Production method for lithium cobalt phosphate

Abstract

To provide a method capable of obtaining X-ray diffractometrically single-phase lithium cobalt phosphate in a high yield by an industrially advantageous method.SOLUTION: A production method for lithium cobalt phosphate comprises: a first step of adding and mixing an organic acid having a carboxy group and a hydroxyl group, phosphoric acid, and, if necessary, a metal (M) source into an aqueous solvent, and then adding cobalt hydroxide to prepare a cobalt-containing raw material solution; a second step of adding a lithium source to the cobalt-containing raw material solution to obtain a cobalt-lithium-containing raw material solution; a third step of spray-drying the cobalt-lithium-containing raw material solution to obtain a reaction precursor; and a fourth step of calcining 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 has the problem that the aqueous raw material slurry needs to be wet-pulverized using a media mill, making the process complicated. Therefore, there is a demand for the development of a method for producing lithium cobalt phosphate that is more advantageous from an industrial standpoint.

[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 lithium cobalt phosphate which is single-phase in terms of X-ray diffraction can be obtained in high yield without undergoing a wet-pulverization treatment step using a media mill, by adding an organic acid having a carboxy group and a hydroxyl group, phosphoric acid, and, if necessary, a metal (M) source to an aqueous solvent and mixing them, and then adding cobalt hydroxide to prepare a cobalt-containing raw material solution, adding a lithium source to the cobalt-containing raw material solution to obtain a cobalt-lithium-containing raw material solution, spray-drying the cobalt-lithium-containing raw material solution to obtain a reaction precursor, and calcining the reaction precursor, thereby completing 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 preparing a cobalt-containing raw material solution by adding an organic acid having a carboxyl group and a hydroxyl group, phosphoric acid, and optionally a metal (M) source to an aqueous solvent and mixing them, and then adding cobalt hydroxide; a second step of adding a lithium source to the cobalt-containing raw material solution to obtain a cobalt-lithium-containing raw material solution; a third step of spray-drying the cobalt-lithium-containing raw material solution to obtain a reaction precursor; a fourth step of calcining the reaction precursor; The present invention provides a method for producing lithium cobalt phosphate, which comprises 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. 1 is an X-ray diffraction pattern of lithium nickel cobalt phosphate obtained in Example 2. [Figure 4] FIG. 1 is an X-ray diffraction pattern of lithium nickel cobalt phosphate obtained in Example 3. [Figure 5] FIG. 1 is an X-ray diffraction pattern of lithium nickel cobalt phosphate obtained in Example 4. [Figure 6] FIG. 1 is an X-ray diffraction diagram of the fired product obtained in Comparative Example 1. [Figure 7] FIG. 1 is an X-ray diffraction pattern of the reaction precursor obtained in Reference Example 1. [Figure 8] FIG. 1 is an X-ray diffraction pattern of lithium cobalt phosphate obtained in Reference 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 preparing a cobalt-containing raw material solution by adding an organic acid having a carboxyl group and a hydroxyl group, phosphoric acid, and optionally a metal (M) source to an aqueous solvent and mixing them, and then adding cobalt hydroxide; a second step of adding a lithium source to the cobalt-containing raw material solution to obtain a cobalt-lithium-containing raw material solution; a third step of spray-drying the cobalt-lithium-containing raw material solution to obtain a reaction precursor; a fourth step of calcining the reaction precursor; The present invention is characterized by having the following.

[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): Lix Co 1-y M y PO4(1) (where 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 an organic acid having a carboxy group and a hydroxyl group, phosphoric acid, and, if necessary, a metal (M) source to an aqueous solvent, mixing them, and then adding cobalt hydroxide to prepare a cobalt-containing raw material solution.

[0017] Examples of the organic acid having a carboxy group and a hydroxyl group in the first step include citric acid, gluconic acid, malic acid, lactic acid, tartaric acid, etc. In the method for producing cobalt lithium phosphate of the present invention, citric acid, gluconic acid, or malic acid is preferable in terms of excellent reactivity with the metal (M) source and cobalt hydroxide to be added as necessary and easy availability.

