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

Abstract

Improved durability. [Solution] The positive electrode active material contains tertiary particles. The tertiary particles contain a plurality of secondary particles. Each of the plurality of secondary particles contains a plurality of primary particles. Each of the plurality of primary particles contains an olivine-type phosphate compound. In at least a portion of the tertiary particles, voids are formed between the secondary particles.

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material, an electrode, a battery, and a method for manufacturing a positive electrode active material. [Background technology]

[0002] Japanese Patent Publication No. 2014-002857 discloses tertiary particles formed by a mechanochemical method. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-002857 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Olivine-type phosphate compounds are being investigated as positive electrode active materials. For example, nanoparticles containing olivine-type phosphate compounds, secondary particles formed by aggregation of these nanoparticles, and higher-order aggregates (tertiary particles) formed by aggregation of these secondary particles have been proposed. The formation of tertiary particles is expected to improve electrode density.

[0005] However, if the volume change of the active material (olivine-type phosphate compound) is large due to the charge-discharge cycle, strain may accumulate within the tertiary particles due to the volume change of the active material. This strain accumulation may cause the tertiary particle structure to break down. This breakdown of the tertiary particle structure may expose newly formed surfaces of the active material. The leaching of metal from these newly formed surfaces may accelerate capacity degradation. In other words, there is room for improvement in durability.

[0006] The purpose of this disclosure is to improve durability. [Means for solving the problem]

[0007] The technical configuration and effects of this disclosure are described below. However, the mechanism of action of this disclosure includes assumptions. The mechanism of action does not limit the technical scope of this disclosure.

[0008] 1. One aspect of this disclosure is a positive electrode active material. The positive electrode active material comprises tertiary particles. The tertiary particles comprise a plurality of secondary particles. Each of the plurality of secondary particles comprises a plurality of primary particles. Each of the plurality of primary particles comprises an olivine-type phosphate compound. In at least a portion of the tertiary particles, voids are formed between the secondary particles.

[0009] Within the tertiary particles, the voids formed between secondary particles are expected to absorb and alleviate strain caused by volume changes in the active material. Therefore, it is expected that the tertiary particle structure will be more easily maintained during the charge-discharge cycle. In other words, improved durability is expected. Furthermore, it is thought that the voids formed at the joints between secondary particles are more strongly related to the maintenance of the tertiary particle structure than the voids formed within the secondary particles themselves.

[0010] 2. The positive electrode active material described in "1" above may include, for example, the following configuration: The relationship "4.8% ≤ Sv ≤ 29%" is satisfied. "Sv" represents the ratio of the area of ​​the voids formed between secondary particles to the area of ​​the region enclosed by the contour lines of the tertiary particles in the cross-section of the tertiary particles.

[0011] The relationship "4.8% ≤ Sv ≤ 29%" is satisfied, which is expected to improve durability.

[0012] 3. The positive electrode active material described in "1" or "2" above may include, for example, the following configuration: The tertiary particles include 2 to 20 secondary particles.

[0013] 4. The positive electrode active material described in any one of items "1" to "3" above may include, for example, the following components: The olivine-type phosphate compound contains lithium iron manganese phosphate.

[0014] Olivine-type phosphate compounds may include, for example, lithium iron phosphate (hereinafter abbreviated as "LFP") and lithium manganese iron phosphate (hereinafter abbreviated as "LMFP"). LMFP tends to exhibit larger volume changes during charging and discharging compared to LFP. The elution of manganese (Mn) from newly formed surfaces resulting from the collapse of the three-dimensional structure tends to accelerate the degradation of LMFP's capacity. The tertiary particle structure of this disclosure is expected to have a high affinity for LMFP.

[0015] 5. One aspect of this disclosure is an electrode. The electrode includes a positive electrode layer. The positive electrode layer includes a positive electrode active material as described in any one of items 1 to 4.

[0016] The positive electrode layer can be referred to as the "positive electrode active material layer," "positive electrode composite material layer," etc. Furthermore, the "electrode" may be either a "monopolar electrode (positive electrode)" or a "bipolar electrode," as long as it includes the positive electrode layer.

[0017] 6. One aspect of this disclosure is a battery, which includes the electrodes described in "5" above.

[0018] The battery is expected to have excellent durability.

[0019] 7. The battery described in "6" above may include, for example, the following configuration: The battery has a bipolar structure.

[0020] A bipolar structure can be formed by stacking bipolar electrodes. This bipolar structure is expected to improve, for example, output characteristics.

[0021] 8. One aspect of this disclosure is a method for producing a positive electrode active material. The method for producing a positive electrode active material includes (a) to (c) below. (a) A slurry is formed containing a lithium compound, a phosphate compound, a pore-forming agent, and a solvent. (b) Tertiary particles are formed by spray-drying the slurry. (c) The positive electrode active material is manufactured by applying heat treatment to the tertiary particles. The above (b) includes (b1) through (b3) below. (b1) Forms moist secondary particles. (b2) Wet secondary particles are brought into contact with other wet secondary particles to form wet tertiary particles. (b3) By drying the moist tertiary particles, tertiary particles containing multiple secondary particles are formed. The wet secondary particles consist of a solvent, a pore-forming material, and multiple precursor primary particles. Each of the multiple precursor primary particles contains a precursor. The above (c) includes (c1) and (c2) below. (c1) By eliminating at least a portion of the porosity-forming material, voids are formed between the secondary particles. (c2) Synthesize an olivine-type phosphate compound from the precursor.

[0022] For example, a pore-forming agent that disappears during firing may be added to the slurry (raw material mixture). During spray drying, at least a portion of the pore-forming agent may adhere to the surface of secondary particles. Tertiary particles are formed by the bonding of the secondary particles together. During firing, the pore-forming agent disappears, which may create voids at the bonding points between the secondary particles. That is, voids may be formed between the secondary particles.

[0023] 9. The method for producing the positive electrode active material described in "8" above may include, for example, the following components: The pore-forming material contains boric acid (H3BO3).

[0024] Boric acid can decompose during the firing process.

[0025] Hereinafter, one embodiment of the present disclosure (which may be abbreviated as "this embodiment") and one example of the present disclosure (which may be abbreviated as "this example") will be described. However, this embodiment and this example will not limit the technical scope of the present disclosure. This embodiment and this example are illustrative in all respects. This embodiment and this example are not restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the claims. For example, it is intended from the outset that any configuration may be extracted from this embodiment and combined in any way. [Brief explanation of the drawing]

[0026] [Figure 1] This is the first conceptual diagram of the tertiary particle in this embodiment. [Figure 2] This is a second conceptual diagram of the tertiary particle in this embodiment. [Figure 3] This is a conceptual diagram of the contact angle of secondary particles. [Figure 4] This is a schematic flowchart of the method for manufacturing the positive electrode active material in this embodiment. [Figure 5] This is a schematic perspective view of the battery in this embodiment. [Figure 6] This is a schematic cross-sectional view along the line VI-VI in Figure 5. [Figure 7] This is a table showing the experimental results. [Figure 8] This is the temperature profile during firing. [Modes for carrying out the invention]

[0027] -Terminology and vocabulary- "Equipped with," "includes," "possesses," and variations thereof are open-ended expressions. Configurations expressed in an open-ended manner may or may not include additional elements in addition to the essential elements. The statement "consists of" is a closed expression. However, even configurations expressed in a closed manner may include additional elements that are usually incidental impurities or irrelevant to the subject technology. The statement "substantially consists of..." is a semi-closed expression. In configurations expressed in a semi-closed manner, the addition of elements that do not substantially affect the basic and novel characteristics of the subject technology is permitted.

