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

Abstract

The invention relates to a positive electrode active material, a battery and a method for manufacturing the positive electrode active material. An object of the present disclosure is to improve magnification characteristics. A positive electrode active material includes a plurality of secondary particles, each of the plurality of secondary particles includes a plurality of primary particles, each of the plurality of primary particles includes an olivine-type phosphate compound, and in a scanning electron microscope image of the secondary particles, the olivine-type phosphate compound includes an olivine-type phosphate compound. In the primary particles having a maximum Feret diameter of 100 nm or more, the proportion of the primary particles having a contact angle of 90 DEG or less is 40% or more.

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] International Publication No. 2021 / 153007 discloses a secondary battery electrode active material with an olivine-type crystal structure and a carbon layer on its surface, with a crystallite diameter of less than 60 nm. Summary of the Invention

[0003] Compounds with an olivine-type crystal structure have been developed as positive electrode active materials. However, compounds with an olivine-type crystal structure tend to have low conductivity. In International Patent Publication No. 2021 / 153007, a compound with an olivine-type crystal structure possessing the above-mentioned characteristics was provided to improve conductivity. However, there is still room for improvement in rate performance.

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

[0005] The following describes the technical solution and effects of this disclosure. However, the mechanism of action of this disclosure includes presumptions. 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] In the scanning electron microscope image of the secondary particles,

[0011] Of the primary particles with a maximum Feret diameter of 100 nm or more, the proportion of primary particles with a contact angle of 90° or less is 40% or more.

[0012] In the positive electrode active material, a certain proportion of the area in contact with other primary particles present around the primary particle is important for forming the interface between the positive electrode active material and the liquid electrolyte, i.e., improving rate performance. In particular, in the scanning electron microscope (SEM) images of secondary particles, an improvement in rate performance can be expected if the proportion of primary particles with a contact angle of less than 90° among primary particles with a maximum Feretta diameter of 100 nm or more is greater than 40%.

[0013] [2] According to the positive electrode active material described in [1], in the scanning electron microscope image of the secondary particles,

[0014] Of the primary particles with a maximum Feret diameter of 100 nm or more, the proportion of primary particles with a contact angle of 90° or less is 75% or more.

[0015] In the SEM images of secondary particles, the proportion of primary particles with a contact angle of less than 90° among primary particles with a maximum Ferete diameter of more than 100 nm is more than 75%, which makes it possible to expect further improvement in rate performance.

[0016] [3] According to the positive electrode active material described in [1] or [2],

[0017] The olivine-type phosphate compound is lithium manganese iron phosphate.

[0018] [4] A battery comprising the positive electrode active material described in any one of [1] to [3].

[0019] [5] The battery described in [4] has a bipolar structure.

[0020] [6] A method for manufacturing a positive electrode active material, comprising the following steps:

[0021] Step (a): A slurry is formed by mixing a manganese compound, a first lithium compound, a phosphoric acid compound, and a solvent;

[0022] Step (b): Forming the first precursor particles by drying the slurry;

[0023] Step (c): Forming the second precursor particles by mixing the first precursor particles and the second lithium compound and performing a first heat treatment; and

[0024] Process (d): To manufacture olivine-type phosphate compounds by subjecting the second precursor particles to a second heat treatment.

[0025] By following the manufacturing process described above [6], it is expected that the positive electrode active material described above [1] can be manufactured.

[0026] [7] According to the manufacturing method of the positive electrode active material described in [6],

[0027] The duration of the first heat treatment is more than 2 hours and less than 4 hours.

[0028] The second heat treatment temperature is above 600°C and below 750°C.

[0029] 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.

[0030] The above and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the invention, which will be understood in conjunction with the accompanying drawings. Attached Figure Description

[0031] Figure 1A This is a schematic cross-sectional view showing a portion of the secondary particles in this embodiment.

[0032] Figure 1B This is a schematic cross-sectional view showing a portion of the secondary particles in this embodiment.

