Positive electrode material for lithium-ion secondary battery and method for producing positive electrode material for lithium-ion secondary battery

Abstract

This positive electrode material for a lithium-ion secondary battery includes a granulate (10) composed of LMFP. In the granulate (10), as measured by the BET / BJH method, the total pore volume of pores having a pore diameter of 300 nm or less is 0.15 cm3 or less, and in the pore distribution, the volume fraction of pores having a pore diameter of 50 nm or more to the total pore volume is greater than 11%, and the volume fraction of pores having a pore diameter of 20 nm or less to the total pore volume is 23% or less.

Description

Positive electrode material for lithium-ion secondary battery and method for manufacturing positive electrode material for lithium-ion secondary battery

[0001] The present disclosure relates to a positive electrode material for a lithium-ion secondary battery and a method for manufacturing a positive electrode material for a lithium-ion secondary battery.

[0002] Patent Document 1 discloses a power storage device including a positive electrode using olivine-type lithium iron phosphate (LiFePO ４ 4) as a positive electrode active material. The olivine-type structure active material typified by olivine-type lithium iron phosphate is a positive electrode active material having excellent thermal stability.

[0003] Japanese Patent Application Laid-Open No. 2019-185920

[0004] Olivine-type lithium manganese iron phosphate (LiMnFePO ４ 4) is a substance in which a part of iron constituting olivine-type lithium iron phosphate is substituted with manganese. The positive electrode active material using olivine-type lithium manganese iron phosphate can increase the battery capacity as compared with the positive electrode active material using olivine-type lithium iron phosphate. However, the positive electrode material including granulated bodies composed of olivine-type lithium manganese iron phosphate has the following problems. That is, when the pore volume of the granulated bodies is reduced, the discharge capacity per unit volume in a lithium-ion secondary battery to which the positive electrode material is applied can be increased as compared with the case where the pore volume is large, but the discharge capacity per unit mass tends to decrease. For this reason, it has been difficult to reduce the pore volume of the granulated bodies without reducing the discharge capacity per unit mass.

[0005] A positive electrode material for a lithium-ion secondary battery for solving the above problems is a positive electrode material for a lithium-ion secondary battery including granulated bodies composed of olivine-type lithium manganese iron phosphate represented by the general formula Li ａ xMn ｘ yFe ｙ zMe ｚ PO ４ 4, wherein the general formula Li ａ xMn ｘ yFe ｙ zMe ｚ PO ４In this equation, a, x, y, and z are numerical values ​​that satisfy 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, and the general formula Li ａ Mn ｘ Fe ｙ Me ｚ PO ４ In this formula, 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, and the granulated material has a total pore volume of 0.15 cm³ of pores with a pore diameter of 300 nm or less, as measured by the BET / BJH method. ３ The ratio is less than or equal to / g, and in the pore distribution, the proportion of the volume of pores with a pore diameter of 50 nm or more relative to the total pore volume is greater than 11%, and the proportion of the volume of pores with a pore diameter of 20 nm or less relative to the total pore volume is 23% or less.

[0006] The positive electrode material for the lithium-ion secondary battery described above has a total pore volume of 0.13 cm³. ３ It is preferable that the amount be less than or equal to / g. In the above-mentioned positive electrode material for lithium-ion secondary batteries, it is preferable that the proportion of the volume of pores having a pore diameter of 50 nm or more to the total pore volume in the pore distribution is 12% or more.

[0007] The positive electrode material for the lithium-ion secondary battery described above is preferably such that, in the pore distribution, the proportion of the volume of pores having a pore diameter of 20 nm or less to the total pore volume is 20% or less.

[0008] The positive electrode material for the lithium-ion secondary battery described above preferably has a particle size of 35 nm or more and 100 nm or less of primary particles constituting the granules. A method for manufacturing the positive electrode material for the lithium-ion secondary battery described above to solve the above problem comprises a slurry preparation step of obtaining a slurry from components for forming the olivine-type lithium iron manganese phosphate, a granulation step of obtaining precursor particles by spray drying the slurry, and a calcination step of obtaining the olivine-type lithium iron manganese phosphate by calcining the precursor particles, wherein the slurry preparation step includes a pulverization step of pulverizing the components for forming the olivine-type lithium iron manganese phosphate in the presence of a carboxylic acid, the slurry contains the carboxylic acid, and the content of the carboxylic acid in the slurry, excluding water, is 10% by mass or more.

[0009] According to this disclosure, a positive electrode material for lithium-ion secondary batteries can be obtained that has a large discharge capacity per unit mass even when the pore volume of the granules is reduced.

[0010] Figure 1 is a micrograph of a cross-section of the granules containing the cathode material. Figure 2 is a schematic diagram showing the aggregated structure of primary particles in the cross-section of the granules in Figure 1. Figure 3 is a graph showing the pore distribution in the granules in Figure 1. Figure 4 is a flowchart of the manufacturing method of the cathode material in Figure 1.

[0011] Hereinafter, an embodiment of this disclosure will be described with reference to the drawings. Hereinafter, the positive electrode material for lithium-ion secondary batteries and the electrodes for lithium-ion secondary batteries may be abbreviated as positive electrode material and electrodes, respectively.

[0012] <Positive Electrode Material> (Regarding the structure of the positive electrode material) The positive electrode material of this 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 intercepting and releasing charge carriers such as lithium ions in a positive electrode for a lithium-ion secondary battery.

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

[0014] An example of the granulated body 10 shown in Figure 1 has a core 11 made of LMFP and a carbon coating 12 formed on the surface of the core 11. The LMFP constituting the core 11 has the general formula Li ａ Mn ｘ Fe ｙ Me ｚ PO ４ It is a polyanionic compound having an olivine-type structure represented by the general formula Li. ａ Mn ｘ Fe ｙ Me ｚ PO ４ In this context, 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.

[0015] General formula Li ａ Mn ｘ Fe ｙ Me ｚ PO ４ In this equation, a, x, y, and z are numerical values ​​that satisfy 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. Preferably, a is a numerical value that satisfies (x + y + z) ≤ a ≤ 1.1(x + y + z).

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

[0017] Specific examples of the ranges of x, y, and z when z = 0 include x + y = 1, 0.75 ≤ x ≤ 0.9, and 0.1 ≤ y ≤ 0.25. Specific examples of the ranges of x, y, and z when z is not 0 include 0.9 ≤ x + y < 1, 0.675 ≤ x < 0.9, 0.09 ≤ y < 0.25, and 0 < z ≤ 0.1. The olivine-type manganese iron lithium phosphate constituting core 11 may be one type or two or more types.

