Method for producing transition metal-containing lithium phosphate and method for producing transition metal-containing lithium phosphate-carbon composite

Abstract

To provide a method for obtaining X-ray diffractive single phase transition metal-containing lithium pyrophosphate with a high yield by an industrially advantageous method.SOLUTION: A method for producing transition metal-containing lithium pyrophosphate represented by general formula (1), LixM1-yAyPO4 (1) includes: a first step of mixing at least lithium metaphosphate and an M source with an aqueous solvent to obtain a raw material mixture; a second step of subjecting the raw material mixture to wet pulverization treatment to obtain a slurry containing a raw material pulverized material; a third step of spraying and drying the slurry containing the raw material pulverized material by a spray dry method to obtain spray dry powder; and a fourth step of baking the spray dry powder.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing lithium transition metal phosphate useful as a positive electrode material for lithium secondary batteries, all-solid-state batteries, and the like.

Background Art

[0002] Lithium-ion batteries are being used as batteries for portable devices and notebook personal computers. Lithium-ion batteries are generally considered to be excellent in terms of capacity and energy density. In addition, their use in hybrid automobiles and electric automobiles is also expected.

[0003] Olivine-type phosphates such as lithium cobalt phosphate (LiCoPO4) do not release oxygen from their strong structures even at high temperatures, and because of their high safety, they have attracted attention as positive electrode active materials for lithium secondary batteries, all-solid-state batteries, etc. for automotive applications. As a method for producing lithium cobalt phosphate, for example, Patent Document 1 proposes a method of dry-mixing lithium carbonate, cobalt trioxide, and phosphorus pentoxide and firing the mixture at 780°C in the air. Further, Patent Document 2 discloses a method in which lithium acetate, cobalt acetate, and ammonium hydrogen phosphate are added to water, adjusted to a pH of 1.5 or less with concentrated nitric acid and dissolved to obtain a solution, then glycolic acid is added as a chelating agent for suppressing particle growth, the solvent is removed, and the resulting precursor is fired at 600°C in an argon atmosphere. Also, Patent Document 3 proposes a method in which lithium hydroxide and ammonium hydrogen phosphate are dissolved in water bubbled with N2, an aqueous solution in which cobalt sulfate is dissolved is added to obtain a mixed solution, the solvent is removed, and the resulting precursor is fired at 600°C in a nitrogen atmosphere.

[0004]

[0005]

[0006]

[0006] In addition, in the examples of Patent Document 5, a method for producing lithium iron phosphate having an olivine structure by mixing lithium metaphosphate, an Fe compound, and a reducing agent and firing them in a hydrogen-argon atmosphere has been proposed.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the method of dry-mixing each raw material as in Patent Document 1, it is difficult to obtain single-phase cobalt lithium phosphate in X-ray diffraction analysis. Further, what is obtained in the examples of Patent Document 5 is LiFePO4, and even if the method of Patent Document 5 is simply used, it is difficult to obtain X-ray diffraction single-phase lithium phosphate containing Co, Mn, or Ni.

[0009] On the other hand, in the method of Patent Document 4, single-phase cobalt lithium phosphate can be obtained by X-ray diffraction in an industrially advantageous method. However, the method of Cited Document 4 has a problem that when the slurry containing the raw material pulverized product is spray-dried with a spray dryer, the slurry containing the raw material pulverized product adheres to the spray dryer, resulting in a low yield of cobalt lithium phosphate.

[0010] In addition, lithium transition metal phosphates such as lithium cobalt phosphate are attracting attention as safe cathode active materials, and further development by more industrially advantageous methods is desired.

[0011] Lithium metaphosphate is a compound represented by LiPO3, which contains Li and P, and further contains Li and P in equimolar amounts. Therefore, compared with other compounds containing Li and P, at least in the case of producing a compound containing Li and P in an atomic molar ratio of 1:1, when used as a production raw material, there are advantages such as easy composition preparation. However, industrially available lithium metaphosphate has coarse particles and has problems with reactivity. Except for Patent Document 5, in fields where the presence of heterogeneous phases is disliked by X-ray diffraction, it has hardly been used as a production raw material for compounds containing Li and P.

