Cathode material for lithium-ion secondary battery

Abstract

To provide a positive electrode material that achieves both high battery capacity and high capacity retention rate.SOLUTION: A positive electrode material includes granules 10 made of LMFP. When a scattering curve of the granules 10 measured by a SAXS method is expressed as a function y=f(x) with the horizontal axis x representing the logarithm of the scattering vector and the vertical axis y representing the scattering intensity, the second derivative y=f''(x) of the function y=f(x) has a maximum peak in the range of -3.0≤x≤-2.0 and is located in the range of -2.5≤x≤-2.3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a positive electrode material for a lithium-ion secondary battery. [Background technology]

[0002] Patent Document 1 describes an olivine-type lithium iron phosphate (LiFePO 4 The olivine-type structure active material, typified by olivine-type lithium iron phosphate, is a positive electrode active material with excellent thermal stability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-185920 A Summary of the Invention [Problem to be solved by the invention]

[0004] Olivine-type lithium manganese iron phosphate (LiMnFePO 4 ) is a material in which part of the iron constituting olivine-type lithium iron phosphate is replaced with manganese. A positive electrode active material using olivine-type lithium manganese iron phosphate can increase the battery capacity compared to a positive electrode active material using olivine-type lithium iron phosphate.

[0005] As a result of intensive research, the present inventors have found that, with regard to olivine-type lithium manganese iron phosphate, by designing a specific parameter based on a scattering curve measured by small-angle X-ray scattering to be within a specific range, it is possible to obtain a positive electrode material that achieves both high battery capacity and high capacity retention rate. [Means for solving the problem]

[0006] The positive electrode material to solve the above problems is a material having the general formula Li a Mn x Fey Me z PO 4 A positive electrode material containing granulated bodies composed of olivine-type lithium manganese iron phosphate represented by the formula, wherein in the general formula Li a Mn x Fe y Me z PO 4 a, x, y, and z are numerical values satisfying 0 < a < 2, 0 < x + y + z < 2, 0.75 ≤ x / (x + y) ≤ 0.9, 0.1 ≤ y / (x + y) ≤ 0.25, and 0 ≤ z ≤ 0.1; in the general formula Li a Mn x Fe y Me z PO 4 Me is at least one element selected from the group consisting of Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te, and Mo; when the scattering curve measured by the small-angle X-ray scattering method of the granulated bodies is defined as a function y = f(x) with the logarithmic value of the scattering vector on the horizontal axis x and the scattering intensity on the vertical axis y, the second derivative y = f′′(x) of the function y = f(x) has a maximum peak in the range of -2.5 ≤ x ≤ -2.3 located in the range of -3.0 ≤ x ≤ -2.0.

[0007] In the above positive electrode material, for the second derivative y = f′′(x) of the function y = f(x), the maximum peak is located in the range of -2.5 ≤ x ≤ -2.4. In the above positive electrode material, for the second derivative y = f′′(x) of the function y = f(x), the maximum peak is located in the range of -2.36 ≤ x ≤ -2.3.

[0008] In the above positive electrode material, the granulated bodies have a core composed of the olivine-type lithium manganese iron phosphate and a carbon coating formed on the surface of the core. [[Effect of the Invention]]

[0009] According to the present invention, a positive electrode material can be obtained that achieves both high battery capacity and high capacity retention rate. [[Brief Description of the Drawings]]

[0010] [Figure 1] 1 is a micrograph of a cross section of a granule. [Diagram 2] FIG. 2 is a schematic diagram showing the structure of a primary particle in a cross section of a granule. [Diagram 3] 1 is a graph showing a scattering curve. [Figure 4] 1 is a graph showing the second derivative of a scattering curve. [Diagram 5] 1 is a flowchart of a method for producing a positive electrode material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the drawings. Hereinafter, a positive electrode material for a lithium ion secondary battery and an electrode of the lithium ion secondary battery may be abbreviated to a positive electrode material and an electrode, respectively.

[0012] <Cathode materials> (Regarding the structure of the positive electrode material) The positive electrode material of the present embodiment will be described with reference to Figures 1 and 2. The positive electrode material is used, for example, as a positive electrode active material capable of absorbing and releasing charge carriers such as lithium ions in a positive electrode for a lithium ion secondary battery.

[0013] The positive electrode material includes granules 10 composed of olivine-type lithium manganese iron phosphate (hereinafter, referred to as LMFP). The positive electrode material may be composed only of the granules, or may contain components other than the granules 10 as necessary.

[0014] An example of a granule 10 shown in FIG. 1 has a core 11 made of LMFP and a carbon coating 12 formed on the surface of the core 11. The LMFP constituting core 11 has the general formula Li a Mn x Fe y Me z PO 4It is a polyanionic compound having an olivine-type structure represented by. General formula Li a Mn x Fe y Me z PO 4 In, Me is at least one element selected from the group consisting of Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te, Mo.

[0015] General formula Li a Mn x Fe y Me z PO 4 In, a, x, y, z are numerical values satisfying 0 < a < 2, 0 < x + y + z < 2, 0.75 ≤ x / (x + y) ≤ 0.9, 0.1 ≤ y / (x + y) ≤ 0.25, 0 ≤ z ≤ 0.1. a is preferably a numerical value satisfying (x + y + z) ≤ a ≤ 1.1(x + y + z).

[0016] Also, regarding the polyanionic compound having an olivine-type structure represented by the general formula Li a Mn x Fe y Me z PO 4 Let the molar ratio of P constituting the compound be "b". In this case, b, x, y, z are preferably numerical values satisfying (x + y + z) ≤ b ≤ 1.1(x + y + z). In other words, x, y, z are preferably numerical values satisfying 1 / 1.1 ≤ x + y + z ≤ 1.

[0017] Specific examples of the ranges of x, y, and z when z = 0 include the case where x + y = 1, 0.75 ≤ x ≤ 0.9, 0.1 ≤ y ≤ 0.25. Specific examples of the ranges of x, y, and z when z ≠ 0 include the case where 0.9 ≤ x + y < 1, 0.675 ≤ x < 0.9, 0.09 ≤ y < 0.25, 0 < z ≤ 0.1. The olivine-type lithium manganese iron phosphate constituting the core 11 may be one kind or two or more kinds.