[0018] LMFP preferably contains Mg as an element constituting Me. When Mg is included, the ratio of the molar ratio of Mg (Mg / T) 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 above specific metal element is the general formula Li ａ Mn ｘ Fe ｙ Me ｚ PO ４ These are the metallic elements that make up Mn, Fe, and Me in the LMFP represented by [formula].

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

[0020] Figure 2 schematically shows the structure of the area indicated by arrow A within the core 11 in Figure 1. As shown in Figure 2, the core 11 has a structure in which primary particles 11a of LMFP are aggregated. The core 11 also has pores 11b formed between multiple primary particles 11a. Figure 2 illustrates an example of the interparticle distance PS, which is the distance between adjacent primary particles 11a. The interparticle distance PS corresponds to the pore diameter.

[0021] The particle diameter of the primary particle 11a is, for example, 100 nm or less, preferably 70 nm or less, and more preferably 50 nm or less. Alternatively, the particle diameter of the primary particle 11a is, for example, 35 nm or more, preferably 37 nm or more, and more preferably 40 nm or more. The particle diameter of the primary particle 11a is a value obtained by small-angle X-ray scattering (hereinafter also referred to as the SAXS method). More specifically, the particle diameter of the primary particle 11a is a value defined as the average particle diameter (D50) obtained from the particle diameter distribution of the primary particle 11a, after determining the particle diameter distribution of the primary particle 11a assuming that the primary particle 11a is spherical. Unless otherwise specified, the particle diameter values ​​described below are values ​​obtained by the same SAXS method as described above.

[0022] The pore volume of core 11 is 0.15 cm³. ３ It is less than or equal to / g. The pore volume of the core 11 is preferably 0.13 cm³. ３ It is less than or equal to / g. Furthermore, the pore volume is, for example, 0.05 cm³. ３ The amount is 0.10 cm or more, preferably 0.10 cm. ３ The value is 1 / g or more. The above pore volume can be determined by performing nitrogen adsorption / desorption measurements on the granular material 10 and using the BJH (Barrett Joyner Hallenda) method. In this document, pore volume refers to the total pore volume of pores with a pore diameter of 300 nm or less.

[0023] Figure 3 illustrates the pore distribution of the core 11. The core 11 is not a uniform aggregate of primary particles 11a, but rather has areas with relatively small pore diameters and areas with relatively large pore diameters. Figure 3 shows two examples of different pore distributions. Comparing the first distribution example X1, shown by a solid line in Figure 3, with the second distribution example X2, shown by a dashed line, the first distribution example X1 has a high proportion of pores with large pore diameters and a low proportion of pores with small pore diameters. In contrast, the second distribution example X2 has a low proportion of pores with large pore diameters and a high proportion of pores with small pore diameters.

[0024] In the pore distribution of core 11, the proportion of the volume of pores 11b having a pore diameter of 50 nm or more to the total pore volume is greater than 11%. Preferably, the proportion of the volume of pores 11b having a pore diameter of 50 nm or more is 12% or more, and more preferably 17% or more. Also, the proportion of the volume of pores 11b having a pore diameter of 50 nm or more is, for example, 22% or less. In the pore distribution of core 11, the proportion of the volume of pores having a pore diameter of 20 nm or less to the total pore volume is 23% or less. Preferably, the proportion of the volume of pores having a pore diameter of 20 nm or less is 20% or less, and more preferably 18% or less. Also, the proportion of the volume of pores having a pore diameter of 20 nm or less is, for example, 13% or more, and may also be 15% or more. Pore ​​size distribution can be measured using the BET (Brunauer Emmett Teller) / BJH (Barrett Joyner Hallenda) method.

[0025] 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. Alternatively, the carbon content may be, 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). Note that the carbon content of the granules 10 refers to the carbon content constituting the carbon coating 12. The carbon coating 12 may be omitted.

[0026] The LMFP content in the granulated body 10 is, for example, 95% by mass or more, preferably 96% by mass or more. Alternatively, the above content is, for example, 99% by mass or less, preferably 98% by mass or less.

[0027] The granulated material 10 may contain other components besides 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 granulated material 10 is, for example, 3.0 μm or more, preferably 5.0 μm or more. Alternatively, the average particle size (D50) of the granulated material 10 is, for example, 30 μm or less, preferably 20 μm or less. The average particle size of the granulated material 10 can be measured, for example, using a laser diffraction particle size analyzer.

[0028] <Method for Manufacturing Cathode Material> Next, an example of a method for manufacturing a cathode material will be described. The above-mentioned pore volume and pore distribution can be adjusted by changing various conditions when manufacturing the granules 10. Note that the method for manufacturing the cathode material is not limited to the method described below.

[0029] As shown in Figure 4, the manufacturing method for the granulated body 10, which is the positive electrode material, includes a slurry preparation step S10, a granulation step S20, and a calcination step S30. The granulated body 10 is manufactured by sequentially going through the slurry preparation step S10, the granulation step S20, and the calcination step S30.

[0030] (Slurry preparation step) Slurry preparation step S10 is a step to obtain a precursor slurry containing lithium phosphate, a manganese-containing phosphate compound, iron oxide, and a dispersion medium. Slurry preparation step S10 includes a grinding step S11 in which lithium phosphate and the manganese-containing phosphate compound are ground together with iron oxide.

[0031] First, we will explain the components contained in the precursor slurry obtained in slurry preparation step S10. The components that the precursor slurry may contain can be broadly classified into components for forming LMFPs, dispersion media, and other components.

[0032] [Components for forming LMFP] Lithium phosphate (Li ３ PO ４ ) is a Li source for forming LMFP. The lithium phosphate may be a commercially available product or may be produced in the slurry preparation step S10. Lithium phosphate can be produced, for example, by reacting a lithium-containing compound with phosphoric acid (hereinafter referred to as the first reaction). Details of the first reaction will be described later.

[0033] Manganese-containing phosphate compounds are both a source of Mn and a source of phosphate for forming LMFPs. 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.

