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

Abstract

Reduction of reaction resistance. [Solution] A positive electrode active material comprising secondary particles, wherein the secondary particles comprise a plurality of primary particles and a plurality of titanium bodies, the primary particles comprise a phosphate compound having an olivine-type structure, the titanium bodies comprise titanium oxide having a rutile-type structure, and at least a portion of the plurality of titanium bodies are present on the surface of the primary particles.

Description

[Technical Field]

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

[0002] Japanese Patent Publication No. 2017-21999 (Patent Document 1) discloses a positive electrode active material for lithium-ion secondary batteries in which a portion of the Mn in manganese iron lithium phosphate (LMFP) is further substituted with Co alone, or with both Co and Zn. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2017-21999 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Olivine-type phosphate compounds have been developed as positive electrode active materials. Olivine-type phosphate compounds tend to have poor charge-discharge characteristics. Patent document 1 provides an LMFP having the above-mentioned characteristics in order to improve charge-discharge characteristics. In lithium-ion secondary batteries, there is room to improve charge-discharge characteristics by reducing reaction resistance.

[0005] The purpose of this disclosure is to reduce reaction resistance. [Means for solving the problem]

[0006] 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.

[0007] [1] A positive electrode active material, The positive electrode active material includes secondary particles, The aforementioned secondary particles include a plurality of primary particles and a plurality of titanium bodies. The primary particles contain a phosphate compound with an olivine-type structure. The titanium body contains titanium oxide with a rutile-type structure, At least a portion of the plurality of titanium bodies are present on the surface of the primary particles. Cathode active material.

[0008] In the secondary particles constituting the positive electrode active material, the presence of a titanium body containing rutile-type titanium oxide on the surface of primary particles containing olivine-type phosphate compounds is expected to reduce the reaction resistance of lithium-ion secondary batteries.

[0009] [2] The positive electrode active material according to [1], wherein at least a portion of the plurality of titanium bodies is on the surface of the primary particles and is present at the grain boundaries of the primary particles.

[0010] [3] The titrated active material according to

[11] or [2], wherein the titanium body has a maximum Ferret diameter of 100 nm or more and 500 nm or less.

[0011] [4] The titrated active material according to any one of [1] to [3], further comprising a titanium body having a spinel-type lithium titanate.

[0012] In the case of titanium materials, if lithium titanate with a spinel-type structure is included, it is expected that it will be fixed to the surface of the primary particles.

[0013] [5] The titanium body may further contain titanium oxide with anatase structure, The positive electrode active material according to [4], wherein the molar fraction of the content of lithium titanate with a spinel structure relative to the total content of lithium titanate with a spinel structure, titanium oxide with a rutile structure, and titanium oxide with anatase structure is 0.01 or more and 0.50 or less.

[0014] Regarding lithium titanate with a spinel-type structure contained in the titanium material, if its molar fraction falls within the above range, a further reduction in the reaction resistance of lithium-ion secondary batteries can be expected.

[0015] [6] The olivine-type phosphate compound is manganese iron lithium phosphate, the positive electrode active material according to any one of [1] to [5].

[0016] [7] A battery comprising a positive electrode active material as described in any one of items [1] through [6].

[0017] [8] A battery, The aforementioned battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises the positive electrode active material described in any one of items [1] to [6], The aforementioned electrolyte contains ethylene carbonate, and the battery is otherwise in this state.

[0018] [9] The battery according to [8], wherein the battery has a bipolar structure.

[0019]

[10] A method for producing a positive electrode active material according to any one of items [1] to [6], (a) A step of forming a slurry by mixing a manganese compound, a lithium compound, a phosphate compound, titanium dioxide with a rutile structure, and a solvent. (b) A step of forming first precursor particles by drying the slurry, (c) A step of forming second precursor particles by subjecting the first precursor particles to a first heat treatment, (d) A step of producing an olivine-type phosphate compound by subjecting the second precursor particles to a second heat treatment, A method for manufacturing a positive electrode active material.

[0020] The positive electrode active material described in any one of the above items [1] to [6] can be produced by the manufacturing method described in

[10] above.

[0021] 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]

[0022] [Figure 1] This is a conceptual diagram showing secondary particles in this embodiment. [Figure 2] This is a schematic flowchart illustrating the method for producing the positive electrode active material in this embodiment. [Figure 3] This is a schematic perspective view of the battery in this embodiment. [Figure 4] This is a schematic cross-sectional view along the line VI-VI in Figure 3. [Figure 5] This table shows the experimental results for positive electrode active materials No. 1 to 7 in the examples. [Modes for carrying out the invention]

[0023] <Terms and phrases> "Equipped with," "includes," "possesses," and variations thereof are open-ended expressions. Configurations expressed in an open-ended manner may or may not include additional elements in addition to the essential elements. The statement "consists of" is a closed expression. However, even configurations expressed in a closed manner may include additional elements that are usually incidental impurities or irrelevant to the subject technology. The statement "substantially consists of..." is a semi-closed expression. In configurations expressed in a semi-closed manner, the addition of elements that do not substantially affect the basic and novel characteristics of the subject technology is permitted.