[0028] Expressions such as "may do" and "may be" are used in a permissive sense, meaning "there is a possibility," rather than in an obligatory sense, meaning "it must be done."

[0029] Unless otherwise specified, the order in which the various steps, actions, and operations included in each method are executed is not limited to the order in which they are described. For example, multiple steps may occur simultaneously. For example, multiple steps may occur one after the other.

[0030] Expressions such as "first," "second," etc., are used solely to distinguish between multiple elements. These expressions do not limit the elements to which they are attached. They are unrelated, for example, to the order or importance of the elements to which they are attached.

[0031] Geometric terms should not be interpreted strictly. Examples of geometric terms include "parallel," "perpendicular," and "orthogonal." For example, direction, angle, distance, etc., may be relatively distorted within a range where substantially the same or similar function is obtained. Geometric terms may include tolerances, errors, etc., in design, operation, and manufacturing. Dimensional relationships in each figure may not match actual dimensional relationships. Dimensional relationships in each figure may be modified to aid the reader's understanding. For example, length, width, thickness, etc., may be changed. Some components may be omitted.

[0032] Elements described in the singular form may also include plural forms unless otherwise specified. For example, "particle" may refer to multiple particles, a collection of particles, or a granular material.

[0033] Numerical ranges such as "m to n%" include upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less". Also, "m% or more and n% or less" includes "greater than m% and less than n%". "Greater than or equal to" and "less than or equal to" are represented by the equals sign inequality signs "≦" and "≧". "Greater than" and "less than" are represented by the inequality signs without an equals sign "<" and ">". A number arbitrarily selected from within the numerical range may be used as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a number within the numerical range with a number listed in another part of this specification, in a table, in a figure, etc.

[0034] All numerical values ​​are modified by the term "approximately." The term "approximately" can mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximations that can vary depending on the application of the technology in question. All numerical values ​​may be expressed with significant figures. Unless otherwise specified, measured values ​​may be the average of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. Generally, the more measurements taken, the more reliable the average value is expected to be. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors such as those associated with the detection limits of the measuring device.

[0035] The devices used to measure various values ​​are merely examples. Equivalent devices may be used. If equivalent devices are used, the measurement conditions may be adjusted to suit the device.

[0036] Figure 1 is a first conceptual diagram of the tertiary particle in this embodiment. Figure 2 is a second conceptual diagram of the tertiary particle in this embodiment. In Figure 2, a cross-section of the tertiary particle 3 in Figure 1 is conceptually shown. The number of secondary particles 2 constituting the tertiary particle 3, "Sn", can be measured by the following procedure. For example, a dispersion is formed by dispersing 1 g of positive electrode active material (powder) in a mixture (10 g) of the main component and curing agent of epoxy resin (product name "EPOTEX JP", manufactured by Nisshin EM Co., Ltd.). The dispersion is stirred and mixed for 1 minute using a mixer (product name "Awatori Rentaro", manufactured by Shinky Co., Ltd.). The stirring speed may be, for example, about 2000 rpm. The dispersion is degassed under vacuum. After degassing under vacuum, the dispersion is filled into a cylindrical container made of resin. The epoxy resin hardens when the dispersion is left for 1 day. After hardening, a cross-sectional sample with a smooth cross-section is prepared by wet polishing the hardened material. A cross-sectional SEM (Scanning Electron Microscope) observation of the smooth cross-section is performed to obtain a cross-sectional SEM image of the positive electrode active material. Within the image, multiple tertiary particles 3 are randomly selected. For example, five or more tertiary particles 3 may be selected. The number of secondary particles 2 "Sn" contained in each tertiary particle 3 is counted. In the cross-sectional SEM image, "secondary particles 2" are aggregates of primary particles 1 contained in the tertiary particles 3 and represent regions with closed contour lines. The arithmetic mean of Sn for five or more tertiary particles 3 is adopted.

[0037] The void ratio "Sv" is also measured in the cross-sectional SEM image described above. The area (S0) of the region enclosed by the contour lines of the tertiary particle 3 is measured. For example, the area may be measured using image analysis software such as "ImageJ". The voids 4 formed between the secondary particles 2 are identified. The voids 4 formed between the secondary particles 2 satisfy the following conditions (1) and (2). (1) The gap 4 is a closed vent. (2) The outline of the void 4 includes part of the outlines of two or more secondary particles 2. For example, voids 4 may be identified by applying a binarization process to the SEM image. The area "S1" of the voids 4 formed between secondary particles 2 is measured. If multiple voids 4 exist, the total area of ​​the multiple voids 4 is considered "S1". Voids formed within secondary particles 2 are not counted. Sv is calculated by dividing the area "S1" of voids 4 by the area "S0" of the tertiary particles. Sv is expressed as a percentage. The arithmetic mean of Sv for five or more tertiary particles 3 is used. Note that the determination of whether or not a void 4 is formed between secondary particles 2 may be performed using supervised machine learning.

[0038] A "closed pore" refers to a void that does not connect to the outside. An "open pore" refers to a void that connects to the outside. Whether or not a pore is closed is determined by its appearance in the cross-sectional SEM image. In other words, even if there is a possibility of connecting to the outside in areas that are not visible in the cross-sectional SEM image, as long as it is recognized as a closed pore in the cross-sectional SEM image, the void is considered a closed pore.

[0039] The "maximum Ferret diameter" of a particle or similar object indicates the length of the longer side of the bounding rectangle (rectangle or square) around the particle. If the bounding rectangle is a square, the length of the longer side indicates the length of one side. The maximum Ferret diameter of a primary particle can be measured, for example, in a TEM (Transmission Electron Microscopy) image. The arithmetic mean of 30 particles (tertiary, secondary, or primary particles) is used to determine the maximum Ferret diameter.

[0040] "D50" indicates the particle size at which the cumulative particle size distribution (cumulative distribution) reaches 50% in the volume-based particle size distribution. The particle size distribution can be measured by laser diffraction.

[0041] "Wet" refers to a state of being moist due to a solvent. For example, "wet secondary particles" refers to secondary particles that are not completely dry and are in a moist state because some solvent remains.

[0042] The stoichiometric composition formula shows a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to compounds with a molar ratio of "Al / O = 2 / 3". Unless otherwise specified, "Al2O3" refers to a compound containing Al and O in any molar ratio. For example, the compound may be doped with trace elements. Some of the Al and O may be substituted with other elements.

[0043] The chemical composition of a compound can be measured by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy). A sample solution is prepared by dissolving 0.1 g of the sample (e.g., positive electrode active material) in a mixed acid (10 ml) of hydrochloric acid and sulfuric acid. The sample solution is diluted to an appropriate concentration in a volumetric flask. After dilution, compositional analysis is performed using an ICP-AES instrument. For example, a product name such as "PS3520 UVDD II (manufactured by Hitachi High-Tech Science Corporation)" may be used.