[0018] When citric acid is used as the organic acid having a carboxy group and a hydroxyl group, the amount of citric acid added is an amount such that the ratio of the molar amount of carbon atoms in citric acid to the total molar amount of cobalt atoms in the cobalt hydroxide and M atoms in the metal (M) source added as needed (C / (Co+M)) is 4.0 or more. If the molar amount ratio (C / (Co+M)) is less than 4.0, some of the raw materials will not dissolve, resulting in a non-uniform composition of the cobalt-containing raw material solution. From the viewpoint of industrial superiority, a smaller amount of citric acid is preferable, and therefore an amount such that the molar amount ratio (C / (Co+M)) is 5.0 to 12.0 is preferred, and an amount such that the molar amount ratio (C / (Co+M)) is more preferably 5.0 to 10.0.

[0019] When gluconic acid is used as the organic acid having a carboxy group and a hydroxyl group, the amount of gluconic acid added is an amount such that the ratio of the molar amount of carbon atoms in gluconic acid to the total molar amount of cobalt atoms in the cobalt hydroxide and M atoms in the metal (M) source added as needed (C / (Co+M)) is 8.0 or more. If the molar amount ratio (C / (Co+M)) is less than 8.0, some of the raw materials will not dissolve, resulting in a non-uniform composition of the cobalt-containing raw material solution. From the viewpoint of industrial superiority, a smaller amount of gluconic acid is preferable, and therefore an amount such that the molar amount ratio (C / (Co+M)) is 9.0 to 12.0 is preferred, and an amount such that the molar amount ratio (C / (Co+M)) is more preferably 9.0 to 10.0.

[0020] When malic acid is used as the organic acid having a carboxy group and a hydroxyl group, the amount of malic acid added is an amount such that the ratio of the molar amount of carbon atoms in malic acid to the total molar amount of cobalt atoms in the cobalt hydroxide and M atoms in the metal (M) source added as needed (C / (Co+M)) is 7.0 or more. If the molar amount ratio (C / (Co+M)) is less than 7.0, some of the raw materials will not dissolve, resulting in a non-uniform composition of the cobalt-containing raw material solution. From the viewpoint of industrial superiority, a smaller amount of malic acid is preferable, and therefore an amount such that the molar amount ratio (C / (Co+M)) is 7.0 to 12.0 is preferred, and an amount such that the molar amount ratio (C / (Co+M)) is more preferably 7.0 to 10.0.

[0021] In the first step, when a metal (M) source is added, an organic acid having a carboxyl group and a hydroxyl group, phosphoric acid, and the metal (M) source are added to an aqueous solvent and mixed, and then cobalt hydroxide is added to prepare a cobalt-containing raw material solution. When a carboxylic acid, phosphoric acid, a metal (M) source, and cobalt hydroxide are simultaneously added to and mixed with an aqueous solvent, the metal (M) source may not completely dissolve in the aqueous solvent. Therefore, a cobalt-containing raw material solution of uniform composition can be obtained by adding an organic acid having a carboxyl group and a hydroxyl group, phosphoric acid, and a metal (M) source to an aqueous solvent, thoroughly stirring and mixing them, and then adding cobalt hydroxide.

[0022] The mixing method for preparing the cobalt-containing raw material solution is not particularly limited as long as the raw materials are completely dissolved in the aqueous solvent, and examples thereof include a method using a device such as a stirrer or a mixer with stirring blades. However, the mixing is not limited to the means exemplified above.

[0023] Examples of the metal (M) source in the first step include hydroxides of the metal (M), oxides of the metal (M), etc. In the method for producing lithium cobalt phosphate of the present invention, hydroxides of the metal (M) are preferred because they are stably supplied and easily available, and nickel hydroxide is particularly preferred.