[0024] 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."

[0025] 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.

[0026] 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.

[0027] For example, the expression "at least one of A and B" includes both "A or B" and "A and B". "At least one of A and B" can also be written as "A and / or B".

[0028] 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.

[0029] 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.

[0030] Numerical ranges such as "m~n%" include upper and lower limits unless otherwise specified. That is, "m~n%" indicates a numerical range of "m% or more and n% or less". Also, "m% or more and n% or less" includes "greater than m% and less than n%". "Greater than or equal to" and "less than or equal to" are represented by the equals sign inequality signs "≦" and "≧". "Greater than" and "less than" are represented by the equals sign inequality signs "<" and ">". A number arbitrarily selected from within the numerical range may be used as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a number within the numerical range with a number listed in another part of this specification, in a table, in a figure, etc.

[0031] 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.

[0032] The devices, software, etc., used to measure various values ​​are merely examples. Equivalent devices may be used. If equivalent devices are used, the measurement conditions may be adjusted to suit the device.

[0033] The particle's "D50" indicates the particle size at which the cumulative value in the volume-based particle size distribution (cumulative distribution) reaches 50%. D50 is measured, for example, by a laser diffraction particle size distribution analyzer.

[0034] The "maximum Ferret diameter" of a particle is determined from a scanning electron microscope (SEM) image. In the SEM image, it indicates the length of the longer side of the particle's circumscribing rectangle (rectangle or square). If the circumscribing rectangle is a square, the length of the longer side indicates the length of one side.

[0035] 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.

[0036] <Cathode active material> The positive electrode active material comprises a plurality of secondary particles and a plurality of titanium bodies. The secondary particles comprise a plurality of primary particles. The positive electrode active material may also contain primary particles that do not constitute secondary particles. At least a portion of the plurality of titanium bodies are present on the surface of the primary particles. The positive electrode active material may also contain titanium bodies present elsewhere than on the surface of the primary particles. The positive electrode active material may be, for example, a powder or granular material.

[0037] Figure 1 is a conceptual diagram showing secondary particles, primary particles, and titanium bodies present on the surface of primary particles in the positive electrode active material of this embodiment. Secondary particles 2 are aggregates of primary particles 1. That is, secondary particles 2 contain a plurality of primary particles 1. Titanium bodies 3 are present on the surface of primary particles 1. The surface of primary particles 1 on which titanium bodies 3 are present may be a grain boundary of primary particles 1 or the surface of secondary particles 2. Preferably, at least a portion of the titanium bodies 3 are present at the grain boundaries of primary particles 1. The presence of titanium bodies 3 at the grain boundaries of primary particles 1 means that titanium bodies 3 are in contact with a grain interface formed by the contact of two primary particles 1. The presence of titanium bodies 3 on the surface of secondary particles 2 means that at least a portion of the surface of titanium bodies 3 is exposed on the surface of secondary particles 2. The presence of titanium bodies 3 on the surface of primary particles 1 can be confirmed by SEM images.

[0038] According to the positive electrode active material of this embodiment, the presence of titanium material 3 on the surface of primary particles 1 can further reduce the reaction resistance of the lithium secondary battery. One of the factors that influences the magnitude of the reaction resistance of a lithium-ion secondary battery is the interfacial resistance at the reaction surface of the positive electrode active material. In the positive electrode active material of this embodiment, the presence of titanium material 3 containing rutile-type titanium oxide, which has a dielectric constant close to that of the solvent contained in the electrolyte, on the surface of primary particles 1 constituting secondary particles 2 is thought to reduce the interfacial resistance of the reaction surface of the positive electrode active material, thereby reducing the reaction resistance of the lithium-ion secondary battery. Furthermore, the presence of titanium material 3 at the grain boundaries of primary particles 1 constituting secondary particles 2 further reduces the interfacial resistance of the reaction surface of the positive electrode active material, and a further reduction in the reaction resistance of the lithium-ion secondary battery can be expected.

[0039] Titanium material 3 contains titanium oxide with a rutile structure. Industrially used titanium oxide (TiO2) has two crystalline forms: rutile and anatase. Both rutile and anatase belong to the tetragonal crystal system, and the rutile form has a denser atomic arrangement and higher density compared to the anatase form. By including titanium oxide with a rutile structure as titanium material 3, it is expected that the reaction resistance of lithium-ion secondary batteries will be reduced. Titanium material 3 may also contain anatase titanium oxide.

