Positive electrode active material and battery

Abstract

Improved cycle characteristics. [Solution] The positive electrode active material contains lithium manganese phosphate. Lithium manganese phosphate has a crystal structure belonging to the space group Pnma. In the crystal structure, the manganese sites are doped with a first dopant and a second dopant. The first dopant and the second dopant have different valencies. The first dopant has an ionic radius of less than 0.830 Å (83 pm). The second dopant has an ionic radius greater than 0.645 Å (64.5 pm).

Description

[Technical Field]

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

[0002] Japanese Patent Publication No. 2024-045748 discloses positive electrode active material particles having regions at and near the grain boundaries where the magnesium concentration is higher than that inside the grains. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-045748 [Overview of the project] [Problems that the invention aims to solve]

[0004] Lithium iron phosphate (hereinafter sometimes abbreviated as "LFP") is widely used. Because LFP does not contain rare metals, its raw material costs are low. However, because LFP has a low discharge voltage, it tends to have a low energy density.

[0005] Lithium manganese phosphate (hereinafter sometimes abbreviated as "LMP") is promising in terms of cost, similar to LFP. Furthermore, LMP can have a higher voltage than LFP. However, LMP has room for improvement in its cycle characteristics.

[0006] The purpose of this disclosure is to improve cycle characteristics. [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 contains lithium manganese phosphate. Lithium manganese phosphate has a crystal structure belonging to the space group Pnma. In the crystal structure, the manganese sites are doped with a first dopant and a second dopant. The first dopant and the second dopant have different valencies. The first dopant has an ionic radius of less than 0.830 Å (83 pm). The second dopant has an ionic radius greater than 0.645 Å (64.5 pm).

[0009] During charging of an LMP (Large Multiplier), the valence of manganese (Mn) increases from 2+ to 3+. At this time, localized structural relaxation can occur, potentially generating Jahn-Teller strain (hereinafter abbreviated as "JT strain"). The generation of JT strain is thought to make Mn more likely to dissolve during charging and discharging. For example, Mn can dissolve when LMP reacts with hydrogen fluoride (HF) generated within the battery. The dissolved Mn can precipitate on the negative electrode. The Mn on the negative electrode can act as a catalyst for the decomposition reaction of the electrolyte. Since a portion of the electricity used during charging is used for the decomposition reaction of the electrolyte, the Coulomb efficiency decreases. As a result, the cycle characteristics are thought to deteriorate.

[0010] The ionic radius of divalent Mn(2+) is 0.830 Å. The first dopant has an ionic radius of less than 0.830 Å. That is, the first dopant has a smaller ionic radius than Mn(2+).

[0011] The ionic radius of trivalent Mn(3+) is 0.645 Å. The second dopant has an ionic radius greater than 0.645 Å. That is, the second dopant has a larger ionic radius than Mn(3+).

[0012] Figure 1 is a conceptual diagram showing the Mn-O bond state. In Figure 1, atomic arrangements and angles are depicted as being close to straight lines in order to simplify conceptual understanding. Atomic arrangements and angles are not necessarily specified as shown in the figure. Within the Mn site, Mn has a coordination number of 6. First dopant (D 1) is a relatively small atom compared to divalent Mn(2+). The first dopant (D 1 ) has a strong tendency to attract oxygen (O). The first dopant (D 1 The attraction of oxygen by the carbon atom increases the Mn-O bond distance. This can relieve the JT strain. On the other hand, other strains may be introduced within the crystal structure.

[0013] Second Dopant (D 2 ) is a relatively large atom compared to trivalent Mn(3+). Second dopant (D 2 ) is the first Dopant (D 1 It is expected to absorb the distortion caused by the second dopant (D 2 By easing the strain, the entire structure is expected to be stabilized. This overall structural stabilization may reduce Mn elution. As a result, improved cycle characteristics are expected.

[0014] 2. The positive electrode active material described in "1" above may include, for example, the following configuration: The first dopant has a valence of 2+ or higher. The second dopant has a valence of 3+ or lower.

[0015] For example, the first dopant may have a valency equivalent to or greater than that of divalent Mn(2+). For example, the second dopant may have a valency equivalent to or less than that of trivalent Mn(3+).

[0016] 3. The positive electrode active material described in "1" or "2" above may include, for example, the following components: The first dopant includes at least one selected from the group consisting of beryllium (Be), boron (B), titanium (Ti), zirconium (Zr), niobium (Nb), silicon (Si), gallium (Ga), ruthenium (Ru), rhodium (Rh), molybdenum (Mo), and aluminum (Al). The second dopant includes at least one selected from the group consisting of magnesium (Mg), zinc (Zn), calcium (Ca), strontium (Sr), yttrium (Y), and barium (Ba).