[0024] The amount of the metal (M) source added to the aqueous solvent is such that the total amount of the metal (M) source and cobalt hydroxide added 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 amount of the metal (M) source added to the aqueous solvent is within the above range, a cobalt-containing raw material solution of uniform composition is obtained.

[0025] The phosphoric acid used in the first step is not particularly limited as long as it is industrially available. The phosphoric acid may be an aqueous solution of phosphoric acid. The amount of phosphoric acid added is such that the ratio ((Co+M) / P) of the total molar amount of cobalt atoms in the cobalt hydroxide and M atoms in the metal (M) source added as needed to the molar amount of phosphorus atoms in 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 in the cobalt hydroxide and M atoms in the metal (M) source added as needed to the molar amount of phosphorus atoms in phosphoric acid is within the above range, lithium cobalt phosphate that is single-phase in terms of X-ray diffraction can be easily obtained.

[0026] The metal (M) source used in the first step may have any manufacturing history, but preferably has as little impurity content as possible in order to produce high-purity lithium cobalt phosphate.

[0027] The cobalt hydroxide used in the first step does not need to have a manufacturing history, but it is preferable that the impurity content be as low as possible in order to produce high-purity lithium cobalt phosphate.

[0028] The second step in the method for producing lithium cobalt phosphate of the present invention is a step of adding a lithium source to the cobalt-containing raw solution obtained in the first step to obtain a cobalt-lithium-containing raw solution.

[0029] Examples of the lithium source for the second step include lithium hydroxide, lithium carbonate, etc. It is preferable to add the lithium source to the cobalt-containing raw material solution obtained in the first step as a lithium-containing solution obtained by dissolving the lithium source in water or as a lithium-containing suspension using water as a dispersion solvent, from the viewpoint of making the composition of the cobalt-lithium-containing raw material solution uniform.

[0030] The amount of lithium source added is an amount such that the ratio of the molar amount of lithium atoms in the lithium source to the total molar amount of cobalt atoms in the cobalt hydroxide and M atoms in the metal (M) source 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 source to the total molar amount of cobalt atoms in the cobalt hydroxide and M atoms in the metal (M) source 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.

[0031] The temperature at which the lithium source is added is not particularly limited, and is often 15 to 90°C, preferably 20 to 80°C.

[0032] The lithium source may have any manufacturing history, but it is preferable that the impurity content be as low as possible in order to produce high-purity lithium cobalt phosphate.

[0033] The third step in the method for producing lithium cobalt phosphate of the present invention is a step of spray-drying the cobalt-lithium-containing raw material solution obtained in the second step to obtain a reaction precursor.

[0034] Although methods other than spray drying are known as methods for drying a cobalt-lithium-containing raw material solution, 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.

[0035] 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 can be 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 fourth step described below, lithium cobalt phosphate that is single-phase in terms of X-ray diffraction can be obtained.

[0036] In the spray drying in the third step, the cobalt-lithium-containing raw material solution is atomized by a predetermined means, and the resulting fine droplets are dried to obtain a reaction precursor. The cobalt-lithium-containing raw material solution can be atomized, for example, by a method using a rotating disk or a method using a pressure nozzle. Either method can be used in the third step.

[0037] In the spray drying treatment in the third step, the size of the droplets of the atomized cobalt-lithium-containing raw material solution affects stable drying and the properties of the resulting dried powder. From this viewpoint, the size of the atomized droplets is preferably 1 to 50 μm, and particularly preferably 10 to 40 μm. The amount of the cobalt-lithium-containing raw material solution to be supplied to the spray drying apparatus is preferably determined taking this viewpoint into consideration.

[0038] The reactive precursor obtained by the spray drying treatment in the third step is subjected to calcination in the fourth 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 third 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).

[0039] In the third 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.