[0040] Titanium body 3 is lithium titanate (Li4Ti5O) with a spinel-type structure. 12 Preferably, the positive electrode active material further contains lithium titanate (Li4Ti5O) with a spinel structure, titanium oxide with a rutile structure, and titanium oxide with anatase structure. 12 The amount fraction (X) of the content of ) is preferably 0.01 or more and 0.50 or less. This range is expected to further reduce the reaction resistance of the lithium-ion secondary battery. The amount fraction (X) may be 0.02 or more, or 0.03 or more, or 0.40 or less, or 0.35 or less.

[0041] In the positive electrode active material, it is preferable that the titanium body 3 is sufficiently fixed to the surface of the primary particle 1. This is because a reduction in the reaction resistance of the lithium secondary battery can be expected. During the manufacturing of the positive electrode active material, excess lithium present on the surface of the primary particle 1 and titanium oxide partially solid-solve to form a spinel-type lithium titanate, and this lithium titanate improves the adhesion between the surface of the primary particle 1 and the titanium body 3. If the range of the amount fraction (X) of this lithium titanate is within the range described above, it can be considered that sufficient adhesion between the titanium body 3 and the surface of the primary particle 1 is ensured.

[0042] The above molar fraction (X) is determined by X-ray absorption fine structure (XAFS) analysis of the positive electrode active material. The XAFS measurement conditions are as follows:

[0043] Measurement equipment: Hard X-ray XAFS located within the Aichi Synchrotron Radiation Center, Japan Science and Technology Exchange Foundation. Measurement range: 4955-5025eV Measurement method: The positive electrode is measured by fluorescence, and the standard substance is measured by transmission.

[0044] In the above measurement method, the transmission method for measuring the standard substance detects the transmitted X-rays when incident X-rays are irradiated, while the fluorescence method for measuring the positive electrode active material detects the fluorescent X-rays generated when incident X-rays are irradiated. Even though the measurement methods are different, they can be represented as the same spectrum. By normalizing the XAFS measurement data using the analysis software Athena, it is possible to calculate the proportion of the standard substance content in the positive electrode active material. As standard substances, titanium dioxide with a rutile structure, titanium dioxide with anatase structure, and lithium titanate with a spinel structure are measured, and the molar fraction (X) of the positive electrode active material is calculated.

[0045] The maximum ferret diameter of the titanium body 3 may be between 100 nm and 500 nm. A reduction in the reaction resistance of the lithium secondary battery can be expected if the maximum ferret diameter of the titanium body 3 is within the above range. The maximum ferret diameter of the titanium body 3 may be, for example, 110 nm or more, 120 nm or more, 130 nm or more, or 140 nm or more. The maximum ferret diameter of the titanium body 3 may be, for example, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, or 250 nm or less.

[0046] The maximum Ferret diameter of primary particle 1 may 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, or 80 nm or more. The maximum Ferret diameter of primary particle 1 may also be, for example, 120 nm or less, 100 nm or less, 80 nm or less, or 60 nm or less.

[0047] The D50 of the primary particles may be between 20 nm and 90 nm. The D50 of the primary particles may be between 25 nm and 30 nm, 35 nm and 40 nm, or 45 nm and 45 nm. The D50 of the primary particles may be 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, or 50 nm or less.

[0048] The maximum Ferret diameter of secondary particle 2 may 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 Ferret diameter of secondary particle 2 may also be, for example, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 15 μm or less.

[0049] The D50 of secondary particles may be, for example, 1 μm or larger, 2.5 μm or larger, 5 μm or larger, 7.5 μm or larger, 10 μm or larger, 15 μm or larger, or 20 μm or larger. The D50 of secondary particles may also be, for example, 50 μm or smaller, 40 μm or smaller, 30 μm or smaller, 20 μm or smaller, or 15 μm or smaller.

[0050] Secondary particles 2 may have any shape. Secondary particles 2 may have a spherical shape. If secondary particles 2 are spherical, for example, improved packing performance can be expected. The sphericity of secondary particles 2 may be 0.85 or higher, 0.90 or higher, or 0.95 or higher. The sphericity of secondary particles 2 may be, for example, 1 or less, 0.95, or 0.90 or less. "Sphericity" refers to the circularity in the surface SEM image (two-dimensional image). Sphericity (circularity) is calculated by the following formula.

[0051] ψ = 4πS / L 2 ψ: Sphericity (Circularity) π: Pi S: Cross-sectional area of ​​secondary particle 2 (area of ​​the region enclosed by the contour line of secondary particle 2) L: Circumference of secondary particle 2 (length of the outline of secondary particle 2) Sphericity is expressed as the arithmetic mean of 30 secondary particles.