[0012] Therefore, an object of the present invention is to provide a method capable of obtaining a single-phase transition metal-containing lithium phosphate by X-ray diffraction in a highly industrially advantageous manner and with a high yield.

Means for Solving the Problems

[0013] In view of the above circumstances, the present inventors have conducted intensive studies and as a result, the following general formula (1): Li x M 1-y A y PO4(1) (In the formula, 0.8 ≦ x ≦ 1.2, 0.0 ≦ y ≦ 0.5. M represents one or more transition metal elements selected from Co, Mn, and Ni. A represents one or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) In the method for producing a transition metal-containing lithium phosphate represented by [LixMyA1−x−yPO4], lithium metaphosphate is used as the phosphorus source and the lithium source, and the slurry obtained by mixing the lithium metaphosphate and the M source in an aqueous solvent and subjecting the mixture to wet grinding has little adhesion to the spray drying apparatus. As a result, the slurry containing the raw material pulverized product obtained by the wet grinding treatment is spray-dried by the spray drying method, and then the obtained spray-dried powder is fired, whereby it has been found that a single-phase transition metal-containing lithium phosphate can be obtained in a high yield by X-ray diffraction, and the present invention has been completed. Further, the present inventors have found that by pulverizing the transition metal-containing lithium phosphate thus obtained, a product having a uniform particle size can be obtained.

[0014] That is, the present invention (1) provides a method for producing a transition metal-containing lithium phosphate represented by the following general formula (1): Li x M 1-y A y PO4(1) (wherein 0.8 ≤ x ≤ 1.2 and 0.0 ≤ y ≤ 0.5. M represents one or more transition metal elements selected from Co, Mn, and Ni. A represents one or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) The method for producing a transition metal-containing lithium phosphate represented by the following general formula (1): A first step of obtaining a raw material mixture by mixing at least lithium metaphosphate and an M source with an aqueous solvent; A second step of subjecting the raw material mixture to wet grinding to obtain a slurry containing a raw material pulverized product; A third step of spray-drying the slurry containing the raw material pulverized product by the spray drying method to obtain a spray-dried powder; A fourth step of firing the spray-dried powder; The present invention provides a method for producing a transition metal-containing lithium phosphate, characterized by comprising the above steps.

[0015] Further, in the present invention (2), in the first step, an A source (A represents one or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho) is added to the aqueous solvent, and a method for producing the transition metal-containing lithium phosphate of (1) is provided.

[0016] Further, in the present invention (3), in the 2 step, wet grinding treatment is performed by a media mill, and a method for producing the transition metal-containing lithium phosphate of (1) or (2) is provided. Uri

[0017] Further, in the present invention (4), in the second step, the average particle diameter of the solid content in the slurry containing the raw material pulverized product after wet grinding treatment is 10.0 μm or less, and a method for producing the transition metal-containing lithium phosphate according to any one of (1) to (3) is provided.

[0018] Further, in the present invention (5), M in the general formula (1) is Co, and a method for producing the transition metal-containing lithium phosphate according to any one of (1) to (4) is provided.

[0019] Further, in the present invention (6), the M source is cobalt hydroxide, and a method for producing the transition metal-containing lithium phosphate according to any one of (1) to (5) is provided.

[0020] Further, in the present invention (7), the firing temperature in the fourth step is 600 to 900 °C, and a method for producing the transition metal-containing lithium phosphate according to any one of (1) to (6) is provided.

[0021] ​Further, the present invention (8) provides a method for producing a lithium transition metal phosphate according to any one of (1) to (7), characterized by further comprising a fifth step of pulverizing the lithium transition metal phosphate obtained by performing the fourth step.