[0040] The reaction precursor obtained in the third step contains at least lithium, cobalt, carbon, and optionally added metal (M). The lithium, cobalt, carbon, and optionally added metal (M) in the reaction precursor can be identified by X-ray diffraction analysis of the reaction precursor. In addition, the reaction precursor is preferably an amorphous reaction precursor. In the present invention, the reaction precursor being amorphous means that in X-ray diffraction analysis, only a broad peak is observed in the range of 2θ=10 to 70°, and no sharp diffraction peak (half width of 1.0° or less) is observed.

[0041] In this manner, by carrying out the third step, a reaction precursor to be subjected to calcination in the fourth step can be obtained.

[0042] The fourth step in the method for producing lithium cobalt phosphate of the present invention is a step of calcining the reaction precursor obtained in the third step.

[0043] The firing temperature in the fourth 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.

[0044] The firing atmosphere in the fourth step is an air atmosphere, 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 fourth step, or when carbon derived from an organic acid is to be contained in the lithium cobalt phosphate obtained by firing, it is preferable to use an inert gas atmosphere or a reducing gas atmosphere for the firing. The inert gas is not particularly limited, and examples thereof include nitrogen gas, helium gas, and argon gas.

[0045] The calcination time in the fourth step varies depending on the calcination temperature, but is preferably 0.5 hours or more, and particularly preferably 2 to 20 hours. In the fourth 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.

[0046] In the fourth step, the lithium cobalt phosphate obtained by the first calcination may be calcined multiple times as necessary. When the calcination is performed multiple times, the calcined product may be crushed or disintegrated and then calcined.

[0047] The lithium cobalt phosphate obtained in the fourth step may be crushed or pulverized, and further classified, if necessary.

[0048] 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.

[0049] Furthermore, in the method for producing lithium cobalt phosphate of the present invention, the lithium cobalt phosphate obtained in the fourth step can be subjected to the following fifth (A) step or fifth (B) step, if necessary.

[0050] Step 5(A) is a step of further heat-treating the lithium cobalt phosphate obtained in Step 4 to adjust the amount of carbon contained in the lithium cobalt phosphate. Specifically, in Step 5(A), the lithium cobalt phosphate obtained in Step 4 is heat-treated to oxidize the carbon in the lithium cobalt phosphate. The heat treatment in Step 5(A) is preferably carried out in an oxygen-containing atmosphere. In Step 5(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 5(A) is 200 to 500°C, preferably 250 to 400°C. By setting the heat treatment temperature in Step 5(A) within the above range, the remaining carbon can be highly efficiently oxidized. The heat treatment time in Step 5(A) is not critical in the method for producing lithium cobalt phosphate of the present invention. The longer the heat treatment time in step 5(A), the lower the amount of carbon contained in the lithium cobalt phosphate. In step 5(A), it is preferable to perform the heat treatment under appropriate conditions set in advance so as to achieve a desired carbon content.

[0051] Step 5(B) is a step of mixing the lithium cobalt phosphate obtained in Step 4 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.

[0052] The conductive carbon material source is one that undergoes thermal decomposition to precipitate carbon by at least heat treatment in step 5(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).

[0053] 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.

[0054] 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.

[0055] In the fifth step (B), the lithium cobalt phosphate and the conductive carbon material source can be mixed by a dry method or a wet method.

[0056] In step 5(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.

[0057] In addition, examples of a method for performing a wet mixing treatment in the step 5(B) 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.

[0058] The apparatus used for wet mixing is not particularly limited as long as it can produce a uniform slurry, and examples thereof include a stirrer, an agitator with agitating blades, a three-roll mill, a ball mill, a disper mill, a homogenizer, a vibration mill, a sand grind mill, an attritor, and a powerful agitator. The wet mixing process is not limited to the mixing process using mechanical means exemplified above. During wet mixing, a surfactant may be added to the slurry before the mixing process.

[0059] 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.

[0060] 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.