[0052] A carbon layer may be attached to at least a portion of the surface of the primary particle 1. The carbon layer contains carbon (C). The amount of carbon layer attached 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 secondary particle 2. The amount of carbon layer 4 attached may be, for example, 5% or less, 4% or less, or 3% or less by mass fraction relative to the secondary particle 2.

[0053] Primary particle 1 contains a phosphate compound with an olivine-type structure. Here, "olivine-type" refers to a crystal structure (olivine-type structure) belonging to the space group Pnma. The space group is identified by powder X-ray diffraction (XRD) measurement. Primary particle 1 may be, for example, a single-phase compound. Primary particle 1 may further contain phases belonging to other space groups, as long as it contains an olivine-type crystalline phase. Primary particle 1 may further contain, for example, an amorphous phase.

[0054] Olivine-type phosphate compounds may include, for example, LFP, LMP, etc. In LMP, some of the manganese (Mn) may be substituted with iron (Fe). The Fe-substituted LMP is also called lithium iron manganese phosphate and is written as LMFP. LMP may have a composition represented by, for example, the following general formula.

[0055] Li 1-a Mn 1-x Fe x PO4 For example, the relationship -0.5 ≤ a ≤ 0.5 may be satisfied. The Fe substitution amount (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. The Fe substitution amount (x) may be, for example, 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.

[0056] In LMFPs, elements other than lithium (Li), manganese (Mn), iron (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.

[0057] The positive electrode active material may further contain other components, as long as it contains a phosphate compound with an olivine-type structure. Other components may 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 to 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".

[0058] LNO may have a crystal structure belonging to the space group R-3m, for example. LNO may have a composition represented by the following general formula, for example.

[0059] Li 1-a Ni x M 1-x O2 In the formula, the relationships of -0.5 ≤ a ≤ 0.5 and 0 ≤ x ≤ 1 are satisfied. M may contain at least one selected from the group consisting of, for example, 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 contain, for example, at least one selected from the group consisting of LiNi 0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O₂, and LiNiO₂.

[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".

[0062] Li 1-a Ni x Co y Mn z O2 In the formula, the relationships of -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied. For example, the relationship of 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x < 1 may be satisfied. For example, the relationship of 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9, or 0.9 ≤ y < 1 may be satisfied. For example, the relationship of 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1 may be satisfied.

[0063] NCM is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 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 0.3O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and LiNi 0.9 Co 0.05 Mn 0.05 It may contain at least one selected from the group consisting of O2.

[0064] 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".

[0065] 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.

[0066] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O2, LiNi 0.7 Co 0.2 Al 0.1 O2, LiNi0.8 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.

[0067] <Method for manufacturing positive electrode active material> Figure 2 is a schematic flowchart showing the method for producing the positive electrode active material in this embodiment. Hereinafter, "the method for producing the positive electrode active material in this embodiment" may be abbreviated as "this method". This method may include, for example, "(a) a mixing step", "(b) a granulation step", "(c) a first calcination step", and "(d) a second calcination step".

[0068] (a) Mixing process This process involves mixing a manganese compound, a lithium compound, a phosphate compound, and a solvent to form a slurry. The following explanation will use the case of producing LMFP as the cathode active material as an example. However, the cathode active material in this disclosure is not limited to LMFP.

[0069] For example, the chemical formula "Li 1-a Mn 1-x Fe x The manganese compound, lithium compound, phosphate compound, and iron compound may be weighed out to achieve the composition ratio (mole ratio) shown in PO4 (-0.5 ≤ a ≤ 0.5, 0 ≤ x < 1). The manganese compound may include, for example, manganese carbonate. The lithium compound may include, for example, lithium hydroxide. The phosphate compound may include, for example, lithium dihydrogen phosphate. The iron compound may include, for example, ferric phosphate.

[0070] In this method, it is preferable to mix rutile-type titanium oxide into the raw material mixture in order to produce a positive electrode active material in which titanium bodies exist on the surface of primary particles. The amount of rutile-type titanium oxide added may be, for example, 0.5 to 5% by mass fraction relative to the raw material mixture. The rutile-type titanium oxide may also be mixed after the second calcination step (d).

[0071] When forming a carbon layer 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. The carbon raw material may also include, for example, glucose, sucrose, fructose, citric acid, etc. The amount of carbon raw material added may be, for example, 1 to 20% by mass fraction relative to the raw material mixture.

[0072] The solvent may include, for example, water. The solid content concentration of the slurry may be, for example, 20-40% by mass fraction.

[0073] The particle size in the slurry may be adjusted by wet grinding. For example, wet grinding may be performed so that D50 is 0.10 to 1 μm. Wet grinding may be performed using, for example, a bead mill, ball mill, planetary mill, jet mill, planetary mixer, homogenizer, etc. To obtain a positive electrode active material having fine titanium particles, wet grinding may be performed using, for example, a bead mill with beads containing zirconia. The beads containing zirconia may also contain ZrO2. Wet grinding may be performed under vacuum conditions, and to achieve a vacuum, for example, a diaphragm pump may be used to create a vacuum.

