Positive electrode active material and battery

Abstract

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

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open 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 Application Publication No. 2024-045748 Summary of the Invention [Problem to be solved by the invention]

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

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

[0006] An object of the present disclosure is to improve cycle characteristics. [Means for solving the problem]

[0007] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action of the present disclosure includes speculation. The mechanism of action does not limit the technical scope of the present disclosure.

[0008] 1. One aspect of the present disclosure is 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. In the crystal structure, a first dopant and a second dopant are doped at the manganese site. The first dopant and the second dopant have different valences. The first dopant has an ionic radius of less than 0.830 Å (83 pm). The second dopant has an ionic radius of more than 0.645 Å (64.5 pm).

[0009] During charging of LMP, the valence of manganese (Mn) increases from divalent (2+) to trivalent (3+). This can lead to local structural relaxation, resulting in Jahn-Teller distortion (hereafter abbreviated as "JT distortion"). The occurrence of JT distortion is thought to make Mn more susceptible to leaching during charging and discharging. For example, Mn can be leached by reacting LMP with hydrogen fluoride (HF) generated within the battery. The leached Mn can deposit on the negative electrode. Mn on the negative electrode can act as a catalyst for the decomposition reaction of the electrolyte. Because a portion of the electricity consumed during charging is used for the decomposition reaction of the electrolyte, the coulombic efficiency decreases. This is thought to result in a decrease in cycle performance.

[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 an ionic radius smaller than that of 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 an ionic radius larger than that of Mn(3+).

[0012] Figure 1 is a conceptual diagram showing the bonding state of Mn-O. In Figure 1, in order to facilitate conceptual understanding, the atomic arrangement and angles are depicted as being close to a straight line. The atomic arrangement and angles are not necessarily specified as shown in the figure. In the Mn site, Mn has a coordination number of 6. The first dopant (D 1) is a relatively small atom compared to divalent Mn(2+). 1 ) has a tendency to strongly attract oxygen (O). 1 ) attracts O, expanding the Mn-O bond distance. This can relieve the JT strain. On the other hand, it can also cause other strains in the crystal structure.

[0013] Second dopant (D 2 ) is a relatively large atom compared to the trivalent Mn(3+). 2 ) is the first dopant (D 1 ) is expected to absorb the strain caused by the second dopant (D 2 ) is expected to relieve the strain, stabilizing the entire structure. This stabilization of the entire structure can reduce Mn dissolution, which is expected to result in improved cycle characteristics.

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

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

[0016] 3. The positive electrode active material according to the above paragraphs "1" and "2" may include, for example, the following: 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 positive electrode active material according to any one of the above items "1" to "3" may include, for example, the following configuration: At the manganese site, the site occupancy rate of the first dopant is higher than the site occupancy rate of the second dopant.

[0018] By having more first dopant than second dopant at the Mn site, improvement in cycle characteristics is expected.

[0019] 5. The positive electrode active material according to any one of the above items "1" to "4" may have, for example, the following configuration: At the manganese site, the site occupancy of the first dopant is 0.0005 to 0.05; and the site occupancy of the second dopant is 0.0005 to 0.05.

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

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

[0022] 7. The positive electrode active material according to any one of the above items 1 to 6 may include, for example, the following structure: 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 relationships 0.05≦x≦0.50, 0.0005≦y≦0.05, and 0.0005≦z≦0.05 are satisfied. 1 " indicates the first dopant. 2 " indicates the second dopant.

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

[0024] 8. One aspect of the present 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 when the positive electrode potential is 4.3 V vs. Li / Li. + "b" represents the lattice constant in the a-axis direction of lithium manganese phosphate in a charged state. "b" represents the lattice constant in the b-axis direction of lithium manganese phosphate in a charged state.

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

[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" represents the lattice constant of lithium manganese phosphate in the c-axis direction in a charged state.

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

[0028] 10. The battery described in "8" or "9" above may have, 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 according to any one of the above items "8" to "10" may include, for example, the following configuration: The battery has a bipolar structure.