[0033] Figure 1C This is a schematic cross-sectional view showing a portion of the secondary particles in this embodiment.

[0034] Figure 2 This is a conceptual diagram representing the secondary particles in this embodiment.

[0035] Figure 3 This is a schematic flowchart illustrating the method for manufacturing the positive electrode active material according to this embodiment.

[0036] Figure 4 This is a schematic perspective view of the battery according to this embodiment.

[0037] Figure 5 It is along Figure 4 A rough cross-sectional view of line VI-VI in the diagram.

[0038] Figure 6 This is a table showing the manufacturing conditions and experimental results of the positive electrode active material in the examples. Detailed Implementation

[0039] <Terminology and Phrases>

[0040] "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.

[0041] 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").

[0042] 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.

[0043] 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.

[0044] For example, expressions for "at least one of A and B" include "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".

[0045] 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 include 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.

[0046] 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 powder particles.

[0047] Unless otherwise specified, the numerical range of "m~n%" includes both an upper and lower limit. That is, "m~n%" represents a numerical range of "above m% and below n%". Furthermore, "above 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.

[0048] 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, the higher the reliability of the average value can be expected. 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.

[0049] 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.

[0050] The contact angle was measured in the following order. A dispersion was formed by dispersing 1g of the sample (positive electrode active material) in a mixture (10g) of the main agent and curing agent of epoxy resin (product name "EPOTEX JP", manufactured by Nisshin EM Co., Ltd.). The dispersion was stirred for 1 minute using a mixer (product name "Awatori Rentaro", manufactured by THINKY Co., Ltd.). The dispersion was then degassed under vacuum. After degassed, the dispersion was filled into a cylindrical container made of resin. The epoxy resin was cured by allowing the dispersion to stand for 1 day. After curing, a smooth cross-section of the cured material was formed by ion milling. A cross-sectional SEM image was obtained by observing the smooth cross-section using SEM. Multiple secondary particles were randomly picked up in multiple fields of view (e.g., about 5 fields of view). For example, more than 20 secondary particles could be picked up. In the cross-sectional SEM image, the secondary particles showed areas with closed contour lines. From the multiple picked secondary particles, a total of 100 primary particles with a maximum Fereth diameter of 100nm or more were randomly picked up.

[0051] Figures 1A-1C This is a schematic cross-sectional view showing a portion of the secondary particle in this embodiment. (Refer to...) Figures 1A-1C The method for determining the contact angle of a single primary particle 1a is described. The grain boundary lines (line segments) where primary particle 1a interacts with other primary particles are determined within the outline of the primary particle 1a. The grain boundaries between primary particles can be confirmed, for example, by electron backscatter diffraction (EBSD). Figure 1A The x and y segments are line segments. Determine the center of the smallest circumcircle opposite the contour line of the primary particle. Figure 1B The center is O. The angle θ formed by the ray Ox originating from the center O and passing through the endpoint x of the line segment and the ray Oy originating from the center O and passing through the endpoint y of the line segment is the contact angle.

[0052] When multiple grain boundaries (segments) exist within a single primary particle (resulting in multiple contact angles θ), the contact angle θ represents the sum of these multiple contact angles θ. For example, in... Figure 1C In this context, the contact angle θ is the sum of the contact angles θ1 and θ2.

[0053] The proportion of primary particles with a contact angle of less than 90° among primary particles with a maximum Feretta diameter of 100 nm or more is determined by measuring the contact angle θ of 100 primary particles with a maximum Feretta diameter of 100 nm or more, and dividing the number of primary particles with a contact angle of less than 90° by 100.

[0054] The "maximum Feret diameter" of a particle represents the length of the longer side of the particle's circumscribed rectangle (rectangle or square). In the case of a square circumscribed rectangle, the length of the longer side represents the side length. The maximum Feret diameter of primary and secondary particles can be determined from the SEM images described above.

[0055] "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.