[0044] A "derivative" refers to a compound in which a part of the parent compound has been modified by at least one of the following chemical reactions: introduction of a functional group, substitution of atoms, oxidation, reduction, and other chemical reactions. The modification may be at one location or multiple locations. The "substituents" may include at least one selected from the group consisting of, for example, alkyl groups, alkenyl groups, alkynyl groups, cycloalkyl groups, unsaturated cycloalkyl groups, aromatic groups, heterocyclic groups, halogen atoms (F, Cl, Br, I, etc.), OH groups, SH groups, CN groups, SCN groups, OCN groups, nitro groups, alkoxy groups, unsaturated alkoxy groups, amino groups, alkylamino groups, dialkylamino groups, aryloxy groups, acyl groups, alkoxycarbonyl groups, acyloxy groups, aryloxycarbonyl groups, acylamino groups, alkoxycarbonylamino groups, aryloxycarbonylamino groups, sulfonylamino groups, sulfamoyl groups, carbamoyl groups, alkylthio groups, arylthio groups, sulfonyl groups, sulfinyl groups, ureido groups, phosphate amide groups, sulfo groups, carboxyl groups, hydroxamic acid groups, sulfino groups, hydrazino groups, imino groups, and silyl groups. These substituents may be further substituted. If there are two or more substituents, the substituents may be the same or different. Multiple substituents may be bonded to each other to form a ring.

[0045] -Cathode active material- The positive electrode active material contains tertiary particles 3. The positive electrode active material may also be an aggregate of tertiary particles 3. That is, the positive electrode active material may be a powder. The D50 of the positive electrode active material may be, for example, 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more. The D50 of the positive electrode active material may also be, for example, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0046] The positive electrode active material may further contain secondary particles that do not constitute tertiary particles 3, as long as it contains tertiary particles 3. The number ratio of tertiary particles 3 in the positive electrode active material may be, for example, 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more. The proportion of tertiary particles 3 in the positive electrode active material may also be, for example, 100% or less, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less.

[0047] A tertiary particle 3 contains multiple secondary particles 2. That is, the number of secondary particles 2 constituting the tertiary particle 3, "Sn," is 2 or more. The number of secondary particles "Sn" may be, for example, 3 or more, 4 or more, 5 or more, 10 or more, 15 or more, or 20 or more. The number of secondary particles "Sn" may also be, for example, 50 or less, 40 or less, 30 or less, 20 or less, 15 or less, 10 or less, or 5 or less.

[0048] In at least a portion of the tertiary particle 3, voids 4 (closed pores) are formed between the secondary particles 2. In other words, voids 4 are formed in at least a portion of the bonding areas between the secondary particles 2. It is expected that durability will be improved as the voids 4 absorb the strain caused by the volume change of the active material.

[0049] The area ratio "Sv" of void 4 may be between 4.8% and 29%. Improved durability is expected when the relationship "4.8% ≤ Sv ≤ 29%" is satisfied. The area ratio "Sv" of void 4 may be, for example, 5% or more, 7.5% or more, 10% or more, 12.5% ​​or more, 15% or more, 17.5% or more, 20% or more, 22.5% or more, 25% or more, or 27.5% or more. The area ratio "Sv" of void 4 may be, for example, 27.5% or less, 25% or less, 22.5% or less, 20% or less, 17.5% or less, 15% or less, 12.5% ​​or less, 10% or less, 7.5% or less, or 5% or less. Note that open pores may be formed in the secondary particles 2.

[0050] Figure 3 is a conceptual diagram of the contact angle of secondary particles. The contact angle "θ" between secondary particles 2 is measured in a cross-sectional SEM image. A straight line "L0" is drawn passing through both ends of the joint between the secondary particles 2. A tangent line "L1" is drawn at the intersection of the straight line "L0" and the contour line of the secondary particle 2. The angle formed within the secondary particle 2 from the angle between the straight line "L0" and the tangent line "L1" is considered to be the contact angle "θ". If multiple contact angles "θ" can be identified within a single tertiary particle 3, the arithmetic mean of two or more contact angles "θ" within that tertiary particle 3 is adopted. Furthermore, the arithmetic mean of the contact angles "θ" in 10 or more tertiary particles 3 is considered to be the contact angle of the object being measured (positive electrode active material). The contact angle "θ" may be greater than 90°, for example. The contact angle "θ" may be less than 180°, for example. The contact angle "θ" may be, for example, 105° or more, 120° or more, 135° or more, 150° or more, or 165° or more. The contact angle "θ" may also be, for example, 165° or less, 150° or less, 135° or less, 120° or less, or 105° or less. For example, it may be difficult to achieve a contact angle greater than 90° and less than 180° by mechanochemical methods.

[0051] The maximum Ferret diameter of the tertiary particle 3 may be, for example, 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more. The maximum Ferret diameter of the tertiary particle 3 may be, for example, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0052] The maximum Ferret diameter of secondary particle 2 may be, for example, 2.5 μm or more, 5 μm or more, 7.5 μm or more, or 10 μm or more. The maximum Ferret diameter of secondary particle 2 may be, for example, 15 μm or less, 10 μm or less, 7.5 μm or less, 5 μm or less, or 2.5 μm or less.

[0053] The maximum Ferret diameter of primary particle 1 may be, for example, 10 to 90 nm. The maximum Ferret diameter of primary particle 1 may be, for example, 20 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, or 80 nm or more. The maximum Ferret diameter of primary particle 1 may be, for example, 80 nm or less, or 60 nm or less.

[0054] Carbon may be attached to at least a portion of the surface of the primary particle 1. The carbon may form a carbon layer 5. The amount of attached carbon may be, for example, 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, or 4% or more by mass fraction relative to the tertiary particle 3. The amount of attached carbon may be, for example, 5% or less, 4% or less, or 3% or less by mass fraction relative to the tertiary particle 3.

[0055] Each of the multiple primary particles 1 contains an olivine-type phosphate compound. The olivine-type phosphate compound contains an olivine-type crystalline phase. "Olivine-type" refers to a crystalline structure belonging to the space group Pnma. The space group is identified by powder XRD (X-ray diffraction) measurement. The olivine-type phosphate compound may further contain any crystalline phase as long as it contains an olivine-type crystalline phase. The olivine-type phosphate compound may contain, for example, at least one selected from the group consisting of LFP, lithium manganese phosphate (which may be abbreviated as "LMP"), and LMFP.

[0056] Olivine-type phosphate compounds may have, for example, a composition represented by the following general formula. Li 1-a Mn 1-x Fe x PO4 For example, the relationship "-0.5 ≤ a ≤ 0.5" may be satisfied. x may be, for example, 0 or greater, 0.05 or greater, 0.1 or greater, 0.2 or greater, 0.3 or greater, 0.4 or greater, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.8 or greater, or 0.9 or greater. x may be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0057] In LMFPs, elements other than lithium (Li), manganese (Mn), Fe, phosphorus (P), and oxygen (O) may be doped (dopants). The doping amount (molecular fraction relative to the amount of Li) may be, for example, 0.01 to 0.1. Examples of dopants include boron (B), nitrogen (N), halogens, silicon (Si), sodium (Na), magnesium (Mg), aluminum (Al), chromium (Cr), scandium (Sc), titanium (Ti), vanadium (V), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), selenium (Se), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), and lead (Pb). It may also contain at least one selected from the group consisting of 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.

[0058] The positive electrode active material may further contain other components as long as it contains an olivine-type phosphate compound. The other components may include, for example, lithium nickel composite oxide (LNO), lithium cobalt composite oxide (LCO), lithium manganese composite oxide (LMO), and the like. The mixing ratio (mass ratio) of the olivine-type phosphate compound and the other components may 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". The positive electrode active material may be, for example, a mixture of a powder of an olivine-type phosphate compound and a powder of other components.