[0030] Hereinafter, one embodiment of the present disclosure (hereinafter may be abbreviated as "this embodiment") and one example of the present disclosure (hereinafter may be abbreviated as "this example") will be described. However, this embodiment and this example do 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 non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is originally intended that any configurations may be extracted from this embodiment and arbitrarily combined. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a conceptual diagram showing the bonding state of Mn—O. [Figure 2] FIG. 2 is a conceptual diagram showing a positive electrode active material according to the present embodiment. [Figure 3] 1 is a schematic flowchart of a method for producing a positive electrode active material according to the present embodiment. [Figure 4] 1 is a schematic perspective view of a battery according to an embodiment of the present invention. [Figure 5] FIG. 5 is a schematic cross-sectional view taken along line VV in FIG. [Figure 6] This is the temperature profile during firing. [Figure 7] 10 is a table showing experimental results. DETAILED DESCRIPTION OF THE INVENTION

[0032] -Terms and phrases- "Comprises," "includes," "has," and variations thereof are open-ended expressions. An open-ended structure may or may not further include additional elements in addition to the required elements. "Consists of" is a closed expression. However, even a closed structure may include additional elements that are normally associated impurities or unrelated to the subject technology. "Consists essentially of..." is a semi-closed expression. A semi-closed structure allows the addition of elements that do not substantially affect the basic and novel characteristics of the subject technology.

[0033] Expressions such as "may" and "may" are used in the permissive sense, meaning "to have the possibility," rather than in the obligatory sense, meaning "to have to."

[0034] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0035] The terms "first," "second," etc. are used only to distinguish between multiple elements. Such terms do not limit the elements to which they are attached. Such terms have no bearing on, for example, the order or importance of the elements to which they are attached.

[0036] For example, the phrase "at least one of A and B" includes "A or B" as well as "A and B." "At least one of A and B" can also be written as "A and / or B."

[0037] Geometric terms should not be interpreted in a strict sense. Examples of geometric terms include "parallel," "perpendicular," and the like. For example, directions, angles, distances, and the like may be displaced relative to one another as long as substantially the same or similar functions are obtained. Geometric terms may include, for example, tolerances, errors, and the like in design, work, manufacturing, and the like. The dimensional relationships in each figure may not match the actual dimensional relationships. The dimensional relationships in each figure may be changed to aid the reader's understanding. For example, length, width, thickness, and the like may be changed. Some components may be omitted.

[0038] Elements described in the "singular" can also include the plural unless otherwise specified. For example, a particle can refer to a plurality of particles, a collection of particles, and granular matter.

[0039] Numerical ranges such as "m to n%" include the upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." "Equal to or more" and "equal to or less" are represented by inequality signs with an equal sign "≦, ≧." "More than" and "less than" are represented by inequality signs without an equal sign "<, >." A numerical value 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 numerical value within the numerical range with a numerical value described elsewhere in this specification, in a table, a figure, or the like.

[0040] All numerical values ​​are modified by the term "about." The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximate values ​​that may vary depending on the application of the subject technology. All numerical values ​​may be expressed with significant figures. Unless otherwise specified, measured values ​​may be average values ​​of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, 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. Products equivalent to the devices, etc. exemplified may also be used. When equivalent products are used, the measurement conditions may be adjusted to suit the device.

[0042] The space group to which the crystal structure belongs is identified by powder X-ray diffraction (XRD) measurement. A crystal structure belonging to the space group Pnma is also called an "olivine-type structure." The measurement conditions for XRD are, for example, as follows: Analysis method: Wide-angle method Measurement device: Smart Lab II (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: +The battery is charged so that the positive electrode (positive electrode layer) is obtained. After charging, the battery is disassembled and the positive electrode (positive electrode layer) is recovered. The positive electrode is then washed. After washing, the positive electrode is cut to a specified size to prepare a measurement sample for XRD measurement. The XRD pattern obtained by 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] "Dopant" refers to any element contained in LMP other than lithium (Li), Mn, Fe, phosphorus (P), and oxygen (O). The valence and ionic radius of the dopant are those when the coordination number is 6.

[0045] The "site occupancy" refers to the fraction of the number of atoms of a target element relative to the total number of atoms (ions) occupying the Mn site. The site occupancy may also be referred to as the fraction of the amount of substance.

[0046] The "D50" of a powder or granular material indicates the particle size at which the cumulative distribution reaches 50% in the volumetric particle size distribution (cumulative distribution). The particle size distribution can be measured by laser diffraction.

[0047] The "maximum Feret diameter" of a particle refers to the distance between the two most distant points on the outline of the particle in a two-dimensional projection image of the particle (for example, an electron microscope image).

[0048] The stoichiometric composition formula indicates a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to a compound having a molar ratio of "Al / O=2 / 3". Unless otherwise specified, "Al2O3" indicates a compound containing Al and O in any molar ratio. For example, the compound may be doped with a trace element. A portion of the Al and O may be substituted with another element.

[0049] The chemical composition of a compound can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). A sample solution is prepared by dissolving 0.1 g of a sample (e.g., a 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 using a measuring flask. After dilution, composition analysis is performed using an ICP-AES device. For example, a device with the product name "PS3520 UVDD II (manufactured by Hitachi High-Tech Science Corporation)" may be used.