[0056] 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 mass ratio. For example, trace elements can be doped into the compound. A portion of Al and O can also be replaced by other elements.

[0057] 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 the appropriate concentration using a volumetric flask. After dilution, compositional analysis is performed using an ICP-AES apparatus. For example, product names such as "PS3520 UVDD II (manufactured by Hitachi High Technology Co., Ltd.)" can also be used.

[0058] "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.

[0059] <Positive Electrode Active Material>

[0060] The positive electrode active material can have any morphology. For example, it can also be in the form of powder or granules. 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 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.

[0061] Figure 2This is a conceptual diagram representing the secondary particles in this embodiment. The positive electrode active material includes multiple secondary particles 2. The secondary particles 2 are an aggregate of primary particles 1. That is, the secondary particles 2 include multiple primary particles 1. In this embodiment, the primary particle 1 is a particle observed as a single particle in a SEM image, and is a continuous body without gaps.

[0062] Multiple secondary particles 2 can also include open-pore particles 2a and non-open-pore particles 2b. Open-pore particles 2a are secondary particles with open pores 3. Non-open-pore particles 2b are secondary particles without open pores 3. The presence or absence of open pores 3 is determined in the SEM image. Furthermore, non-open-pore particles 2b may also have open pores 3 in locations not visible from the SEM image, but the presence or absence of open pores 3 is determined based on their appearance in the SEM image.

[0063] The maximum Feret diameter of secondary particles 2 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 Feret diameter of secondary particles 2 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. The maximum Feret diameter of primary particles 1 can be, for example, 10 nm or more, 20 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, or 100 nm or more. The maximum Feret diameter of primary particles 1 can be, for example, less than 200 nm, less than 190 nm, less than 180 nm, less than 170 nm, less than 160 nm, less than 150 nm, less than 140 nm, less than 130 nm, or less than 120 nm.

[0064] Secondary particles 2 can also have a spherical shape. By making secondary particles 2 spherical, for example, improved filling properties can be expected. The sphericity of secondary particles 2 can be 0.85 or higher, 0.90 or higher, or 0.95 or higher. Alternatively, the sphericity of secondary particles 2 can be less than 1, less than 0.95, or less than 0.90. "Sphericity" refers to the roundness in a surface SEM image (two-dimensional image). Sphericity (roundness) is calculated using the following formula.

[0065] ψ = 4πS / L 2

[0066] ψ: Sphericity (roundness)

[0067] π: Pi

[0068] S: Cross-sectional area of ​​secondary particle 2 (the area of ​​the region enclosed by the outline of secondary particle 2)

[0069] L: The perimeter of secondary particle 2 (the length of the outline of secondary particle 2).

[0070] Sphericity is expressed as the arithmetic mean of 30 secondary particles 2. The sphericity of the 30 secondary particles 2 is measured regardless of whether there is an open hole 3.

[0071] A carbon layer 4 may also be attached to the surface of the secondary particles 2. The carbon layer 4 contains carbon (C). The amount of carbon layer 4 attached, for example, relative to the secondary particles 2, may 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 layer 4 attached, for example, relative to the secondary particles 2, may be less than 5%, less than 4%, or less than 3% by mass fraction.

[0072] Each of the multiple primary particles 1 contains an olivine-type phosphate compound. "Olivine-type" indicates a crystal structure belonging to space group Pnma. The space group is identified by powder X-ray diffraction (XRD). Primary particles 1 can also be, for example, single-phase compounds. As long as primary particles 1 contain an olivine-type crystalline phase, they can also contain phases belonging to other space groups. Primary particles 1 can also further contain, for example, amorphous phases, etc.

[0073] Olivine-type phosphate compounds may include, for example, lithium iron phosphate (LFP) and lithium manganese phosphate (LMP). In LMP, some manganese (Mn) can be replaced by iron (Fe). The Fe-substituted form of LMP is also referred to as lithium manganese iron phosphate (LMFP). LMP may, for example, have a composition represented by the following general formula.