[0022] Further, the present invention (9) provides a method for producing a lithium transition metal phosphate according to any one of (1) to (7), characterized by further comprising a fifth step of pulverizing the lithium transition metal phosphate obtained by performing the fourth step, and a sixth step of re-firing the pulverized product obtained by performing the fifth step.

[0023] Further, the present invention (10) provides a method for producing a lithium transition metal phosphate-carbon composite, comprising a first step (A) of mixing the lithium transition metal phosphate obtained by performing the method for producing a lithium transition metal phosphate according to any one of (1) to (9) with a conductive carbon material source that deposits carbon by thermal decomposition to obtain a mixture of the lithium transition metal 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 transition metal phosphate-carbon composite. [[Effect of the Invention]]

[0024] According to the method for producing a lithium transition metal phosphate of the present invention, it is possible to provide a method capable of obtaining a single-phase lithium transition metal phosphate by X-ray diffraction in a high yield by an industrially advantageous method. It can be provided. [[Brief Description of the Drawings]]

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0026] The method for producing a lithium transition metal phosphate of the present invention is represented by the following general formula (1): Li x M 1-y A y PO4(1) (In the formula, 0.8 ≤ x ≤ 1.2 and 0.0 ≤ y ≤ 0.5. M represents one or more transition metal elements selected from Co, Mn, and Ni. A represents one or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) It is a method for producing a lithium transition metal phosphate represented by: A first step of mixing at least lithium metaphosphate and an M source with an aqueous solvent to obtain a raw material mixture; A second step of subjecting the raw material mixture to wet grinding treatment to obtain a slurry containing a raw material ground product; A third step of spray-drying the slurry containing the raw material ground product by a spray-drying method to obtain a spray-dried powder; A fourth step of firing the spray-dried powder; A method for producing a lithium transition metal phosphate, characterized by comprising the above steps.

[0027] The lithium transition metal phosphate obtained by the method for producing a lithium transition metal phosphate of the present invention is a lithium transition metal phosphate having an olivine structure and is represented by the following general formula (1): Li x M 1-y A y PO4(1) (In the formula, 0.8 ≤ x ≤ 1.2 and 0.0 ≤ y ≤ 0.5. M represents one or more transition metal elements selected from Co, Mn, and Ni. A represents one or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) It is lithium transition metal phosphate represented by the formula.

[0028] In the formula of 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 0.0 or more and 0.5 or less, preferably 0.0 or more and 0.4 or less. M in the formula represents one or more transition metal elements selected from Co, Mn, and Ni, and being Co is preferable in that it becomes a positive electrode active material from which a lithium secondary battery or an all-solid-state battery with high capacity and high energy density can be obtained. A in the formula is a metal element that is contained as necessary for the purpose of improving battery characteristics. A represents one or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.

[0029] The first step according to the method for producing lithium transition metal phosphate of the present invention is a step of mixing at least lithium metaphosphate and an M source with an aqueous solvent to obtain a raw material mixture. The lithium metaphosphate (LiPO3) according to the first step is not particularly limited as long as it is industrially available. Usually, industrially available lithium metaphosphate is hard coarse particles with an average particle diameter of 200 μm or more determined by the laser scattering / diffraction method, but in the present invention, even such hard coarse particle lithium metaphosphate can be used without problems.

[0030] ​

[0031] Examples of the M source related to the first step include oxides, hydroxides, carbonates, organic acid salts, nitrates, and phosphates containing the M element. As the M source, oxides, hydroxides, and carbonates containing the M element are preferable from the viewpoints of industrial availability and ease of handling.

[0032] As the M source related to the first step, compounds containing Co, such as oxides, hydroxides, carbonates, organic acid salts, nitrates, and phosphates containing Co, are preferable in that a cathode active material capable of obtaining a high-capacity and high-energy density lithium secondary battery or all-solid-state battery can be obtained, and cobalt hydroxide is particularly preferable in that it has excellent reactivity.

[0033] The aqueous solvent related to the first step may be water alone or a mixed solvent of water and a hydrophilic solvent.