[0017] 4. The cathode active material according to any one of the above items "1" to "3" may, for example, include the following configuration. In the manganese site, the site occupancy of the first dopant is higher than that of the second dopant.

[0018] In the Mn site, since the first dopant is more than the second dopant, an improvement in cycle characteristics is expected.

[0019] 5. The cathode active material according to any one of the above items "1" to "4" may, for example, include the following configuration. In the manganese site, the site occupancy of the first dopant is from 0.0005 to 0.05. The site occupancy of the second dopant is from 0.0005 to 0.05.

[0020] 6. The cathode active material according to any one of the above items "1" to "5" may, for example, include the following configuration. The first dopant contains Si. The second dopant contains at least one selected from the group consisting of Mg and Ca. In the manganese site, the site occupancy of Si is 0.001 or more.

[0021] When the site occupancy of Si is 0.001 or more, an improvement in cycle characteristics is expected.

[0022] 7. The cathode active material according to any one of the above items "1" to "6" may, for example, include the following configuration. Lithium manganese phosphate has a composition represented by the following general formula. LiMn 1-x-y-z Fe x D 1 y D 2 z PO4 In the formula, the relationship of 0.05 ≤ x ≤ 0.50, 0.0005 ≤ y ≤ 0.05, and 0.0005 ≤ z ≤ 0.05 is satisfied. "D 1 " represents the first dopant. "D 2 " represents the second dopant.

[0023] At the Mn site, some of the Mn may be substituted with iron (Fe).

[0024] 8. One aspect of this disclosure is a battery. The battery includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode active material. The positive electrode active material includes lithium manganese phosphate. The lithium manganese phosphate has a crystal structure belonging to the space group Pnma. The relationship "b / a ≤ 0.613" is satisfied. "a" is the positive electrode potential of 4.3V vs. Li / Li + The lattice constant in the a-axis direction of lithium manganese phosphate in the charged state is shown. "b" represents the lattice constant in the b-axis direction of lithium manganese phosphate in the charged state.

[0025] The stabilization of the lithium manganese phosphate structure is expected to improve cycle characteristics. Overall structural stabilization can reduce at least one of the elongation of the crystal structure in the b-axis direction and the c-axis direction in the charged state (when Li is extracted from LMP). For example, when the ratio of lattice constants "b / a" is 0.613 or less, improved cycle characteristics can be expected.

[0026] 9. The battery described in "8" above may include, for example, the following configuration: The relationship "c / a ≤ 0.505" is further satisfied, where "c" is the lattice constant in the c-axis direction of lithium manganese phosphate in the charged state.

[0027] For example, when the ratio of lattice constants "c / a" is 0.505 or less, an improvement in cycle characteristics can be expected.

[0028] 10. The batteries described in "8" or "9" above may include, for example, the following configuration: the relationships "0.588 ≤ b / a ≤ 0.613" and "0.486 ≤ c / a ≤ 0.505" are further satisfied.

[0029] 11. The battery described in any one of items "8" through "10" above may include, for example, the following configuration: The battery has a bipolar structure.

[0030] 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]

[0031] [Figure 1] This is a conceptual diagram showing the Mn-O bonding state. [Figure 2] This is a conceptual diagram showing the positive electrode active material in this embodiment. [Figure 3] This is a schematic flowchart of the method for manufacturing the positive electrode active material in this embodiment. [Figure 4] This is a schematic perspective view of the battery in this embodiment. [Figure 5] This is a schematic cross-sectional view along the VV line in Figure 4. [Figure 6] This is the temperature profile during firing. [Figure 7] This is a table showing the experimental results. [Modes for carrying out the invention]

[0032] -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.

[0033] 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."

[0034] 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.

[0035] 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.

[0036] 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".

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The space group to which a crystal structure belongs is identified by powder X-ray diffraction (XRD) measurements. Crystal structures belonging to the space group Pnma are also called "olivine-type structures." The XRD measurement conditions are as follows, for example: Analysis method: Wide-angle method Measurement device: Smart Lab II (manufactured by Rigaku Corporation) Measurement angle: 10 to 120° Tube:CuKα Tube voltage: 45kV Tube current: 200mA Measurement method: Continuous method Step: 0.02 Speed: 2° / min RS: 20mm Detection mode: 1D

[0043] The lattice constants (a, b, c) are measured using the following procedure: Positive electrode potential is 4.3V vs. Li / Li +The battery is charged to the following state. After charging, the battery is disassembled and the positive electrode (positive electrode layer) is recovered. The positive electrode is cleaned. After cleaning, the positive electrode is cut to a predetermined size to prepare a sample for XRD measurement. The XRD pattern obtained by the XRD measurement is subjected to background processing and structural refinement processing using the software "GSAS-II". This allows the "lattice constants (a, b, c)" to be derived.