[0050] The term "derivative" refers to a compound in which a part of a parent compound has been modified by at least one method selected from the group consisting of the introduction of a functional group, atomic substitution, oxidation, reduction, and other chemical reactions. The modification may be at one or more locations. The "substituent" 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 (e.g., F, Cl, Br, I), 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, phosphoric acid amide groups, sulfo groups, carboxy groups, hydroxamic acid groups, sulfino groups, hydrazino groups, imino groups, and silyl groups. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different. A plurality of substituents may be bonded to each other to form a ring.

[0051] Unit of potential: V vs. Li / Li + " 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] FIG. 2 is a conceptual diagram showing a positive electrode active material according to this embodiment. The positive electrode active material may include, for example, secondary particles 2. The secondary particles 2 are aggregates of primary particles 1. The maximum Feret diameter of the 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 Feret diameter of the 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 Feret diameter of the 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 Feret diameter of the 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 the 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 in mass fraction relative to the secondary particle 2. The amount of the carbon layer 3 attached may be, for example, 5% or less, 4% or less, or 3% or less in mass fraction relative to the secondary particle 2.

[0055] The primary particle 1 includes an LMP. The LMP has a crystal structure belonging to the space group Pnma. The LMP may be, for example, a single-phase compound. As long as the LMP includes a crystal phase belonging to the space group Pnma, it may further include a crystal phase belonging to another space group. The LMP may further include, for example, an amorphous phase.

[0056] LMP contains Li sites and Mn sites. The Li sites are usually occupied by Li. The Mn sites are usually occupied by Mn. The coordination number of Mn at the Mn sites is thought to be 6. In this embodiment, the Mn sites are doped with both a first dopant and a second dopant. The synergistic action of the first dopant and the second dopant is thought to stabilize the entire structure and improve cycle characteristics.

[0057] The first dopant is a relatively small atom 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 greater, 0.240 Å or greater, 0.280 Å or greater, 0.320 Å or greater, 0.360 Å or greater, 0.400 Å or greater, 0.440 Å or greater, 0.480 Å or greater, 0.520 Å or greater, 0.560 Å or greater, 0.600 Å or greater, 0.640 Å or greater, 0.680 Å or greater, 0.720 Å or greater, 0.760 Å or greater, or 0.800 Å or greater.

[0058] The first dopant and the second dopant have different valences. The first dopant may have a valence of, for example, 2+ or greater. The valence of the first dopant may be, for example, 3+ or greater, 4+ or greater, 5+ or greater, 6+ or greater, or 7+ or greater. The valence of the first dopant may be, for example, 8+ or less, 7+ or less, 6+ or less, 5+ or less, 4+ or less, or 3+ or less.

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

[0060] The first dopant may be a single dopant or a combination of two or more dopants. The combination of two or more dopants may result in high entropy and may facilitate the formation of a solid solution of the dopant. For example, a combination of Si and Ti may be used as the first dopant.

[0061] The site occupancy (y) of the first dopant at the Mn site may be, for example, 0.0005 to 0.05. The site occupancy (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 site occupancy (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. Note that when the first dopant contains two or more elements, the site occupancy (y) of the first dopant represents the sum of the site occupancies of the respective elements. The same applies to the second dopant.

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

[0063] For example, the following relationship may 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 at least one selected from the group consisting of Mg(2+, 0.720 Å), Zn(2+, 0740 Å), Ca(2+, 1.00 Å), Sr(2+, 1.18 Å), Y(3+, 0.900 Å), and Ba(2+, 1.35 Å). As with the first dopant, the second dopant may be doped singly or in combination of two or more.

[0067] The site occupancy (z) of the second dopant at the Mn site may be, for example, 0.0005 to 0.05. The site occupancy (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 site occupancy (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 site occupancy (y) of the first dopant at the Mn site may be higher than the site occupancy (z) of the second dopant. The ratio (y / z) of the site occupancy (y) of the first dopant to the site occupancy (z) of the second dopant may be, for example, 1.1 or more, 1.2 or more, 1.5 or more, 2.0 or more, 3.0 or more, 4.0 or more, or 5.0 or more. The site occupancy ratio (y / z) may be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, 4.0 or less, 3.0 or less, 2.0 or less, 1.5 or less, or 1.2 or less.