[0018] The LMFP preferably contains Mg as an element constituting Me. When Mg is contained, the ratio (Mg / T) of the molar ratio of Mg (Mg) to the total molar ratio (T) of the specific metal elements in the LMFP is, for example, 0.0001 or more and 0.05 or less. The specific metal element is represented by the general formula Li a Mn x Fe y Me z PO 4 These are the metallic elements that constitute Mn, Fe, and Me in the LMFP represented by the formula:

[0019] The LMFP preferably contains Ti as an element constituting Me. When Ti is contained, the ratio (Ti / T) of the molar ratio of Ti (Ti) to the total molar ratio (T) of specific metal elements in the LMFP is, for example, 0.0001 or more and 0.05 or less.

[0020] Fig. 2 shows a schematic structure of the range indicated by the arrow A in Fig. 1. As shown in Fig. 2, the core 11 has a structure in which primary particles 11a of the LMFP are aggregated. The core 11 also has pores 11b formed between the multiple primary particles 11a.

[0021] The particle diameter of the primary particles 11a is, for example, 100 nm or less, preferably 70 nm or less, and more preferably 50 nm or less. The particle diameter of the primary particles 11a is, for example, 20 nm or more. The particle diameter of the primary particles 11a is a value obtained by small angle X-ray scattering (SAXS). In detail, the particle diameter of the primary particles 11a is a value defined as an average particle diameter (D50) obtained from the particle diameter distribution after obtaining a particle diameter distribution of the primary particles 11a assuming that the primary particles 11a are spherical. Note that the particle diameter values ​​described below are values ​​obtained by the same SAXS method as above, unless otherwise specified.

[0022] The pore volume of the core 11 is not particularly limited, but is preferably small. The pore volume of the core 11 is, for example, 0.2 cm 3 / g or less, preferably 0.15 cm 3 / g or less. The pore volume is, for example, 0.05 cm 3 / g or more. The pore volume can be determined by performing nitrogen adsorption / desorption measurement on the granule 10 and using the BJH (Barrett Joyner Hallenda) method. The pore volume means the total pore volume in the range of pore diameters of 300 nm or less.

[0023] The carbon content in the granules 10 is, for example, 1.8% by mass or more, preferably 1.9% by mass or more, and more preferably 2.0% by mass or more. The carbon content is, for example, 3.0% by mass or less, and preferably 2.7% by mass or less. The carbon content can be measured using a carbon-sulfur analyzer (CS meter). The carbon coating 12 of the granules 10 may be omitted.

[0024] The content of the LMFP in the granules 10 is, for example, 95% by mass or more, and preferably 96% by mass or more. The content is, for example, 99% by mass or less, and preferably 98% by mass or less.

[0025] The granules 10 may contain other components in addition to the LMFP and carbon. In this case, the content of the other components is, for example, 2% by mass or less. The average particle size (D50) of the granules 10 is, for example, 3.0 μm or more, and preferably 5.0 μm or more. The average particle size (D50) of the granules 10 is, for example, 30 μm or less, and preferably 20 μm or less. The average particle size of the granules 10 can be measured, for example, using a laser diffraction particle size analyzer.

[0026] (For specific parameters) The granule 10 is designed so that a specific parameter based on a scattering curve measured by the SAXS method falls within a specific range. The specific parameter is a parameter that indicates the position of a peak of a specific function derived from the scattering curve. The specific parameter will be described below with reference to Figs. 3 and 4.

[0027] Fig. 3 is a graph showing an example of a scattering curve. As shown in Fig. 3, the horizontal axis of the scattering curve is the logarithm (logQ) of the scattering vector Q (=(4πsinθ) / λ), and the vertical axis is the logarithm (log(Int)) of the scattering intensity. Note that the vertical axis of the scattering curve may be the scattering intensity. Note that the logarithm is a common logarithm.

[0028] The specific function derived from the scattering curve is a second derivative y=f′′(x) derived by differentiating twice a function y=f(x) whose horizontal axis is x and whose vertical axis is y. FIG. 4 is a graph showing an example of a second derivative. As shown in FIG. 4, the second derivative has at least one peak in the range of −3.0≦x(=logQ)≦−2.0. FIG. 4 shows an example having one peak. The specific parameter is a parameter indicating the position of the maximum peak among the peaks located in the above range. In this specification, the position of the peak is specified by the position of the apex of the peak.

[0029] In the second derivative of the granule 10, the maximum peak in the range of -3.0≦x≦-2.0 is located in the range of -2.5≦x≦-2.3. This allows both a high battery capacity and a high capacity retention rate to be achieved. The maximum peak is preferably located in the range of -2.5≦x≦-2.4. In this case, the capacity retention rate can be further improved. In addition, the maximum peak is preferably located in the range of -2.36≦x≦-2.3. In this case, the battery capacity can be further improved.

[0030] The position of the maximum peak is a parameter related to the particle shape based on the major axis and particle size distribution based on the major axis of the primary particles 11a constituting the granule 10. For example, a small value of the maximum peak means that the major axis of the primary particles 11a is small (shape with a small aspect ratio), the proportion of large primary particles 11a is small, or both. A large value of the maximum peak means that the major axis of the primary particles 11a is small (shape with a large aspect ratio), the proportion of large primary particles 11a is large, or both. Therefore, the position of the maximum peak contains information about the particle shape that is different from the average particle size.

[0031] <Method of manufacturing positive electrode material> Next, an example of a method for producing the positive electrode material will be described. The position of the maximum peak can be adjusted by changing various conditions when producing the granules 10. The method for producing the positive electrode material is not limited to the method described below.

[0032] 5, the method for producing the granules 10, which are the positive electrode material, includes a slurry preparation step S10, a granulation step S20, and a firing step S30. The granules 10 are produced by sequentially carrying out the slurry preparation step S10, the granulation step S20, and the firing step S30.

[0033] (Slurry preparation process) The slurry preparation step S10 is a step of obtaining a precursor slurry containing lithium phosphate, a manganese-containing phosphate compound, iron oxide, and a dispersion medium. The slurry preparation step S10 includes a grinding step S11 of grinding the lithium phosphate and the manganese-containing phosphate compound together with the iron oxide.

[0034] First, the components contained in the precursor slurry obtained in the slurry preparation step S10 will be described. The components that the precursor slurry may contain can be roughly divided into components that form an LMFP, a dispersion medium, and other components.

[0035] [Components that form LMFP] Lithium phosphate (Li 3 PO 4 ) is the Li source for forming LMFP. The lithium phosphate may be a commercially available product or may be produced in the slurry preparation step S10. The lithium phosphate may be produced, for example, by reacting a lithium-containing compound with phosphoric acid (hereinafter, referred to as the first reaction). The details of the first reaction will be described later.