[0059] LNO may have, for example, a crystal structure belonging to the space group R-3m. LNO may have, for example, a composition represented by the following general formula. Li 1-a Ni x M 1-x O2 In the formula, the relationship of -0.5 ≦ a ≦ 0.5 and 0 ≦ x ≦ 1 is satisfied. M may include, for example, at least one selected from the group consisting of Co, Mn, and Al. For example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x ≦ 1 may be satisfied. For example, the relationship of -0.4 ≦ a ≦ 0.4, -0.3 ≦ a ≦ 0.3, -0.2 ≦ a ≦ 0.2, or -0.1 ≦ a ≦ 0.1 may be satisfied.

[0060] LNO may include, for example, at least one selected from the group consisting of LiNi 0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O2, and LiNiO2.

[0061] LNO may be represented, for example, by the following general formula. The compound represented by the following general formula may also be referred to as "NCM". Li 1-a Ni x Co y Mn z O2 In the formula, the relationships -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y <  1, 0 < z < 1, and x + y + z = 1 are satisfied. For example, the relationship 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4,   0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1 may be satisfied. For example, the relationship 0 < y ≦ 0.1, 0.1 ≦ y ≦ 0.2, 0.2 ≦ y ≦ 0.3,   0.3 ≦ y ≦ 0.4, 0.4 ≦ y ≦ 0.5, 0.5 ≦ y ≦ 0.6, 0.6 ≦ y ≦ 0.7, 0.7 ≦ y ≦ 0.8, 0.8 ≦ y ≦ 0.9, or 0.9 ≦ y < 1 may be satisfied. For example, the relationship 0 < z ≦ 0.1, 0.1 ≦ z ≦ 0.2, 0.2 ≦ z ≦ 0.3, 0.3 ≦ z ≦ 0.4, 0.4 ≦ z ≦ 0.5, 0.5 ≦ z ≦ 0.6, 0.6 ≦ z ≦ 0.7, 0.7 ≦ z ≦ 0.8, 0.8 ≦ z ≦ 0.9, or 0.9 ≦ z < 1 may be satisfied.

[0062] NCM is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn<000003五>O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi0.6 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 [[ID=4)]] It may contain at least one selected from the group consisting of O2.

[0063] LNO may be represented by, for example, the following general formula. The compound represented by the following general formula may also be referred to as "NCA". Li 1-a Ni x Co y Al z O2 In the formula, the relationships -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied. For example, the relationship 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x < 1 may be satisfied. For example, the relationship 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9, or 0.9 ≤ y < 1 may be satisfied. For example, the relationship 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1 may be satisfied.

[0064] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O2, LiLiLi 0.7 Co 0.2 Al 0.1 O2, LiLiLi 0.8 Co 0.1 Al 0.1 O2, LiLiLi 0.8 Co 0.17 Al 0.03 O2, LiLiLi 0.8 Co 0.15 Al 0.05 O2 and LiNi 0.9 Co 0.05 Al 0.05 It may contain at least one selected from the group consisting of O2.

[0065] -Method for manufacturing positive electrode active material- Figure 4 is a schematic flowchart of the method for producing the positive electrode active material in this embodiment. Hereinafter, "the method for producing the positive electrode active material in this embodiment" may be abbreviated as "this method". This method includes "(a) slurry formation", "(b) granulation", and "(c) calcination".

[0066] (a) Formation of slurry This method involves forming a slurry containing a lithium compound, a phosphate compound, a pore-forming agent, and a solvent. The slurry may further contain, for example, a manganese compound and an iron compound. For example, the slurry may be formed by dispersing each material in a solvent. For example, a material with the composition formula "Li 1-a Mn 1-x Fe x Lithium compounds, manganese compounds, phosphate compounds, and iron compounds may be weighed out to achieve the composition ratio (mole ratio) shown in PO4 (-0.5 ≤ a ≤ 0.5, 0 ≤ x ≤ 1). The lithium compound may include, for example, lithium hydroxide. The manganese compound may include, for example, manganese carbonate. The phosphate compound may include, for example, lithium dihydrogen phosphate. The iron compound may include, for example, ferric phosphate.

[0067] The slurry may be formed to further contain carbon material. The carbon material may form a carbon layer on the surface of the primary particles. The carbon material may include, for example, glucose, sucrose, fructose, citric acid, etc. The amount of carbon material added may be, for example, 1 to 20% by mass fraction relative to the raw material mixture (total of lithium compounds, manganese compounds, phosphate compounds, and iron compounds).

[0068] The pore-forming material forms voids in the tertiary particles. The pore-forming material may have a decomposition point below the firing temperature. The decomposition point of the pore-forming material may be, for example, 150°C or higher, 200°C or higher, or 250°C or higher. The decomposition point of the pore-forming material may be, for example, 300°C or lower, 250°C or lower, or 200°C or lower. The pore-forming material may contain, for example, boric acid. The aforementioned void ratio "Sv" may be adjusted, for example, by the amount of pore-forming material added. The amount of pore-forming material added to the raw material mixture may be, for example, 0.1% or more, 0.5% or more, 1% or more, 3% or more, 5% or more, or 7% or more by mass fraction. The amount of pore-forming material added may be, for example, 10% or less, 9% or less, 8% or less, 7% or less, 5% or less, or 3% or less. The range of the amount of pore-forming material added may change depending on the density of the pore-forming material, etc.

[0069] The solvent may include, for example, water. The solid content concentration of the slurry may be, for example, 20 to 40% by mass fraction.

[0070] (b) Granulation This method involves forming tertiary particles by spray-drying a slurry. Here, since LMP and LMFP have higher resistance than LFP, miniaturization of the primary particles is required compared to LFP in order to achieve a practical level of resistance. When the size of the primary particles becomes smaller, they enter a stable energy state, which promotes aggregation and tends to form larger secondary particles. Furthermore, by lowering the spray pressure (nozzle pressure) during spray drying and drying at a low temperature, collisions between wet secondary particles can be induced before the granules (wet secondary particles) are completely dry. Tertiary particles can be formed through collisions and contact between wet secondary particles. In conventional spray drying, wet secondary particles are dried rapidly at high temperatures, making collisions between wet secondary particles less likely, and thus making it difficult for tertiary particles to form.

[0071] In this method, "(b) Granulation" more specifically includes "(b1) Formation of wet secondary particles," "(b2) Formation of wet tertiary particles," and "(b3) Drying of wet tertiary particles." In (b1), wet secondary particles are formed. Wet secondary particles are precursors of secondary particles. Wet secondary particles contain a solvent, a pore-forming agent, and a plurality of precursor primary particles. Precursor primary particles contain precursors such as LMFP. In (b2), wet tertiary particles are formed by the contact of wet secondary particles with other wet secondary particles. In (b3), the solvent evaporates as the wet tertiary particles are dried, forming tertiary particles containing a plurality of secondary particles. The settings of the spray dryer are combined so that (b1), (b2), and (b3) occur during the granulation process. The intake port temperature may be, for example, around 250°C. The exhaust port temperature may be, for example, 115±15°C. The intake pressure may be, for example, around 2.0 MPa. The nozzle pressure may be, for example, 0.2 to 0.3 MPa.