[0034] In the first step, at least lithium metaphosphate and the M source are added to the aqueous solvent, and at least lithium metaphosphate and the M source are mixed with the aqueous solvent to obtain a raw material mixture.

[0035] In the first step, the mixing amount of lithium metaphosphate in the aqueous solvent is preferably 5.0 to 40.0 parts by mass, particularly preferably 8.0 to 30.0 parts by mass, based on 100.0 parts by mass of the aqueous solvent. When the mixing amount of lithium metaphosphate in the first step is within the above range, the pulverization efficiency can be increased or the increase in the slurry viscosity after pulverization can be suppressed.

[0036] In the first step, the mixing amount of the M source in the aqueous solvent is an amount such that the molar ratio (M / P) of the M atom in the M source to the P atom in lithium metaphosphate is preferably 0.80 to 1.2, particularly preferably 0.90 to 1.1. When the molar ratio (M / P) of the M atom in the M source to the P atom in lithium metaphosphate is within the above range, it becomes easier to obtain a single-phase transition metal-containing lithium phosphate by X-ray diffraction.

[0037] In this way, a raw material mixture is obtained in the first step. In the method for producing lithium transition metal phosphate of the present invention, if necessary, in the first step, an A source (A represents one or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho) can be further mixed into the aqueous solvent. That is, in the method for producing lithium transition metal phosphate of the present invention, in addition to lithium metaphosphate and the M source in the aqueous solvent, an A source can be added as necessary, and by mixing lithium metaphosphate, the M source, and the A source with the aqueous solvent, in addition to lithium metaphosphate and the M source, the A source can be contained in the raw material mixture related to the first step.

[0038] Examples of the A source include oxides, hydroxides, carbonates, organic acid salts, nitrates, and phosphates containing the A element.

[0039] The mixing amount of the A source is such that the molar ratio of A atoms in the A source to the total molar ratio of A atoms in the A source and M atoms in the M source (A / (A + M)) is preferably in the range of 0.10 to 0.20.

[0040] It should be noted that lithium metaphosphate, the M source, and the A source (mixed as necessary) related to the first step are preferably high-purity products in terms of obtaining high-purity lithium transition metal phosphate.

[0041] The second step in the method for producing lithium transition metal phosphate of the present invention is a step of subjecting the raw material mixture obtained by performing the first step to wet grinding treatment to obtain a slurry containing a raw material ground product.

[0042] ​In the second step, when performing wet grinding treatment, the solid content concentration in the raw material mixture is preferably 5 to 40% by mass, particularly preferably 10 to 30% by mass. When the solid content concentration in the raw material mixture during wet grinding is within the above range, the operability is good, and the grinding treatment can be performed efficiently. Therefore, after performing the first step, if necessary, the solid content concentration of the raw material mixture may be adjusted to the above solid content concentration and then the second step may be performed.

[0043] And in the second step, the raw material mixture is subjected to wet grinding treatment. The wet grinding treatment in the second step can be performed using, for example, a media mill, a grinding type grinder utilizing the principle of a mortar, a wet jet mill, an ultrasonic grinder that grinds using ultrasonic waves, a grinder using the supersonic droplet collision dispersion method, etc., and it is preferable to perform the wet grinding treatment using a media mill. By subjecting the raw material mixture to wet grinding treatment using a media mill, the solid content contained in the raw material mixture can be ground more finely industrially advantageously, so that by spray drying by the spray drying method in the third step, a spray dried powder having more excellent reactivity can be obtained.

[0044] Examples of the media mill include a bead mill, a ball mill, a paint shaker, an attritor, a sand mill, etc., and a bead mill is preferable. When using a bead mill, the operating conditions, the type and size of the beads are appropriately selected according to the size of the apparatus and the throughput.

[0045] From the viewpoint of performing the wet grinding treatment more efficiently, a dispersant may be added to the raw material mixture. The dispersant is appropriately selected according to the type and characteristics of the slurry. Examples of the dispersant include various surfactants, ammonium polycarboxylate salts, etc. 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 terms of obtaining a sufficient dispersion effect.

