Production method of cobalt lithium phosphate

Abstract

To provide a method which can obtain cobalt lithium phosphate which is a single-phase in terms of x-ray diffractometry, with high yield in an industrially advantageous way.SOLUTION: A production method of cobalt lithium phosphate includes: a first step of adding carboxylic acid, cobalt hydroxide, and, if necessary, a metal (M) hydroxide to an aqueous solvent and then adding lithium carbonate to prepare aqueous slurry (1); a second step of wet milling-treating the aqueous slurry (1) with a media mill to obtain slurry (2) containing a milling treated product; a third step of adding phosphoric acid to the slurry (2) containing the milling treated product to obtain mixed raw material slurry (3); a fourth step of spray drying-treating the mixed raw material slurry (3) to obtain a reaction precursor; and a fifth step of firing the reaction precursor.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing lithium cobalt phosphate, which is useful as a positive electrode material for lithium secondary batteries, all-solid-state batteries, etc. [Background technology]

[0002] Lithium-ion batteries are used in portable devices and laptop computers. They are generally considered to have excellent capacity and energy density. They are also expected to be used in hybrid and electric vehicles. When used in automotive applications, lithium-ion secondary batteries are subject to harsher conditions in terms of temperature and charge / discharge current than conventional batteries.

[0003] Olivine-type phosphates, such as lithium cobalt phosphate (LiCoPO4) or lithium cobalt phosphate in which part of the cobalt is substituted with another metal, do not release oxygen even at high temperatures due to their strong structure, making them highly safe. Therefore, they have attracted attention as positive electrode active materials for lithium secondary batteries for automobiles, all-solid-state batteries, and the like (Patent Documents 1 to 3).

[0004] The present inventors have previously proposed a method for producing lithium cobalt phosphate, which comprises: a first step of adding an organic acid and cobalt hydroxide to an aqueous solvent, and then adding phosphoric acid and lithium hydroxide to prepare an aqueous raw material slurry (1); a second step of wet-pulverizing the aqueous raw material slurry (1) using a media mill to obtain a slurry (2) containing a pulverized raw material; a third step of spray-drying the slurry (2) containing the pulverized raw material to obtain a reaction precursor; and a fourth step of calcining the reaction precursor (Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-134724 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-88266 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-170464 [Patent Document 4] International Publication No. 2020 / 012970 Summary of the Invention [Problem to be solved by the invention]

[0006] The method of Patent Document 4 can obtain lithium cobalt phosphate that is single-phase in terms of X-ray diffraction, but when the slurry containing the pulverized raw material is dried with a spray dryer, there is a problem of adhesion to the spray dryer, so it is necessary to use lithium hydroxide as a lithium source, which is expensive and difficult to handle. Therefore, there is a demand for the development of a method for producing lithium cobalt phosphate in a more industrially advantageous manner.

[0007] Therefore, an object of the present invention is to provide an industrially advantageous method by which lithium cobalt phosphate of a single phase as determined by X-ray diffraction can be obtained in high yield. [Means for solving the problem]

[0008] In view of the above circumstances, the present inventors have conducted extensive research and have found that, in a method for producing lithium cobalt phosphate, (i) an aqueous slurry obtained by adding a carboxylic acid, cobalt hydroxide, and optionally a hydroxide of a metal (M) to an aqueous solvent, and then adding inexpensive and easy-to-handle lithium carbonate as a lithium source, can be wet-pulverized using a media mill; (ii) a raw material mixed slurry obtained by wet-pulverizing the aqueous slurry and adding phosphoric acid to the resulting slurry contains a pulverized product, in which the raw materials are uniformly dispersed and is easy to handle; and (iii) lithium cobalt phosphate that is single-phase as measured by X-ray diffraction can be obtained in high yield by spray-drying the raw material mixed slurry and calcining the resulting reaction precursor, which has led to the completion of the present invention.