[0069] For example, the first dopant may include Si. The second dopant may include at least one selected from the group consisting of Mg and Ca. The site occupancy of Si at the Mn site may be 0.001 or more. When the site occupancy of Si is 0.001 or more, improved cycle characteristics are expected. The site occupancy of Si may be, for example, 0.005 or more, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more. The site occupancy of Si 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] Note that nickel (Ni) and cobalt (Co) are unlikely to undergo valence changes in the LMP operating voltage range, and are therefore unlikely to contribute to structural stabilization in this embodiment. When copper (Cu) is doped into the Mn site, the structure is expected to become unstable. Monovalent silver (Ag) is expected to be difficult to dope into the Mn site. Sulfur (S) is expected to substitute into the P site, not the Mn site.

[0071] At the Mn site, a portion of the Mn may be substituted with Fe. The Fe-substituted LMP is also referred to as "LMFP." At the Mn site, for example, the relationship "Mn:Fe=1-x:x" or "0≦x<1" may be satisfied. "1-x" indicates the Mn composition ratio (amount of substance ratio), and "x" indicates the Fe composition ratio (Fe substitution amount). The Fe substitution amount (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 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. It is considered that the smaller the Fe substitution amount (x), the more likely JT distortion occurs.

[0072] The 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 (site occupancy of the first dopant): 0.0005≦y≦0.05 z (site occupancy of 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 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 powders.

[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 relationships 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 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 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 O2.

[0079] LNO may be represented, for example, by the following general formula: Compounds represented by the following general formula may also be referred to as "NCAs." Li 1-a Ni x Co y Al 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 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.

[0080] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O2, LiNi 0.7 Co 0.2 Al 0.1 O2, LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi[[ID=2)3]] 0.8 Co 0.17 Al 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, and LiNi 0.9 Co 0.05 Al 0.05 may include at least one selected from the group consisting of O2.

[0081] -Method for manufacturing a positive electrode active material- Figure 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".

[0082] (a) Slurry formation The method includes forming a slurry by mixing a lithium compound, a manganese compound, a phosphate compound, and a solvent. If LMFP is the target material, an iron compound is added to the raw material mixture. For example, an iron compound having the formula "Li a Mn 1-x Fe x The lithium compound, manganese compound, phosphate compound, and iron compound may be weighed out so as to achieve a composition ratio (ratio of amounts of substances) shown in "PO4 (0.90≦a≦1.10, 0≦x<1)". The lithium compound may contain, for example, lithium hydroxide. The manganese compound may contain, for example, manganese carbonate. The phosphate compound may contain, for example, lithium dihydrogen phosphate. The iron compound may contain, for example, ferric phosphate.

[0083] When a carbon layer is formed on the surface of the 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 include, for example, glucose, sucrose, fructose, citric acid, etc. The amount of the 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, etc. The solids concentration of the slurry may be, for example, 20 to 40% by mass.

[0085] The particle size in the slurry may be adjusted by wet milling, for example, so that the D50 is 0.10 to 1 μm.

[0086] (b) Secondary particle formation The method includes drying the slurry to form secondary particles, which may be formed, for example, by spray drying.

[0087] (c) Firing This method involves producing an LMP by heat-treating the secondary particles. Any heat-treating furnace (e.g., an electric furnace, a muffle furnace, etc.) can be used. In this method, the secondary particles (precursor) are molten by high-temperature firing in an inert atmosphere, and a dopant is added to the molten state. This is believed to allow two or more dopants to dissolve in the Mn sites. For example, the secondary particles (precursor) and a dopant source are placed in a graphite crucible. The dopant source may contain, for example, at least one of a hydroxide and a carbonate of the dopant. For example, firing is performed at 1000 to 1100°C in a nitrogen atmosphere 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 passing through a mesh.

[0088] -Liquid battery- In some embodiments, the battery may be a liquid battery. "Liquid battery" refers to a battery that contains an electrolyte. For example, polymer batteries belong to the liquid battery category because they contain an electrolyte. In some embodiments, the battery has a monopolar structure. In some embodiments, the battery has a bipolar structure. As an example, a battery with a bipolar structure (bipolar battery) will be described.

[0089] FIG. 4 is a schematic perspective view of a battery in this embodiment. FIG. 5 is a schematic cross-sectional view taken along line VV in FIG. 4. Hereinafter, "plane-perpendicular direction" refers to the normal direction to the surface of a sheet-like member (e.g., foil, electrode, etc.). "In-plane direction" refers to any direction perpendicular to the plane-perpendicular direction. In the drawings of this embodiment, the Z-axis direction corresponds to the plane-perpendicular direction. The X-axis direction and the Y-axis direction are examples of in-plane directions.