[0074] Li 1-a Mn 1-x Fe x PO4

[0075] 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.

[0076] In LMFP, elements (dopants) other than lithium (Li), Mn, Fe, phosphorus (P), and oxygen (O) can also be doped. The doping amount (mass fraction relative to the amount of substance of Li) can be, for example, 0.01 to 0.1. The dopant can 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.

[0077] As long as the positive electrode active material contains an olivine-type phosphate compound, it can also contain other components. The other components can include, for example, lithium nickel composite oxide (LNO), lithium cobalt composite oxide (LCO), lithium manganese composite oxide (LMO), etc. 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".

[0078] LNO can have, for example, a crystal structure belonging to the space group R-3m. LNO can have, for example, a composition represented by the following general formula.

[0079] Li 1-a Ni x M 1-x O2

[0080] In the formula, the relationship of -0.5 ≤ a ≤ 0.5 and 0 ≤ x ≤ 1 is satisfied. M can include, for example, 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 can be satisfied. For example, the relationship of -0.4 ≤ a ≤ 0.4, -0.3 ≤ a ≤ 0.3, -0.2 ≤ a ≤ 0.2, or -0.1 ≤ a ≤ 0.1 can be satisfied.

[0081] LNO may include, for example, at least one selected from LiNi 0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O2, and LiNiO2.

[0082] LNO may be represented, for example, by the following general formula. The compound represented by the following general formula may also be referred to as "NCM".

[0083] Li 1-a Ni x Co y Mn z O2

[0084] 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 may 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 may 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 may be satisfied.

[0085] NCM may include, for example, at least one 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 Co0.4 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.

[0086] LNO can be represented by the following general formula. The compound represented by the following general formula can also be referred to as "NCA".

[0087] Li 1-a Ni x Co y Al z O2

[0088] In the formula, the relationship -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1 is satisfied. For example, the relationship 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9 or 0.9 ≤ x < 1 can be satisfied. For example, the relationship 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9 or 0.9 ≤ y < 1 can be satisfied. For example, the relationship 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9 or 0.9 ≤ z < 1 can be satisfied.

[0089] NCA may, for example, contain components 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 At least one of O2.

[0090] In the SEM images of secondary particles, the proportion of primary particles with a contact angle of less than 90° among primary particles with a maximum Feret diameter of 100 nm or more should be 40% or more. This proportion can also be 45% or more, 50% or more, 52% or more, 55% or more, 57% or more, 60% or more, 62% or more, 65% or more, 67% or more, 70% or more, 72% or more, 75% or more, 77% or more, 80% or more, 82% or more, 85% or more, 87% or more, 90% or more, 92% or more, 95% or more, 97% or more, or 100%. The higher this proportion, the more improvement in rate capability can be expected.

[0091] The average contact angle can be, for example, less than 100°, less than 90°, less than 80°, less than 70°, less than 60°, or less than 50°. With a small average contact angle, ion conduction is promoted, and improved rate capability can be expected. Furthermore, the average contact angle is the contact angle of 100 primary particles.

[0092] <Methods for Manufacturing Positive Electrode Active Materials>

[0093] Figure 3 This is a schematic flowchart illustrating the method for manufacturing the positive electrode active material according to this embodiment. Hereinafter, "the method for manufacturing the positive electrode active material according to this embodiment" may be simply referred to as "this method". This method may include, for example, "(a) a mixing process", "(b) a granulation process", "(c) a first calcination process" and "(d) a second calcination process".

[0094] (a) Mixing process

[0095] This process involves forming a slurry by mixing a manganese compound, a first lithium compound, a phosphoric acid compound, and a 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.

[0096] For example, it can be formed as the compositional formula "Li 1-a Mn 1-x Fe x Weigh the manganese compound, lithium compound 1, phosphate compound, and iron compound according to the composition ratio (mass ratio) shown in "PO4 (-0.5≤a≤0.5, 0≤x<1)". The manganese compound may include, for example, manganese carbonate. The lithium compound 1 may include, for example, lithium hydroxide. The phosphate compound may include, for example, lithium dihydrogen phosphate. The iron compound may include, for example, iron phosphate.