[0034] Mn ５ (HPO ４ ) ２ (PO ４ ) ２ is an anhydride obtained by removing the water molecules that constitute the hydrate from Mn ５ (HPO ４ ) ２ (PO ４ ) ２ (H ２ O). ４ Hereinafter, Mn ５ (HPO ４ ) ２ (PO ４ ) ２ and Mn ５ (HPO ４ ) ２ (PO ４ ) ２ (H ２ O). ４ may be collectively referred to as Mn54. Mn ３ (PO ４ ) ２ is an anhydride obtained by removing the water molecules that constitute the hydrate from Mn ３ (PO ４ ) ２ ・3H ２ O. Hereinafter, Mn ３ (PO ４ ) ２ ・3H ２ O and Mn ３ (PO ４ ) ２ may be collectively referred to as Mn32.

[0035] When the manganese-containing phosphate compound is Mn54, compared with the case where it is Mn32, LiH ２ PO ４The formation of by-products such as [specific by-products] can be suppressed. Furthermore, when used as a hydrate, Mn54 has a smaller proportion of water molecules constituting the hydrate compared to Mn32. Therefore, when Mn54 is used, the amount of water that volatilizes in the calcination process S30 is reduced. As a result, a granular material 10 with a small pore volume can be obtained.

[0036] The manganese-containing phosphate compound may be a commercially available product or one produced in the slurry preparation step S10. The manganese-containing phosphate compound can be produced, for example, by reacting the manganese-containing compound with phosphoric acid (hereinafter referred to as the second reaction). Details of the second reaction will be described later.

[0037] Iron oxide is an Fe source for forming LMFPs and is also a component included in the grinding step S11 to finely grind the manganese-containing phosphate compound. As 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 greater than "5" is selected as iron oxide. For example, Fe ２ O ３ (Mohs hardness 5.5), Fe ３ O ４ (Mohs hardness 6.0) is one example. The iron oxide contained in the precursor slurry may be one type or two or more types.

[0038] Here, the precursor slurry is, if necessary, of the general formula Li ａ Mn ｘ Fe ｙ Me ｚ PO ４The LMFP may contain a metal source (hereinafter referred to as an arbitrary metal source) for forming "Me" in the LMFP represented by . Examples of arbitrary metal sources include Co source, Ni source, Cu source, Mg source, Zn source, V source, Ca source, Sr source, Ba source, Ti source, Al source, Si source, B source, Te source, and Mo source. Specific examples of arbitrary metal sources include metal oxides, metal hydroxides, and metal salts of various metal elements. The arbitrary metal source is preferably a metal oxide. In this case, volume shrinkage during firing in the firing process S30 can be suppressed. The precursor slurry may contain one or more arbitrary metal sources.

[0039] The precursor slurry preferably contains a magnesium (Mg) source as an optional metal source. In this case, the resistance of the granulated body 10 can be reduced. Examples of magnesium compounds that can be used as the Mg source include magnesium oxide, magnesium acetate, magnesium carbonate, and magnesium hydroxide. The Mg source is preferably magnesium oxide. In this case, volume shrinkage during firing in the firing process S30 can be suppressed.

[0040] The precursor slurry preferably contains a Ti source as an optional metal source. Examples of Ti sources include titanium compounds such as titanium oxide and titanium nitride. The Ti source is preferably titanium oxide. In this case, volume shrinkage during firing in the firing process S30 can be suppressed.

[0041] The content of lithium phosphate, manganese-containing phosphate compounds, iron oxides, and any metal source in the precursor slurry is adjusted so that the molar ratio of each metal element satisfies a specific relationship.

[0042] The amount of manganese-containing phosphate compound and iron oxide is such that the molar ratio of manganese to the total molar ratio of manganese and iron in the precursor slurry is 75% or more and 90% or less. The molar ratio of manganese is preferably 77% or more, more preferably 78% or more. Furthermore, the molar ratio of manganese is preferably 85% or less, more preferably 83% or less.

[0043] The lithium phosphate content is preferably such that the ratio of the molar ratio of lithium (Li) to the total molar ratio (T) of specific metal elements in the precursor slurry (Li / T) is 1.00 or more and 1.10 or less. The specific metal elements are manganese contained in manganese-containing phosphate compounds, iron contained in iron oxide, and metal elements contained in any metal source. In other words, the general formula Li ａ Mn ｘ Fe ｙ Me ｚ PO ４ These are the metallic elements that make up Mn, Fe, and Me in the LMFP represented by [formula].

[0044] When a magnesium source is included, the amount of magnesium source is such that, for example, the ratio of the molar ratio of magnesium (Mg) to the total molar ratio (T) of specific metal elements in the precursor slurry (Mg / T) is 0.0001 or more and 0.05 or less. Furthermore, the molar ratio of magnesium is preferably 0.005 or more, more preferably 0.01 or more. Furthermore, the molar ratio of magnesium is preferably 0.045 or less, more preferably 0.04 or less.

[0045] When a Ti source is included, the Ti source content is such that, for example, the ratio of the molar ratio of titanium (Ti) to the total molar ratio (T) of specific metal elements in the precursor slurry (Ti / T) is 0.0001 or more and 0.05 or less. Furthermore, the molar ratio of titanium is preferably 0.005 or more, more preferably 0.01 or more. Furthermore, the molar ratio of titanium is preferably 0.045 or less, more preferably 0.04 or less.

[0046] In the precursor slurry, each of the above components that form the LMFP is contained in powder form. The particle size of lithium phosphate contained in the precursor slurry is, for example, 50 nm or less, preferably 40 nm or less, and more preferably 30 nm or less. Also, the particle size of lithium phosphate is, for example, 5 nm or more. The lithium phosphate becomes a powder of the above particle size by going through the grinding step S11 described later.

[0047] The particle size of the manganese-containing phosphate compound contained in the precursor slurry is, for example, 100 nm or less, preferably 70 nm or less, and more preferably 50 nm or less. Alternatively, the particle size of the manganese-containing phosphate compound may be, for example, 10 nm or more. The manganese-containing phosphate compound is converted into a powder of the above particle size by going through the grinding step S11 described later.

[0048] 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. Alternatively, the particle size of the iron oxide is, for example, 10 nm or more. The iron oxide is converted into a powder with the above particle size through the pulverization step S11 described later.

[0049] The particle size of the arbitrary 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. Alternatively, the particle size of the arbitrary metal source may be, for example, 10 nm or more.

[0050] [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 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, are preferred. 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 dimethyl sulfoxide. One non-aqueous solvent may be used alone, or two or more may be used in combination. The volume percentage 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 for example, it is an amount such that the solid content ratio is 20% by mass or more and 50% by mass or less.