[0036] The manganese-containing phosphate compound is a source of Mn and a source of phosphate for forming the LMFP. 5 (HPO 4 ) 2 (PO 4 ) 2 (H 2 O) 4 , Mn 5 (HPO 4 ) 2 (PO 4 ) 2 , Mn 3 (PO 4 ) 2 3H 2 O, Mn 3 (PO 4 ) 2 , or a mixture thereof.

[0037] Mn 5 (HPO 4 ) 2 (PO 4 ) 2 is Mn 5 (HPO 4 ) 2 (PO 4 ) 2 (H 2 O) 4 It is an anhydrous form in which the water molecules that make up the hydrate have been removed from the Mn 5 (HPO 4 ) 2 (PO 4 ) 2 and Mn 5 (HPO 4 ) 2 (PO 4 ) 2(H 2 O) 4 These are sometimes referred to as Mn54. 3 (PO 4 ) 2 is Mn 3 (PO 4 ) 2 3H 2 It is an anhydrous form in which the water molecules that make up the hydrate have been removed from Mn 3 (PO 4 ) 2 3H 2 O and Mn 3 (PO 4 ) 2 These are sometimes collectively referred to as Mn32.

[0038] When the manganese-containing phosphate compound is Mn54, the granule 10 having a large maximum peak value is easily obtained. When the manganese-containing phosphate compound is Mn32, the granule 10 having a small maximum peak value is easily obtained. In addition, when the manganese-containing phosphate compound is Mn54, the LiH 2 PO 4 It is possible to suppress the generation of by-products such as those mentioned above. In addition, in the case of a hydrate, Mn54 has a smaller proportion of water molecules constituting the hydrate than Mn32. Therefore, when Mn54 is used, the amount of water volatilized in the firing step S30 is reduced. This makes it possible to obtain a granule 10 having a small pore volume.

[0039] The manganese-containing phosphate compound may be a commercially available product or may be produced in the slurry preparation step S10. The manganese-containing phosphate compound can be produced, for example, by reacting a manganese-containing compound with phosphoric acid (hereinafter, referred to as the second reaction). The second reaction will be described in detail later.

[0040] The iron oxide is an Fe source for forming the LMFP, and is also a component included in the milling step S11 to mill the manganese-containing phosphate compound more finely. As the iron oxide, a substance harder than the manganese-containing phosphate compound is selected. Since the Mohs hardness of the manganese-containing phosphate compounds Mn54 and Mn32 is "5", a substance with a Mohs hardness of more than "5" is selected as the iron oxide. As the iron oxide, for example, Fe 2 O 3 (Mohs hardness 5.5), Fe 3 O 4 (Mohs hardness: 6.0). The precursor slurry may contain one type of iron oxide, or two or more types of iron oxide.

[0041] Here, the precursor slurry may be, as required, a compound having the general formula Li a Mn x Fe y Me z PO 4 The optional metal source may contain a metal source (hereinafter, referred to as an optional metal source) for forming "Me" of the LMFP represented by the formula (1). The optional metal source is, for example, a Co source, a Ni source, a Cu source, a Mg source, a Zn source, a V source, a Ca source, a Sr source, a Ba source, a Ti source, an Al source, a Si source, a B source, a Te source, or a Mo source. Specific examples of the optional metal source include metal oxides, metal hydroxides, and metal salts of various metal elements. The optional metal source is preferably a metal oxide. In this case, volumetric shrinkage during firing in the firing step S30 can be suppressed. The optional metal source contained in the precursor slurry may be one type, or two or more types.

[0042] The precursor slurry preferably contains a Mg source as an optional metal source. In this case, the resistance of the granule 10 can be reduced. Examples of the Mg source include magnesium compounds such as magnesium oxide, magnesium acetate, magnesium carbonate, and magnesium hydroxide. The Mg source is preferably magnesium oxide. In this case, volumetric shrinkage during firing in the firing step S30 can be suppressed.

[0043] The precursor slurry preferably contains a Ti source as an optional metal source. In this case, the granule 10 having a large maximum peak value is likely to be obtained. Examples of the Ti source include titanium compounds such as titanium oxide and titanium nitride. The Ti source is preferably titanium oxide. In this case, volumetric shrinkage during firing in the firing step S30 can be suppressed.

[0044] The contents of the lithium phosphate, the manganese-containing phosphate compound, the iron oxide, and the optional metal source in the precursor slurry are adjusted so that the molar ratios of each of the metal elements satisfy a specific relationship.

[0045] The manganese-containing phosphate compound and iron oxide are contained in an amount such that the molar ratio of manganese in the precursor slurry is 75% or more and 90% or less of the total molar ratio of manganese and iron. The molar ratio of manganese is preferably 77% or more, more preferably 78% or more. The molar ratio of manganese is preferably 85% or less, more preferably 83% or less.

[0046] The content of lithium phosphate is preferably such that the ratio (Li / T) of the molar ratio of lithium (Li) to the total molar ratio (T) of the specific metal elements in the precursor slurry is 1.00 or more and 1.10 or less. The specific metal elements are manganese contained in the manganese-containing phosphate compound, iron contained in the iron oxide, and metal elements contained in the optional metal source. In other words, the general formula Li a Mn x Fe y Me z PO 4 These are the metallic elements that constitute Mn, Fe, and Me in the LMFP represented by the formula:

[0047] When the Mg source is contained, the content of the Mg source is, for example, an amount such that the ratio (Mg / T) of the molar ratio of magnesium (Mg) to the total molar ratio (T) of the specific metal elements in the precursor slurry is 0.0001 or more and 0.05 or less. The molar ratio of magnesium is preferably 0.005 or more, more preferably 0.01 or more. The molar ratio of magnesium is preferably 0.045 or less, more preferably 0.04 or less.

[0048] When the Ti source is contained, the content of the Ti source is, for example, an amount such that the ratio (Ti / T) of the molar ratio of titanium (Ti) to the total molar ratio (T) of the specific metal elements in the precursor slurry is 0.0001 or more and 0.05 or less. The molar ratio of titanium is preferably 0.005 or more, more preferably 0.01 or more. The molar ratio of titanium is preferably 0.045 or less, more preferably 0.04 or less.

[0049] In the precursor slurry, each of the above components forming the LMFP is contained in a powder form. The lithium phosphate contained in the precursor slurry has a particle size of, for example, 50 nm or less, preferably 40 nm or less, and more preferably 30 nm or less. The lithium phosphate has a particle size of, for example, 5 nm or more. The lithium phosphate becomes a powder having the above particle size by undergoing a pulverization process described later.