[0097] When a carbon layer forms on the surface of primary particles, a carbon raw material is added to the raw material mixture. The carbon raw material may include, for example, sugars, organic acids, etc. Examples of carbon raw materials include glucose, sucrose, fructose, citric acid, etc. The amount of carbon raw material added relative to the raw material mixture, in mass fraction, may be, for example, 1 to 20%.

[0098] Solvents may include, for example, water. The concentration of solids in the slurry, expressed as a mass fraction, may be, for example, 20-40%.

[0099] The particle size in the slurry can be adjusted by performing wet milling. For example, wet milling can be performed to make the D50 0.10~1μm.

[0100] (b) Granulation process

[0101] This process involves drying the slurry to form the first precursor particles.

[0102] For example, the first precursor particles can also be granulated by 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, 5–15 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.

[0103] (c) First firing process

[0104] This process involves forming the second precursor particles by mixing the first precursor particles and the second lithium compound and performing a first heat treatment.

[0105] The second lithium compound may include, for example, lithium hydroxide. The amount of the second lithium compound added relative to the first precursor particles, in mass fraction, may be, for example, 1 to 10%.

[0106] Any heat treatment furnace (e.g., electric furnace, muffle furnace, etc.) can be used. The atmosphere for this process can be, for example, a nitrogen atmosphere. The first heat treatment temperature can be, for example, 200~500℃. The first heat treatment time can be, for example, 2~4 hours. During the firing process, the temperature can be raised intermittently, stopping around 200℃ and maintaining that temperature for about 1 hour. The contact angle can be adjusted by adjusting the first heat treatment time.

[0107] (d) Second firing process

[0108] This process involves manufacturing olivine-type phosphate compounds by subjecting the second precursor particles to a second heat treatment.

[0109] The same heat treatment furnace as the first firing step can be used. The atmosphere in this step can be, for example, a nitrogen atmosphere. The second heat treatment temperature can be, for example, 600~750℃. The contact angle can be adjusted by adjusting the second heat treatment temperature. The second heat treatment time can be, for example, approximately 4 hours.

[0110] Before subjecting the second precursor particles to the second heat treatment, the second precursor particles may also be washed with water and dried. Washing with water removes any remaining second lithium compound mixed in the first calcination step. The second precursor particles may also be crushed before subjecting the second heat treatment. Crushing can be performed using any type of pulverizer (e.g., a jet mill).

[0111] <Battery>

[0112] 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.

[0113] Figure 4 This is a schematic perspective view of the battery according to this embodiment. Figure 5 It is along Figure 4 A schematic cross-sectional view of line VI-VI in the diagram. Hereinafter, "perpendicular direction" 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 perpendicular direction of the plane. Figure 5 In this context, the Z-axis direction corresponds to the direction perpendicular to the plane. The X-axis and Y-axis directions are examples of in-plane directions.

[0114] 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.

[0115] 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.

[0116] 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 relative 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.

[0117] 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.

[0118] 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.

[0119] (Positive electrode layer)

[0120] A positive electrode layer 11 is attached to one side of the current collector foil 13. For example, a groove may be formed in the positive electrode layer 11. The positive electrode layer 11 may be formed in a strip 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.

[0121] In addition to the positive electrode active material, the positive electrode layer 11 may also 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 optional 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).

[0122] 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 may contain optional 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.

[0123] The positive electrode layer 11 may also contain, for example, inorganic fillers, organic fillers, solid electrolytes, surface modifiers, dispersants, lubricants, flame retardants, protective agents, fluxes, coupling agents, adsorbents, etc. The positive electrode layer 11 may contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, silane coupling agents, MoS2, WO3, etc.