[0044] A "dopant" refers to an element in LMP other than lithium (Li), manganese (Mn), femur (Fe), phosphorus (P), and oxygen (O). The valence and ionic radius of a dopant are determined based on the values ​​obtained when its coordination number is 6.

[0045] "Site occupancy rate" indicates the fraction of the number of atoms of the target element relative to the total number of atoms (ions) occupying the Mn site. Site occupancy rate can also be expressed as the molar fraction.

[0046] In granular materials, "D50" indicates the particle size at which the cumulative particle size distribution (cumulative distribution) reaches 50% based on volume. The particle size distribution can be measured by laser diffraction.

[0047] The "maximum Ferret diameter" of a particle indicates the distance between the two furthest points on the particle's contour line in a two-dimensional projection image of the particle (e.g., an electron microscope image).

[0048] 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.

[0049] 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.

[0050] 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.

[0051] Electric potential unit "V vs. Li / Li + This indicates the potential with the oxidation-reduction potential of Li as the reference (zero).

[0052] -Cathode active material- The positive electrode active material may have any form. The positive electrode active material may be, for example, a powder or granular material. The D50 of the positive electrode active material 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 D50 of the positive electrode active material may be, for example, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 15 μm or less.

[0053] Figure 2 is a conceptual diagram showing the positive electrode active material in this embodiment. The positive electrode active material may, for example, include secondary particles 2. Secondary particles 2 are aggregates of primary particles 1. The maximum Ferret diameter of secondary particles 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 particles 2 may be, for example, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 15 μm or less. The maximum Ferret diameter of primary particles 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 particles 1 may be, for example, 120 nm or less, 100 nm or less, 80 nm or less, or 60 nm or less.

[0054] A carbon layer 3 may be attached to the surface of the primary particle 1. The carbon layer 3 contains carbon (C). The amount of carbon layer 3 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 3 attached may be, for example, 5% or less, 4% or less, or 3% or less by mass fraction relative to the secondary particle 2.

[0055] Primary particle 1 contains LMP. LMP has a crystalline structure belonging to the space group Pnma. LMP may be, for example, a single-phase compound. LMP may further contain crystalline phases belonging to other space groups, as long as it contains a crystalline phase belonging to the space group Pnma. LMP may further contain, for example, an amorphous phase.

[0056] LMP includes a Li site and a Mn site. The Li site is typically occupied by Li. The Mn site is typically occupied by Mn. The coordination number of Mn at the Mn site is considered to be 6. In this embodiment, both the first dopant and the second dopant are doped into the Mn site. It is believed that the synergistic action of the first and second dopants stabilizes the entire structure and improves the cycle characteristics.

[0057] The first dopant is an atom that is relatively small compared to Mn(2+). The first dopant has an ionic radius of less than 0.830 Å. The ionic radius of the first dopant may be, for example, 0.800 Å or less, 0.760 Å or less, 0.720 Å or less, 0.680 Å or less, 0.640 Å or less, 0.600 Å or less, 0.560 Å or less, 0.520 Å or less, 0.480 Å or less, 0.440 Å or less, 0.400 Å or less, 0.360 Å or less, 0.320 Å or less, 0.280 Å or less, or 0.240 Å or less. The ionic radius of the first dopant may be, for example, 0.200 Å or more, 0.240 Å or more, 0.280 Å or more, 0.320 Å or more, 0.360 Å or more, 0.400 Å or more, 0.440 Å or more, 0.480 Å or more, 0.520 Å or more, 0.560 Å or more, 0.600 Å or more, 0.640 Å or more, 0.680 Å or more, 0.720 Å or more, 0.760 Å or more, or 0.800 Å or more.

[0058] The first dopant and the second dopant have different valencies. The first dopant may have a valency of, for example, 2+ or higher. The valency of the first dopant may be, for example, 3+ or higher, 4+ or higher, 5+ or higher, 6+ or higher, or 7+ or higher. The valency of the first dopant may be, for example, 8+ or lower, 7+ or lower, 6+ or lower, 5+ or lower, 4+ or lower, or 3+ or lower.