[0072] (c) Firing This method involves producing a positive electrode active material by heat-treating tertiary particles. In this method, "(c) calcination" specifically includes "(c1) void formation" and "(c2) synthesis of the active material." In (c1), voids may be formed between secondary particles by the disappearance of at least a portion of the pore-forming material. Part of the pore-forming material may disappear, or all of it may disappear. For example, during the heating process in calcination, the pore-forming material may decompose if the furnace temperature exceeds the decomposition point of the pore-forming material. In (c2), an olivine-type phosphate compound is synthesized from the precursor by heating the precursor primary particles. (c1) and (c2) may proceed substantially simultaneously.

[0073] In this method, any heat treatment furnace (e.g., electric furnace, muffle furnace, etc.) may be used. The heat treatment atmosphere may be, for example, an inert atmosphere. The inert atmosphere may be, for example, a nitrogen atmosphere. The heat treatment temperature may be, for example, 400 to 700°C. The heat treatment time may be, for example, 4 to 6 hours.

[0074] -Liquid battery- In some embodiments of this invention, the battery may be a liquid-based battery. A "liquid-based battery" refers to a battery containing an electrolyte. For example, polymer batteries, because they contain an electrolyte, belong to the category of liquid-based batteries. In some embodiments of this invention, the battery has a monopolar structure. In some embodiments of this invention, the battery has a bipolar structure. As an example, a battery having a bipolar structure (a bipolar battery) is described.

[0075] Figure 5 is a schematic perspective view of the battery in this embodiment. Figure 6 is a schematic cross-sectional view along the line VI-VI in Figure 5. Hereinafter, "orthoplane direction" refers to the direction normal to the surface of a sheet-like member (e.g., foil, electrode, etc.). "In-plane direction" refers to any direction perpendicular to the orthoplane direction. In the figures of this embodiment, the Z-axis direction corresponds to the orthoplane direction. The X-axis and Y-axis directions are examples of in-plane directions.

[0076] The battery 100 includes an outer casing 90 and a power generation element 50. The outer casing 90 houses the power generation element 50. The outer casing 90 may include, for example, a first current collector plate 91, a first laminate film 92, a second laminate film 93, and a second current collector plate 94. The first laminate film 92 and the second laminate film 93 are joined to each other at their in-plane edges. At the joint between the first laminate film 92 and the second laminate film 93, a sealing material (not shown) may be interposed between the first laminate film 92 and the second laminate film 93.

[0077] The first current collector plate 91 and the second current collector plate 94 are joined to the power generation element 50 at their ends in the stacking direction (Z-axis direction). The first laminate film 92 is joined to the first current collector plate 91. The second laminate film 93 is joined to the second current collector plate 94. A sealing material (not shown) may be interposed between the current collector plate and the laminate film at the joint between the current collector plate and the laminate film.

[0078] The power generation element 50 includes a plurality of bipolar electrodes 10. The plurality of bipolar electrodes 10 are stacked in the direction perpendicular to the plane (Z-axis direction). Each of the plurality of bipolar electrodes 10 includes, in the direction perpendicular to the plane, a positive electrode layer 11, a current collector foil 13, and a negative electrode layer 12 in this order. In the in-plane direction (for example, in the X-axis direction), the current collector foil 13 extends outward relative to the positive electrode layer 11 and the negative electrode layer 12. For example, the current collector foil 13 may extend outward relative to the positive electrode layer 11 and the negative electrode layer 12 over the entire circumference in the in-plane direction.

[0079] The current collector foil 13 is a conductor. The current collector foil 13 may include, for example, a metal foil, a conductive resin layer, etc. For example, the current collector foil 13 may be formed by bonding an Al foil and a Cu foil together. A carbon material may be coated on the surface of the current collector foil 13. The carbon material may include, for example, carbon black.

[0080] The power generation element 50 includes a sealing material 30. At its in-plane end, the sealing material 30 is joined to the current collector foil 13. The sealing material 30 may, for example, be heat-welded to the current collector foil 13. For example, the sealing material 30 may be arranged around the entire circumference of the in-plane periphery. The sealing material may include, for example, a resin material. The sealing material 30 seals between adjacent current collector foils 13 in the direction perpendicular to the plane. The sealing material 30 between the current collector foils 13 partitions the cells 40. A cell 40 is the smallest unit of the power generation element 50. The battery 100 includes multiple cells 40 and may also be called a "bipolar module". Each of the multiple cells 40 is sealed. The multiple cells 40 are isolated from each other. Each of the multiple cells 40 includes a positive electrode layer 11, a separator 20, a negative electrode layer 12, and an electrolyte.

[0081] Positive electrode layer The positive electrode layer 11 is attached to one side of the current collector foil 13. For example, grooves may be formed in the positive electrode layer 11. The positive electrode layer 11 may be formed in a striped pattern, for example. The positive electrode layer 11 contains a positive electrode active material. That is, the battery 100 contains a positive electrode active material. Details of the positive electrode active material are as described above.

[0082] The positive electrode layer 11 may further contain, for example, a conductive material and a binder, in addition to the positive electrode active material. The amount of conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of positive electrode active material. The conductive material may contain any components. For example, the conductive material may contain at least one selected from the group consisting of graphite, acetylene black (AB), Ketjenblack (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF).

[0083] The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of positive electrode active material. The binder may contain any components. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ethers, and derivatives thereof.

[0084] The positive electrode layer 11 may further contain, for example, inorganic fillers, organic fillers, solid electrolytes, surface modifiers, dispersants, lubricants, flame retardants, protective agents, fluxes, coupling agents, adsorbents, etc. The positive electrode active material layer may contain, for example, polyoxyethylene allylphenyl ether phosphate, zeolite, silane coupling agents, MoS2, WO3, etc.

[0085] Negative electrode layer The negative electrode layer 12 is attached to one side of the current collector foil 13. The negative electrode layer 12 is located on the back side of the positive electrode layer 11. The negative electrode layer 12 may have a larger area than the positive electrode layer 11. The negative electrode layer 12 contains a negative electrode active material.

[0086] The negative electrode active material may be in the form of parts or sheets, for example. The D50 of the negative electrode active material may be, for example, 1 μm or more, 5 μm or more, or 10 μm or more. The D50 of the negative electrode active material may be, for example, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0087] The negative electrode active material may contain any components. For example, the negative electrode active material may include at least one selected from the group consisting of carbon-based active materials, alloy-based active materials, Si-C composite materials, Li metal, Li-based alloys, and lithium titanate. In some embodiments of this invention, the battery may be a Li metal negative electrode battery.

[0088] The carbon-based active material may contain at least one selected from the group consisting of, for example, graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. Graphite may be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1", "natural graphite / artificial graphite = 2 / 8 to 8 / 2", or "natural graphite / artificial graphite = 3 / 7 to 7 / 3".

[0089] The surface of the graphite may be coated with, for example, amorphous carbon. The surface of the graphite may be coated with, for example, a different material. The different material may contain at least one selected from the group consisting of, for example, P, W, Al, and O. The different material may contain at least one selected from the group consisting of, for example, Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO 3、 and, for example, at least one selected from the group consisting of Li3PO4.

[0090] The alloy-based active material may contain at least one selected from the group consisting of, for example, Si, Li silicate, SiO, Si-based alloy, tin (Sn), SnO, and Sn-based alloy.