[0050] The manganese-containing phosphate compound contained in the precursor slurry has a particle size of, for example, 100 nm or less, preferably 70 nm or less, more preferably 50 nm or less. The manganese-containing phosphate compound has a particle size of, for example, 10 nm or more. The manganese-containing phosphate compound becomes a powder having the above particle size by undergoing a pulverization process described later.

[0051] The particle size of the iron oxide contained in the precursor slurry is, for example, 100 nm or less, preferably 70 nm or less, and more preferably 50 nm or less. The particle size of the iron oxide is, for example, 10 nm or more. The iron oxide becomes a powder of the above particle size by going through a pulverization process described later.

[0052] The particle size of the optional metal source contained in the precursor slurry is, for example, 300 nm or less, preferably 200 nm or less, and more preferably 100 nm or less. The particle size of the optional metal source is, for example, 10 nm or more.

[0053] [Dispersion medium] The dispersion medium is water or a mixed solvent of water and a non-aqueous solvent. The water is not particularly limited, but is preferably, for example, ion-exchanged water, which is water treated with an ion-exchange resin, and ultrapure water, which is water treated by a reverse osmosis membrane water purification system. Examples of non-aqueous solvents constituting the mixed solvent include solvents that are miscible with water, such as lower alcohols, acetone, tetrahydrofuran, ethylene glycol, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, acetonitrile, and dimethylsulfoxide. The non-aqueous solvent may be used alone or in combination of two or more. The volume ratio of water in the mixed solvent is preferably, for example, 50% by volume or more and 99.9% by volume or less, and more preferably 60% by volume or more and 99% by volume or less. The content of the aqueous solvent in the precursor slurry is not particularly limited, but is, for example, an amount that results in a solid content ratio of 20% by mass or more and 50% by mass or less.

[0054] [Other ingredients] The precursor slurry may contain a carbon source for forming the carbon coating 12. For example, an organic compound may be used as the carbon source. For example, the organic compound may be glucose, fructose, galactose, mannose, maltose, sucrose, lactose, glycogen, pectin, alginic acid, glucomannan, chitin, hyaluronic acid, chondroitin, agarose, polyether, polyhydric alcohol, polyvinyl alcohol, polyvinylpyrrolidone, cellulose, starch, gelatin, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polystyrene sulfonic acid, polyacrylamide, and polyvinyl acetate. For example, the polyhydric alcohol may be polyethylene glycol, polypropylene glycol, polyglycerin, and glycerin. The carbon source may be used alone or in combination of two or more.

[0055] The carbon source is contained in the precursor slurry so that the mass of carbon in the carbon source (when a carboxylic acid described later is contained, the total mass of carbon in the carboxylic acid) is a specific amount. The carbon source is contained in an amount of, for example, 3 parts by mass or more and 30 parts by mass or less when the total mass of the components forming the LMFP in the precursor slurry is 100 parts by mass.

[0056] The precursor slurry may contain a carboxylic acid as an optional component, which can reduce the pore volume of the granules 10. Examples of the carboxylic acid include citric acid, formic acid, acetic acid, propionic acid, butanoic acid, pentanoic acid, malic acid, fumaric acid, tartaric acid, ascorbic acid, gluconic acid, and polyacrylic acid. The carboxylic acid may be used alone or in combination of two or more. Among these carboxylic acids, it is preferable to use citric acid.

[0057] The content of the carboxylic acid in the precursor slurry is, for example, 1 part by mass or more and 30 parts by mass or less when the total mass of the components forming the LMFP in the precursor slurry is 100 parts by mass.

[0058] Furthermore, the precursor slurry may contain components other than the above-mentioned components, as necessary. Examples of such components include a dispersant. [Crushing process] The pulverization step S11 is performed on a slurry containing lithium phosphate, a manganese-containing phosphate compound, iron oxide, and a dispersion medium (hereinafter, referred to as intermediate slurry). The pulverization step S11 is a step of pulverizing the lithium phosphate, the manganese-containing phosphate compound, and the iron oxide, which are solid contents contained in the intermediate slurry, to reduce their diameter.

[0059] The pulverization method used in the pulverization step S11 is not particularly limited as long as it is a pulverization method in which solids collide with each other in the intermediate slurry. Examples of the pulverization method include a method using a pulverizer such as a bead mill, a hammer mill, an agitation mill, a jet mill, or a ball mill. Among the above pulverization methods, a pulverization method that crushes by applying a shear force, such as a method using a bead mill, is preferred.

[0060] When a bead mill is used, the beads, which are medium particles, are harder than the solid content contained in the intermediate slurry, for example, harder than iron oxide. The bead diameter is, for example, 1 mm or less, and preferably 0.5 mm or less. The bead diameter is, for example, 0.01 mm or more. The temperature during pulverization is, for example, 10°C or more and 50°C or less.

[0061] Here, when a bead mill is used, by reducing the bead diameter of the beads, it becomes easier to obtain granules 10 having a large maximum peak value, and by increasing the bead diameter, it becomes easier to obtain granules 10 having a small maximum peak value. Furthermore, by increasing the grinding time in the grinding step, it becomes easier to obtain granules 10 having a large maximum peak value, and by shortening the grinding time, it becomes easier to obtain granules 10 having a small maximum peak value.

[0062] The particle diameters of the solid contents in the intermediate slurry before the pulverization step S11 are as follows: The particle diameter of the lithium phosphate is, for example, 50 nm or more and 50 μm or less; The particle diameter of the manganese-containing phosphate compound is, for example, 50 nm or more and 50 μm or less; and The particle diameter of the iron oxide is, for example, 50 nm or more and 10 μm or less.

[0063] The particle size of each solid content in the intermediate slurry after the pulverization step S11 is, as a value in a mixed state of the lithium phosphate, the manganese-containing phosphate compound, and the iron oxide particles, is, for example, 100 nm or less, preferably 70 nm or less, and more preferably 50 nm or less. Also, the value is, for example, 10 nm or more.

[0064] Here, in the pulverization step S11, the lithium phosphate and the manganese-containing phosphate compound are pulverized together with the iron oxide in the dispersion medium. In this case, the lithium phosphate and the manganese-containing phosphate compound, particularly the manganese-containing phosphate compound, can be pulverized more finely based on the difference in hardness between the lithium phosphate and the manganese-containing phosphate compound and the iron oxide.