[0059] The first dopant may include, for example, at least one selected from the group consisting of Be(2+, 0.450Å), B(3+, 0.270Å), Ti(4+, 0.605Å), Zr(4+, 0.720Å), Nb(5+, 0.640Å), Si(4+, 0.400Å), Ga(3+, 620Å), Ru(5+, 0.565Å), Rh(5+, 0.550Å), Mo(6+, 0.590Å), and Al(3+, 0.535Å). The notation "Be(2+, 0.450Å)" indicates that the valence of Be is 2+ and the ionic radius is 0.450Å.

[0060] The first dopant may be doped with a single element or with a combination of two or more elements. Doping with two or more elements may lead to high entropy, potentially making the dopant more easily soluble. For example, a combination of Si and Ti may be doped as the first dopant.

[0061] The seat occupancy rate (y) of the first dopant at the Mn site may be, for example, between 0.0005 and 0.05. The seat occupancy rate (y) of the first dopant may be, for example, 0.001 or more, 0.005 or more, 0.01 or more, 0.02 or more, 0.03 or more, or 0.04 or more. The seat occupancy rate (y) of the first dopant may be, for example, 0.04 or less, 0.03 or less, 0.02 or less, 0.01 or less, 0.005 or less, or 0.001 or less. If the first dopant contains two or more elements, the seat occupancy rate (y) of the first dopant represents the sum of the seat occupancy rates of each element. The same applies to the second dopant.

[0062] The second dopant is an atom that is relatively larger than Mn(3+). The second dopant has an ionic radius greater than 0.645 Å. The ionic radius of the second dopant may be larger than, for example, the ionic radius of the first dopant.

[0063] For example, the following relationship may also be satisfied. d1 <d Mn(3+) <d Mn(2+) <d2 d1: Ionic radius of the first dopant d Mn(3+) : Ionic radius of trivalent Mn d Mn(2+) : Ionic radius of divalent Mn d2: Ionic radius of the second dopant

[0064] The ionic radius of the second dopant may be, for example, 0.680 Å or greater, 0.720 Å or greater, 0.760 Å or greater, 0.800 Å or greater, 0.840 Å or greater, 0.880 Å or greater, 0.920 Å or greater, 0.960 Å or greater, 1.00 Å or greater, 1.04 Å or greater, 1.08 Å or greater, 1.12 Å or greater, 1.16 Å or greater, 1.20 Å or greater, 1.24 Å or greater, 1.28 Å or greater, 1.32 Å or greater, or 1.36 Å or greater. The ionic radius of the second dopant may be, for example, 1.40 Å or less, 1.36 Å or less, 1.32 Å or less, 1.28 Å or less, 1.24 Å or less, 1.20 Å or less, 1.16 Å or less, 1.12 Å or less, 1.08 Å or less, 1.04 Å or less, 1.00 Å or less, 0.960 Å or less, 0.920 Å or less, 0.880 Å or less, 0.840 Å or less, 0.800 Å or less, 0.760 Å or less, or 0.720 Å or less.

[0065] The second dopant may have a valence of, for example, 3+ or less. The valence of the second dopant may be, for example, 3+ or 2+.

[0066] The second dopant may include, for example, at least one selected from the group consisting of Mg(2+, 0.720 Å), Zn(2+, 0.740 Å), Ca(2+, 1.00 Å), Sr(2+, 1.18 Å), Y(3+, 0.900 Å), and Ba(2+, 1.35 Å). Similar to the first dopant, the second dopant may be doped with a single substance or with a combination of two or more substances.

[0067] The seat occupancy rate (z) of the second dopant at the Mn site may be, for example, 0.0005 to 0.05. The seat occupancy rate (z) of the second dopant may be, for example, 0.001 or more, 0.005 or more, 0.01 or more, 0.02 or more, 0.03 or more, or 0.04 or more. The seat occupancy rate (z) of the second dopant may be, for example, 0.04 or less, 0.03 or less, 0.02 or less, 0.01 or less, 0.005 or less, or 0.001 or less.

[0068] The seat occupancy rate (y) of the first dopant at the Mn site may be higher than that of the second dopant (z). The ratio (y / z) of the seat occupancy rate (y) of the first dopant to the seat occupancy rate (z) of the second dopant may be, for example, 1.1 or higher, 1.2 or higher, 1.5 or higher, 2.0 or higher, 3.0 or higher, 4.0 or higher, or 5.0 or higher. The seat occupancy rate ratio (y / z) may be, for example, 10.0 or lower, 9.0 or lower, 8.0 or lower, 7.0 or lower, 6.0 or lower, 5.0 or lower, 4.0 or lower, 3.0 or lower, 2.0 or lower, 1.5 or lower, or 1.2 or lower.