[0061] 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 preparing a cobalt-containing raw material solution by adding an organic acid having a carboxyl group and a hydroxyl group, phosphoric acid, and optionally a metal (M) source to an aqueous solvent and mixing them, and then adding cobalt hydroxide; a second step of adding a lithium source to the cobalt-containing raw material solution to obtain a cobalt-lithium-containing raw material solution; a third step of spray-drying the cobalt-lithium-containing raw material solution to obtain a reaction precursor; a fourth 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 metal (M) source is nickel hydroxide. [3] The method for producing lithium cobalt phosphate according to [1] or [2], wherein the organic acid is citric acid, gluconic acid, or malic acid. [4] The method for producing lithium cobalt phosphate according to any one of [1] to [3], wherein the lithium source is lithium carbonate or lithium hydroxide. [5] The method for producing lithium cobalt phosphate according to any one of [1] to [4], wherein the reaction precursor is an amorphous reaction precursor. [Example]

[0062] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0063] Example 1 <1st process> To 800 g of pure water, 246.0 g (1.17 mol) of citric acid monohydrate, 52.2 g of nickel hydroxide (0.56 mol as Ni atoms), and 185.8 g of 85% phosphoric acid (1.61 mol as phosphoric acid) were added at room temperature and stirred for 4 hours using a three-one motor stirrer. Next, 80.0 g of cobalt hydroxide (0.86 mol as Co atoms) was added and stirred for an additional hour to obtain a cobalt-containing raw material solution containing cobalt and nickel in a Co:Ni molar ratio of 6:4. <Second process> Next, 52.0 g of lithium carbonate (0.70 mol as Li atoms) was added to 150 ml of pure water to prepare a lithium-containing suspension. Next, the lithium-containing suspension was added to the cobalt-containing raw material solution and stirred for 1 hour using a three-one motor stirrer to obtain a cobalt-lithium-containing raw material solution. <3rd process> Next, the cobalt-lithium-containing raw material solution was fed at a feed rate of 2.4 L / h into a spray dryer with the hot air inlet temperature set to 220°C, yielding 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 an amorphous reaction precursor. 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 10 to 30 μm. <4th process> The resulting reactive precursor was then fired in an air atmosphere at 650°C for 4 hours to obtain a fired product. The average particle size of the fired product determined by scanning electron microscope (SEM) observation was 0.5µm, and the specific surface area (BET method) was 3.5m. 2 / g. 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 0.5PO4), 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. Furthermore, elemental mapping of phosphorus (P), cobalt (Co), and nickel (Ni) was performed on the obtained fired product using SEM-EDS (energy dispersive X-ray spectroscopy), and it was confirmed that phosphorus, cobalt, and nickel were present uniformly, without uneven distribution.

[0064] Example 2 <1st process> At room temperature, 918.9 g of 50% gluconic acid solution (2.34 mol as gluconic acid), 52.2 g of nickel hydroxide (0.56 mol as Ni atoms), and 185.8 g of 85% phosphoric acid (1.61 mol as phosphoric acid) were added to 400 g of pure water and stirred for 4 hours using a three-one motor stirrer. Next, 80.0 g of cobalt hydroxide (0.86 mol as Co atoms) was added and stirred for another hour to obtain a cobalt-containing raw material solution containing cobalt and nickel in a Co:Ni molar ratio of 6:4. <Second process> Next, 52.0 g of lithium carbonate (0.70 mol as Li atoms) was added to 150 ml of pure water to prepare a lithium-containing suspension. Next, the lithium-containing suspension was added to the cobalt-containing raw material solution and stirred for 1 hour using a three-one motor stirrer to obtain a cobalt-lithium-containing raw material solution. <3rd process> Next, the cobalt-lithium-containing raw material solution was supplied at a supply rate of 2.4 L / h to a spray dryer with a hot air inlet temperature set to 220°C, to obtain a reaction precursor. There was little adhesion inside the spray dryer, and the recovery rate was 91%. X-ray diffraction analysis of the obtained reaction precursor confirmed that it was an amorphous reaction precursor. The secondary particle diameter of the reaction precursor determined by scanning electron microscope (SEM) observation was 10 to 30 μm. <4th process> The resulting reactive precursor was then calcined in an air atmosphere at 650°C for 4 hours to obtain a calcined product. The average particle size of the calcined product determined by scanning electron microscope (SEM) observation was 0.5µm, and the specific surface area (BET method) was 3.9m. 2 / g. 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 3. Furthermore, elemental mapping of phosphorus (P), cobalt (Co), and nickel (Ni) was performed on the obtained fired product using SEM-EDS (energy dispersive X-ray spectroscopy), and it was confirmed that phosphorus, cobalt, and nickel were present uniformly, without uneven distribution.