[0065] In detail, the Mohs hardness of lithium phosphate is "4", and the Mohs hardness of manganese-containing phosphate compounds Mn54 and Mn32 is "5". In contrast, iron oxide (Fe 2 O 3 ) has a Mohs hardness of 5.5, and iron oxide is harder than lithium phosphate and manganese-containing phosphate compounds. In this case, by performing two-stage pulverization in the pulverization step S11, the lithium phosphate and manganese-containing phosphate compound can be pulverized more finely.

[0066] In more detail, in the first step, the lithium phosphate, the manganese-containing phosphate compound, and the iron oxide are pulverized by applying shear force, compression force, etc., generated in a pulverizer such as a bead mill to each solid content in the intermediate slurry. Then, as the pulverization process is continued, the pulverized solid content collides with each other in the second step. At this time, the pulverized material of the relatively hard iron oxide collides with the relatively soft lithium phosphate and the manganese-containing phosphate compound, so that the pulverized material of the lithium phosphate and the manganese-containing phosphate compound are pulverized further finely. In the pulverization step S11, the first step and the second step are performed in parallel or simultaneously.

[0067] In the pulverization step S11, the lithium phosphate, the manganese-containing phosphate compound, and the iron oxide are divided along the grain boundaries. Therefore, theoretically, each particle after pulverization has a size in units of the grain of the crystal particle, and the theoretical minimum size is a size corresponding to the grain diameter of the crystal particle. Therefore, the smaller the constituent crystal particles, the finer the pulverization can be performed. In the case of the manganese-containing phosphate compound, the grain diameter of the crystal particles forming the phase is smaller in Mn54 than in Mn32. Therefore, when it is desired to pulverize more finely, the manganese-containing phosphate compound is preferably Mn54.

[0068] Components other than lithium phosphate, manganese-containing phosphate compound, iron oxide, and dispersion medium may be mixed in advance with the intermediate slurry to be subjected to the pulverization step S11, or may be mixed with the intermediate slurry after the pulverization step S11. Also, a part of the components other than lithium phosphate, manganese-containing phosphate compound, iron oxide, and dispersion medium may be mixed in advance with the intermediate slurry to be subjected to the pulverization step S11, and the remainder of the components may be mixed with the intermediate slurry after the pulverization step S11. Note that components other than lithium phosphate, manganese-containing phosphate compound, iron oxide, and dispersion medium may be mixed after being pulverized in advance to a predetermined particle size, or may be pulverized in the pulverization step to a predetermined particle size.

[0069] Here, the intermediate slurry preferably contains a carboxylic acid. In other words, the pulverization step S11 is preferably carried out in the presence of a carboxylic acid. In this case, the pore volume of the granules 10 can be reduced.

[0070] When the intermediate slurry to be subjected to the pulverization step S11 contains all components other than the manganese-containing phosphate compound, iron oxide, and dispersion medium, a precursor slurry is obtained as the intermediate slurry after the pulverization step S11. When the intermediate slurry to be subjected to the pulverization step S11 does not contain all components other than the manganese-containing phosphate compound, iron oxide, and dispersion medium, a precursor slurry is obtained by mixing the remaining components with the intermediate slurry after the pulverization step S11.

[0071] [Specific example of a method for preparing a precursor slurry] Next, a specific example of the slurry preparation step S10 will be described. First, lithium phosphate is produced in a first reaction, and a manganese-containing phosphate compound is produced in a second reaction.

[0072] More specifically, phosphoric acid is dropped into a liquid in which a lithium-containing compound and a manganese-containing compound are dissolved or dispersed in a dispersion medium containing water at normal pressure at 0° C. to 90° C. As a result, the lithium-containing compound reacts with the phosphoric acid to produce lithium phosphate (first reaction), and the manganese-containing compound reacts with the phosphoric acid to produce a manganese-containing phosphate compound (second reaction).

[0073] The components other than the lithium phosphate and the manganese-containing phosphate compound contained in the precursor slurry may be added in advance to the liquid in which the first and second reactions are carried out, or may be added to the reaction liquid after the first and second reactions. When iron oxide is added to the liquid in which the first and second reactions are carried out, the viscosity of the liquid increases, making it difficult to handle, so it is preferable to add it after the first and second reactions.

[0074] Examples of the lithium-containing compound used in the first reaction include lithium hydroxide, lithium carbonate, and lithium oxide. The lithium-containing compound is preferably lithium hydroxide or lithium carbonate.

[0075] In the first reaction, the ratio of the lithium-containing compound and phosphoric acid to the metal compound other than lithium can be adjusted to suppress the production of by-products and increase the production rate of lithium phosphate. Examples of the by-products include LiOH·H 2 O, LiH 2 PO 4 If the precursor slurry contains the above by-products, the amount of water volatilized in the firing step S30 increases, resulting in a large pore volume of the granules 10. 2 PO 4 This can cause the formation of coarse particles in the granulation step S20 and can also adhere to various devices used in the production. Therefore, in the first reaction, it is preferable to reduce the amount of the above-mentioned by-products produced.

[0076] The metal compound other than lithium is the manganese compound, iron oxide, and any of the above-mentioned metal sources such as magnesium oxide and titanium oxide used in the second reaction. In the first reaction, the amount of the metal compound other than lithium added is an amount such that the ratio (Li / MA) of the molar ratio of lithium (Li) to the sum (MA) of the molar ratios of the metal components constituting the metal compound is 1.0 to 1.1, and the ratio (P / MA) of the molar ratio of phosphorus (P) to the sum (MA) of the molar ratios of the metal components constituting the metal compound is 1.0 to 1.1. The generation of the by-products can be suppressed by adjusting the amount of the metal compound other than lithium added to the lithium-containing compound and phosphoric acid so as to satisfy the above conditions.

[0077] Examples of the manganese-containing compound used in the second reaction include manganese carbonate, manganese sulfate, and manganese oxalate. The manganese-containing compound is preferably manganese carbonate. By using manganese carbonate, which has a relatively small particle size compared to other manganese-containing compounds, the primary particle size of the granules 10 can be made smaller. When manganese sulfate is used, it is necessary to perform a post-treatment of washing the generated manganese-containing phosphate compound before the pulverization step S11 described later.

[0078] In the second reaction, the type of manganese-containing phosphate compound produced can be adjusted by adjusting the reaction temperature. When producing Mn54, the reaction temperature of the second reaction is preferably 60°C or higher and 90°C or lower. When producing Mn32, the reaction temperature of the second reaction is preferably 0°C or higher and lower than 60°C.