[0069] For example, the first dopant may contain Si. The second dopant may contain at least one selected from the group consisting of Mg and Ca. The Si occupancy rate at the Mn site may be 0.001 or higher. An improvement in cycle characteristics can be expected when the Si occupancy rate is 0.001 or higher. The Si occupancy rate may be, for example, 0.005 or higher, 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, or 0.05 or higher. The Si occupancy rate may be, for example, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less.

[0070] Furthermore, nickel (Ni) and cobalt (Co) are not expected to undergo valency changes within the operating voltage range of the LMP, and therefore are not expected to contribute much to structural stabilization in this embodiment. If copper (Cu) is doped into the Mn site, it is expected that the structure will become unstable. Monovalent silver (Ag) is not expected to be easily doped into the Mn site. Sulfur (S) is expected to be substituted into the P site rather than the Mn site.

[0071] At the Mn site, a portion of the Mn may be substituted with Fe. Fe-substituted LMPs are also written as "LMFP". At the Mn site, for example, the relationship "Mn:Fe = 1-x:x" and "0 ≤ x < 1" may be satisfied. "1-x" represents the composition ratio (amount of substance) of Mn, and "x" represents the composition ratio (amount of Fe substitution). The amount of Fe substitution (x) may be, for example, 0 or more, 0.05 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. The amount of Fe substitution (x) 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. It is thought that the smaller the amount of Fe substitution (x), the more likely JT strain is to occur.

[0072] LMP may have a composition represented by the following general formula, for example. LiMn 1-x-y-z Fe x D 1 y D 2 z PO4 x (Fe substitution amount): 0.05≦x≦0.50 y (seat occupancy rate of the first Dopant): 0.0005 ≤ y ≤ 0.05 z (seat occupancy rate of the second Dopant): 0.0005 ≤ z ≤ 0.05 D 1 (First dopant): The first dopant includes at least one selected from the group consisting of Be, B, Ti, Zr, Nb, Si, Ga, Ru, Rh, Mo, and Al. D 2(Second Dopant): The second dopant contains at least one selected from the group consisting of Mg, Zn, Ca, Sr, Y, and Ba.

[0073] In the above general formula, for example, relationships such as "1≦(y / z)", "1<(y / z)", "1.2≦(y / z)", or "2.0≦(y / z)≦5.0" may be satisfied.

[0074] As long as the positive electrode active material contains LMP (LMFP), it may further contain other components. The other components may include, for example, LFP, lithium nickel composite oxide (LNO), lithium cobalt composite oxide (LCO), lithium manganese composite oxide (LMO), etc. The mixing ratio (mass ratio) of LMP and the other components may be, for example, "LMP / other components = 9 / 1 to 1 / 9", "LMP / other components = 8 / 2 to 2 / 8", "LMP / other components = 7 / 3 to 3 / 7", or "LMP / other components = 6 / 4 to 4 / 6". The positive electrode active material may be, for example, a mixture of LMP powder and other component powder.

[0075] LNO may have 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 relationships -0.5≦a≦0.5 and 0≦x≦1 are satisfied. M may include, for example, at least one selected from the group consisting of Co, Mn, and Al. For example, relationships such as 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, relationships such as -0.4≦a≦0.4, -0.3≦a≦0.3, -0.2≦a≦0.2, or -0.1≦a≦0.1 may be satisfied.

[0076] LNO is, for example, LiNi0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O2, and may contain at least one selected from the group consisting of LiNiO2.

[0077] 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.

[0078] 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 0.5Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and LiNi 0.9 Co 0.05 Mn 0.05 It may contain at least one selected from the group consisting of O2.

[0079] 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 "NCA". Li 1-a Ni x Co y Al z [[ID=​In the formula, the relationships of -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied. For example, the relationships of 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x < 1 may be satisfied. For example, the relationships of 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9, or 0.9 ≤ y < 1 may be satisfied. For example, the relationships of 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1 may be satisfied. [[ID=!]] [[ID=!]]

[0080] [[ID=!]] NCA is, for example, LiNi[[ID=!]] 0.7 Co[[ID=!]] 0.1 Al[[ID=!]] 0.2 O2, LiNi[[ID=!]] 0.7 Co[[ID=!]] 0.2 Al[[ID=!]] 0.1 O2, LiNi[[ID=!]] 0.8 Co[[ID=!]] 0.1 Al[[ID=!]] 0.1 O2, LiNi[[ID=!]] 0.8 Co[[ID=!]] 0.17 Al[[ID=!]] 0.03 O2, LiNi[[ID=!]] 0.8 Co[[ID=!]] 0.15 Al[[ID=!]] 0.05 O2, and LiNi[[ID=!]] 0.9 Co[[ID=!]] 0.05 Al[[ID=!]] 0.05 It may contain at least one selected from the group consisting of O2. [[ID=!]] [[ID=!]]