[0074] (b) Granulation process This process involves drying the slurry to form first precursor particles.

[0075] For example, the first precursor particles may be granulated by spray drying. The intake port temperature may be, for example, 230 to 270°C. The exhaust port temperature may be, for example, 100 to 130°C. The spray rate may be, for example, 16 to 20 mL / min. The intake pressure may be, for example, about 1.8 to 2.2 MPa. The nozzle pressure of the spray nozzle may be, for example, 0.1 to 0.3 MPa.

[0076] (c) First firing process This process involves forming second precursor particles by subjecting first precursor particles to a first heat treatment.

[0077] Any heat treatment furnace (e.g., electric furnace, muffle furnace, etc.) may be used. The atmosphere in this process may be, for example, a nitrogen atmosphere. The first heat treatment temperature may be, for example, 200 to 500°C. The first heat treatment time may be, for example, 1 to 3 hours.

[0078] (d) Second firing process This process involves subjecting the second precursor particles to a second heat treatment to produce a phosphate compound with an olivine-type structure.

[0079] The same heat treatment furnace used in the first firing process may be used. The atmosphere in this process may be, for example, a nitrogen atmosphere. The second heat treatment temperature may be, for example, 550 to 750°C. The second heat treatment time may be, for example, 4 to 6 hours.

[0080] The above-mentioned positive electrode active material can be obtained by cooling after the second firing step (d).

[0081] <Battery> In some embodiments of this invention, the battery has a monopolar structure. In some embodiments of this invention, the battery has a bipolar structure. As an example, a battery having a bipolar structure (a bipolar battery) will be described.

[0082] Figure 3 is a schematic perspective view of the battery in this embodiment. Figure 4 is a schematic cross-sectional view along the line VI-VI in Figure 3. Hereinafter, "orthoplane direction" refers to the direction normal to the surface of a sheet-like member (e.g., foil, electrode, etc.). "In-plane direction" refers to any direction perpendicular to the orthoplane direction. In Figure 4, the Z-axis direction corresponds to the orthoplane direction. The X-axis and Y-axis directions are examples of in-plane directions.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] The power generation element 50 includes a sealing material 30. At its in-plane end, the sealing material 30 is joined to the current collector foil 13. The sealing material 30 may, for example, be heat-welded to the current collector foil 13. For example, the sealing material 30 may be arranged around the entire circumference of the in-plane periphery. The sealing material 30 may include, for example, a resin material. The sealing material 30 seals between adjacent current collector foils 13 in the direction perpendicular to the plane. The sealing material 30 between the current collector foils 13 partitions the cells 40. A cell 40 is the smallest unit of the power generation element 50. The battery 100 includes a plurality of cells 40 and may therefore also be called a "bipolar module". Each of the plurality of cells 40 is sealed. The plurality of cells 40 are isolated from each other. Each of the plurality of cells 40 includes a positive electrode layer 11, a separator 20, a negative electrode layer 12, and an electrolyte.

[0088] (Positive electrode layer) The positive electrode layer 11 is attached to one side of the current collector foil 13. For example, grooves may be formed in the positive electrode layer 11. The positive electrode layer 11 may be formed in a striped pattern, for example. The positive electrode layer 11 contains a positive electrode active material. That is, the electrode contains a positive electrode active material. Details of the positive electrode active material are as described above.

[0089] The positive electrode layer 11 may further contain, in addition to the positive electrode active material, a conductive material and a binder, for example. The amount of conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of positive electrode active material. The conductive material may contain any components. For example, the conductive material may contain at least one selected from the group consisting of graphite, acetylene black (AB), Ketjenblack (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF).

[0090] The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of positive electrode active material. The binder may contain any components. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, and derivatives thereof.

[0091] The positive electrode layer 11 may further contain, for example, inorganic fillers, organic fillers, solid electrolytes, surface modifiers, dispersants, lubricants, flame retardants, protective agents, fluxes, coupling agents, adsorbents, etc. The positive electrode layer 11 may also contain, for example, polyoxyethylene allylphenyl ether phosphate, zeolite, silane coupling agents, MoS2, WO3, etc.

[0092] (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.

[0093] 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.

[0094] The negative electrode active material may contain any component. The negative electrode active material may contain, for example, 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, the battery may be a Li metal negative electrode battery.

[0095] The carbon-based active material may contain, for example, at least one selected from the group consisting of graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. The 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".

[0096] 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, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may contain, for example, at least one selected from the group consisting of Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO 3、 and at least one selected from the group consisting of Li3PO4.