[0079] The first and second reactions may be carried out in sequence in the same system instead of simultaneously. For example, phosphoric acid is dropped into a liquid in which one of a lithium-containing compound and a manganese-containing compound is dissolved or dispersed in a dispersion medium, and then the other of the lithium-containing compound and the manganese-containing compound is added to the reaction liquid. This results in a reaction liquid containing lithium phosphate and a manganese-containing compound. In addition, since it is easy to adjust the component ratio to suppress the generation of by-products in the first reaction, it is preferable to carry out the first and second reactions simultaneously, or to carry out the second reaction after the first reaction.

[0080] The first reaction and the second reaction may be carried out separately in different systems. For example, the first reaction and the second reaction are carried out in different systems, and then the reaction liquid after the first reaction is mixed with the reaction liquid after the second reaction. This produces a reaction liquid containing lithium phosphate and a manganese-containing compound.

[0081] Next, an intermediate slurry is prepared by mixing iron oxide with the reaction liquid containing lithium phosphate and the manganese-containing compound. In addition, an optional metal source and other components are also mixed as necessary. For example, an Mg source and a Ti source are mixed as the optional metal sources, and a carbon source and a carboxylic acid are mixed as the other components. In the first and second reactions, if the corresponding components have been added in advance, this step is omitted.

[0082] The optional metal source and other components may be mixed in advance in the reaction system in which the first and second reactions are carried out, but it is preferable to mix them after each of the first and second reactions. When at least one of the first and second reactions is a reaction accompanied by the generation of carbon dioxide gas, the discharge of the generated carbon dioxide gas from the intermediate slurry can be promoted by carrying out a step of mixing some component after each reaction. Carbon dioxide gas is generated, for example, when at least one of the lithium compound, the manganese compound, and the optional metal source is a carbonate.

[0083] Next, the obtained intermediate slurry is subjected to a pulverization step S11. Then, a precursor slurry is obtained as the intermediate slurry after the pulverization step S11. (granulation process) The granulation step S20 is a step of obtaining precursor particles by spray-drying the precursor slurry. The precursor particles are granules formed by agglomeration of solids contained in the precursor slurry. Examples of the spraying method in the spray drying include a spraying method using a disk type, a pressurized nozzle, a pressurized two-fluid nozzle, a pressurized four-fluid nozzle, etc. The spraying temperature in the spray drying is, for example, 180°C or more and 300°C or less.

[0084] (Firing process) The firing step S30 is a step of obtaining an LMFP by firing the precursor particles obtained in the granulation step S20, specifically, a step of forming a crystal phase of the LMFP. The firing step S30 is also a step of forming a carbon coating 12 by carbonizing the carbon source contained in the precursor particles. The firing temperature in the firing step is, for example, 500° C. or higher and 750° C. or lower. The firing time in the firing step is, for example, 1 hour or higher and 12 hours or lower. The atmosphere in the firing step is, for example, a non-oxidizing atmosphere. The non-oxidizing atmosphere can be, for example, nitrogen (N 2 ), argon (Ar), and hydrogen (H 2 ) or the like.

[0085] When the precursor slurry contains a carbon source, the carbon source contributes to lowering the oxygen partial pressure during firing. By lowering the oxygen partial pressure during firing, it is possible to suppress the generation of a different phase of LMFP in the granules 10 obtained after firing.

[0086] <Effects> Next, the operation and effects of this embodiment will be described. (1) The positive electrode material includes granules 10 made of LMFP. When a scattering curve of granules 10 measured by a SAXS method is expressed as a function y=f(x) with the horizontal axis x representing the logarithm of the scattering vector and the vertical axis y representing the scattering intensity, the second derivative y=f′′(x) of the function y=f(x) has a maximum peak in the range of −3.0≦x≦−2.0 and is located in the range of −2.5≦x≦−2.3.

[0087] The position of the maximum peak is a parameter related to the particle shape of the primary particles 11a constituting the granule 10. Therefore, the above configuration means that the granule 10 is composed of primary particles 11a having a particle shape in which the position of the maximum peak falls within the range of -2.5≦x≦-2.3. By using the granule 10 in which the primary particles 11a have the above particle shape as a positive electrode material for a lithium ion secondary battery, it is possible to achieve both a high battery capacity and a high capacity retention rate.

[0088] (2) The second derivative y=f''(x) of the function y=f(x) has the maximum peak located in the range of -2.5≦x≦-2.4. That is, the granules 10 are composed of primary particles 11a having a particle shape in which the position of the maximum peak falls within the range of -2.5≦x≦-2.4. With this configuration, the capacity retention rate can be further improved.

[0089] (3) The second derivative y=f''(x) of the function y=f(x) has the maximum peak located in the range of -2.36≦x≦-2.3. In other words, the granules 10 are composed of primary particles 11a having a particle shape in which the position of the maximum peak falls within the range of -2.36≦x≦-2.3. With this configuration, the battery capacity can be further improved.

[0090] (4) The granules 10 have a core 11 made of an LMFP and a carbon coating 12 formed on the surface of the core 11. According to the above-mentioned configuration, the film-formability is improved when a film-like positive electrode active material layer is formed using a slurry containing the granules 10.

[0091] (5) General formula Li a Mn x Fe y Me z PO 4 In the above formula, Me includes at least Mg. According to the above-mentioned structure, the resistance of the granules 10 can be reduced. <Example of change> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0092] Regarding the method for producing a positive electrode, a crushing step S11 may be performed in which lithium phosphate and a manganese-containing phosphate compound are crushed in the absence of iron oxide. In this case, iron oxide may be added to the intermediate slurry after the crushing step S11.

[0093] Regarding the manufacturing method of the positive electrode, an Fe source other than iron oxide may be used. Examples of the Fe source other than iron oxide include FeSO. 4 7H2 O, FeC 2 O 4 2H 2 O is one example. EXAMPLES

[0094] A test example that further embodies the above embodiment will be described below. (Test Examples 1 to 19) Lithium phosphate and a manganese-containing phosphate compound were generated by dispersing a Li source and a Mn source in water at room temperature or 60° C., and then dropping phosphoric acid into the water. Next, an Fe source, a Mg source, a Ti source, fructose, and citric acid were mixed into the reaction liquid containing the lithium phosphate and the manganese-containing phosphate compound to obtain an intermediate slurry.

[0095] In the intermediate slurry, the molar ratio of manganese to the sum of the molar ratio of manganese and the molar ratio of iron is 80%. In the intermediate slurry, the ratio (P / T) of the molar ratio of phosphoric acid (P) to the sum (T) of the molar ratios of specific metal elements (Mn, Fe, Mg, Ti) is 1.03. In the intermediate slurry, the ratio (Li / T) of the molar ratio of lithium (Li) to the sum (T) of the molar ratios of specific metal elements (Mn, Fe, Mg, Ti) is 1.05.