[0009] That is, the present invention provides a compound represented by the following general formula (1): Li x Co 1-y M y PO4(1) (In the formula, 0.8≦x≦1.2, 0≦y≦0.7, and M represents one or more metal elements selected from Ni, Mg, Zn, Cu, Fe, Cr, Mn, Al, Na, K, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Mo, W, V, Bi, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) A method for producing lithium cobalt phosphate represented by the formula: a first step of adding a carboxylic acid, cobalt hydroxide, and optionally a hydroxide of a metal (M) to an aqueous solvent, and then adding lithium carbonate to prepare an aqueous slurry (1); a second step of wet-pulverizing the aqueous slurry (1) using a media mill to obtain a slurry (2) containing the pulverized product; a third step of adding phosphoric acid to the slurry (2) containing the pulverized material to obtain a raw material mixed slurry (3); a fourth step of spray-drying the raw material mixed slurry (3) to obtain a reaction precursor; a fifth step of calcining the reaction precursor; The present invention relates to a method for producing lithium cobalt phosphate, characterized by comprising the steps of: [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an industrially advantageous method by which lithium cobalt phosphate that is single-phase in terms of X-ray diffraction can be obtained in high yield. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an X-ray diffraction pattern of the reaction precursor obtained in Example 1. [Figure 2] FIG. 1 is an X-ray diffraction pattern of lithium nickel cobalt phosphate obtained in Example 1. [Figure 3] FIG. 2 is an X-ray diffraction pattern of the solid content obtained in Comparative Example 1. [Figure 4]1 is a scanning electron microscope (SEM) photograph of lithium nickel cobalt phosphate obtained in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described below based on preferred embodiments. The method for producing lithium cobalt phosphate of the present invention is carried out by reacting lithium cobalt phosphate with a compound represented by the following general formula (1): Li x Co 1-y M y PO4(1) (In the formula, 0.8≦x≦1.2, 0≦y≦0.7, and M represents one or more metal elements selected from Ni, Mg, Zn, Cu, Fe, Cr, Mn, Al, Na, K, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Mo, W, V, Bi, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) A method for producing lithium cobalt phosphate represented by the formula: a first step of adding a carboxylic acid, cobalt hydroxide, and optionally a hydroxide of a metal (M) to an aqueous solvent, and then adding lithium carbonate to prepare an aqueous slurry (1); a second step of wet-pulverizing the aqueous slurry (1) using a media mill to obtain a slurry (2) containing the pulverized product; a third step of adding phosphoric acid to the slurry (2) containing the pulverized material to obtain a raw material mixed slurry (3); a fourth step of spray-drying the raw material mixed slurry (3) to obtain a reaction precursor; a fifth step of calcining the reaction precursor; The present invention relates to a method for producing lithium cobalt phosphate, characterized by comprising the steps of:

[0013] The lithium cobalt phosphate obtained by the method for producing lithium cobalt phosphate of the present invention is a lithium cobalt phosphate having an olivine structure, and is represented by the following general formula (1): Li x Co 1-y M y PO4(1) (In the formula, 0.8 ≦ x ≦ 1.2, 0 < y ≦ 0.7, and M represents one or more metal elements selected from Ni, Mg, Zn, Cu, Fe, Cr, Mn, Al, Na, K, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Mo, W, V, Bi, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) It is cobalt lithium phosphate represented by the formula.

[0014] In the general formula (1), x is 0.8 or more and 1.2 or less, preferably 0.9 or more and 1.1 or less. y is 0 or more and 0.7 or less, preferably 0.1 or more and 0.6 or less, and M is a metal element that is contained as necessary for the purpose of improving battery performance.

[0015] M in the general formula (1) represents one or more metal elements selected from Ni, Mg, Zn, Cu, Fe, Cr, Mn, Al, Na, K, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Mo, W, V, Bi, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho. From the viewpoint of improving battery performance, M is particularly preferably Ni.

[0016] The first step according to the method for producing cobalt lithium phosphate of the present invention is a step of adding a carboxylic acid, cobalt hydroxide, and, if necessary, a hydroxide of metal (M) to an aqueous solvent, and then adding lithium carbonate to prepare an aqueous slurry (1).

[0017] When cobalt hydroxide, lithium carbonate, and optionally a hydroxide of the metal (M) are simultaneously added to an aqueous solvent, the mixture becomes cake-like, making it impossible to stir, etc. In the first step, a carboxylic acid, cobalt hydroxide, and optionally a hydroxide of the metal (M) are added to an aqueous solvent to generate a carboxylate of cobalt and a carboxylate of the metal (M) that is added as needed, and lithium carbonate is then added thereto as a lithium source to prepare a stirrable aqueous slurry (1) containing lithium carbonate, a carboxylate of cobalt, and a carboxylate of the metal (M) that is added as needed.

[0018] As the carboxylic acid in the first step, oxalic acid is preferred because it has excellent reactivity with cobalt hydroxide and the hydroxide of the metal (M) that is added as needed.

[0019] The amount of carboxylic acid added is an amount such that the ratio of the molar amount of carbon atoms in the carboxylic acid to the total molar amount of cobalt atoms in the cobalt hydroxide and M atoms in the hydroxide of the metal (M) added as needed (C / (Co+M)) is 1.5 or more. If the molar amount ratio (C / (Co+M)) is less than 1.5, the slurry tends to become cake-like and unstirable. In order to stabilize the slurry viscosity, the amount of carboxylic acid added is preferably an amount such that the molar amount ratio (C / (Co+M)) is 1.5 to 2.5, and particularly preferably an amount such that the molar amount ratio is 1.7 to 2.3.

[0020] The total amount of cobalt hydroxide and optionally added hydroxide of metal (M) added to the aqueous solvent is 5 to 30 parts by mass, preferably 7 to 25 parts by mass, per 100 parts by mass of the aqueous solvent. When the total amount of cobalt hydroxide and optionally added hydroxide of metal (M) added to the aqueous solvent is within the above range, the viscosity of the slurry is stable.