[0097] The alloy-based active material may contain, for example, at least one selected from the group consisting of Si, Li silicate, SiO, Si-based alloys, tin (Sn), SnO, and Sn-based alloys.

[0098] SiO may be represented, for example, by the following general formula.

[0099] 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.

[0100] "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).

[0101] (Separator) The separator 20 can separate the positive electrode layer 11 from the negative electrode layer 12. The separator 20 has electrical insulation. The separator 20 may include, 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.

[0102] The resin film is porous. The resin film may include, for example, a microporous membrane, a non-woven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may be continuously reticulated, for example. Pores are formed in the gaps of the resin skeleton. The resin film can permeate the electrolyte. The resin film may have an average pore diameter of, for example, 1 μm or less. The average pore diameter of the resin film may be, for example, 0.01 - 1 μm, or 0.1 - 0.5 μm. The "average pore diameter" can be measured by the mercury intrusion method. The Gurley value of the resin film may be, for example, 50 - 250 s / 100 cm 3 or the like. The "Gurley value" can be measured by the Gurley test method.

[0103] 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 a stretching method, a phase separation method, or the like. The thickness of the resin film may be, for example, 5 to 50 μm or 10 to 25 μm.

[0104] 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.

[0105] 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.

[0106] The inorganic particle layer is porous. The inorganic particle layer contains inorganic particles. Inorganic particles may also be called "inorganic fillers." Pores are formed in the gaps between the inorganic particles. The thickness of the inorganic particle layer may be, for example, 0.5 to 10 μm or 1 to 5 μm. The inorganic particles may contain, for example, a heat-resistant material. An inorganic particle layer containing a heat-resistant material is also called an "HRL (Heat Resistance Layer)." The inorganic particles may contain at least one selected from the group consisting of boehmite, alumina, zirconia, titania, magnesia, and silica. The inorganic particles may have any shape. For example, the inorganic particles may be spherical, rod-shaped, plate-shaped, fibrous, etc. The D50 of the inorganic particles may be, for example, 0.1 to 10 μm or 0.5 to 3 μm. The inorganic particle layer may further contain a binder. The binder may include, for example, at least one selected from the group consisting of acrylic resins, polyamide resins, fluororesins, aromatic polyether resins, and liquid crystal polyester resins.

[0107] 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.

[0108] 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.

[0109] The separator 20 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0110] (electrolyte) The electrolyte is a liquid electrolyte. The electrolyte contains a solute and a solvent. The concentration of the solute may be, for example, 0.5-1 mole / L, 1-1.5 mole / L, 1.5-2 mole / L, 2-2.5 mole / L, or 2.5-3 mole / L. "mol / L" may also be written as "M". The solute contains a supporting salt (Li salt). The solute may also contain, for example, inorganic acid salts, imide salts, oxalate complexes, halides, etc. The solute may include, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiAsF6, LiSbF6, LiN(SO2F)2 "LiFSI", LiN(SO2CF3)2 "LiTFSI", LiB(C2O4)2 "LiBOB", LiBF2(C2O4) "LiDFOB", LiPF2(C2O4)2 "LiDFOP", LiPO2F2, FSO3Li, LiI, LiBr, and derivatives thereof.

[0111] 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.

[0112] 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".

[0113] 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".

[0114] The solvent may contain, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy, for example, the relationship represented by the following formula.

[0115] V EC +V FEC +V EMC +V DMC +V DEC =10 In the above formula, V EC 、V FEC 、V EMC 、V DMC 、V DEC respectively represent the volume ratios of EC, FEC, EMC, DMC, and DEC.

[0116] 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≦VEMC +V DMC +V DEC ≤9 The relationship is satisfied.

[0117] For example, 1 ≤ V EC ≤ 2, or 2 ≤ V EC The condition ≤ 3 may also be satisfied.

[0118] For example, 1 ≤ V FEC ≤ 2, or 2 ≤ V FEC The condition ≤ 4 may also be satisfied.

[0119] For example, 3 ≤ V EMC ≤4, or 6 ≤V EMC The condition ≤ 8 may also be satisfied.

[0120] For example, 3 ≤ V DMC ≤4, or 6 ≤V DMC The condition ≤ 8 may also be satisfied.

[0121] For example, 3 ≤ V DEC ≤4, or 6 ≤V DEC The condition ≤ 8 may also be satisfied.

[0122] 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. In the positive electrode active material contained in the positive electrode layer 11, the relative permittivity of the titanium material present on the surface of the primary particles is close to the relative permittivity of EC (90). When the solvent contains EC, a further decrease in reaction resistance can be expected. The relative permittivity of titanium dioxide with a rutile structure is about 70 to 100, and the relative permittivity of titanium dioxide with anatase structure is about 30 to 50.

[0123] 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.