[0096] When the intermediate slurry contains a Mg source, the ratio (Mg / T) of the molar ratio of magnesium (Mg) to the sum (T) of the molar ratios of specific metal elements (Mn, Fe, Mg, Ti) in the intermediate slurry is 0.03.When the intermediate slurry contains a Ti source, the ratio (Ti / T) of the molar ratio of titanium (Ti) to the sum (T) of the molar ratios of specific metal elements (Mn, Fe, Mg, Ti) in the intermediate slurry is 0.02.

[0097] In the intermediate slurry, the proportion of fructose in the components excluding water is 20 mass %.In the intermediate slurry, the proportion of citric acid in the components excluding water is 10 mass %.

[0098] The raw material columns in Tables 1 and 2 show the combinations of Li, Mn, Fe, Mg, and Ti sources used. The reaction temperature and type columns in Table 2 show the reaction temperature when lithium phosphate and manganese-containing phosphate compounds are produced, and the type of manganese-containing phosphate compound produced. When the reaction temperature is room temperature, Mn32 is produced. When the reaction temperature is 60° C., Mn54 is produced. The Mn32 produced in this example is Mn 3 (PO 4 ) 2 3H 2 O, and the Mn54 produced in this example is Mn 5 (HPO 4 ) 2 (PO 4 ) 2 (H 2 O) 4 It is.

[0099] Next, beads were added to the intermediate slurry, and the solid content in the intermediate slurry was pulverized using a bead mill (MSC50 manufactured by Nippon Coke Co., Ltd.) to obtain a precursor slurry. The bead diameter and pulverization time are shown in Table 2. The beads were ZrO 2 The milling process was carried out at a peripheral speed of 15 m / s using beads.

[0100] The precursor slurry was then dried and granulated using a spray dryer (drying outlet temperature: 100° C.) to obtain precursor particles as aggregates. 2 The mixture was heated at 650° C. for 6 hours in an atmosphere to obtain granules of Test Examples 1 to 19.

[0101] (SAXS measurement) The primary particle size and scattering curve of the granules of each test example were measured using the SAXS method. The measurement conditions for the SAXS measurement were as follows:

[0102] Measurement device: NANOPIX mini (manufactured by RIGAKU) Source: Cu kα Tube voltage / current: 40kV-15mA Detector: D / teX Ultre250 Scan axis: 2θ Measurement method: Continuous scan Angle range: -0.05~2.0° Scan speed: 0.1° / min Sampling width: 0.0008° The scattering image obtained by SAXS measurement was subjected to a circular average from -180 to 180° to convert it to one dimension, and a scattering curve was obtained. From the obtained scattering curve, the particle size distribution of the primary particles was obtained assuming that the primary particles were spherical. The average particle size (D50) obtained from the obtained particle size distribution was calculated, and this value was regarded as the particle size of the primary particles. The results are shown in Table 2.

[0103] Furthermore, from the obtained scattering curve, a function y = f(x) was obtained, with the horizontal axis of the scattering curve being x and the vertical axis being y. The obtained function y = f(x) was differentiated twice to derive the second derivative y = f''(x). In the second derivative y = f''(x), the position of the maximum peak among the peaks located in the range of -3.0≦x(=logQ)≦-2.0 was obtained. The results are shown in the Maximum Peak column in Table 2.

[0104] (Evaluation of battery properties of granules) [Evaluation of discharge capacity] The positive electrode mixture was applied to one surface of an aluminum foil with a thickness of 15 μm. The applied positive electrode mixture was dried to produce a positive electrode in which a positive electrode active material layer was formed on one surface of a positive electrode current collector. The positive electrode mixture was a slurry containing the granules (positive electrode active material) of each test example, acetylene black, and polyvinylidene fluoride (PVdF) in a solid content mass ratio of 90:5:5, with water as the solvent. The basis weight of the positive electrode active material layer was 15 mg / cm. 2 The density of the positive electrode active material layer was 1.8 g / cm 3 It was.

[0105] A positive electrode half cell was prepared using the prepared positive electrode. A separator was sandwiched between a positive electrode (evaluation electrode) obtained by cutting the positive electrode into 25 mm squares and a negative electrode obtained by cutting a 200 μm thick metal lithium foil into 27 mm squares to prepare an electrode body battery. The electrode body battery was housed in a laminate as an exterior material, and a non-aqueous electrolyte was injected and the exterior material was sealed to obtain a half cell for electrochemical testing. A glass filter manufactured by Hoechst Celanese was used as the separator. As the non-aqueous electrolyte, a non-aqueous electrolyte was used in which lithium hexafluorophosphate was dissolved to a concentration of 1 M in a mixed solvent obtained by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 3:3:4.

[0106] The prepared positive electrode half cell was charged to 4.3 V at a constant current of 0.05 C at 25° C. and discharged to 3.0 V. The discharge capacity at this time was measured. The discharge capacity of each test example was evaluated based on the obtained measured values. The results are shown in Table 2. The evaluation criteria for discharge capacity are as follows:

[0107] "A": Discharge capacity is 147mAh / g or more. "B": Discharge capacity is 145mAh / g or more and less than 147mAh / g. "C": Discharge capacity is 143mAh / g or more and less than 145mAh / g.

[0108] "D": Discharge capacity is less than 143mAh / g. [Evaluation of capacity retention rate] The positive electrode prepared for the discharge capacity evaluation was cut into a rectangular shape of 30 mm long x 25 mm wide to prepare a positive electrode, a negative electrode, and a separator, which were then combined to prepare an electrode body battery. The electrode body battery was placed in a battery case, an electrolyte was poured into it, and the battery case was sealed to obtain a lithium ion secondary battery.

[0109] The negative electrode used had a negative electrode current collector made of copper, and a negative electrode active material layer made of graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a dispersant. The separator used was made of polyethylene. The electrolyte used was a mother liquid prepared by dissolving lithium hexafluorophosphate to a concentration of 1.2 M in a mixed solvent of ethylene carbonate and methyl propionate in a volume ratio of 15:85, and adding vinylene carbonate in an amount equivalent to 1 mass% to the mother liquid.