[0091] SiO may be represented, for example, by the following general formula. SiO x In the formula, the relationship 0 < x < 2 is satisfied. For example, the relationship 0.5 ≤ x ≤ 1.5, or 0.8 ≤ x ≤ 1.2 may be satisfied.

[0092] "Si-C composite material" refers to a composite material of a carbon-based active material (such as graphite) and an alloy-based active material (such as Si). For example, Si fine particles may be dispersed in carbon particles. For example, Si fine particles may be dispersed in graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon).

[0093] \7]] Separator The separator 20 can separate the positive electrode layer 11 from the negative electrode layer 12. The separator 20 has electrical insulating properties. The separator 20 may include, for example, at least one selected from the group consisting of a resin film (polymer film), an inorganic particle layer, and an organic particle layer. The separator 20 may include, for example, a resin film and an inorganic particle layer.

[0094] The resin film is porous. The resin film may include, for example, a microporous membrane, a nonwoven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may be continuous, for example, in a mesh-like manner. Pores are formed in the gaps of the resin skeleton. The resin film can permeate the electrolyte. The resin film may have, for example, an average pore diameter of 1 μm or less. The average pore diameter of the resin film may be, for example, 0.01 to 1 μm, or 0.1 to 0.5 μm. The "average pore diameter" can be measured by the mercury intrusion method. The Gaurle value of the resin film is, for example, 50 to 250 s / 100 cm. 3 It may also be the case that the "Gehré value" can be measured by the Gehré test method.

[0095] The resin film may contain at least one selected from the group consisting of, for example, olefin resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, acrylic resins, and polyester resins. The resin film may also contain at least one selected from the group consisting of, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamide-imide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and derivatives thereof. The resin film can be formed, for example, by stretching, phase separation, or the like. The thickness of the resin film may be, for example, 5 to 50 μm or 10 to 25 μm.

[0096] The resin film may have, for example, a single-layer structure. The resin film may consist of, for example, a PE layer. The framework of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multilayer structure. The resin film may include, for example, a PP layer and a PE layer. The framework of the PP layer is formed of PP. The resin film may have, for example, a three-layer structure. The resin film may be formed by laminating a PP layer, a PE layer and a PP layer in this order. The thickness of the PE layer may be, for example, 5 to 20 μm. The thickness of the PP layer may be, for example, 3 to 10 μm.

[0097] The inorganic particle layer may be formed on the surface of the resin film. The inorganic particle layer may be formed on only one side of the resin film or on both sides. The inorganic particle layer may be formed on the surface facing the positive electrode layer 11 or on the surface facing the negative electrode layer 12. The inorganic particle layer may be formed on the surface of the positive electrode layer 11 or on the surface of the negative electrode layer 12.

[0098] The inorganic particle layer is porous. The inorganic particle layer contains inorganic particles. The inorganic particles may also be called "inorganic fillers." Pores are formed in the gaps between the inorganic particles. The thickness of the inorganic particle layer may be, for example, 0.5 to 10 μm or 1 to 5 μm. The inorganic particles may contain, for example, a heat-resistant material. An inorganic particle layer containing a heat-resistant material is also called an "HRL (Heat Resistance Layer)." The inorganic particles may contain at least one selected from the group consisting of boehmite, alumina, zirconia, titania, magnesia, and silica. The inorganic particles may have any shape. For example, the inorganic particles may be spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the inorganic particles may be, for example, 0.1 to 10 μm or 0.5 to 3 μm. The inorganic particle layer may further contain a binder. The binder may include, for example, at least one selected from the group consisting of acrylic resins, polyamide resins, fluororesins, aromatic polyether resins, and liquid crystal polyester resins.

[0099] The separator 20 may include, for example, an organic particle layer. The separator 20 may include, for example, an organic particle layer instead of a resin film. The separator 20 may include, for example, an organic particle layer instead of an inorganic particle layer. The separator 20 may include both a resin film and an organic particle layer. The separator 20 may include both an inorganic particle layer and an organic particle layer. The separator 20 may include a resin film, an inorganic particle layer, and an organic particle layer.

[0100] The thickness of the organic particle layer may be, for example, 0.1 to 50 μm, 0.5 to 20 μm, 0.5 to 10 μm, or 1 to 5 μm. The organic particle layer contains organic particles. The organic particles may also be called "organic fillers". The organic particles may contain heat-resistant materials. The organic particles may contain at least one selected from the group consisting of, for example, PE, PP, PTFE, PI, PAI, PA, and aramid. The organic particles may be spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the organic particles may be, for example, 0.1 to 10 μm, or 0.5 to 3 μm.

[0101] The separator 20 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0102] electrolyte The electrolyte is a liquid electrolyte. The electrolyte contains a solute and a solvent. The concentration of the solute may be, for example, 0.5 to 1 mole / L, 1 to 1.5 mole / L, 1.5 to 2 mole / L, 2 to 2.5 mole / L, or 2.5 to 3 mole / L. "mol / L" may also be written as "M". The solute contains a supporting salt (Li salt). The solute may also contain, for example, inorganic acid salts, imide salts, oxalate complexes, halides, etc. The solute may include, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiAsF6, LiSbF6, LiN(SO2F)2 "LiFSI", LiN(SO2CF3)2 "LiTFSI", LiB(C2O4)2 "LiBOB", LiBF2(C2O4) "LiDFOB", LiPF2(C2O4)2 "LiDFOP", LiPO2F2, FSO3Li, LiI, LiBr, and derivatives thereof.

[0103] The electrolyte may contain, for example, a carbonate-based solvent (carbonate ester-based solvent). The solvent may contain, for example, cyclic carbonates, linear carbonates, fluorinated carbonates, etc. The solvent may contain, for example, at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (FEC), difluoroethylene carbonate, 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene carbonate, fluoropropylene carbonate, difluoropropylene carbonate, and derivatives thereof.

[0104] The solvent may contain cyclic carbonates (such as EC, PC, FEC, etc.) and chain carbonates (such as EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate and the chain carbonate may be, for example, "cyclic carbonate / chain carbonate = 1 / 9 to 4 / 6", "cyclic carbonate / chain carbonate = 2 / 8 to 3 / 7", or "cyclic carbonate / chain carbonate = 3 / 7 to 4 / 6".

[0105] The solvent may contain cyclic carbonates (such as EC, PC, etc.) and fluorinated cyclic carbonates (such as FEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate and the fluorinated cyclic carbonate may be, for example, "cyclic carbonate / fluorinated cyclic carbonate = 99 / 1 to 90 / 10", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 1 / 9", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 7 / 3", or "cyclic carbonate / fluorinated cyclic carbonate = 3 / 7 to 1 / 9".

[0106] The solvent may contain, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy the relationship represented by, for example, the following formula. V EC +V FEC +V EMC +V DMC +V DEC =10 In the above formula, V EC 、V FEC 、V EMC 、V DMC 、V[[ID=3〗] DEC respectively represent the volume ratios of EC, FEC, EMC, DMC, and DEC. 1≦V EC ≦4、0≦V FEC ≦3、V EC +V FEC ≦4、 0≦V EMC ≦9、0≦V DMC ≦9、0≦V DEC ≦9、6≦V EMC +V DMC +V DEC ≦9 The relationship is satisfied. For example, 1 ≤ V EC ≤ 2, or 2 ≤ V EC The condition ≤ 3 may also be satisfied. For example, 1 ≤ V FEC ≤ 2, or 2 ≤ V FEC The condition ≤ 4 may also be satisfied. For example, 3 ≤ V EMC ≤4, or 6 ≤V EMC The condition ≤ 8 may also be satisfied. For example, 3 ≤ V DMC ≤4, or 6 ≤V DMC The condition ≤ 8 may also be satisfied. For example, 3 ≤ V DEC ≤4, or 6 ≤V DEC The condition ≤ 8 may also be satisfied.