[0124] The electrolyte may contain any additives. The amount of additive (mass fraction of the total electrolyte) may be, for example, 0.01-5%, 0.05-3%, or 0.1-1%. The additives may include, for example, SEI (Solid Electrolyte Interphase) formation promoters, SEI formation inhibitors, gas generators, overcharge inhibitors, flame retardants, antioxidants, electrode protectants, surfactants, etc.

[0125] Additives include, for example, vinylene carbonate (VC), vinylethylene carbonate (VEC), 1,3-propanesultone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfite (ES), propanesultone (PS), ethylene sulfate (DTD), γ-butyrolactone, phosphazene compounds, carboxylic acid esters [e.g., methyl formate (MF), methyl acetate (MA), methyl propionate (MP), diethyl malonate (DEM), etc.], fluorobenzenes [e.g., monofluorobenzene (FB), 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, etc.), fluorotoluene (e.g., 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene, 3,4-difluorotoluene, octafluorotoluene, etc.), benzotrifluorides (e.g., benzotrifluoride, 2-fluorobenzotrifluoride, 3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, 2-methylbenzotrifluoride, 3-methylbenzotrifluoride, 4-methylbenzotrifluoride, etc.), fluoroxylenes (e.g., 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m-xylene, etc.), sulfur-containing heterocyclic compounds (e.g., benzothiazole, 2-methyl benzothiazole) It may contain at least one selected from the group consisting of (e.g., nzothiazole, tetrathiafulvalene), nitrile compounds (e.g., adiponitrile, succinonitrile), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate), carboxylic acid anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride), alcohols (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, diethylene glycol monomethyl ether), and derivatives thereof.

[0126] 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.

[0127] 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.

[0128] In some embodiments of this invention, the battery may include a gel electrolyte; that is, the battery may be a polymer battery. The gel electrolyte may include an electrolyte solution and a polymer material. The polymer material may form a polymer matrix. The polymer material may include, for example, at least one selected from the group consisting of PVdF, PVdF-HFP, polyacrylonitrile (PAN), PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof. [Examples]

[0129] [Manufacturing of positive electrodes] <No.1> (a) Mixing process Compositional formula “Li 1.04 Mn 0.6 Fe 0.4 A raw material mixture 1 was prepared by weighing lithium hydroxide monohydrate, manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate to match the composition ratio shown in "PO4". 8% glucose was weighed by mass fraction relative to the total mass of raw material mixture 1. A slurry was formed by mixing the weighed raw material mixture 1, glucose, and 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.

[0130] (b) Granulation process The slurry was spray-dried to form first precursor particles. The target D50 value of the first precursor particles was 9 ± 1 μm. The intake port temperature was 250°C, the exhaust port temperature of the spray dryer was 115 ± 15°C, the spray velocity was 10 mL / min, the intake pressure was 2.0 MPa, and the nozzle pressure of the spray nozzle was 0.2 ± 0.1 MPa.

[0131] (c) First firing process Second precursor particles were formed by calcining the obtained first precursor particles under a nitrogen atmosphere. The conditions for this process were as follows: 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.

[0132] (d) Second firing process Following the first firing process, the furnace temperature was raised to 650°C at a 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 rate of 2°C / min. Furthermore, the furnace temperature was cooled to room temperature at a rate of 15°C / min. In this way, Li 1.04 Mn 0.6 Fe 0.4 A positive electrode active material was obtained consisting of secondary particles containing primary particles containing PO4.

[0133] (Coin cell production) A mixture was formed by mixing the positive electrode active material, conductive material (acetylene black), and binder (PVdF). The mixing ratio (mass ratio) was "positive electrode active material / conductive material / binder = 92 / 5 / 3". A paste was formed by dispersing the mixture in a solvent (N-methyl-2-pyrrolidone). The solid content concentration of the paste was 50% by mass fraction. The positive electrode layer was formed by applying the paste to the surface of an Al foil and drying it. The density of the positive electrode layer was 1.8 g / cm³ by roll pressing. 3 The cathode material was formed by adjusting the material. The cathode material was subjected to vacuum drying at 120°C for 12 hours. After drying, a disc sample (diameter: 14 mm) was removed from the cathode material by punching.

[0134] The coin cell was assembled inside the glove compartment. The cell configuration is as follows:

[0135] Working electrode: Disc sample (positive electrode) Opposite pole: Li foil Separator: Polymer porous membrane Electrolyte: "EC / DMC=3 / 7 (volume ratio)", LiPF6 (1mol / L)

[0136] <No.2 to No.6> In the mixing step (a), the positive electrode active material was produced in the same manner as in No. 1, except for the following (i) and (ii).

[0137] (i) Lithium hydroxide monohydrate (LiOH·H2O) was added in excess in the mass shown in FIG. 5 when the mass of lithium hydroxide monohydrate (LiOH·H2O) contained in the raw material mixture 1 was taken as 1.