[0021] After adding the carboxylic acid, cobalt hydroxide, and optionally the hydroxide of the metal (M) to the aqueous solvent, the mixture is stirred at 15 to 90°C, preferably 20 to 80°C, for 10 minutes or more, preferably 20 minutes to 2 hours, in order to sufficiently react the carboxylic acid with the cobalt hydroxide and the hydroxide of the metal (M) added as needed. Then, by reacting the carboxylic acid with the cobalt hydroxide and the hydroxide of the metal (M) added as needed, a slurry (A) containing the carboxylate of cobalt and the carboxylate of the metal (M) added as needed can be obtained.

[0022] In preparing the slurry (A) containing the cobalt carboxylate and the optionally added metal (M) carboxylate, the order of addition of the carboxylic acid, cobalt hydroxide, and the optionally added hydroxide of the metal (M) is not particularly limited, but it is preferable to add the carboxylic acid to the aqueous solvent, and then add the cobalt hydroxide and the optionally added hydroxide of the metal (M) separately, in order to stabilize the viscosity of the slurry. Note that the order of addition of the cobalt hydroxide and the optionally added hydroxide of the metal (M) is not critical, and they may be added simultaneously.

[0023] Next, in the first step, lithium carbonate as a lithium source is added to the slurry (A) containing the carboxylate of cobalt and the carboxylate of the metal (M) that is added as needed.

[0024] Lithium carbonate may be added as a powder as it is, but it is preferable to add it as a suspension dispersed in water to a slurry (A) containing a carboxylate of cobalt and a carboxylate of a metal (M) to be added as needed, from the viewpoint of improving the dispersibility of the solid content in the slurry.

[0025] The amount of lithium carbonate added is an amount such that the ratio of the molar amount of lithium atoms in the lithium carbonate to the total molar amount of cobalt atoms in the cobalt hydroxide and M atoms in the hydroxide of the metal (M) added as needed (Li / (Co+M)) is preferably 1.2 to 0.8, particularly preferably 1.1 to 0.9. When the ratio of the molar amount of lithium atoms in the lithium carbonate to the total molar amount of cobalt atoms in the cobalt hydroxide and M atoms in the hydroxide of the metal (M) added as needed (Li / (Co+M)) is within the above range, lithium cobalt phosphate that is single-phase in terms of X-ray diffraction can be easily obtained.

[0026] The temperature at which lithium carbonate is added is not particularly limited, and in most cases it is 15 to 90°C, preferably 20 to 80°C.

[0027] The lithium carbonate, cobalt hydroxide, and hydroxide of the metal (M) added as needed may have any manufacturing history, but in order to produce high-purity lithium cobalt phosphate, it is preferable that the impurity content be as low as possible.

[0028] The second step in the method for producing lithium cobalt phosphate of the present invention is a step of wet-pulverizing the aqueous slurry (1) obtained in the first step using a media mill to obtain a slurry (2) containing the pulverized product.

[0029] The aqueous slurry (1) obtained in the first step contains, as solid components, lithium carbonate, a cobalt carboxylate, and a metal (M) carboxylate that is added as needed. By making the cobalt carboxylate and the metal (M) carboxylate that is added as needed into finer particles, a reaction precursor with increased reactivity can be obtained in the fourth step described below.

[0030] In the second step, the solids concentration of the aqueous slurry (1) to be wet-pulverized by the media mill is preferably 10 to 40% by mass, and more preferably 15 to 30% by mass, from the viewpoint of good operability and efficient wet-pulverization. Therefore, after the first step, it is desirable to adjust the solids concentration of the aqueous slurry (1) as necessary so that the concentration falls within the above range, and then wet-pulverize the aqueous slurry (1) in the second step.

[0031] Examples of media mills include bead mills, ball mills, paint shakers, attritors, sand mills, etc., with bead mills being preferred. When using a bead mill, the operating conditions and the type and size of the beads may be appropriately selected depending on the size of the apparatus and the processing amount.

[0032] A dispersant may be added to the slurry (A) or aqueous slurry (1) containing the carboxylate of cobalt and the carboxylate of the metal (M) to be added as needed.

[0033] To more efficiently perform wet grinding using a media mill, the dispersant is appropriately selected depending on the type and properties of the slurry. Examples of dispersants include various surfactants and ammonium polycarboxylates. The concentration of the dispersant in the slurry is preferably 0.01 to 10% by mass, particularly preferably 0.1 to 5% by mass, in order to obtain a sufficient dispersion effect. In the second step, it is preferable to carry out wet grinding using a media mill until the average particle size of the solid content reaches preferably 1.5 μm or less, particularly preferably 0.1 to 1.4 μm, as measured by a laser scattering / diffraction method, in order to obtain a reaction precursor with excellent reactivity. The average particle size is determined by measuring the volume frequency particle size distribution using the laser diffraction scattering method. 50 ) refers to the particle size.