[0051] [Other Components] The precursor slurry may contain a carbon source for forming the carbon film 12. For example, an organic compound can be used as the carbon source. Examples of organic compounds include 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, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, polyacrylic acid, polystyrene sulfonic acid, polyacrylamide, and polyvinyl acetate. Examples of polyhydric alcohols include polyethylene glycol, polypropylene glycol, polyglycerin, and glycerin. The carbon source may be used alone or in combination of two or more types.

[0052] The carbon source content in the precursor slurry is such that the mass of carbon in the carbon source (or, if a carboxylic acid is included as described later, the total amount including the mass of carbon in the carboxylic acid) is a specific amount. For example, the carbon source content is such that, when the total mass of the components forming the LMFP in the precursor slurry is 100 parts by mass, the carbon source content is between 3 parts by mass and 30 parts by mass.

[0053] The precursor slurry may contain a carboxylic acid as an optional component. In this case, the pore volume of the granule 10 can be reduced. Examples of carboxylic acids 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. One carboxylic acid may be used alone, or two or more may be used in combination. Among these carboxylic acids, citric acid is preferred.

[0054] The carboxylic acid content in the precursor slurry is such that, for example, when the total mass of the components forming the LMFP in the precursor slurry is 100 parts by mass, the carboxylic acid content is between 10 parts by mass and 30 parts by mass. If the carboxylic acid content in the precursor slurry is less than 10 parts by mass, it is difficult to obtain the effect of reducing the pore volume of the granule 10. A smaller pore volume in the granule 10 results in a higher electrode density, which increases the discharge capacity per unit volume in the lithium-ion secondary battery. On the other hand, a larger pore volume in the granule 10 results in a lower electrode density, which is a problem as it reduces the discharge capacity per unit volume in the lithium-ion secondary battery.

[0055] Furthermore, the precursor slurry may contain components other than those described above, if necessary. Examples of such components include dispersants. [Grinding process] The grinding process S11 is performed on a slurry (hereinafter referred to as the intermediate slurry) containing lithium phosphate, a manganese-containing phosphate compound, iron oxide, and a dispersion medium. The grinding process S11 is a process of grinding the solid components contained in the intermediate slurry, namely lithium phosphate, a manganese-containing phosphate compound, and iron oxide, to reduce their diameter.

[0056] The grinding method used in grinding step S11 is not particularly limited as long as it is a grinding method that causes collisions between solid particles in the intermediate slurry. Examples of such grinding methods include methods using grinders such as bead mills, hammer mills, agitator mills, jet mills, and ball mills. Among these grinding methods, grinding methods that crush by applying shear force, such as methods using bead mills, are preferred.

[0057] When using a bead mill, the beads used as the medium particles are harder than the solid content in the intermediate slurry, for example, harder than iron oxide. The bead diameter is, for example, 1 mm or less, preferably 0.5 mm or less. The bead diameter is, for example, 0.01 mm or more. The temperature during grinding is, for example, 10°C to 50°C. The peripheral speed during grinding with a grinder such as a bead mill is, for example, 13 m / s to 20 m / s.

[0058] In this case, when using a bead mill, reducing the diameter of the beads makes it easier to obtain a granulated material 10 in which the primary particles 11a have a small particle size. Also, reducing the bead diameter makes it easier to obtain a granulated material 10 in which the proportion of primary particles 11a with a small particle size is high. On the other hand, increasing the bead diameter makes it easier to obtain a granulated material 10 in which the primary particles 11a have a large particle size. Also, increasing the bead diameter makes it easier to obtain a granulated material 10 in which the proportion of primary particles 11a with a large particle size is high.

[0059] The grinding time, which is the time from the start of grinding process S11 to the end of grinding process S11, is not particularly limited, but for example, it is 5 hours or more and less than 8 hours. By increasing the grinding time in grinding process S11, it becomes easier to obtain a granule 10 in which the particle size of the primary particles 11a is small. Also, by increasing the grinding time, it becomes easier to obtain a granule 10 in which the proportion of primary particles 11a with small particle size is large. On the other hand, by decreasing the grinding time, it becomes easier to obtain a granule 10 in which the particle size of the primary particles 11a is large. By decreasing the grinding time, it becomes easier to obtain a granule 10 in which the proportion of primary particles 11a with large particle size is large. There is a relationship between the particle size of the primary particles 11a and the pore distribution in which the proportion of primary particles 11a with large particle size is higher, and the proportion of pores with large pore diameters tends to be higher.

[0060] The particle sizes of each solid component in the intermediate slurry before the grinding step S11 are as follows: The particle size of lithium phosphate is, for example, 50 nm to 50 μm. The particle size of manganese-containing phosphate compounds is, for example, 50 nm to 50 μm. The particle size of iron oxide is, for example, 50 nm to 10 μm.

[0061] The particle size of each solid component in the intermediate slurry after the grinding step S11 is, for example, 100 nm or less, preferably 70 nm or less, and more preferably 50 nm or less, when expressed as a mixture of lithium phosphate, manganese-containing phosphate compound, and iron oxide particles. Furthermore, the above values ​​are, for example, 10 nm or more.

[0062] In the grinding step S11, lithium phosphate and manganese-containing phosphate compounds are ground together with iron oxide in a dispersion medium. In this case, based on the difference in hardness between lithium phosphate and manganese-containing phosphate compounds and iron oxide, lithium phosphate and manganese-containing phosphate compounds, especially manganese-containing phosphate compounds, can be ground more finely.

[0063] To elaborate, lithium phosphate has a Mohs hardness of "4," while manganese-containing phosphate compounds Mn54 and Mn32 have a Mohs hardness of "5." In contrast, iron oxide (Fe ２ O ３ The Mohs hardness of iron oxide is 5.5, which means that iron oxide is harder than lithium phosphate and manganese-containing phosphate compounds. In this case, two stages of grinding are performed in the grinding process S11, allowing the lithium phosphate and manganese-containing phosphate compounds to be ground more finely.

[0064] More specifically, in the first step, shear forces, compressive forces, etc., generated in a grinder such as a bead mill act on each solid component in the intermediate slurry, thereby grinding lithium phosphate, manganese-containing phosphate compounds, and iron oxide. Subsequently, as the grinding process continues, in the second step, collisions occur between the ground solid components. At this time, the relatively hard ground iron oxide pulverizes the relatively softer lithium phosphate and manganese-containing phosphate compounds, further grinding the ground lithium phosphate and manganese-containing phosphate compounds. Note that in grinding step S11, the first and second steps described above are performed in parallel or simultaneously.