[0046] In the second step, the wet grinding treatment using a media mill is such that the average particle diameter of the solid content in the slurry containing the raw material ground product is D determined by the laser scattering / diffraction method.50 It is preferably carried out until it reaches 10.0 μm or less, particularly preferably 1.0 to 8.0 μm. When the average particle diameter of the solid content in the slurry containing the raw material pulverized product is within the above range, it becomes easy to obtain a spray-dried powder having excellent reactivity. The D 50 refers to, for example, the particle diameter at 50% in volume integration in the particle size distribution curve determined by the laser scattering / diffraction method using MT3300 manufactured by Microtrac Bell.

[0047] In this way, by performing the second step, a slurry containing the raw material pulverized product can be obtained.

[0048] In the method for producing lithium transition metal phosphate of the present invention, the first step of mixing lithium metaphosphate, the M source and, if necessary, the A source with an aqueous solvent may be carried out in a device or container different from the wet pulverization treatment device for performing the second step.

[0049] Further, in the method for producing lithium transition metal phosphate of the present invention, in the wet pulverization treatment device for performing the second step, the first step of mixing lithium metaphosphate, the M source and, if necessary, the A source with an aqueous solvent and the second step of performing wet pulverization treatment by the wet pulverization treatment device may be carried out. For example, when using a media mill as the wet pulverization treatment device, media, lithium metaphosphate, the M source and, if necessary, the A source, and an aqueous solvent are added to the media mill for performing the second step, and then lithium metaphosphate, the M source, the aqueous solvent, and, if necessary, the A source are mixed in the media mill to obtain a raw material mixture. Subsequently, the obtained raw material mixture is wet pulverized, or media, lithium metaphosphate, the M source and, if necessary, the A source, and an aqueous solvent are added to the media mill for performing the second step, and then the operation of the media mill is started, and the mixing of lithium metaphosphate, the M source, if necessary, the A source, and the aqueous solvent and the wet pulverization treatment of the obtained raw material mixture can be carried out.

[0050] The third step according to the method for producing a transition metal-containing lithium phosphate of the present invention is a step of spray-drying a slurry containing the raw material pulverized product obtained by performing the second step to obtain a spray-dried powder.

[0051] Although methods other than the spray-dry method are known as the method for drying the slurry, based on the finding that it is advantageous to select the spray-dry method in the method for producing a transition metal-containing lithium phosphate of the present invention, this drying method is adopted. Specifically, by using the spray-dry method, a dried powder in a state where particles are clogged can be obtained. Therefore, by firing the obtained dried powder in the fourth step, a single-phase transition metal-containing lithium phosphate can be obtained by X-ray diffraction.

[0052] In the spray-drying in the third step, the slurry containing the raw material pulverized product is atomized by a predetermined means, and the resulting fine droplets are dried to obtain a spray-dried powder. For atomizing the slurry, there are, for example, a method using a rotating disk and a method using a pressure nozzle. In the third step, either method can be used.

[0053] In the spray-dry method in the third step, the relationship between the size of the droplets of the atomized slurry and the size of the particles of the raw material pulverized product contained therein affects stable drying and the properties of the obtained dried powder. Specifically, if the size of the particles of the raw material pulverized product is too small relative to the size of the droplets, the droplets become unstable and it becomes difficult to perform drying successfully. From this viewpoint, the size of the atomized droplets is preferably 5 to 50 μm, particularly preferably 10 to 40 μm. The supply amount of the slurry to the spray-drying apparatus is preferably determined in consideration of this viewpoint.