[0034] The third step in the method for producing lithium cobalt phosphate of the present invention is a step of adding phosphoric acid to the slurry (2) containing the pulverized product obtained in the second step.

[0035] In the third step, phosphoric acid is added to the slurry (2) containing the pulverized material, whereby lithium carbonate reacts with phosphoric acid to form lithium phosphate.

[0036] In this production method, the reason why phosphoric acid is added in the third step is that the viscosity of the slurry becomes more stable than when phosphoric acid is added in the second step.

[0037] The amount of phosphoric acid added to the slurry (2) containing the pulverized product is such that the ratio ((Co+M) / P) of the total molar amount of cobalt atoms and optionally added M atoms in the slurry (2) containing the pulverized product to the molar amount of phosphorus atoms in the phosphoric acid is preferably 0.7 to 1.3, particularly preferably 0.8 to 1.2. When the ratio ((Co+M) / P) of the total molar amount of cobalt atoms and optionally added M atoms in the slurry (2) containing the pulverized product to the molar amount of phosphorus atoms in the phosphoric acid is within the above range, lithium cobalt phosphate that is single-phase in terms of X-ray diffraction is easily obtained. The phosphoric acid may be added all at once or in multiple portions.

[0038] The temperature at which phosphoric acid is added to the slurry (2) containing the pulverized product is not particularly limited, but is preferably 15 to 90°C, and more preferably 20 to 80°C. In order to sufficiently react phosphoric acid with lithium carbonate, the mixture is stirred for 10 minutes or more, and preferably 20 minutes to 2 hours.

[0039] The fourth step in the method for producing lithium cobalt phosphate of the present invention is a step of spray-drying the raw material mixture slurry (3) obtained in the third step to obtain a reaction precursor.

[0040] Although methods other than spray drying are known as methods for drying a slurry, the method for producing lithium cobalt phosphate of the present invention employs spray drying based on the finding that it is advantageous to select this drying method.

[0041] In detail, when drying is performed by spray drying, granulated material containing each raw material component uniformly and in which raw material particles are densely packed is obtained. Therefore, in the method for producing lithium cobalt phosphate of the present invention, this granulated material is used as a reaction precursor, and by firing the reaction precursor in the fifth step described below, lithium cobalt phosphate that is single-phase in terms of X-ray diffraction can be obtained.

[0042] In the fourth step, spray drying involves atomizing the slurry by a predetermined means and drying the resulting fine droplets to obtain a reaction precursor. The slurry can be atomized, for example, by using a rotating disk or a pressure nozzle. Either method can be used in the fourth step.

[0043] In the spray drying process in the fourth step, the relationship between the size of the atomized slurry droplets and the size of the pulverized solids contained therein affects stable drying and the properties of the resulting dried powder. Specifically, if the average particle size of the pulverized solids is too small relative to the size of the droplets, the droplets become unstable, making it difficult to successfully dry. From this perspective, the size of the atomized droplets is preferably 1 to 50 μm, and particularly preferably 10 to 40 μm. The amount of slurry supplied to the spray drying apparatus is preferably determined taking this into consideration.

[0044] The reactive precursor obtained by the spray drying treatment in the fourth step is subjected to calcination in the fifth step, and the powder properties of the obtained lithium cobalt phosphate, such as the average particle size, largely inherit the properties of the reactive precursor. Therefore, in the spray drying treatment in the fourth step, from the viewpoint of controlling the particle size of the target lithium cobalt phosphate, it is preferable to perform the spray drying treatment so that the size of the secondary particles of the reactive precursor is 1 to 50 μm, and it is particularly preferable to perform the spray drying treatment so that the particle size is 10 to 40 μm, as determined by observation with a scanning electron microscope (SEM).

[0045] In the fourth step, it is preferable to adjust the drying temperature in the spray dryer so that the hot air inlet temperature is 150 to 350°C, preferably 200 to 330°C, and the hot air outlet temperature is 80 to 200°C, preferably 100 to 170°C, since this prevents moisture absorption by the powder and makes it easier to recover the powder.

[0046] The reaction precursor obtained in the fourth step preferably contains at least a lithium phosphate, a cobalt carboxylate, and an optionally added metal (M) carboxylate. The lithium phosphate, cobalt carboxylate, and optionally added metal (M) carboxylate in the reaction precursor can be identified by X-ray diffraction analysis of the reaction precursor. The lithium phosphate contained in the reaction precursor is preferably Li(H2PO4). The cobalt carboxylate varies depending on the type of carboxylic acid used, but examples of the cobalt carboxylate include cobalt oxalate (Co(C2O4)(H2O)2) when oxalic acid is used. The optionally added metal (M) carboxylate varies depending on the type of carboxylic acid used, but examples of the metal (M) oxalate include M(C2O4)(H2O)2).