[0065] In the grinding step S11, lithium phosphate, manganese-containing phosphate compound, and iron oxide are separated along the grain boundaries. Therefore, theoretically, each particle after grinding will be the same size as the crystal grain, and the theoretical minimum size will be the same as the particle diameter of the crystal grain. Consequently, the smaller the constituent crystal grains, the finer the grinding will be. In the case of manganese-containing phosphate compound, the particle diameter of the crystal grains forming the phase is smaller for Mn54 than for Mn32. Therefore, if finer grinding is desired, it is preferable that the manganese-containing phosphate compound be Mn54.

[0066] Components other than lithium phosphate, manganese-containing phosphate compounds, iron oxide, and the dispersion medium may be pre-mixed into the intermediate slurry subjected to the grinding step S11, or mixed into the intermediate slurry after the grinding step S11. Alternatively, some of the components other than lithium phosphate, manganese-containing phosphate compounds, iron oxide, and the dispersion medium may be pre-mixed into the intermediate slurry subjected to the grinding step S11, and the remainder of these components may be mixed into the intermediate slurry after the grinding step S11. Furthermore, components other than lithium phosphate, manganese-containing phosphate compounds, iron oxide, and the dispersion medium may be pre-ground to a predetermined particle size before mixing, or they may be ground to a predetermined particle size during the grinding step.

[0067] Here, the intermediate slurry after the grinding step S11 preferably contains a carboxylic acid. In other words, the grinding step S11 is preferably carried out in the presence of a carboxylic acid. In the intermediate slurry, the proportion of carboxylic acid to the components excluding water is not particularly limited, but is, for example, 10% by mass or more. The proportion of carboxylic acid is, for example, 18% by mass or less, and preferably 15% by mass or less. The higher the carboxylic acid content in the intermediate slurry, the smaller the pore volume of the granule 10 can be. A smaller pore volume in the granule 10 allows for a higher electrode density, which in turn increases the discharge capacity per unit volume in the lithium-ion secondary battery.

[0068] If the intermediate slurry subjected to grinding step S11 contains all components except manganese-containing phosphate compounds, iron oxide, and dispersion medium, a precursor slurry is obtained as the intermediate slurry after grinding step S11. If the intermediate slurry subjected to grinding step S11 does not contain all components except manganese-containing phosphate compounds, iron oxide, and dispersion medium, a precursor slurry is obtained by mixing the remaining components into the intermediate slurry after grinding step S11.

[0069] [Specific Example of Precursor Slurry Preparation Method] Next, a specific example of slurry preparation step S10 will be described. First, lithium phosphate is produced by the first reaction, and a manganese-containing phosphate compound is produced by the second reaction.

[0070] In more detail, phosphoric acid is added dropwise to a solution in which a lithium-containing compound and a manganese-containing compound are dissolved or dispersed in a dispersion medium containing water, at atmospheric pressure and a temperature between 0°C and 90°C. As a result, the lithium-containing compound reacts with phosphoric acid to produce lithium phosphate (first reaction), and the manganese-containing compound reacts with phosphoric acid to produce a manganese-containing phosphate compound (second reaction).

[0071] Components other than lithium phosphate and manganese-containing phosphate compounds contained in the precursor slurry may be added beforehand to the solution in which the first and second reactions take place, or they may be added to the reaction solution after the first and second reactions. However, if iron oxide is added to the solution in which the first and second reactions take place, the viscosity of the solution will increase and it will become difficult to handle, so it is preferable to add it after the first and second reactions.

[0072] Examples of lithium-containing compounds used in the first reaction include lithium hydroxide, lithium carbonate, and lithium oxide. Lithium hydroxide and lithium carbonate are preferred as the lithium-containing compound.

[0073] In the first reaction, the formation of by-products can be suppressed and the production rate of lithium phosphate increased by adjusting the ratio of the lithium-containing compound and phosphoric acid to the metal compound other than lithium. Examples of the above by-products include LiOH·H ２ O, LiH ２ PO４ For example, if the precursor slurry contains the above-mentioned by-products, the amount of water that volatilizes in the calcination process S30 increases, which leads to an increase in the pore volume of the granules 10. Also, LiH ２ PO ４ This can cause the formation of coarse particles in the granulation process S20, and can also adhere to various equipment used in manufacturing. Therefore, it is preferable to reduce the amount of the above-mentioned by-products generated in the first reaction.

[0074] Other metal compounds are manganese compounds, iron oxides, and any of the above-mentioned optional metal sources such as magnesium oxide and titanium oxide, which are used in the second reaction. In the first reaction, the amount of other metal compound added is such that the ratio of the molar ratio of lithium (Li) to the total molar ratio (MA) of the metal components constituting the metal compound (Li / MA) is 1.0 or more and 1.1 or less, and the ratio of the molar ratio of phosphorus (P) to the total molar ratio (MA) of the metal components constituting the metal compound (P / MA) is 1.0 or more and 1.1 or less. By adjusting the amount of other metal compound added to the lithium-containing compound and phosphoric acid to satisfy the above conditions, the formation of the above-mentioned by-products can be suppressed.

[0075] Examples of manganese-containing compounds used in the second reaction include manganese carbonate, manganese sulfate, and manganese oxalate. Manganese carbonate is preferred as the manganese-containing compound. By using manganese carbonate, which has a relatively smaller particle size compared to other manganese-containing compounds, the primary particle size of the granules 10 can be made even smaller. If manganese sulfate is used, it is necessary to perform a post-treatment to wash the generated manganese-containing phosphate compound before the grinding step S11 described later.

[0076] In the second reaction, the type of manganese-containing phosphate compound produced can be adjusted by controlling the reaction temperature. When producing Mn54, the reaction temperature of the second reaction is preferably 60°C to 90°C. When producing Mn32, the reaction temperature of the second reaction is preferably 0°C to less than 60°C.

[0077] The first and second reactions may be carried out sequentially within the same system, rather than simultaneously. For example, phosphoric acid may be added dropwise to a solution in which one of the lithium-containing compound and the 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 may be added to the reaction solution. This yields a reaction solution containing lithium phosphate and the manganese-containing compound. It is preferable to carry out the first and second reactions simultaneously, or to carry out the second reaction after the first reaction, as this makes it easier to adjust the component ratio to suppress the formation of by-products in the first reaction.

[0078] The first and second reactions may be carried out separately in different systems. For example, after carrying out the first and second reactions in separate systems, the reaction solution from the first reaction and the reaction solution from the second reaction are mixed. This yields a reaction solution containing lithium phosphate and a manganese-containing compound.