[0110] The obtained lithium ion secondary battery was charged at 4.3V and 0.5C with constant current and constant voltage (CCCV), and then discharged at 1C with constant current (CC) to 3V, and the discharge capacity was measured. The above charge and discharge were repeated 100 cycles. The capacity retention rate was calculated as the ratio of the charge capacity after 100 cycles to the charge capacity after the initial charge, which was set to 100. The capacity retention rate was evaluated for each test example based on the calculated value. The results are shown in Table 2. The evaluation criteria for the capacity retention rate are as follows:

[0111] "A": Capacity retention rate is 88% or more. "B": The capacity retention rate is 86% or more and less than 88%. "C": Capacity retention rate is 84% ​​or more and less than 86%.

[0112] "D": Capacity retention rate is less than 84%.

[0113] [Table 1]

[0114] [Table 2] As shown in Table 2, the maximum peak value in the second derivative of the scattering curve has a correlation with the discharge capacity and the capacity retention rate in the range of -3.0 or more and -2.0 or less. The discharge capacity gradually increases as the maximum peak value increases, and changes to be approximately constant in the range of -2.36 or more. In particular, the discharge capacity changes significantly around -2.5. On the other hand, the capacity retention rate changes in an upwardly convex curve as the maximum peak value increases. In particular, the capacity retention rate changes significantly around -2.3.

[0115] From these results, it is found that if the maximum peak value is appropriately set, it is possible to achieve both a high battery capacity and a high capacity retention rate. More specifically, when the maximum peak value is in the range of -2.5 to -2.3 (Test Examples 8 to 17), both the discharge capacity and the capacity retention rate are rated A or B, so it is found that both a high battery capacity and a high capacity retention rate can be achieved. Among the above ranges, when the maximum peak value is in the range of -2.5 to -2.4 (Test Examples 8 to 13), the capacity retention rate is rated A, so it is found that a higher capacity retention rate can be achieved. Furthermore, among the above ranges, when the maximum peak value is in the range of -2.36 to -2.3 (Test Examples 15 to 18), the discharge capacity is rated A, so it is found that a higher battery capacity can be achieved.

[0116] Next, the relationship between the maximum peak and the primary particle size of the granules will be considered. The maximum peaks of Test Examples 3 to 5 are "-2.56", "-2.55", and "-2.53", respectively, and the values ​​are successively smaller. On the other hand, the primary particle sizes of Test Examples 3 to 5 are "61.7", "71.6", and "62", respectively, and the values ​​fluctuate greatly, and the size relationship does not match with the maximum peak. Such a discrepancy in the size relationship between the maximum peak and the primary particle size also occurs in Test Examples 10 to 17. From these results, it can be seen that the maximum peak is a parameter that cannot be substituted by the primary particle size.

[0117] Next, the technical ideas that can be grasped from the above embodiments and modified examples are added below. [Aspect 1] General formula Li a Mn x Fe y Me z PO 4 A positive electrode material containing granulated particles composed of olivine-type lithium manganese iron phosphate represented by the formula, In the general formula Li a Mn x Fe y Me z PO 4 a, x, y, z in the formula are numerical values satisfying 0 < a < 2, 0 < x + y + z < 2, 0.75 ≤ x / (x + y) ≤ 0.9, 0.1 ≤ y / (x + y) ≤ 0.25, 0 ≤ z ≤ 0.1, In the general formula Li a Mn x Fe y Me z PO 4 Me in the formula is at least one element selected from the group consisting of Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te, Mo, When the scattering curve measured by the small-angle X-ray scattering method of the granulated particles is a function y = f(x) with the logarithmic value of the scattering vector on the horizontal axis x and the scattering intensity on the vertical axis y, The second derivative y = f′′(x) of the function y = f(x) is A positive electrode material characterized in that the maximum peak in the range of -3.0 ≤ x ≤ -2.0 is located in the range of -2.5 ≤ x ≤ -2.3.

[0118] [Aspect 2] The positive electrode material according to Aspect 1, wherein the second derivative y = f′′(x) of the function y = f(x) has the maximum peak located in the range of -2.5 ≤ x ≤ -2.4.

[0119] [Aspect 3] The positive electrode material according to Aspect 1, wherein the second derivative y = f′′(x) of the function y = f(x) has the maximum peak located in the range of -2.36 ≤ x ≤ -2.3.

[0120] [Aspect 4] 4. The positive electrode material according to any one of Aspects 1 to 3, wherein the granules have a core constituted by the olivine-type lithium manganese iron phosphate and a carbon coating formed on a surface of the core.

[0121] [Aspect 5] The general formula Li a Mn x Fe y Me z PO 4 The positive electrode material according to any one of aspects 1 to 4, wherein Me contains at least Mg.

[0122] [Aspect 6] The general formula Li a Mn x Fe y Me z PO 4 6. The positive electrode material according to any one of aspects 1 to 5, wherein Me contains at least Ti. [Explanation of symbols]

[0123] 10...Granules 11. Core 11a...Primary particle 11b…pore 12...Carbon coating

Claims

1. General formula Li ａ Mn ｘ Fe ｙ Me ｚ P.O. ４ A positive electrode material comprising a granule composed of an olivine-type lithium manganese iron phosphate represented by the formula: The general formula Li ａ Mn ｘ Fe ｙ Me ｚ P.O. ４ a, x, y, and z in the formula are numbers that satisfy the following: 0<a<2, 0<x+y+z<2, 0.75≦x / (x+y)≦0.9, 0.1≦y / (x+y)≦0.25, and 0≦z≦0.

1. The general formula Li ａ Mn ｘ Fe ｙ Me ｚ P.O. ４ Me in the formula (I) is at least one element selected from the group consisting of Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te, and Mo; When the scattering curve of the granules measured by small angle X-ray scattering is expressed as a function y=f(x) with the horizontal axis representing the logarithmic value of the scattering vector and the vertical axis representing the scattering intensity, The second derivative of the function y=f(x) is y=f″(x) A positive electrode material characterized in that the maximum peak in the range of -3.0≦x≦-2.0 is located in the range of -2.5≦x≦-2.

3.

2. 2. The positive electrode material according to claim 1, wherein the second derivative y=f''(x) of the function y=f(x) has the maximum peak located in a range of -2.5≦x≦-2.

4.

3. 2. The positive electrode material according to claim 1, wherein the second derivative y=f''(x) of the function y=f(x) has the maximum peak located in a range of -2.36≦x≦-2.

3.

4. The positive electrode material according to any one of claims 1 to 3, wherein the granules have a core constituted by the olivine-type lithium manganese iron phosphate and a carbon coating formed on a surface of the core.

Images