[0090] The battery 100 includes an exterior body 90 and a power generating element 50. The exterior body 90 houses the power generating element 50. The exterior body 90 may include, for example, a first current collecting plate 91, a first laminate film 92, a second laminate film 93, and a second current collecting plate 94. The first laminate film 92 and the second laminate film 93 are joined to each other at their in-plane end portions. At the joint between the first laminate film 92 and the second laminate film 93, a sealant (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 generating element 50 at their ends in the stacking direction (Z-axis direction). A first laminate film 92 is joined to the first current collector plate 91. A second laminate film 93 is joined to the second current collector plate 94. A sealant (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 generating 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 a positive electrode layer 11, a current collecting foil 13, and a negative electrode layer 12, in this order, in the direction perpendicular to the plane. In the in-plane direction (e.g., the X-axis direction), the current collecting foil 13 extends outward relative to the positive electrode layer 11 and the negative electrode layer 12. For example, the current collecting foil 13 may extend outward relative to the positive electrode layer 11 and the negative electrode layer 12 over the entire periphery in the in-plane direction.

[0093] The current collecting foil 13 is a conductor. The current collecting foil 13 may include, for example, a metal foil, a conductive resin layer, or the like. For example, the current collecting foil 13 may be formed by laminating an Al foil and a Cu foil together. A carbon material may be applied to the surface of the current collecting foil 13. The carbon material may include, for example, carbon black, or the like.

[0094] The power generating element 50 includes a sealing material 30. The sealing material 30 is bonded to the current collecting foil 13 at an end in the in-plane direction. The sealing material 30 may be, for example, heat-welded to the current collecting foil 13. For example, the sealing material 30 may be disposed around the entire periphery in the in-plane direction. The sealing material may include, for example, a resin material. The sealing material 30 seals between adjacent current collecting foils 13 in the direction perpendicular to the surface. The sealing material 30 seals between the current collecting foils 13, thereby dividing them into cells 40. A cell 40 is the smallest unit of the power generating element 50. The battery 100 includes multiple cells 40, and may therefore also be referred to as a "bipolar module." Each of the multiple cells 40 is sealed. The multiple cells 40 are isolated from one another. 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 surface of the current collector foil 13. For example, the positive electrode layer 11 may have a groove formed therein. For example, the positive electrode layer 11 may be formed in a striped pattern. The positive electrode layer 11 includes a positive electrode active material. That is, the battery 100 includes the positive electrode active material. Details of the positive electrode active material are as described above.

[0096] Charging state (4.3V vs. Li / Li + In the positive electrode layer 11, 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 be satisfied.

[0097] Charging state (4.3V vs. Li / Li + In the positive electrode layer 11, 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, in addition to the positive electrode active material, for example, a conductive material and a binder. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material. The conductive material may contain any component. For example, the conductive material may contain at least one material selected from the group consisting of graphite, acetylene black (AB), Ketjen Black (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 the positive electrode active material. The binder may contain any component. 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), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, and derivatives thereof.

[0100] The positive electrode layer 11 may further contain, for example, an inorganic filler, an organic filler, a solid electrolyte, a surface modifier, a dispersant, a lubricant, a flame retardant, a protective agent, a flux, a coupling agent, an adsorbent, etc. The positive electrode active material layer may also contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, a silane coupling agent, MoS2, WO3, etc.

[0101] negative electrode layer The negative electrode layer 12 is attached to one surface of the current collector foil 13. The negative electrode layer 12 is disposed on the back side of the positive electrode layer 11. The negative electrode layer 12 may have a larger area than the positive electrode layer 11. The negative electrode layer 12 includes a negative electrode active material.

[0102] The negative electrode active material may be, for example, in the form of particles or a sheet. 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 include any component. For example, the negative electrode active material may include at least one selected from the group consisting of a carbon-based active material, an alloy-based active material, a Si-C composite material, Li metal, a Li-based alloy, and lithium titanate. In some embodiments of the present invention, the battery may be a Li metal negative electrode battery.

[0104] 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."

[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 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.

[0106] The alloy-based active material may contain, 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, for example, by 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. [[ID=ID=17]]

[0108] ID=18 "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 contain, 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 contain, 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 film, a nonwoven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may be continuous, for example, in a network form. Pores are formed in the gaps in the resin skeleton. The resin film is permeable to an electrolyte solution. 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 mercury intrusion porosimetry. The Gurley value of the resin film is, for example, 50 to 250 s / 100 cm. 3 The "Gurley value" can be measured by the Gurley test method.

[0111] The resin film may contain at least one selected from the group consisting of, for example, olefin-based resins, polyurethane-based resins, polyamide-based resins, cellulose-based resins, polyether-based resins, acrylic-based resins, and polyester-based resins. The resin film may contain at least one selected from the group consisting of, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and derivatives thereof. The resin film may be formed by, for example, 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.

