the relationship "0 ≤ a + b ≤ 6" can also be satisfied, for example. 'a' can be 0 or higher, 1 or higher, 2 or higher, 3 or higher, 4 or higher, or 5 or higher. 'b' can be 6 or lower, 5 or lower, 4 or lower, 3 or lower, 2 or lower, or 1 or lower.

[0215] Oxide solid electrolytes may contain, for example, those selected from LiNbO3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, La 2 / 3-x Li 3x TiO3 and Li7La3Zr2O 12 At least one of the following. Hydride solid electrolytes may contain, for example, LiBH4. Nitride solid electrolytes may contain, for example, Li3N, Li3BN2, etc.

[0216] [Example]

[0217] <The Manufacturing of the Positive Electrode>

[0218] (No. 1)

[0219] (a) First mixing process

[0220] To become the composition "Li 1.04 Mn 0.6 Fe 0.4As shown in the composition ratio of "PO4", weigh lithium hydroxide monohydrate, manganese carbonate, iron phosphate, and lithium dihydrogen phosphate. Weigh glucose at a mass fraction of 8% relative to the total mass of the raw materials. Mix the weighed materials with water to form the first slurry. The solids concentration of the slurry is 30% by mass. Perform wet milling to achieve a D50 of 0.30 μm.

[0221] (b) Granulation process

[0222] Precursor particles were formed by spray drying the first slurry. The target D50 value of the precursor particles was 9 ± 1 μm. The inlet temperature was 250 °C, the outlet temperature of the spray dryer was 115 ± 15 °C, the spray rate was 10 mL / min, the inlet pressure was 2.0 MPa, and the nozzle pressure of the spray nozzle was 0.2 ± 0.1 MPa.

[0223] (c) Firing process

[0224] The first particle was formed by sintering precursor particles under a nitrogen atmosphere. Figure 7 shows the temperature profile during sintering. First, the furnace temperature was increased to 200°C at a heating rate of 3°C / min. The furnace temperature was maintained at 200°C for 1 hour. Next, the furnace temperature was increased to 650°C at a heating rate of 5°C / min. The furnace temperature was maintained at 650°C for 5 hours. Subsequently, the furnace temperature was cooled to 400°C at a cooling rate of 2°C / min. Finally, the furnace temperature was cooled to room temperature at a cooling rate of 15°C / min.

[0225] (d) Second mixing process

[0226] Lithium hydroxide and phosphoric acid were weighed to achieve the concentration (mass fraction) shown in Figure 6 in the second slurry. The weighed materials, the first particle, and water were mixed to form the second slurry.

[0227] (e) Drying process

[0228] The second particles are formed by spray drying the second slurry. In this process, the same conditions as the granulation process described in (b) above are used.

[0229] The spray-dried material is further subjected to hot air drying at 200°C for 6 hours to produce the second particle (positive electrode active material).

[0230] (Making the button unit)

[0231] 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 by rolling. 3 This forms the positive electrode plate. The positive electrode plate is then subjected to vacuum drying at 120°C for 12 hours. After drying, a disc sample (diameter: 14 mm) is removed from the positive electrode plate through punching.

[0232] Button units were assembled inside the glove box. The unit structure is described below.

[0233] Working electrode: Disk-shaped sample (positive electrode)

[0234] Counter electrode: Li foil

[0235] Separator: Polymer porous membrane

[0236] Electrolyte: EC / DMC = 3 / 7 (volume ratio), LiPF6 (1 mol / L)

[0237] (No. 2 ~ No. 7)

[0238] As shown in Figure 6, the manufacturing process conditions are changed, but the positive electrode active material is manufactured in the same manner as No. 1. Furthermore, the positive electrode is manufactured in the same manner as No. 1, and the button cell is assembled.

[0239] <Evaluation>

[0240] (Measurement)

[0241] Figure 6 shows C LPO / X LPO It is calculated using the method described above.

[0242] (Specific capacity)

[0243] Specific capacity is determined by the following steps.

[0244] Based on the discharge capacity (theoretical capacity) calculated according to the coating quality of the positive electrode layer, a rate equivalent to 1C is determined. "C" is a notation representing the current rate (time rate). At a rate of 1C, the theoretical capacity is flowed for 1 hour. The button cell is charged under constant current-constant voltage (CCCV) charging conditions at a temperature of 25°C.