[0081] [[ID=!]] [[ID=!]]-Method for manufacturing a positive electrode active material-[[ID=!]] FIG. 3 is a schematic flowchart of the method for manufacturing a positive electrode active material in the present embodiment. Hereinafter, "the method for manufacturing a positive electrode active material in the present embodiment" may be abbreviated as "this method". This method includes "(a) formation of a slurry", "(b) formation of secondary particles", and "(c) firing". [[ID=!]] [[ID=!]]

[0082] (a) Formation of slurry This method involves forming a slurry by mixing a lithium compound, a manganese compound, a phosphate compound, and a solvent. When LMFP is the target substance, an iron compound is added to the raw material mixture. For example, a compound with the composition formula "Li 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 (0.90 ≤ a ≤ 1.10, 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.

[0083] 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 contain, for example, sugars, organic acids, etc. The carbon raw material may also contain, 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.

[0084] The solvent may include, for example, water. The solid content concentration of the slurry may be, for example, 20 to 40% by mass fraction.

[0085] The particle size in the slurry may be adjusted by wet grinding. For example, wet grinding may be performed so that D50 is between 0.10 and 1 μm.

[0086] (b) Formation of secondary particles This method involves forming secondary particles by drying the slurry. For example, secondary particles may be formed by a spray-drying method.

[0087] (c) Firing This method involves generating LMP by heat-treating secondary particles. Any heat treatment furnace (e.g., electric furnace, muffle furnace, etc.) can be used. In this method, secondary particles (precursors) are brought to a molten state by high-temperature firing under an inert atmosphere, and dopants are added while they are molten. This allows two or more dopants to be solid-dissolved in the Mn site. For example, secondary particles (precursors) and a dopant source are placed in a graphite crucible. The dopant source may contain, for example, at least one of the dopant hydroxide and carbonate. For example, firing is carried out under a nitrogen atmosphere at 1000 to 1100°C to form a sintered body (LMP). The heat treatment time may be, for example, 4 to 6 hours. After firing, the sintered body is crushed, for example, using a mortar and pestle, a ball mill, etc. After crushing, the particle size may be adjusted, for example, by a mesh pass.

[0088] -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.

[0089] Figure 4 is a schematic perspective view of the battery in this embodiment. Figure 5 is a schematic cross-sectional view along the VV line in Figure 4. 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] Charging status (4.3V vs. Li / Li) + In the positive electrode layer 11 of the ), the positive electrode active material (LMP) has a specific lattice constant ratio. For example, the ratio "b / a" of the lattice constant "b" in the b-axis direction to the lattice constant "a" in the a-axis direction may be 0.613 or less. That is, the relationship "b / a ≤ 0.613" may be satisfied. The lattice constant ratio "b / a" may be, for example, 0.609 or less, 0.606 or less, 0.598 or less, 0.597 or less, 0.595 or less, or 0.590 or less. The lattice constant ratio "b / a" may be, for example, 0.580 or more, 0.585 or more, 0.588 or more, 0.590 or more, 0.595 or more, 0.597 or more, 0.598 or more, 0.600 or more, 0.606 or more, or 0.609 or more. For example, the relationship "0.588 ≤ b / a ≤ 0.613" may also be satisfied.

[0097] Charging status (4.3V vs. Li / Li) + In the positive electrode layer 11 of the positive electrode active material, for example, the ratio "c / a" of the lattice constant "b" in the c-axis direction to the lattice constant "a" in the a-axis direction of the positive electrode active material may be 0.505 or less. That is, the relationship "c / a ≤ 0.505" may be satisfied. The lattice constant ratio "c / a" may be, for example, 0.499 or less, 0.495 or less, 0.494 or less, 0.490 or less, 0.488 or less, or 0.486 or less. The lattice constant ratio "c / a" may be, for example, 0.480 or more, 0.484 or more, 0.486 or more, 0.488 or more, 0.490 or more, 0.494 or more, 0.495 or more, or 0.499 or more. For example, the relationship "0.486 ≤ c / a ≤ 0.505" may be satisfied.

[0098] 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).

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] The carbon-based active material may include, 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. Graphite may also be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1", "natural graphite / artificial graphite = 2 / 8 to 8 / 2", or "natural graphite / artificial graphite = 3 / 7 to 7 / 3".

[0105] 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 include, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may include, 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.

[0106] The alloy-based active material may include, for example, at least one selected from the group consisting of Si, Li silicate, SiO, Si-based alloy, tin (Sn), SnO, and Sn-based alloy.