[0047] In this manner, by carrying out the fourth step, a reaction precursor to be subjected to calcination in the fifth step can be obtained.

[0048] The fifth step in the method for producing lithium cobalt phosphate of the present invention is a step of calcining the reaction precursor obtained in the fourth step to obtain lithium cobalt phosphate that is single-phase in terms of X-ray diffraction.

[0049] The firing temperature in the fifth step is 380 to 1100° C., preferably 400 to 1000° C., and particularly preferably 600 to 700° C. If the firing temperature is below the above range, the firing time required to reach a single phase as determined by X-ray diffraction becomes long, which is industrially disadvantageous, whereas if the firing temperature exceeds the above range, the lithium cobalt phosphate becomes a hard sintered body, which is undesirable.

[0050] The firing atmosphere in the fifth step is air, an inert gas atmosphere, or a reducing gas atmosphere. When a metal (M) that needs to be prevented from oxidation is contained during firing in the fifth step, the firing atmosphere is preferably an inert gas atmosphere or a reducing gas atmosphere.

[0051] The calcination time in the fifth step varies depending on the calcination temperature, but is preferably 0.5 hours or more, and particularly preferably 2 to 20 hours. In the fifth step, calcination is carried out at the calcination temperature in the above-mentioned range for 0.5 hours or more, preferably 2 to 20 hours, to obtain lithium cobalt phosphate that is single-phase in terms of X-ray diffraction.

[0052] In the fifth step, the lithium cobalt phosphate obtained by calcination may be calcined multiple times as necessary. When calcination is performed multiple times, the calcined product may be crushed or disintegrated and then calcined.

[0053] The lithium cobalt phosphate obtained in the fifth step may be crushed or pulverized, and further classified, if necessary.

[0054] The lithium cobalt phosphate thus obtained by the production method of the present invention is a single-phase lithium cobalt phosphate in terms of X-ray diffraction, and in addition, has an average particle size determined by observation with a scanning electron microscope (SEM) of preferably 5 μm or less, particularly preferably 0.05 to 3 μm, and particularly preferably 0.1 to 1 μm, and a BET specific surface area of ​​preferably 0.1 m 2 / g or more, particularly preferably 0.3 to 15m 2 / g, particularly preferably 1 to 15m 2 / g.

[0055] Furthermore, in the method for producing lithium cobalt phosphate of the present invention, the lithium cobalt phosphate obtained in the fifth step can be subjected to the following step 6(A) or step 6(B), if necessary.

[0056] Step 6(A) is a step of further heat-treating the lithium cobalt phosphate obtained in Step 5 to adjust the amount of carbon contained in the lithium cobalt phosphate. Specifically, in Step 6(A), the lithium cobalt phosphate obtained in Step 5 is heat-treated to oxidize the carbon in the lithium cobalt phosphate. The heat treatment in Step 6(A) is preferably carried out in an oxygen-containing atmosphere. In Step 6(A), the oxygen concentration of the atmosphere is preferably 5% by volume or more, preferably 10 to 30% by volume, from the viewpoint of highly efficient oxidation of carbon. The temperature of the heat treatment in Step 6(A) is 200 to 500°C, preferably 250 to 400°C. By setting the heat treatment temperature in Step 6(A) within the above range, the remaining carbon can be highly efficiently oxidized. The heat treatment time in Step 6(A) is not critical in the method for producing lithium cobalt phosphate of the present invention. The longer the heat treatment time in Step 6(A), the lower the carbon content of the lithium cobalt phosphate. In Step 6(A), it is preferable to perform the heat treatment under appropriate conditions set in advance so as to achieve a desired carbon content.

[0057] Step 6(B) is a step of mixing the lithium cobalt phosphate obtained in Step 5 with a conductive carbon material source that precipitates carbon upon thermal decomposition (hereinafter also simply referred to as "conductive carbon material source") to obtain a mixture of lithium cobalt phosphate and the conductive carbon material source, and then heat-treating the mixture to thermally decompose the conductive carbon material source to obtain a lithium cobalt phosphate carbon composite.

[0058] The conductive carbon material source is one that undergoes thermal decomposition to precipitate carbon by at least heat treatment in step 6(B). The conductive carbon material source is a component that imparts conductivity to lithium cobalt phosphate, and by forming a composite of conductive carbon and lithium cobalt phosphate, lithium secondary batteries using the lithium cobalt phosphate carbon composite as a positive electrode active material are expected to have improved discharge capacity and cycle characteristics (see, for example, JP-A 2014-514712 and JP-A 2008-117749).