[0112] The resin film may have, for example, a single-layer structure. The resin film may be composed of, for example, a PE layer. The skeleton of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multi-layer structure. The resin film may include, for example, a PP layer and a PE layer. The skeleton 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, for example, 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 referred to as "inorganic filler." 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 referred to as an "HRL (Heat Resistance Layer)." The inorganic particles may contain at least one selected from the group consisting of boehmite, alumina, zirconia, titania, magnesia, silica, and the like. The inorganic particles may have any shape. The inorganic particles may be, for example, spherical, rod-like, plate-like, fibrous, or the like. 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 contain, for example, at least one selected from the group consisting of acrylic resins, polyamide resins, fluorine resins, 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 referred to as "organic filler." The organic particles may contain a heat-resistant material. The organic particles may include, for example, at least one selected from the group consisting of PE, PP, PTFE, PI, PAI, PA, and aramid. The organic particles may be, for example, spherical, rod-like, plate-like, fibrous, or the like. The D50 of the organic particles may be, for example, 0.1 to 10 μm, or 0.5 to 3 μm.

[0117] Separator 20 may include, for example, a mixed layer, which includes both inorganic and organic particles.

[0118] electrolyte The electrolyte is a liquid electrolyte. The electrolyte includes a solute and a solvent. The concentration of the solute may be, for example, 0.5 to 1 mol / L, 1 to 1.5 mol / L, 1.5 to 2 mol / L, 2 to 2.5 mol / L, or 2.5 to 3 mol / L. "mol / L" may also be written as "M." The solute includes a supporting salt (Li salt). The solute may include, for example, an inorganic acid salt, an imide salt, an oxalate complex, a halide, 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 electrolytic solution may contain, for example, a carbonate-based solvent (carbonate ester-based solvent). The solvent may contain, for example, a cyclic carbonate, a chain carbonate, a fluorinated carbonate, or the like. 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 a cyclic carbonate (EC, PC, FEC, etc.) and a chain carbonate (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate to 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."

[0121] The solvent may contain a cyclic carbonate (EC, PC, etc.) and a fluorinated cyclic carbonate (FEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate to 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."

[0122] The solvent may include, 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: V EC +VFEC +V EMC +V DMC +V DEC =10 In the above formula, V EC , V FEC , V EMC , V DMC , V DEC indicates the volume ratio 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 relationship ≦3 may be satisfied. For example, 1 ≤ V FEC ≦2, or 2≦V FEC The relationship ≦4 may be satisfied. For example, 3≦V EMC ≦4, or 6≦V EMC The relationship ≦8 may be satisfied. For example, 3≦V DMC ≦4, or 6≦V DMC The relationship ≦8 may be satisfied. For example, 3≦V DEC ≦4, or 6≦V DEC The relationship ≦8 may be satisfied.

[0123] The solvent may have a composition, for example, in volume ratios of "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," or "EC / FEC / DMC / EMC=1 / 2 / 3 / 4."

[0124] The electrolyte may contain an ether-based solvent, such as 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), ethylglyme, triglyme, tetraglyme, and derivatives thereof.

[0125] The electrolyte may contain any additive. The amount of additive (mass fraction relative to the total amount of the electrolyte) may be, for example, 0.01 to 5%, 0.05 to 3%, or 0.1 to 1%. The additive may include, for example, an SEI (Solid Electrolyte Interphase) formation promoter, an SEI formation inhibitor, a gas generating agent, an overcharge inhibitor, a flame retardant, an antioxidant, an electrode protectant, a surfactant, etc.

[0126] Examples of the additives include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (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.), fluorobenzenes (e.g., monofluorobenzene (FB), 1,2-difluoropropane (DEM), etc.), and the like. 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.), fluorotoluenes (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-methylbenzotrifluoride, The solvent may contain at least one selected from the group consisting of benzotriazole, benzotriazole, tetrathiafulvalene, etc.), nitrile compounds (e.g., adiponitrile, succinonitrile, etc.), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate, etc.), carboxylic acid anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, etc.), alcohols (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, diethylene glycol monomethyl ether, etc.), and derivatives thereof.

[0127] The components described above as solutes and solvents may be used as minor components (additives). The additives may include, for example, at least one selected from the group consisting of LiBF, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPOF, FSOLi, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0128] The electrolyte solution may contain an ionic liquid, which may include, 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 the present 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 the present 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 the electrolyte solution and the separator 20. The solid electrolyte may also be included in the positive electrode layer 11 and the negative electrode layer 12. Instead of the separator 20, a solid electrolyte layer separates the positive electrode layer 11 from the negative electrode layer 12. The solid electrolyte layer includes, for example, a solid electrolyte and a binder.