[0065] Example 3 <1st process> At room temperature, 471.7 g (3.52 mol) of malic acid, 52.2 g of nickel hydroxide (0.56 mol as Ni atoms), and 185.8 g of 85% phosphoric acid (1.61 mol as phosphoric acid) were added to 400 g of pure water and stirred for 4 hours using a three-one motor stirrer. Next, 80.0 g of cobalt hydroxide (0.86 mol as Co atoms) was added and stirred for an additional hour to obtain a cobalt-containing raw material solution containing cobalt and nickel in a Co:Ni molar ratio of 6:4. <Second process> Next, 52.0 g of lithium carbonate (0.70 mol as Li atoms) was added to 150 ml of pure water to prepare a lithium-containing suspension. Next, the lithium-containing suspension was added to the cobalt-containing raw material solution and stirred for 1 hour using a three-one motor stirrer to obtain a cobalt-lithium-containing raw material solution. <3rd process> Next, the cobalt-lithium-containing raw material solution was supplied at a supply rate of 2.4 L / h to a spray dryer with a hot air inlet temperature set to 220°C, to obtain a reaction precursor. X-ray diffraction analysis of the obtained reaction precursor confirmed that it was an amorphous reaction precursor. The secondary particle diameter of the reaction precursor determined by observation with a scanning electron microscope (SEM) was 10 to 30 μm. <4th process> The resulting reactive precursor was then fired in an air atmosphere at 650°C for 4 hours to obtain a fired product. The average particle size of the fired product determined by scanning electron microscope (SEM) observation was 0.4µm, and the specific surface area (BET method) was 4.0m. 2 / g. 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 Ni0.4 The X-ray diffraction pattern of the fired product is shown in Figure 4.

[0066] Example 4 The firing was carried out in the same manner as in Example 1, except that the fourth step was performed at 650°C for 4 hours in a nitrogen atmosphere. The average particle size of the fired product determined by scanning electron microscope (SEM) observation was 0.5 μm, and the specific surface area (BET method) was 3.9 m 2 / g. 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 5. The amount of residual carbon in the obtained fired product was measured using a TOC total organic carbon analyzer (TOC-5000A manufactured by Shimadzu Corporation) to determine the content of C atoms, and the result was that the amount of residual carbon was 15% by mass.

[0067] (Comparative Example 1) 2.5 g of cobalt hydroxide, 1.6 g of nickel hydroxide, 5.8 g of diammonium hydrogen phosphate, and 1.6 g of lithium carbonate were mixed in a mortar. The resulting mixed powder was fired at 650°C for 4 hours in an air atmosphere to obtain a fired product. X-ray diffraction analysis of the resulting fired product confirmed that it was not a single phase. The X-ray diffraction pattern of the fired product is shown in Figure 6.