[0059] Examples of conductive carbon material sources include coal tar pitch ranging from soft pitch to hard pitch; petroleum heavy oils such as coal-based heavy oils such as carbonized liquefied oil, atmospheric residual oil, direct current heavy oil such as vacuum residual oil, crude oil, and cracked heavy oils such as ethylene tar produced as a by-product during thermal decomposition of naphtha; aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene; polyphenylenes such as phenazine, biphenyl, and terphenyl; polyvinyl chloride; water-soluble polymers such as polyvinyl alcohol, polyvinyl butyral, and polyethylene glycol, and insolubilized products thereof; and nitrogen-containing polyacrylonitriles. Examples of suitable materials include nitriles; organic polymers such as polypyrrole; sulfur-containing organic polymers such as polythiophene and polystyrene; natural polymers such as sugars such as glucose, fructose, lactose, maltose, and sucrose; thermoplastic resins such as polyphenylene sulfide and polyphenylene oxide, and thermosetting resins such as phenol-formaldehyde resins and imide resins. Of these, sugars are preferred from the viewpoints of being commercially available at low cost and improving the discharge capacity and cycle characteristics of a lithium secondary battery that uses the finally obtained lithium cobalt phosphate carbon composite as a positive electrode active material.

[0060] The conductive carbon material source is preferably added in such a proportion that the carbon atoms in the conductive carbon material source account for 0.1 to 20.0 mass %, and preferably 0.5 to 15.0 mass %, relative to the lithium cobalt phosphate, from the viewpoint of improving the discharge capacity and cycle characteristics of a lithium secondary battery using the lithium cobalt phosphate carbon composite as a positive electrode active material.

[0061] In the sixth step (B), the lithium cobalt phosphate and the conductive carbon material source can be mixed by a dry method or a wet method.

[0062] In step 6(B), the dry mixing method is preferably carried out by mechanical means, as this results in a uniform mixture. The equipment used for dry mixing is not particularly limited as long as it can produce a uniform mixture, and examples include high-speed mixers, super mixers, turbosphere mixers, Eirich mixers, Henschel mixers, Nauta mixers, ribbon blenders, V-type mixers, conical blenders, jet mills, cosmomizers, paint shakers, bead mills, and ball mills. At the laboratory level, a household mixer is sufficient.

[0063] In addition, examples of a method for performing a wet mixing treatment in the 6(B) step include a method in which lithium cobalt phosphate and a conductive carbon material source are added to an aqueous solvent so that the solid content is 10 to 80 mass %, preferably 20 to 70 mass %, and then mixed by a mechanical means to prepare a slurry, and then the slurry is left to stand and dried, or the slurry is spray-dried and dried, thereby obtaining a mixture of lithium cobalt phosphate and a conductive carbon material source.

[0064] The apparatus used for wet mixing is not particularly limited as long as it can produce a uniform slurry, and examples thereof include stirrers, agitators with stirring blades, three-roll mills, ball mills, disper mills, homogenizers, vibration mills, sand grind mills, attritors, and powerful agitators. The wet mixing process is not limited to the mixing processes using mechanical means exemplified above. During wet mixing, a surfactant may be added to the slurry before the mixing process.

[0065] Next, the mixture of lithium cobalt phosphate and the conductive carbon material source prepared as described above is heat-treated. The heat treatment must be carried out at a temperature at which the conductive carbon material source is thermally decomposed to precipitate carbon. The heat treatment temperature is 180 to 900°C, preferably 210 to 800°C. By maintaining the heat treatment temperature within the above range, it is possible to uniformly coat the particle surfaces with carbon while suppressing aggregation. The heat treatment time is 0.2 hours or more, preferably 0.5 to 5 hours. The heat treatment is preferably carried out in an inert gas atmosphere, which can suppress carbon oxidation. Furthermore, in this heat treatment, it is preferable to first heat the conductive carbon material source used to a temperature above the melting point thereof to melt the conductive carbon material source, and then heat-treat within the above range to precipitate carbon from the conductive carbon material source, which can uniformly coat the particle surfaces with carbon.

[0066] The lithium cobalt phosphate obtained by the production method of the present invention is suitably used as a cathode material for lithium secondary batteries, all-solid-state batteries, etc. In particular, by using lithium cobalt phosphate containing Ni as the metal (M) as a cathode material, battery performance can be further improved.