[0079] Next, an intermediate slurry is prepared by mixing iron oxide with the reaction solution containing lithium phosphate and a manganese-containing compound. If necessary, an optional metal source and other components are also mixed in. For example, a Mg source and a Ti source are mixed as optional metal sources, and a carbon source and a carboxylic acid are mixed as other components. If the relevant components have already been added in the first and second reactions, this step is omitted.

[0080] The optional metal source and other components may be pre-mixed into the reaction system carrying out the first and second reactions, but it is preferable to mix them after each of the first and second reactions. If at least one of the first and second reactions is a reaction that generates carbon dioxide, the process of mixing some components after each reaction can promote the discharge of the generated carbon dioxide from the intermediate slurry. Carbon dioxide is generated, for example, when at least one of the lithium compound, manganese compound, and optional metal source is a carbonate.

[0081] Next, the obtained intermediate slurry is subjected to a grinding step S11. Then, a precursor slurry is obtained as the intermediate slurry after the grinding step S11. (Granulation step) The granulation step S20 is a step in which precursor particles are obtained by spray drying the precursor slurry. The precursor particles are granules formed by the aggregation of solid components contained in the precursor slurry. Examples of spraying methods in spray drying include spraying using a disc type, a pressurized nozzle, a pressurized two-fluid nozzle, a pressurized four-fluid nozzle, etc. The spray temperature in spray drying is, for example, 180°C to 300°C.

[0082] (Castration Process) The calcination process S30 is a process to obtain LMFP by calcining the precursor particles obtained in the granulation process S20, specifically a process to form the crystalline phase of LMFP. The calcination process S30 is also a process to form a carbon film 12 by carbonizing the carbon source contained in the precursor particles. The calcination temperature in the calcination process is, for example, 500°C to 750°C. The calcination time in the calcination process is, for example, 1 hour to 12 hours. The atmosphere in the calcination process is, for example, a non-oxidizing atmosphere. As a non-oxidizing atmosphere, for example, nitrogen (N) ２ ), an inert atmosphere such as argon (Ar), and hydrogen (H ２ Examples include reducing atmospheres containing reducing gases such as ).

[0083] If the precursor slurry contains a carbon source, the carbon source contributes to lowering the oxygen partial pressure during calcination. By lowering the oxygen partial pressure during calcination, the generation of LMFP (Lesser Multipliers) in the granulated body 10 obtained after calcination can be suppressed.

[0084] <Effects of this embodiment> Generally, it is known that the discharge capacity per unit volume in a lithium-ion secondary battery to which a positive electrode material is applied can be increased by reducing the pore volume of the granules constituting the positive electrode material, in other words, by increasing the density of primary particles.

[0085] On the other hand, the inventors have found the following regarding positive electrode materials: Even if the pore volume of the granules constituting the positive electrode material is similar, if the pore distribution is different, the discharge capacity per unit mass of the lithium-ion secondary battery to which the positive electrode material is applied will differ. In other words, in areas with small pore diameters, that is, in areas where the primary particles are locally dense, lithium ions are less likely to be released from the positive electrode material. In this case, it is thought that the discharge capacity per unit mass decreases because lithium ions have difficulty passing through the pores due to the presence of areas where the primary particles are locally dense.

[0086] The operation and effects of this embodiment will be described below. (1) The positive electrode material includes a granulated body 10 composed of LMFP. The granulated body 10 has a pore volume of 0.15 cm³ of pores with a pore diameter of 300 nm or less, as measured by the BET / BJH method. ３ The pore size is less than or equal to / g, and in the pore distribution, the proportion of the volume of pores 11b with a pore diameter of 50 nm or more relative to the total pore volume is greater than 11%, and the proportion of the volume of pores 11b with a pore diameter of 20 nm or less relative to the total pore volume is 23% or less. By using the granule 10 having the above pore distribution as the positive electrode material for a lithium-ion secondary battery, a lithium-ion secondary battery can be obtained in which the decrease in discharge capacity per unit mass is suppressed even when the pore volume of the granule 10 is reduced. This improves the design freedom when manufacturing the positive electrode.

[0087] (2) Pore volume is 0.13 cm ３ Even when the value is less than / g, the decrease in discharge capacity per unit mass can be suppressed. With the above configuration, the pore volume of the granule 10 can be made smaller. (3) In the pore distribution, a positive electrode material in which the volume of pores 11b with a pore diameter of 50 nm or more accounts for 12% or more of the total pore volume has a smaller proportion of pores 11b with a small pore diameter. With the above configuration, the decrease in discharge capacity per unit mass can be suppressed even more.

[0088] (4) In the pore distribution, a cathode material in which the volume of pores 11b with a pore diameter of 20 nm or less accounts for 20% or less of the total pore volume has a smaller proportion of pores 11b with small pore diameters. With the above configuration, the decrease in discharge capacity per unit mass can be further suppressed.

[0089] (5) If the particle diameter of the primary particles 11a constituting the granules 10 is 35 nm or more and 100 nm or less, the proportion of pores 11b having small pore diameters tends to decrease. This makes it possible to suppress the decrease in discharge capacity per unit mass.

[0090] (6) As a method for producing the granules 10, the pore volume of the produced granules 10 can be reduced by carrying out the grinding step S11 in the presence of a carboxylic acid. For example, if the content of carboxylic acid in the components excluding water in the intermediate slurry after the grinding step S11 is 10% by mass or more, it can be expected that granules 10 with a reduced pore volume can be obtained.

[0091] <Examples of Modifications> This embodiment can be implemented with the following modifications. This embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

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

[0093] Regarding the manufacturing method of the positive electrode material, an Fe source other than iron oxide may be used. An example of an Fe source other than iron oxide is FeSO4. ４ 7H ２ O, FeC ２ O ４ ・2H ２ O is one example.

[0094] The following describes examples that further elaborate on the above embodiments. Note that the cathode material is not limited to the configuration described in the Examples section. (Example 1) After dispersing a Li source and a Mn source in water at 60°C, phosphoric acid was added dropwise to produce lithium phosphate and a manganese-containing phosphate compound. Next, an intermediate slurry was obtained by mixing an Fe source, a Mg source, a Ti source, fructose, and citric acid into the reaction solution containing lithium phosphate and the manganese-containing phosphate compound. The Li source was Li ２ CO ３ The Mn source used was MnCO. ３ The Fe source was Fe ２ O ３ The following was used. The Mg source was MgO. The Ti source was TiO. ２ I used it.