[0068] (Comparative Example 2) <1st process> At room temperature, 246.0 g (1.17 mol) of citric acid monohydrate, 80.0 g (0.86 mol of Co atoms), and 185.8 g (1.61 mol of phosphoric acid) of 85% were added to 800 g of pure water and stirred for 4 hours using a three-one motor stirrer. Next, 52.2 g (0.56 mol of Ni atoms) of nickel hydroxide was added, but the nickel hydroxide did not dissolve, resulting in a cobalt-containing raw material suspension with a heterogeneous composition. <Second process> Next, 52.0 g of lithium carbonate (0.70 mol as Li atoms) was added to 150 ml of pure water to prepare a lithium-containing suspension. Next, the lithium-containing suspension was added to the cobalt-containing raw material suspension and stirred for 1 hour using a three-one motor stirrer, resulting in a cobalt-lithium-containing raw material suspension in which nickel hydroxide remained undissolved. <3rd process> Next, when the cobalt-lithium-containing raw material suspension was supplied to a spray dryer with a hot air inlet temperature set to 220°C, the nickel hydroxide clogged the spray dryer, making it impossible to perform the spray drying treatment. Therefore, the subsequent steps were not carried out.

[0069] (Reference example 1) <1st process> At room temperature (25°C), 1604.5g (12.73 mol) of oxalic acid dihydrate was added to 11L of pure water and stirred for 30 minutes using a three-one motor stirrer. 228g of dispersant (ammonium polycarboxylate) was then added. Next, 1200g of cobalt hydroxide (12.91 mol as Co atoms) was added at room temperature (25°C) and stirred for 30 minutes. Next, 1461.2g of 85% by mass phosphoric acid (12.67 mol as phosphoric acid) was added and stirred for 30 minutes. Next, 534.4g of lithium hydroxide monohydrate (12.74 mol as Li atoms) was added and stirred for 1 hour to obtain an aqueous raw material slurry. <Second process> Next, this aqueous raw material slurry was fed while being stirred into a media-agitation type bead mill charged with zirconia beads having a diameter of 0.5 mm, and mixed and wet-pulverized for 3 hours to obtain a slurry (2) containing the pulverized raw material. The average particle size of the solid content in the slurry (2) containing the pulverized raw material determined by laser scattering and diffraction was 0.5 μm. <3rd process> Next, the slurry (2) containing the ground raw material was fed at a rate of 2.4 L / h into a spray dryer with the hot air inlet temperature set to 220 °C, yielding a reaction precursor. There was little adhesion inside the spray dryer, and the recovery rate was 97%. X-ray diffraction analysis of the resulting reaction precursor confirmed that it was a mixture of Co(C2O4)(H2O)2, Co(HCOO)2(H2O)2, and Li(H2PO4). The X-ray diffraction pattern of the reaction precursor is shown in Figure 7. <4th process> The resulting reaction precursor was then calcined at 425°C for 2 hours in an air atmosphere to obtain a calcined product. X-ray diffraction analysis of the obtained fired product confirmed that the fired product was single-phase lithium cobalt phosphate (LiCoPO4). The X-ray diffraction pattern of the fired product is shown in Figure 8.

[0070] Although Examples 1 to 4 do not include a step of wet-pulverizing the aqueous raw slurry using a media mill, it was confirmed that single-phase lithium cobalt phosphate was obtained in high yields as determined by X-ray diffraction, similar to Reference Example 1, which includes a step of wet-pulverizing the aqueous raw slurry using a media mill.

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 a cobalt-containing raw material solution by adding an organic acid having a carboxyl group and a hydroxyl group, phosphoric acid, and optionally a metal (M) source to an aqueous solvent and mixing them, and then adding cobalt hydroxide; a second step of adding a lithium source to the cobalt-containing raw material solution to obtain a cobalt-lithium-containing raw material solution; a third step of spray-drying the cobalt-lithium-containing raw material solution to obtain a reaction precursor; a fourth 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 metal (M) source is nickel hydroxide.

3. 3. The method for producing lithium cobalt phosphate according to claim 1, wherein the organic acid is citric acid, gluconic acid, or malic acid.

4. 3. The method for producing lithium cobalt phosphate according to claim 1, wherein the lithium source is lithium carbonate or lithium hydroxide.

5. 3. The method for producing lithium cobalt phosphate according to claim 1, wherein the reaction precursor is an amorphous reaction precursor.

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