[0107] SiO may be represented by, for example, the following general formula. SiO x In the formula, the relationship of 0 < x < 2 is satisfied. For example, the relationship of 0.5 ≦ x ≦ 1.5 or 0.8 ≦ x ≦ 1.2 may be satisfied.

[0108] "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).

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] The separator 20 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0118] 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.

[0119] 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.

[0120] The solvent may contain cyclic carbonates (EC, PC, FEC, etc.) and linear carbonates (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates to linear carbonates may be, for example, "cyclic carbonate / linear carbonate = 1 / 9 to 4 / 6", "cyclic carbonate / linear carbonate = 2 / 8 to 3 / 7", or "cyclic carbonate / linear carbonate = 3 / 7 to 4 / 6".

[0121] The solvent may contain cyclic carbonates (EC, PC, etc.) and fluorinated cyclic carbonates (FEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates to fluorinated cyclic carbonates may be, for example, "cyclic carbonate / fluorinated cyclic carbonate = 99 / 1 to 90 / 10", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 1 / 9", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 7 / 3", or "cyclic carbonate / fluorinated cyclic carbonate = 3 / 7 to 1 / 9".

[0122] The solvent may include, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy the relationship expressed by, for example, the following formula. V EC +VFEC +V EMC +V DMC +V DEC =10 In the above formula, V EC , V FEC , V EMC , V DMC , V DEC These represent the volume ratios of EC, FEC, EMC, DMC, and DEC, respectively. 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] -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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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)".

[0136] 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.

[0137] 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.

[0138] 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).

[0139] 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, for example, at least one selected from the group consisting of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0140] The sulfide solid electrolyte may have, for example, a composition represented by 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.

[0141] The halide solid electrolyte may have, for example, a composition represented by 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, for example, at least one selected from the group consisting of Y, Al, Ti, Zr, Ca, and Mg. For example, the relationship of "0 < a < 2" may be satisfied. X may contain, for example, at least one selected from the group consisting of F, Cl, Br, and I.

[0142] 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.

[0143] 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.

[0144] 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]

[0145] -LMP Manufacturing- No.1 Compositional formula “Li 1.04 Mn 0.6 Fe 0.4 Lithium hydroxide monohydrate, manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate were weighed to match the composition ratio shown in "PO4". 8% glucose was weighed by mass fraction relative to the total mass of the raw materials. 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.

[0146] Secondary particles were formed by spray drying of the slurry. The target D50 value of the secondary particles was 9 ± 1 μm. The spray dryer settings were as follows: Air intake temperature: 250℃ Exhaust vent temperature: 115±15℃ Intake pressure: 2.0 MPa Spray nozzle pressure: 0.2 ± 0.1 MPa

[0147] Under a nitrogen atmosphere, LMP powder was obtained by calcining secondary particles. The secondary particles were placed in a heat treatment furnace. 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 was cooled to 400°C at a cooling rate of 2°C / min. The furnace was further cooled to room temperature at a cooling rate of 15°C / min.

[0148] No.2 (a) Formation of slurry Compositional formula “Li 1.04 Mn 0.595 Fe 0.4Lithium hydroxide monohydrate, manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate were weighed to match the composition ratio shown in "PO4". 8% glucose was weighed by mass fraction relative to the total mass of the raw materials. 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.

[0149] (b) Formation of secondary particles Secondary particles were formed by spray drying of the slurry. The target D50 value of the secondary particles was 9 ± 1 μm. The spray dryer settings were as follows: Air intake temperature: 250℃ Exhaust vent temperature: 115±15℃ Intake pressure: 2.0 MPa Spray nozzle pressure: 0.2 ± 0.1 MPa

[0150] (c) Firing Compositional formula “Li 1.04 Mn 0.595 Fe 0.4 Si 0.005 Secondary particles (precursors) and Si compounds (dopant sources) were weighed to match the composition ratio shown in "PO4". The secondary particles (precursors) and Si compounds were placed in a graphite crucible. The graphite crucible was placed in a heat treatment furnace. A sintered body was formed by firing the material under a nitrogen atmosphere. Figure 6 shows the temperature profile during firing. 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 1050°C at a heating rate of 5°C / min. The furnace temperature was maintained at 1050°C for 5 hours. After that, the furnace was cooled to 400°C at a cooling rate of 2°C / min. The furnace was further cooled to room temperature at a cooling rate of 15°C / min.

[0151] After firing, the sintered body was crushed. The crushed material was passed through a 75 μm sieve to obtain LMP powder.

[0152] others Figure 7 is a table showing the experimental results. As shown in Figure 7, LMP was synthesized in the same way as in No. 2, except that the type and combination of dopants were changed.