[0131] The solid electrolyte may be, for example, a powder or granule. 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 a sulfide solid electrolyte, a halide solid electrolyte, an oxide solid electrolyte, a hydride solid electrolyte, and a nitride solid electrolyte.

[0133] The sulfide solid electrolyte may contain at least one phase 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). The sulfide solid electrolyte may further contain any optional component in addition to Li and S.

[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, and Li 10 GeP2S 12 , Li4P2S6, Li7P3S 11 , Li3PS4, and Li7PS6.

[0135] For example, "LiI-LiBr-Li3PS4" indicates a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li3PS4 in an arbitrary ratio by mass. For example, the sulfide solid electrolyte may be produced by a mechanochemical method. The mixing ratio may be specified by adding a number before each raw material. For example, "10LiI-15LiBr-75Li3PS4" indicates that the mixing ratio is "LiI / LiBr / Li3PS4=10 / 15 / 75 (mass 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 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 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 more, 0.6 or more, 0.7 or more, 0.75 or more, 0.8 or more, or 0.9 or more. 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 more, 5 or more, 10 or more, 15 or more, 20 or more, or 25 or more. 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 more, 5 or more, 10 or more, 15 or more, 20 or more, or 25 or more. 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 formula, the relationships "0<7-x-2y", "0<6-xy", "0≦x", and "0≦y" are satisfied. X may include, for example, at least one element 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 represents 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 the following general formula, for example: Li 3-a Ti a Al 1-a F6 In the formula, a 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, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. a may be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0143] The halide solid electrolyte may have a composition represented by the following general formula, for example: Li3YCl a Br b I 6-a-b In the formula, for example, the relationship "0≦a+b≦6" may be satisfied. a may be, for example, 0 or more, 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. 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 more, 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. 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] The oxide solid electrolyte is, for example, LiNbO3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, La 2 / 3-x Li 3x TiO3 and Li7La3Zr2O 12 The hydride solid electrolyte may contain, for example, LiBH4, etc. The nitride solid electrolyte may contain, for example, Li3N, Li3BN2, etc. [Example]

[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 out to achieve the composition ratio shown in "PO4". Glucose was weighed out in an amount of 8% by mass based on the total mass of the raw materials. The weighed materials were mixed with water to form a slurry. The solid concentration of the slurry was 30% by mass. Wet milling was carried out to achieve a D50 of 0.30 μm.

[0146] The slurry was spray-dried to form secondary particles. The target D50 of the secondary particles was 9±1 μm. The spray dryer settings were as follows: Intake temperature: 250℃ Exhaust port temperature: 115±15℃ Intake pressure: 2.0 MPa Spray nozzle pressure: 0.2±0.1MPa

[0147] The secondary particles were sintered in a nitrogen atmosphere to obtain LMP powder. The secondary particles were placed in a heat treatment furnace. First, the temperature inside the furnace was increased to 200°C at a heating rate of 3°C / min. The temperature inside the furnace was maintained at 200°C for 1 hour. Next, the temperature inside the furnace was increased to 650°C at a heating rate of 5°C / min. The temperature inside the furnace was maintained at 650°C for 5 hours. After that, the inside of the furnace was cooled to 400°C at a cooling rate of 2°C / min. The inside of the furnace was further cooled to room temperature at a cooling rate of 15°C / min.

[0148] No.2 (a) Slurry formation Compositional formula “Li 1.04 Mn 0.595 Fe 0.4Lithium hydroxide monohydrate, manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate were weighed out to achieve the composition ratio shown in "PO4". Glucose was weighed out in an amount of 8% by mass based on the total mass of the raw materials. The weighed materials were mixed with water to form a slurry. The solid concentration of the slurry was 30% by mass. Wet milling was carried out to achieve a D50 of 0.30 μm.

[0149] (b) Secondary particle formation The slurry was spray-dried to form secondary particles. The target D50 of the secondary particles was 9±1 μm. The spray dryer settings were as follows: Intake temperature: 250℃ Exhaust port temperature: 115±15℃ Intake pressure: 2.0 MPa Spray nozzle pressure: 0.2±0.1MPa

[0150] (c) Firing Compositional formula “Li 1.04 Mn 0.595 Fe 0.4 Si 0.005 The secondary particles (precursor) and Si compound (dopant source) were weighed to achieve the composition ratio shown in "PO4". The secondary particles (precursor) and Si compound were placed in a graphite crucible. The graphite crucible was placed in a heat treatment furnace. The materials were sintered in a nitrogen atmosphere to form a sintered body. Figure 6 shows the temperature profile during sintering. First, the temperature inside the furnace was increased to 200°C at a heating rate of 3°C / min. The temperature inside the furnace was maintained at 200°C for 1 hour. Next, the temperature inside the furnace was increased to 1050°C at a heating rate of 5°C / min. The temperature inside the furnace 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 then cooled to room temperature at a cooling rate of 15°C / min.