[0245] The charging rate during CC charging is 0.1C.

[0246] Charging voltage limit: 4.3V

[0247] The cutoff current ratio during CV charging is 0.01C.

[0248] After charging, the electrode was discharged at a rate of 0.1C to 3.0V using a CC discharge method, and the discharge capacity was measured. The specific capacity (mAh / g) was calculated by dividing the discharge capacity by the mass of the positive electrode active material. The results are shown in Figure 6. Furthermore, the specific capacity values ​​in Figure 6 are relative values ​​when the specific capacity of No. 1 is set to 1.

[0249] (Capacity retention rate)

[0250] Capacity retention is determined using the following steps. A higher capacity retention rate is considered to indicate better durability.

[0251] The CC charge-discharge cycle was repeated 50 times under the following conditions at a temperature of 60°C.

[0252] CC charging: 0.5C, 3.0V

[0253] CC discharge: 1C, 4.3V

[0254] The specific capacity "A" after one cycle and the specific capacity "B" after 50 cycles were measured. The capacity retention rate was calculated by dividing "B / A". The results are shown in Figure 6. Furthermore, the capacity retention rate values ​​in Figure 6 are relative values ​​when the capacity retention rate of No. 1 is set to 1.

[0255] <Results>

[0256] As shown in Figure 6, C can be seen LPO / X LPO The larger the size, the higher the durability tends to be.

[0257] On the other hand, C LPO / X LPO The larger the value, the lower the specific capacity. From the perspective of balancing durability and specific capacity, C can be satisfied. LPO / X LPO The relationship ≤4.5 can also satisfy C. LPO / X LPO Relationships ≤3.0.

[0258] While embodiments of the invention have been described, it should be considered that the embodiments disclosed herein are illustrative rather than restrictive in all respects. The scope of the invention is defined by the claims, including all equivalents thereof and all modifications within the scope of the claims.

Claims

1. A positive electrode active material comprising a plurality of secondary particles, each of the plurality of secondary particles comprising a plurality of primary particles, each of the plurality of primary particles comprising an olivine-type phosphate compound, wherein carbon and lithium phosphate are attached to at least a portion of the surface of the secondary particles, and in cross-section, the secondary particles are composed of a central portion, an intermediate portion, and an outer peripheral portion, satisfying 1.05 ≤ C LPO / X LPO The relationship, the C LPO The X represents the molar concentration of lithium phosphate in the outer periphery. LPO This represents the average molar concentration of lithium phosphate in the central portion, the middle portion, and the outer periphery.

2. The positive electrode active material according to claim 1, satisfying 1.5 ≤ C LPO / X LPO The relationship.

3. The positive electrode active material according to claim 1, satisfying C LPO / X LPO Relationships ≤ 7.

0.

4. The positive electrode active material according to claim 1, satisfying C LPO / X LPO Relationship ≤ 4.

5.

5. The positive electrode active material according to claim 1, satisfying C LPO / X LPO Relationships ≤ 3.

0.

6. The positive electrode active material according to claim 1, wherein the surface of the secondary particles comprises a first attachment portion and a second attachment portion, wherein carbon is attached to the first attachment portion and carbon and lithium phosphate are attached to the second attachment portion.

7. The positive electrode active material according to claim 1, wherein the olivine-type phosphate compound is lithium manganese iron phosphate.

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

9. The battery according to claim 8, having a bipolar structure.

10. A method for manufacturing a positive electrode active material, comprising the following steps: step (a): forming a first slurry by mixing a manganese compound, a first lithium compound, a first phosphate compound, a carbon material, and a first solvent; step (b): forming precursor particles by drying the first slurry; step (c): forming first particles by heat-treating the precursor particles; step (d): forming a second slurry by mixing the first particles, a second lithium compound, a second phosphate compound, and a second solvent; and step (e): manufacturing second particles by drying the second slurry.

11. The method for manufacturing the positive electrode active material according to claim 10, wherein the concentration of the second lithium compound in the second slurry is greater than 0.1% and less than 0.5% by mass fraction, and the concentration of the second phosphoric acid compound in the second slurry is greater than 0.3% and less than 1.5% by mass fraction.

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