[0138] (ii) Titanium dioxide (TiO2) with a mass fraction of 1% was weighed with respect to the total mass of the raw material mixture 1, and a slurry was formed by mixing the weighed raw material mixture 1, the excess lithium hydroxide monohydrate, glucose, titanium dioxide, and water. Titanium dioxide used was any of the following. The type of titanium dioxide used in each sample is as shown in FIG. 5. · Powdered anatase-type titanium dioxide (denoted as "anatase type" in FIG. 5) · Powdered rutile-type titanium dioxide (denoted as "rutile type" in FIG. 5)

[0139] <No.7> After the second firing step (d), titanium dioxide shown in FIG. 5 with a mass fraction of 1% was added with respect to the total mass of the raw material mixture 1.

[0140] [Evaluation] <SEM image measurement> Using the SEM image, the presence or absence of titanium bodies on the surface of the primary particles was confirmed, and the maximum Feret diameter of the titanium bodies was measured. For the positive electrode active materials of No. 2 to No. 7, a plurality of titanium bodies present on the surface of the primary particles were confirmed. For the positive electrode active materials of No. 2 to No. 7, the number average value of the maximum Feret diameters of any 10 titanium bodies present on the surface of the primary particles was calculated. The calculation results are shown in FIG. 5.

[0141] (XAFS measurement) The positive electrode was measured by XAFS by the above method, and Li4Ti5O of the positive electrode active material 12The amount fraction (X) of substance was calculated. The calculation results are shown in Figure 5.

[0142] <Rating> (Reaction resistance) The reaction resistance was measured using the following procedure. In the coin cell described above, the positive electrode was removed after adjusting the state of charge (SOC) to 50%, and a symmetrical cell (coin cell) was fabricated using that positive electrode. In the symmetrical cell, the electrolyte and separator were those described for the coin cell described above. Then, using a potentiometer (Solartron Analytical product), an AC voltage was applied with an amplitude of 5mV, with the frequency gradually changing from 0.1Hz to 100,000Hz. The obtained Nyquist plot was then fitted to an equivalent circuit (R1+R1C circuit), and R1 was defined as the reaction resistance. The results are shown in Figure 5. Note that the reaction resistance values ​​shown in Figure 5 are relative values ​​when the reaction resistance R1 of No. 1 is set to 1.

[0143] <Result> As shown in Figure 5, the addition of rutile-type titanium dioxide reduces the reaction resistance. Also, Li4Ti5O 12 A tendency for the reaction resistance to decrease further is observed when the molar fraction (X) is 0.01 or greater. [Explanation of symbols]

[0144] 1 Primary particle, 2 Secondary particle, 3 Titanium body, 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. It is a positive electrode active material, The positive electrode active material comprises a plurality of secondary particles and a plurality of titanium bodies. The aforementioned secondary particle includes a plurality of primary particles, The primary particles contain a phosphate compound with an olivine-type structure. The titanium body contains titanium oxide with a rutile-type structure, At least a portion of the plurality of titanium bodies are present on the surface of the primary particles. Cathode active material.

2. At least a portion of the plurality of titanium bodies are on the surface of the primary particles and located at the grain boundaries of the primary particles, The positive electrode active material according to claim 1.

3. The positive electrode active material according to claim 1, wherein the titanium body has a maximum ferret diameter of 100 nm or more and 500 nm or less.

4. The positive electrode active material according to claim 1, further comprising a titanium body with a spinel-type structure of lithium titanate.

5. The titanium material may further contain titanium oxide with anatase structure. In the positive electrode active material, the molar fraction of the content of lithium titanate with a spinel structure relative to the total content of lithium titanate with a spinel structure, titanium oxide with a rutile structure, and titanium oxide with anatase structure is 0.01 or more and 0.50 or less. The positive electrode active material according to claim 4.

6. The phosphate compound with the olivine-type structure is lithium iron manganese phosphate. The positive electrode active material according to claim 1.

7. A battery comprising the positive electrode active material according to any one of claims 1 to 6.

8. It is a battery, The aforementioned battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises the positive electrode active material described in any one of claims 1 to 6. The electrolyte contains ethylene carbonate. battery.

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

10. A method for producing a positive electrode active material according to any one of claims 1 to 6, (a) A step of forming a slurry by mixing a manganese compound, a lithium compound, a phosphate compound, titanium dioxide with a rutile structure, and a solvent. (b) A step of forming first precursor particles by drying the slurry, (c) A step of forming second precursor particles by subjecting the first precursor particles to a first heat treatment, (d) A step of producing an olivine-type phosphate compound by subjecting the second precursor particles to a second heat treatment, A method for manufacturing a positive electrode active material.

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