[0067] The present invention also includes the following embodiments. [1] The following general formula (1): Li x Co 1-y M y PO4(1) (In the formula, 0.8≦x≦1.2, 0≦y≦0.7, and M represents one or more metal elements selected from Ni, Mg, Zn, Cu, Fe, Cr, Mn, Al, Na, K, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Mo, W, V, Bi, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) A method for producing lithium cobalt phosphate represented by the formula: a first step of adding a carboxylic acid, cobalt hydroxide, and optionally a hydroxide of a metal (M) to an aqueous solvent, and then adding lithium carbonate to prepare an aqueous slurry (1); a second step of wet-pulverizing the aqueous slurry (1) using a media mill to obtain a slurry (2) containing the pulverized product; a third step of adding phosphoric acid to the slurry (2) containing the pulverized material to obtain a raw material mixed slurry (3); a fourth step of spray-drying the raw material mixed slurry (3) to obtain a reaction precursor; a fifth step of calcining the reaction precursor; A method for producing lithium cobalt phosphate, comprising: [2] The method for producing lithium cobalt phosphate according to [1], wherein in the general formula (1), 0.1≦y≦0.6, and the hydroxide of the metal (M) is nickel hydroxide. [3] The method for producing lithium cobalt phosphate according to [1] or [2], wherein the average particle size of the solid content in the slurry (2) containing the pulverized product is 1.5 μm or less. [4] The method for producing lithium cobalt phosphate according to any one of [1] to [3], wherein the carboxylic acid is oxalic acid. [5] The method for producing lithium cobalt phosphate according to any one of [1] to [4], wherein the reaction precursor contains a phosphate of lithium, a carboxylate of cobalt, and a carboxylate of a metal (M) that is added as needed. [6] The method for producing lithium cobalt phosphate according to any one of [1] to [5], wherein the firing temperature is 380 to 1100°C. [Example]

[0068] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Example 1 <1st process> 1773.8g (14.1 mol) of oxalic acid dihydrate was added to 12L of pure water at room temperature (25°C), and the mixture was stirred for 30 minutes using a three-one motor stirrer. 135.7g of dispersant (ammonium polycarboxylate) was then added. Next, 800.0g of cobalt hydroxide (8.4 mol as Co atoms) and 521.8g of nickel hydroxide (5.6 mol as Ni atoms) were added at room temperature (25°C), and the mixture was stirred for 30 minutes to obtain slurry (A) containing cobalt and nickel in a Co:Ni molar ratio of 6:4. Next, 519.8 g (7.0 mol) of lithium carbonate was added to 2 L of pure water and stirred for 30 minutes to obtain a lithium carbonate-containing suspension. Next, the entire lithium carbonate-containing suspension was added to the previously obtained slurry (A) over 30 minutes at room temperature (25°C) to obtain an aqueous slurry (1). <Second process> Next, this aqueous slurry (1) was fed while being stirred into a media stirring type bead mill charged with zirconia beads having a diameter of 0.5 mm, and mixed for 3 hours to carry out wet pulverization, thereby obtaining a slurry (2) containing a pulverized product. The average particle size of the solid content in the slurry (2) containing the pulverized product was 0.4 μm as determined by laser scattering and diffraction. The pH of the slurry (2) containing the pulverized product was 10.0. <3rd process> Next, 1616.0 g (14.0 mol) of 85% by mass phosphoric acid was added to the slurry (2) containing the pulverized product at room temperature (25°C) and stirred for 30 minutes to obtain a raw material mixture slurry (3). The pH of the raw material mixture slurry (3) was 4.0. <4th process> Next, the raw material mixture slurry (3) was fed into a spray dryer with the hot air inlet temperature set to 220°C at a feed rate of 2.4 L / h (to produce atomized droplets of 18 μm in size) to obtain a reaction precursor. There was little adhesion inside the spray dryer, and the recovery rate was 97%. X-ray diffraction analysis of the obtained reaction precursor confirmed that it was a mixture of Co(C2O4)(H2O)2, Ni(C2O4)(H2O)2, and Li(H2PO4). The X-ray diffraction pattern of the reaction precursor is shown in Figure 1. The secondary particle diameter of the reaction precursor, as determined by scanning electron microscope (SEM) observation, was 18 μm. <5th process> The resulting reaction precursor was then fired at 650°C for 4 hours in an air atmosphere to obtain a fired product. The obtained fired product was subjected to X-ray diffraction analysis, and the detected diffraction peak was that of lithium nickel cobalt phosphate (LiCo 0.5 Ni 0.5 PO4), and no other diffraction peaks were detected. In addition, ICP emission spectroscopy revealed that the fired product contained cobalt and nickel in a molar ratio of Co:Ni of 6:4. Therefore, the fired product was a single-phase lithium nickel cobalt phosphate (LiCo 0.6 Ni 0.4 PO4). The X-ray diffraction pattern of the fired product is shown in Figure 2.

[0069] Example 2 A fired product was obtained in the same manner as in Example 1, except that the fifth step was fired at 600°C for 4 hours in an N2 atmosphere. The obtained fired product was subjected to X-ray diffraction analysis, and the detected diffraction peak was that of lithium nickel cobalt phosphate (LiCo 0.5 Ni 0.5 PO4), and no other diffraction peaks were detected. In addition, ICP emission spectroscopy revealed that the fired product contained cobalt and nickel in a molar ratio of Co:Ni of 6:4. Therefore, the fired product was a single-phase lithium nickel cobalt phosphate (LiCo 0.6 Ni 0.4 PO4).