[0095] In the above intermediate slurry, the molar ratio of manganese to the sum of the molar ratios of manganese and iron is 77%. In the above intermediate slurry, the molar ratio of magnesium to the sum of the molar ratios of manganese, iron and magnesium is 3%. In the above intermediate slurry, the ratio (P / T) of the molar ratio of phosphoric acid (P) to the sum of the molar ratios (T) of the specific metal elements (Mn, Fe, Mg, Ti) is 1.03. In the above intermediate slurry, the ratio (Li / T) of the molar ratio of lithium (Li) to the sum of the molar ratios (T) of the specific metal elements (Mn, Fe, Mg, Ti) is 1.05.

[0096] In the above intermediate slurry, the ratio of the molar ratio of magnesium (Mg) to the total molar ratio of the specific metal elements (Mn, Fe, Mg, Ti) (T) (Mg / T) is 0.03. In the above intermediate slurry, the ratio of the molar ratio of titanium (Ti) to the total molar ratio of the specific metal elements (Mn, Fe, Mg, Ti) (T) (Ti / T) is 0.02.

[0097] In the above intermediate slurry, the proportion of fructose among the components excluding water is 5.2% by mass. In the above intermediate slurry, the proportion of citric acid among the components excluding water is 10% by mass.

[0098] The Mn54 produced in this embodiment is Mn ５ (HPO) ４ ) ２ (PO ４ ) ２ (H ２ O) ４ 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 beads were ZrO ２ Beads were used. The diameter of the beads was 0.1 mm. The grinding process using a bead mill was performed at a peripheral speed of 19 m / s. The grinding time was 6 hours.

[0099] Next, the precursor slurry was dried and granulated using a spray dryer (drying outlet temperature: 100°C) to obtain precursor particles, which are aggregates. The obtained precursor particles were then processed using N ２ The granulated material of Example 1 was obtained by heating at 650°C for 6 hours under controlled conditions.

[0100] (Example 2) Granules of Example 2 were obtained in the same manner as in Example 1, except that the citric acid content in the intermediate slurry was changed, and the fructose content was changed to adjust the total amount of carbon in the citric acid and the carbon in the fructose used as a carbon source. The citric acid content was 13% by mass, as shown in Table 1. The fructose content was 4.3% by mass.

[0101] (Example 3) Granules of Example 3 were obtained in the same manner as in Example 1, except that the citric acid content in the intermediate slurry was changed, and the fructose content was changed to adjust the total amount of carbon in the citric acid and the carbon in the fructose used as a carbon source. The citric acid content was 15% by mass, as shown in Table 1. The fructose content was 3.7% by mass.

[0102] (Example 4) Granules of Example 4 were obtained in the same manner as in Example 3, except that the grinding time for obtaining the precursor slurry was changed. The grinding time was 5 hours, as shown in Table 1.

[0103] (Example 5) Granules of Example 5 were obtained in the same manner as in Example 3, except that the grinding time for obtaining the precursor slurry was changed. The grinding time was 5.5 hours, as shown in Table 1.

[0104] (Comparative Example 1) Granules of Comparative Example 1 were obtained in the same manner as in Example 1, except that the grinding time was changed. The grinding time was 8 hours, as shown in Table 1.

[0105] (Comparative Example 2) Granules of Comparative Example 2 were obtained in the same manner as in Comparative Example 1, except that the citric acid content in the intermediate slurry was changed, and the fructose content was changed to adjust the total amount of carbon in the citric acid and the carbon in the fructose used as a carbon source. The citric acid content was 11% by mass, as shown in Table 1. The fructose content was 4.9% by mass.

[0106] (Comparative Example 3) Granules for Comparative Example 3 were obtained in the same manner as in Comparative Example 1, except that the citric acid content in the intermediate slurry was changed, and the fructose content was changed to adjust the total amount of carbon in the citric acid and the carbon in the fructose used as a carbon source. The citric acid content was 12% by mass, as shown in Table 1. The fructose content was 4.6% by mass.

[0107] (Comparative Example 4) Granules of Comparative Example 4 were obtained in the same manner as in Example 2, except that the grinding time was changed. The citric acid content was 13% by mass, as shown in Table 1. The fructose content was 4.3% by mass. The grinding time was 8 hours, as shown in Table 1.

[0108] (Measurement of particle size in primary particles) The primary particle size of the granules of each example and comparative example was measured using the SAXS method. The measurement conditions for the SAXS measurement are as follows.

[0109] Measurement device: NANOPIX mini (manufactured by RIGAKU) Radiation source: Cu kα Tube voltage / tube current: 40kV-15mA Detector: D / teX Ultre250 Scanning axis: 2θ Measurement method: Continuous scan Angle range: -0.05 to 2.0° Scan speed: 0.1° / min Sampling width: 0.0008° The scattering image obtained by SAXS measurement was converted to a one-dimensional shape by performing a circular averaging from -180 to 180° to obtain a scattering curve. From the obtained scattering curve, the particle size distribution of primary particles was determined 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 taken as the particle size of the primary particles. The results are shown in Table 1.

[0110] (Pore Measurement) For each example and comparative example, the pores of the granulated material were measured using a specific surface area / pore distribution analyzer. The pore volume and pore distribution were determined by the BET / BJH method (ASTM D3663-20). From the obtained pore distribution, the percentage of the total pore volume occupied by pores with a diameter of 50 nm or more, and the percentage of the total pore volume occupied by pores with a diameter of 20 nm or less were calculated. The results are shown in Table 1.

[0111] (Evaluation of Battery Characteristics of Granulated Materials) [Evaluation of Discharge Capacity] A positive electrode mixture was coated onto one side of a 15 μm thick aluminum foil. By drying the coated positive electrode mixture, a positive electrode was prepared in which a positive electrode active material layer was formed on one side of the positive electrode current collector. As the positive electrode mixture, a slurry was used containing the granulated materials (positive electrode active material) of each example and comparative example, carbon nanotubes, carboxymethylcellulose, and acrylic ester (binder) in a solid content mass ratio of 98.2:0.07:0.43:1.3, with water as the solvent. The basis weight of the positive electrode active material layer was 20 mg / cm². ２ The density of the positive electrode active material layer was 1.8 g / cm³ in all cases. ３ That was the case.