[0124] (Negative electrode layer)

[0125] 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 area of ​​the negative electrode layer 12 can be larger than that of the positive electrode layer 11. The negative electrode layer 12 contains a negative electrode active material.

[0126] 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.

[0127] 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.

[0128] 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".

[0129] 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.

[0130] 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.

[0131] SiO can be represented by, for example, the following general formula.

[0132] SiO x

[0133] 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.

[0134] "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).

[0135] (Diaphragm)

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] The membrane 20 may also include, for example, a hybrid layer. The hybrid layer contains both inorganic and organic particles.

[0145] (Electrolyte)

[0146] 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.

[0147] 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.

[0148] 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".

[0149] 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".

[0150] 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.

[0151] V EC +V FEC +V EMC +V DMC +V DEC =10

[0152] 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.

[0153] The following relationship must be satisfied:

[0154] 1≤V EC ≤4、0≤V FEC ≤3、V EC +V FEC ≤4、

[0155] 0≤V EMC ≤9、0≤V DMC ≤9、0≤V DEC ≤9、6≤V EMC +V DMC +V DEC ≤9.

[0156] For example, it can satisfy 1≤V EC ≤2 or 2≤V EC Relationships ≤3.

[0157] For example, it can satisfy 1≤V FEC ≤2 or 2≤V FEC Relationships ≤4.

[0158] For example, it can satisfy 3≤V EMC ≤4 or 6≤V EMC The relationship is ≤8.

[0159] For example, it can satisfy 3≤V DMC ≤4 or 6≤V DMC The relationship is ≤8.

[0160] For example, it can satisfy 3≤V DEC ≤4 or 6≤V DEC The relationship is ≤8.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.).

[0165] 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.

[0166] 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.

[0167] 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.

[0168] [Example]

[0169] <The Manufacturing of the Positive Electrode>

[0170] (No.1)

[0171] (a) Mixing process

[0172] According to the composition formula "Li" 1.04 Mn 0.6 Fe 0.4 As 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. Form a slurry by mixing the weighed materials with water. The solids concentration of the slurry is 30% by mass fraction. Perform wet milling to achieve a D50 of 0.30 μm.

[0173] (b) Drying process

[0174] The first precursor particles were formed by spray drying the slurry. The target D50 value of the first 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.

[0175] (c) First firing process

[0176] Mixed particles are formed by mixing the obtained first precursor particles with lithium hydroxide. The amount of lithium hydroxide added is 5% relative to the mass of the first precursor particles. Second precursor particles are formed by calcining the first precursor particles under a nitrogen atmosphere. The conditions for this process are as follows: First, the furnace temperature is increased to 200°C at a heating rate of 3°C / min. The furnace temperature is maintained at 200°C for 1 hour. Next, the furnace temperature is increased to 480°C at a heating rate of 5°C / min. The furnace temperature is maintained at 480°C. Figure 6 The time shown is used. Afterwards, the furnace temperature is cooled to 400°C at a rate of 2°C / minute. Then, the furnace temperature is cooled to room temperature at a rate of 15°C / minute.

[0177] (d) Second firing process

[0178] The obtained second precursor particles were washed with water and dried. The dried second precursor particles were then crushed using a jet mill. Under a nitrogen atmosphere, the crushed second precursor particles were calcined to form the positive electrode active material (LMFP). The conditions for this process are as follows: The furnace temperature was increased at a rate of 5°C / min to... Figure 6 The temperature shown is maintained at this temperature for 4 hours. Afterward, the furnace temperature is cooled to 400°C at a rate of 2°C / min. Then, the furnace temperature is cooled to room temperature at a rate of 15°C / min.

[0179] (No.2~No.6)

[0180] like Figure 6 As shown, the manufacturing process conditions are changed, but the positive electrode active material is manufactured in the same manner as No.1.