[0070] Example 3 A fired product was obtained in the same manner as in Example 1, except that the fifth step was fired at 620°C for 4 hours in an air atmosphere. The obtained fired product was subjected to X-ray diffraction analysis, and the detected diffraction peak was that of lithium nickel cobalt phosphate (LiCo 0.5 Ni0.5 PO4), and no other diffraction peaks were detected. In addition, ICP emission spectroscopy revealed that the fired product contained cobalt and nickel in a molar ratio of Co:Ni of 6:4. Therefore, the fired product was a single-phase lithium nickel cobalt phosphate (LiCo 0.6 Ni 0.4 PO4).

[0071] (Comparative Example 1) 800.0 g of cobalt hydroxide and 521.8 g of nickel hydroxide were added to 12 L of pure water at room temperature (25°C) and stirred for 30 minutes using a three-one motor stirrer. 135.7 g of dispersant (ammonium polycarboxylate) was then added. Next, 1616.0 g of 85% by weight phosphoric acid was added. The mixture turned into a purple cake, which became unstirrable, and further processing was not possible. X-ray diffraction analysis of the resulting solid revealed it to be a mixture of Co3(PO4)2·8H2O and Co(H2PO4)2(H3PO4)2. The X-ray diffraction pattern of the solid is shown in Figure 3.

[0072] (Comparative Example 2) <1st process> 1773.8 g of oxalic acid dihydrate was added to 12 L of pure water at room temperature (25°C), and the mixture was stirred for 30 minutes using a three-one motor stirrer. 135.7 g of dispersant (ammonium polycarboxylate) was then added. Next, 800.0 g of cobalt hydroxide and 521.8 g of nickel hydroxide were added at room temperature (25°C), and the mixture was stirred for 30 minutes to obtain slurry (A). Next, 519.8 g of lithium carbonate was added to 2 L of pure water and stirred for 30 minutes to obtain a lithium carbonate-containing suspension. Next, the entire lithium carbonate-containing suspension and 1616.0 g of 85 mass % phosphoric acid were added to the previously obtained slurry (A) over 30 minutes at room temperature (25°C) to obtain an aqueous slurry. The pH of the obtained aqueous slurry (1) was 4.0. <Second process> Next, this aqueous slurry (1) was fed to a media-agitation bead mill containing zirconia beads with a diameter of 0.5 mm while stirring, and wet-pulverized. However, the viscosity increased and the mixture became unable to be stirred, so that the subsequent steps could not be carried out.

[0073] <Evaluation of various physical properties> The average particle size and BET specific surface area of ​​the lithium cobalt nickel phosphate obtained in the examples were measured, and the results are shown in Table 1. An SEM photograph of the lithium cobalt nickel phosphate obtained in Example 1 is shown in FIG. The average particle size was measured by observing the particles with a scanning electron microscope at a magnification of 10,000 times, and the average value of 50 or more particles randomly selected was determined as the average particle size.

[0074] [Table 1]

Claims

1. The following general formula (1): Li ｘ Co １－ｙ M ｙ 2O ４ (1) (In the formula, 0.8≦x≦1.2, 0≦y≦0.7, and M represents one or more metal elements selected from Ni, Mg, Zn, Cu, Fe, Cr, Mn, Al, Na, K, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Mo, W, V, Bi, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) A method for producing lithium cobalt phosphate represented by the formula: a first step of preparing an aqueous slurry (1) by adding a carboxylic acid, cobalt hydroxide, and optionally a hydroxide of a metal (M) to an aqueous solvent, and then adding lithium carbonate; a second step of wet-pulverizing the aqueous slurry (1) using a media mill to obtain a slurry (2) containing the pulverized product; a third step of adding phosphoric acid to the slurry (2) containing the pulverized material to obtain a raw material mixed slurry (3); a fourth step of spray-drying the raw material mixed slurry (3) to obtain a reaction precursor; a fifth step of calcining the reaction precursor; A method for producing lithium cobalt phosphate, comprising:

2. 2. The method for producing lithium cobalt phosphate according to claim 1, wherein, in the general formula (1), 0.1≦y≦0.6, and the hydroxide of the metal (M) is nickel hydroxide.

3. 3. The method for producing lithium cobalt phosphate according to claim 1, wherein the average particle size of the solid content in the slurry (2) containing the pulverized material is 1.5 μm or less.

4. 3. The method for producing lithium cobalt phosphate according to claim 1, wherein the carboxylic acid is oxalic acid.

5. 3. The method for producing lithium cobalt phosphate according to claim 1, wherein the reaction precursor contains a phosphate of lithium, a carboxylate of cobalt, and a carboxylate of a metal (M) added as needed.

6. 3. The method for producing lithium cobalt phosphate according to claim 1, wherein the firing temperature is 380 to 1100°C.

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