[0112] A positive electrode half-cell was fabricated using the prepared positive electrode. A positive electrode (evaluation electrode) made by cutting the positive electrode into a 25 mm square and a negative electrode made by cutting a 200 μm thick metallic lithium foil into a 27 mm square were sandwiched together to form an electrode body cell. The electrode body cell was housed in a laminate outer casing, and a non-aqueous electrolyte was injected and the casing 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, lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 3:3:4 to a concentration of 1 M.

[0113] The fabricated positive electrode half-cell was CC charged to 4.3V at 25°C and a constant current of 0.05C, and then CC discharged to 3.0V. The discharge capacity at this time was measured. The obtained measured values ​​are shown in Table 1 as CC discharge capacity. After a 20-minute rest, the cell was CC charged to 4.3V at 25°C and a constant current of 0.05C, and then CV charged at the same voltage for 5 hours. After that, it was CC discharged to 3.0V, and then CV discharged at the same voltage for 5 hours. The discharge capacity at this time was measured. The obtained measured values ​​are shown in Table 1 as CV discharge capacity.

[0114] Based on the obtained measurements, the discharge capacity of each example and comparative example was evaluated. The results are shown in Table 1. The evaluation criteria for CC discharge capacity and CV discharge capacity are as follows.

[0115] - CC discharge capacity evaluation criteria "A (Excellent)": CC discharge capacity is 147 mAh / g or more "B (Good)": CC discharge capacity is 143 mAh / g or more but less than 147 mAh / g "C (Unacceptable)": CC discharge capacity is less than 143 mAh / g - CV discharge capacity evaluation criteria "A (Excellent)": CV discharge capacity is 155 mAh / g or more "C (Unacceptable)": CV discharge capacity is less than 155 mAh / g

[0116]

[0117] As shown in Table 1, Examples 1 to 5 have a pore volume of 0.15 cm³.３ It is less than or equal to / g. Furthermore, in Examples 1 to 5, in the pore distribution, the proportion of the volume of pores with a pore diameter of 50 nm or more relative to the total pore volume is greater than 11%, and the proportion of the volume of pores with a pore diameter of 20 nm or less relative to the total pore volume is 23% or less. In contrast, in Comparative Examples 1 to 4, the pore volume is 0.15 cm³, similar to Examples 1 to 5. ３ Although the values ​​are less than / g, the pore distribution differs. Specifically, in Comparative Examples 1 to 4, the proportion of the volume of pores with a diameter of 50 nm or more relative to the total pore volume is 11% or less, and the proportion of the volume of pores with a diameter of 20 nm or less relative to the total pore volume is greater than 23%. In all of Examples 1 to 5, the CC discharge capacity and CV discharge capacity are higher than those in Comparative Examples 1 to 4. From these results, it can be seen that in Examples 1 to 5, it is possible to suppress the decrease in discharge capacity per unit mass while reducing the pore volume.

[0118] Examples 2 and 3 have a pore volume of 0.12 cm³. ３ It is less than / g. That is, having the above pore distribution results in a smaller pore volume of 0.12 cm³. ３ It can be seen that even at concentrations below / g, it is possible to obtain lithium-ion secondary batteries with increased discharge capacity per unit mass.

[0119] Comparing Example 2 with Comparative Example 4, it can be seen that the difference in grinding time affects the particle size of the primary particles. Specifically, the grinding time in Example 2 is shorter than that in Comparative Example 4. Furthermore, the particle size of the primary particles in Example 2 is larger than that of Comparative Example 4. Thus, in Example 2, where the particle size of the primary particles is larger, the pore volume and pore distribution are within the specified range, unlike in Comparative Example 4.

[0120] Comparing Examples 3, 4, and 5, the grinding time in Examples 4 and 5 is shorter than that in Example 3. In Examples 4 and 5, the proportion of the volume of pores with a diameter of 50 nm or more relative to the total pore volume is larger than in Example 3. Furthermore, in Examples 4 and 5, the proportion of the volume of pores with a diameter of 20 nm or less relative to the total pore volume is smaller than in Example 3. The CC discharge capacity and CV discharge capacity in Examples 4 and 5 are higher than those in Example 3. From these results, it can be seen that increasing the proportion of the volume of pores with a diameter of 50 nm or more relative to the total pore volume, and decreasing the proportion of the volume of pores with a diameter of 20 nm or less relative to the total pore volume, contributes to increasing the discharge capacity.

[0121] 10... Granules 11... Core 11a... Primary particles 11b... Pores 12... Carbon coating

Claims

1. General formula Li ａ Mn ｘ Fe ｙ Me ｚ PO ４ A positive electrode material for a lithium-ion secondary battery comprising granulated particles 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; the granulated particles have a total pore volume of pores having a pore diameter of 300 nm or less measured by the BET / BJH method of 0.15 cm ３ / g or less, and in the pore distribution, the ratio of the volume of pores having a pore diameter of 50 nm or more to the total pore volume is more than 11%, and the ratio of the volume of pores having a pore diameter of 20 nm or less to the total pore volume is 23% or less. A positive electrode material for a lithium-ion secondary battery characterized by this.

2. The total pore volume is 0.13 cm³. ３ A positive electrode material for a lithium-ion secondary battery according to claim 1, wherein the material is less than or equal to / g.

3. The positive electrode material for a lithium-ion secondary battery according to claim 1 or 2, wherein, in the pore distribution, the proportion of the volume of pores having a pore diameter of 50 nm or more to the total pore volume is 12% or more.

4. The positive electrode material for a lithium-ion secondary battery according to any one of claims 1 to 3, wherein, in the pore distribution, the proportion of the volume of pores having a pore diameter of 20 nm or less to the total pore volume is 20% or less.

5. A positive electrode material for a lithium-ion secondary battery according to any one of claims 1 to 4, wherein the particle size of the primary particles constituting the granules is 35 nm or more and 100 nm or less.

6. A method for producing a positive electrode material for a lithium-ion secondary battery according to any one of claims 1 to 5, comprising: a slurry preparation step of obtaining a slurry from components for forming the olivine-type lithium iron manganese phosphate; a granulation step of obtaining precursor particles by spray-drying the slurry; and a calcination step of obtaining the olivine-type lithium iron manganese phosphate by calcining the precursor particles, wherein the slurry preparation step includes a pulverization step of pulverizing the components for forming the olivine-type lithium iron manganese phosphate in the presence of a carboxylic acid, the slurry contains the carboxylic acid, and the content of the carboxylic acid in the slurry, excluding water, is 10% by mass or more.

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