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

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

[0153] -evaluation- Coin cell fabrication 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". The mixture was dispersed in a solvent (N-methyl-2-pyrrolidone) to form a paste. The solid concentration of the paste was 50% by mass. The paste was applied to the surface of Al foil and dried to form a positive electrode layer. The density of the positive electrode layer was reduced to 1.8 g / cm by roll pressing. 3 The positive electrode blank was then subjected to a vacuum drying treatment at 120°C for 12 hours. After drying, a disk sample (diameter: 14 mm) was cut out from the positive electrode blank by punching.

[0154] A coin cell was assembled in a glove box. The cell configuration is as follows: Working electrode: disk sample (positive electrode) Counter electrode: Li foil Separator: Porous polymer membrane Electrolyte: "EC / DMC=3 / 7 (volume ratio)", LiPF6 (1mol / L)

[0155] Evaluation of cycle characteristics An initial charge / discharge cycle was performed at 25°C at a constant current. The upper limit of the charge voltage was 4.3 V. The lower limit of the discharge voltage was 3.0 V. The pre-cycle discharge capacity was measured at 25°C at a rate of 0.1 C. "C" is the symbol for the current rate (hourly rate). At a rate of 1 C, the rated capacity of the battery is passed over 1 hour. Next, 100 charge / discharge cycles were repeated at a rate of 0.1 C at 60°C. After 100 cycles, the post-cycle discharge capacity was measured again at a rate of 0.1 C at 25°C. The capacity retention rate was calculated by dividing the post-cycle discharge capacity by the pre-cycle discharge capacity. A higher capacity retention rate is considered to indicate better cycle characteristics.

[0156] -result- The "capacity retention rate" shown in Fig. 7 is a relative value with the value of No. 1 being 100. As shown in Fig. 7, doping the Mn site with both the first dopant and the second dopant tends to improve the cycle characteristics.

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

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

[0159] 1 primary particles, 2 secondary particles, 3 carbon layer, 10 bipolar electrode, 11 positive electrode layer, 12 negative electrode layer, 13 current collecting foil, 20 separator, 30 sealing material, 40 cell, 50 power generating element, 90 exterior body, 91 first current collecting plate, 92 first laminate film, 93 second laminate film, 94 second current collecting 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 crystal structure, manganese sites are doped with a first dopant and a second dopant; At the manganese site, the site occupancy of the first dopant is higher than the site occupancy of the second dopant; the site occupancy of the first dopant is 0.0005 to 0.05; the first dopant and the second dopant have different valences; the first dopant has an ionic radius of less than 0.830 Å; the second dopant has an ionic radius greater than 0.645 Å; each of the first dopant and the second dopant does not contain at least one selected from the group consisting of Ni, Co, and Cu; the first dopant includes Si; the second dopant includes at least one selected from the group consisting of Mg and Ca, and The site occupancy of Si in the manganese site is 0.001 or more. Cathode active material.

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

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

4. In the manganese site, the site occupancy of the second dopant is 0.0005 to 0.05; The positive electrode active material according to claim 1 .

5. Contains lithium manganese phosphate, The lithium manganese phosphate has a crystal structure belonging to the space group Pnma, In the crystal structure, manganese sites are doped with a first dopant and a second dopant; the first dopant includes Si; the second dopant includes at least one selected from the group consisting of Mg and Ca, and The site occupancy of Si in the manganese site is 0.001 or more. Cathode active material.

6. a positive electrode and a negative electrode; The positive electrode comprises the positive electrode active material according to claim 1 or claim 5, b / a≦0.613 The relationship is satisfied, The a represents the lattice constant in the a-axis direction of the lithium manganese phosphate in a charged state where the positive electrode potential is 4.3 V vs. Li / Li+, and The b represents the lattice constant of the lithium manganese phosphate in the b-axis direction in the charged state. battery.

7. c / a≦0.505 The relationship is further satisfied, and The c represents the lattice constant of the lithium manganese phosphate in the c-axis direction in the charged state. The battery of claim 6.

8. 0.588≦b / a≦0.613, and 0.486≦c / a≦0.505 The relationship is more fulfilled, The battery of claim 6.

9. having a bipolar structure, The battery of claim 6.

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