[0107] The solvent may have compositions such as "EC / EMC=3 / 7", "EC / DMC=3 / 7", "EC / FEC / DEC=1 / 2 / 7", "EC / DMC / EMC=3 / 4 / 3", "EC / DMC / EMC=3 / 3 / 4", "EC / FEC / DMC / EMC=2 / 1 / 4 / 3", "EC / FEC / DMC / EMC=1 / 2 / 4 / 3", "EC / FEC / DMC / EMC=2 / 1 / 3 / 4", and "EC / FEC / DMC / EMC=1 / 2 / 3 / 4" in volume ratio.

[0108] The electrolyte may contain an ether-based solvent. The electrolyte may contain, for example, at least one selected from the group consisting of tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), hydrofluoroether (HFE), ethylglycyle, triglycyle, tetraglycyle, and derivatives thereof.

[0109] The electrolyte may contain any additives. The amount of additive (mass fraction of the total electrolyte) may be, for example, 0.01 to 5%, 0.05 to 3%, or 0.1 to 1%. The additives may include, for example, SEI (Solid Electrolyte Interphase) formation promoters, SEI formation inhibitors, gas generators, overcharge inhibitors, flame retardants, antioxidants, electrode protectants, surfactants, etc.

[0110] Additives include, for example, vinylene carbonate (VC), vinylethylene carbonate (VEC), 1,3-propanesaltone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfite (ES), ethylene sulfate (DTD), γ-butyrolactone, phosphazene compounds, carboxylic acid esters [e.g., methyl formate (MF), methyl acetate (MA), methyl propionate (MP), diethyl malonate (DEM), etc.], and fluorobenzenes [e.g., monofluorobenzene (FB), 1,2-di-butylbenzene]. Fluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, etc.), fluorotoluene (e.g., 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene, 3,4-difluorotoluene, octafluorotoluene, etc.), benzotrifluorides (e.g., benzotrifluoride, 2-fluorobenzotrifluoride, 3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, 2-methylbenzotrifluoride, 3-methylbenzotrifluoride, 4-methylbenzotrifluoride, etc.), fluoroxylenes (e.g., 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m-xylene, etc.), sulfur-containing heterocyclic compounds (e.g., benzothiazole, 2-methyl benzothiazole) It may contain at least one selected from the group consisting of (e.g., nzothiazole, tetrathiafulvalene), nitrile compounds (e.g., adiponitrile, succinonitrile), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate), carboxylic acid anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride), alcohols (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, diethylene glycol monomethyl ether), and derivatives thereof.

[0111] The components mentioned above may be used as solutes and solvents, or as trace components (additives). The additives may include, for example, at least one selected from the group consisting of LiBF4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO2F2, FSO3Li, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0112] The electrolyte may contain an ionic liquid. The ionic liquid may contain, for example, at least one selected from the group consisting of sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, imidazolium salts, and derivatives thereof.

[0113] In some embodiments of this invention, the battery may include a gel electrolyte; that is, the battery may be a polymer battery. The gel electrolyte may include an electrolyte solution and a polymer material. The polymer material may form a polymer matrix. The polymer material may include, for example, at least one selected from the group consisting of PVdF, PVdF-HFP, polyacrylonitrile (PAN), PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0114] -All-solid-state battery- In some embodiments of this invention, the battery may be an all-solid-state battery. The all-solid-state battery may have a bipolar structure. The all-solid-state battery includes a solid electrolyte instead of an electrolyte and a separator 20. The solid electrolyte may also be included in the positive electrode layer 11 and the negative electrode layer 12. Instead of a separator 20, the solid electrolyte layer separates the negative electrode layer 12 from the positive electrode layer 11. The solid electrolyte layer includes, for example, a solid electrolyte and a binder.

[0115] The solid electrolyte may be, for example, a powder or granular material. The D50 of the solid electrolyte may 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 the solid electrolyte may be 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less.

[0116] The solid electrolyte may include, for example, at least one selected from the group consisting of sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, hydride solid electrolytes, and nitride solid electrolytes.

[0117] The sulfide solid electrolyte may contain at least one selected from the group consisting of an amorphous phase, a crystalline phase, and a glass ceramic (crystallized glass) phase. The crystalline phase may be, for example, an argyrodite type or an LGPS type. The sulfide solid electrolyte contains Li and sulfur (S). In addition to Li and S, the sulfide solid electrolyte may further contain any other components.

[0118] Examples of sulfide solid electrolytes include 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 It may include at least one selected from the group consisting of Li3PS4 and Li7PS6.

[0119] For example, "LiI-LiBr-Li3PS4" indicates a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li3PS4 in any molar ratio. For example, the sulfide solid electrolyte may be produced by a mechanochemical method. The mixing ratio may be specified by prefixing each raw material with a number. For example, "10LiI-15LiBr-75Li3PS4" indicates that the mixing ratio is "LiI / LiBr / Li3PS4 = 10 / 15 / 75 (molar ratio)".

[0120] The sulfide solid electrolyte may have a composition represented by the following general formula, for example. xLi2S-(1-x)P2S5 In the formula, x may be, for example, greater than 0, 0.1 or greater, 0.2 or greater, 0.25 or greater, 0.3 or greater, 0.4 or greater, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.75 or greater, 0.8 or greater, or 0.9 or greater. x may also be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.75 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. For example, when x = 0.75, "xLi2S-(1-x)P2S5" may have the composition of Li3PS4.

[0121] The sulfide solid electrolyte may have a composition represented by the following general formula, for example. yLiI-zLiBr-(100-yz)[xLi2S-(1-x)P2S5] In the formula, x may be, for example, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.75 or greater, 0.8 or greater, or 0.9 or greater. x may be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.75 or less, 0.7 or less, or 0.6 or less. y may be, for example, 0 or greater, 5 or greater, 10 or greater, 15 or greater, 20 or greater, or 25 or greater. y may be, for example, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, or 5 or less. z may be, for example, 0 or greater, 5 or greater, 10 or greater, 15 or greater, 20 or greater, or 25 or greater. z may be, for example, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, or 5 or less.

[0122] The sulfide solid electrolyte may have a composition represented by the following general formula, for example. Li 7-x-2y PS 6-x-y X y In the equation, the relationships "0 < 7 - x - 2y", "0 < 6 - xy", "0 ≤ x", and "0 ≤ y" are satisfied. X may include, for example, at least one selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0123] The sulfide solid electrolyte may have a composition represented by the following general formula, for example. Li 4-x M 1-x P x S4 In the formula, x may be, for example, greater than 0, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. x may be, for example, less than 1, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. M may contain at least one selected from the group consisting of, for example, Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0124] The sulfide solid electrolyte may have a composition represented by, for example, the following general formula. Li 10+x Ge 1+x P 2-x S 12 In the formula, x may 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 may be, for example, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. The sulfide solid electrolyte represented by the above general formula may contain, for example, a LGPS-type crystal phase.