[0153] -evaluation- 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.

[0154] The coin cell was assembled inside the glove compartment. The cell configuration is as follows: Working electrode: Disc sample (positive electrode) Opposite pole: Li foil Separator: Polymer porous membrane Electrolyte: "EC / DMC=3 / 7 (volume ratio)", LiPF6 (1mol / L)

[0155] Evaluation of cycle characteristics At 25°C, the initial charge and discharge cycle was performed with a constant current. The upper limit of the charge voltage was 4.3V. The lower limit of the discharge voltage was 3.0V. At 25°C, the pre-cycle discharge capacity was measured at a rate of 0.1C. "C" is a symbol indicating the current rate (time rate). At a rate of 1C, the battery's rated capacity is supplied over one hour. Next, at 60°C, the charge and discharge cycle was repeated 100 times at a rate of 0.1C. After 100 cycles, at 25°C, the post-cycle discharge capacity was measured again at a rate of 0.1C. The capacity retention rate was calculated by dividing the post-cycle discharge capacity by the pre-cycle discharge capacity. A higher capacity retention rate indicates better cycle characteristics.

[0156] -result- The "capacity retention rate" shown in Figure 7 is a relative value with the value of No. 1 set to 100. As shown in Figure 7, the Mn site tends to exhibit improved cycle characteristics when both the first and second dopants are doped.

[0157] In samples with good cycle characteristics, the lattice constant ratio "b / a" at the charged positive electrode is 0.613 or less.

[0158] In samples with good cycle characteristics, the lattice constant ratio "c / a" at the charged positive electrode is 0.505 or less. [Explanation of symbols]

[0159] 1 Primary particle, 2 Secondary particle, 3 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. Contains lithium manganese phosphate, The lithium manganese phosphate has a crystal structure belonging to the space group Pnma, In the aforementioned crystal structure, the manganese site is doped with a first dopant and a second dopant. The first dopant and the second dopant have different valencies. The first dopant has an ionic radius of less than 0.830 Å, and The second dopant has an ionic radius greater than 0.645 Å. Cathode active material.

2. The first dopant has a valence of 2+ or higher, The second dopant has a valence of 3+ or less. The positive electrode active material according to claim 1.

3. The first dopant comprises at least one selected from the group consisting of Be, B, Ti, Zr, Nb, Si, Ga, Ru, Rh, Mo, and Al, The second dopant comprises at least one selected from the group consisting of Mg, Zn, Ca, Sr, Y, and Ba. The positive electrode active material according to claim 1.

4. At the manganese site, the seat occupancy rate of the first dopant is higher than that of the second dopant. The positive electrode active material according to any one of claims 1 to 3.

5. At the aforementioned manganese site, The seat occupancy rate of the first dopant is 0.0005 to 0.05, and The seat occupancy rate of the second dopant is between 0.0005 and 0.

05. The positive electrode active material according to any one of claims 1 to 3.

6. The first dopant contains Si, The second dopant comprises at least one selected from the group consisting of Mg and Ca, The Si occupancy rate in the manganese site is 0.001 or higher. The positive electrode active material according to any one of claims 1 to 3.

7. The aforementioned lithium manganese phosphate has a composition represented by the following general formula: The positive electrode active material according to any one of claims 1 to 3. LiMn 1-x-y-z Fe x D 1 y D 2 z PO 4 (In the equation, the relationships 0.05 ≤ x ≤ 0.50, 0.0005 ≤ y ≤ 0.05, and 0.0005 ≤ z ≤ 0.05 are satisfied.) The aforementioned D 1 This represents the first dopant, and The said D 2 represents the said second dopant.)

8. Including positive and negative electrodes, The positive electrode includes a positive electrode active material. The positive electrode active material includes lithium manganese phosphate, The lithium manganese phosphate has a crystal structure belonging to the space group Pnma, b / a ≤ 0.613 The relationship is satisfied, The above (a) is a positive electrode potential of 4.3V vs. Li / Li + The lattice constant in the a-axis direction of the lithium manganese phosphate in the charged state is shown, and, The value b represents the lattice constant in the b-axis direction of the lithium manganese phosphate in the charged state. battery.

9. c / a ≤ 0.505 The following conditions are also met: The value c represents the lattice constant in the c-axis direction of the lithium manganese phosphate in the charged state. The battery according to claim 8.

10. 0.588 ≤ b / a ≤ 0.613, and, 0.486 ≤ c / a ≤ 0.505 The relationship is further satisfied, The battery according to claim 8 or claim 9.

11. Having a bipolar structure, The battery according to claim 8 or claim 9.

Images