[0181] (Making the button unit)

[0182] A mixture is formed by combining a positive electrode active material, a conductive material (acetylene black), and a binder (PVdF). The mixing ratio (mass ratio) is "positive electrode active material / conductive material / binder = 92 / 5 / 3". The mixture is dispersed in a solvent (N-methyl-2-pyrrolidone), thereby forming a paste. 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 To form the positive electrode plate, the positive electrode plate is 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 by punching.

[0183] Button units were assembled inside the glove box. The unit structure is described below.

[0184] Working electrode: Disk-shaped sample (positive electrode)

[0185] Counter electrode: Li foil

[0186] Separator: Polymer porous membrane

[0187] Electrolyte: EC / DMC = 3 / 7 (volume ratio), LiPF6 (1 mol / L)

[0188] <Evaluation>

[0189] (Measurement)

[0190] Figure 6 The recorded proportions (the proportion of primary particles with a contact angle of less than 90° among primary particles with a maximum Ferete diameter of 100 nm or more) and the average contact angle were calculated using the method described above.

[0191] <Evaluation>

[0192] (Rate control characteristics)

[0193] The discharge capacity ratio (1C / 0.1C) is determined using the following steps. A higher discharge capacity ratio (1C / 0.1C) is considered to indicate better rate performance.

[0194] 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.

[0195] The charging rate during CC charging is 0.1C.

[0196] Charging voltage limit: 4.3V

[0197] The cutoff current ratio during CV charging is 0.01C.

[0198] After charging, the button cell was CC-discharged at a rate of 0.1C to 3.0V, and the discharge capacity (0.1C) (mAh / g) was measured. The button cell was then charged again using the same CCCV charging method. After charging, it was CC-discharged at a rate of 1C to 3.0V, and the discharge capacity (1C) was measured. The discharge capacity ratio (1C / 0.1C) was calculated by dividing the discharge capacity (1C) by the discharge capacity (0.1C). The results are shown below. Figure 6 Furthermore, Figure 6 The value of the rate characteristic is a relative value when the discharge capacity ratio of No.1 is set to 100.

[0199] <Results>

[0200] like Figure 6 As shown, when the proportion of primary particles with a contact angle of 90° or less is 40% or more, an improvement in rate performance can be observed. Furthermore, when the proportion of primary particles with a contact angle of 90° or less is 50% or more, a further improvement in rate performance can be observed. Moreover, when the proportion of primary particles with a contact angle of 90° or less is 75% or more, a further improvement in rate performance can be observed.

[0201] While embodiments of the invention have been described, they should be considered illustrative rather than restrictive in all respects. The scope of the invention is defined by the claims, including all modifications within the same meaning and scope as those claims.

Claims

1. A positive electrode active material, The positive electrode active material contains multiple secondary particles. Each of the plurality of secondary particles comprises a plurality of primary particles. Each of the plurality of said primary particles contains an olivine-type phosphate compound. In the scanning electron microscope image of the secondary particles, Of the primary particles with a maximum Feret diameter of 100 nm or more, the proportion of primary particles with a contact angle of 90° or less is 40% or more.

2. The positive electrode active material according to claim 1, In the scanning electron microscope image of the secondary particles, Of the primary particles with a maximum Feret diameter of 100 nm or more, the proportion of primary particles with a contact angle of 90° or less is 75% or more.

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

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

5. The battery according to claim 4, having a bipolar structure.

6. A method for manufacturing a positive electrode active material, comprising the following steps: Step (a): A slurry is formed by mixing a manganese compound, a first lithium compound, a phosphoric acid compound, and a solvent; Step (b): Forming the first precursor particles by drying the slurry; Step (c): Forming the second precursor particles by mixing the first precursor particles and the second lithium compound and performing a first heat treatment; and Process (d): To manufacture olivine-type phosphate compounds by subjecting the second precursor particles to a second heat treatment.

7. The method for manufacturing the positive electrode active material according to claim 6, The duration of the first heat treatment is more than 2 hours and less than 4 hours. The temperature of the second heat treatment is above 600°C and below 750°C.

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