[0125] The halide solid electrolyte may have a composition represented by, for example, the following general formula. Li 6-na M a X6 In the formula, n indicates the oxidation number of M. M may contain, for example, an atom having an oxidation number of +3. M may contain, for example, an atom having an oxidation number of +4. M may contain at least one selected from the group consisting of, for example, Y, Al, Ti, Zr, Ca, and Mg. For example, the relationship of "0 < a < 2" may be satisfied. X may contain at least one selected from the group consisting of, for example, F, Cl, Br, and I.

[0126] The halide solid electrolyte may have a composition represented by, for example, the following general formula. Li 3-a Ti a Al 1-a F6 In the formula, a may be, for example, 0 or greater, 0.1 or greater, 0.2 or greater, 0.3 or greater, 0.4 or greater, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.8 or greater, or 0.9 or greater. a may also be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0127] The halide solid electrolyte may have a composition represented by, for example, the following general formula. Li3YCl a Br b I 6-a-b In the expression, for example, the relationship "0 ≤ a + b ≤ 6" may be satisfied. a may be, for example, 0 or greater, 1 or greater, 2 or greater, 3 or greater, 4 or greater, or 5 or greater. a may be, for example, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1 or less. b may be, for example, 0 or greater, 1 or greater, 2 or greater, 3 or greater, 4 or greater, or 5 or greater. b may be, for example, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1 or less.

[0128] Oxide solid electrolytes include, for example, LiNbO3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, La 2 / 3-x Li 3x TiO3 and Li7La3Zr2O 12 It may contain at least one selected from the group consisting of the following. The hydride solid electrolyte may include, for example, LiBH4. The nitride solid electrolyte may include, for example, Li3N, Li3BN2, etc. [Examples]

[0129] -Manufacturing of positive electrode active material- Figure 7 is a table showing the experimental results. The positive electrode active materials No. 1 to No. 5 were manufactured according to the following procedure.

[0130] (a) Formation of slurry Compositional formula “Li 1.1 Mn 0.7 Fe 0.3 Lithium hydroxide monohydrate, manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate were weighed out to match the composition ratio shown in "PO4". 8% glucose by mass fraction was weighed out to the raw material mixture. Furthermore, X% pore-forming agent (boric acid) by mass fraction was weighed out to the raw material mixture. The amount of pore-forming agent added "X" in each sample is shown in Figure 7. A slurry was formed by mixing the weighed materials with water. The solid content concentration of the slurry was 30% by mass fraction. Wet grinding was performed to achieve a D50 of 0.30 μm.

[0131] (b) Granulation The slurry was spray-dried, forming tertiary particles (or secondary particles). The target D50 value for the tertiary particles was 9 ± 1 μm. In the spray dryer, the intake air temperature was 250°C. The exhaust port temperature was 115 ± 15°C. The intake pressure was 2.0 MPa. The nozzle pressure of the spray nozzle was Y ± 0.1 MPa. The nozzle pressure "Y" for each sample is shown in Figure 7.

[0132] (c) Firing LMFP was synthesized by calcining tertiary particles under an inert atmosphere. Figure 8 shows the temperature profile during calcination. First, the furnace temperature was raised 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 raised to 650°C at a heating rate of 5°C / min. The furnace temperature was maintained at 650°C for 5 hours. After that, the furnace temperature was cooled to 400°C at a cooling rate of 2°C / min. The furnace temperature was further cooled to room temperature at a cooling rate of 15°C / min.

[0133] -evaluation- A cylindrical lithium-ion secondary battery (cylindrical cell) has been manufactured. The cell configuration is as follows:

[0134] Power generation element: wound type Positive electrode: LMFP / AB / PAN=88 / 10 / 2 (mass ratio) Negative electrode: Negative electrode active material (natural graphite), CMC, SBR Electrolytes: LiPF6 (1 ml / L), EC / DMC / EMC = 3 / 4 / 3 (volume ratio)

[0135] The positive and negative electrodes were manufactured by coating the surface of a substrate (metal foil) with slurry. An Allgood film applicator (with film thickness adjustment function) was used as the coating apparatus. After coating with slurry, the coating film was dried at 80°C for 5 minutes.

[0136] Under room temperature conditions, a cylindrical cell was charged and discharged 200 times with a constant current of 2C within a voltage range of 3.0 to 4.1V. The capacity retention rate (percentage) was calculated by dividing the discharge capacity after the 200th discharge by the discharge capacity after the first discharge. The capacity retention rate is shown in Figure 7. A higher capacity retention rate indicates better durability. Note that "C" is a symbol indicating the current rate (time rate). At a rate of 1C, the theoretical capacity is supplied over one hour.

[0137] -result- In Figure 7, it can be seen that durability tends to improve due to the formation of voids at the bonding points between secondary particles within tertiary particles.

[0138] When the relationship "4.8% ≤ Sv ≤ 29%" is satisfied, there is a tendency for durability to improve. [Explanation of Symbols]

[0139] 1 Primary particle, 2 Secondary particle, 3 Tertiary particle, 4 Void, 5 Carbon layer, 10 Bipolar electrode, 11 Positive electrode layer, 12 Negative electrode layer, 13 Current collector foil, 20 Separator, 30 Sealing material, 40 Cell, 50 Power generation element, 90 Outer casing, 91 First current collector plate, 92 First laminate film, 93 Second laminate film, 94 Second current collector plate, 100 Battery.

Claims

1. Includes tertiary particles, The aforementioned tertiary particle 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 contains an olivine-type phosphate compound, In at least a portion of the tertiary particles, a void is formed between the secondary particles. Cathode active material.

2. 4.8% ≤ Sv ≤ 29% The following conditions are met, and The Sv in the cross-section of the tertiary particle represents the ratio of the area of ​​the void formed between the secondary particles to the area of ​​the region enclosed by the contour line of the tertiary particle. The positive electrode active material according to claim 1.

3. The tertiary particle comprises 2 to 20 of the secondary particles. The positive electrode active material according to claim 1 or claim 2.

4. The olivine-type phosphate compound includes manganese iron lithium phosphate. The positive electrode active material according to claim 1 or claim 2.

5. It includes a positive electrode layer, and The positive electrode layer comprises the positive electrode active material described in claim 1 or claim 2. electrode.

6. The electrode included in claim 5, battery.

7. Having a bipolar structure, The battery according to claim 6.

8. (a) Forming a slurry containing a lithium compound, a phosphate compound, a pore-forming material, and a solvent. (b) Forming tertiary particles by spray-drying the slurry, (c) A positive electrode active material is produced by subjecting the tertiary particles to heat treatment. Includes, The above (b) is, (b1) Forming wet secondary particles, (b2) Forming wet tertiary particles by bringing the wet secondary particles into contact with the wet secondary particles, and (b3) Drying the wet tertiary particles to form tertiary particles containing a plurality of secondary particles, Includes, The wetted secondary particles comprise the solvent, the pore-forming material, and a plurality of precursor primary particles. Each of the plurality of precursor primary particles contains a precursor, The above (c) is, (c1) By removing at least a portion of the pore-forming material, a void is formed between the secondary particles, and (c2) Synthesizing an olivine-type phosphate compound from the precursor, including, A method for manufacturing a positive electrode active material.

9. The aforementioned pore-forming material contains boric acid, A method for producing a positive electrode active material according to claim 8.

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