[0054] The spray-dried powder obtained by spray drying in the third step is subjected to firing in the fourth step, and the powder properties such as the average particle size of the resulting lithium transition metal phosphate generally follow the properties of the spray-dried powder. Therefore, in the spray drying in the third step, from the viewpoint of controlling the particle size of the target lithium transition metal phosphate, it is preferable to perform spray drying so that the size of the secondary particles of the spray-dried powder is 5 to 50 μm in terms of the particle size determined by scanning electron microscope (SEM) observation, and it is particularly preferable to perform spray drying so that the size is 10 to 40 μm.

[0055] In the spray drying method of the third step, the drying temperature is adjusted such that the hot air inlet temperature of the spray dryer is 170 to 320 °C, preferably 190 to 300 °C, and the hot air outlet temperature is adjusted to be 80 to 140 °C, which is preferable because it prevents moisture absorption of the powder and facilitates powder recovery.

[0056] In this way, by performing the third step, a spray-dried powder to be subjected to firing in the fourth step is obtained.

[0057] The fourth step according to the method for producing lithium transition metal phosphate of the present invention is a step of firing the spray-dried powder obtained by performing the third step to obtain X-ray single-phase lithium transition metal phosphate. The firing temperature in the fourth step is 600 to 900 °C, preferably 650 to 850 °C. If the firing temperature is less than the above range, the firing time until X-ray diffraction becomes single-phase becomes long, which is industrially disadvantageous. On the other hand, if the firing temperature exceeds the above range, the lithium transition metal phosphate becomes a hard sintered body, which is not preferable.

[0058]

[0059] ​The firing atmosphere in the fourth step is an oxidizing atmosphere such as an air atmosphere or an oxygen gas atmosphere, or an inert gas atmosphere. In the fourth step, firing in an oxidizing atmosphere is preferable from the viewpoint of promoting crystal growth and obtaining particles with a desired particle size at a low temperature in a short time. Further, when the M source or the A source that needs to prevent oxidation is included during firing in the fourth step, it is preferable to use an inert gas atmosphere as the firing atmosphere.

[0060] The firing time in the fourth step is not particularly limited and is 2 hours or more, preferably 4 to 10 hours. In the fourth step, if firing is performed for 2 hours or more, preferably 4 to 10 hours, single-phase transition metal-containing lithium phosphate can be obtained by X-ray diffraction.

[0061] In the fourth step, the transition metal-containing lithium phosphate obtained by once performing firing may be fired a plurality of times as necessary.

[0062] After performing the fourth step, the transition metal-containing lithium phosphate obtained by performing the fourth step may be further classified as necessary.

[0063] In the method for producing transition metal-containing lithium phosphate of the present invention, in the first step, lithium metaphosphate is used as a phosphorus source and a lithium source, and is mixed with an M source in an aqueous solvent. In the second step, a slurry containing a raw material pulverized product obtained by subjecting a raw material mixed slurry containing lithium metaphosphate and the M source to wet pulverization treatment is less likely to adhere to a spray drying apparatus during spray drying in the third step, and through spray drying by the spray drying method in the third step and firing in the fourth step, it is converted into single-phase transition metal-containing lithium phosphate by X-ray diffraction. Therefore, single-phase transition metal-containing lithium phosphate can be obtained in a high yield.

[0064] Further, in the method for producing a transition metal-containing lithium phosphate of the present invention, if necessary, a fifth step of pulverizing the transition metal-containing lithium phosphate obtained by performing the fourth step can be performed. In the method for producing a transition metal-containing lithium phosphate of the present invention, it is preferable to perform a pulverization treatment on the transition metal-containing lithium phosphate obtained by performing the fourth step because a transition metal-containing lithium phosphate having fine particles and a sharp particle size distribution can be obtained.

[0065] The pulverization treatment in the fifth step may be a dry pulverization treatment or a wet pulverization treatment. Examples of the wet pulverization apparatus include a ball mill and a bead mill. Examples of the dry pulverization apparatus include known pulverization apparatuses such as a jet mill, a pin mill, a roll mill, a ball mill, and a bead mill.

[0066] After performing the fifth step, the transition metal-containing lithium phosphate obtained by performing the fifth step may be further classified if necessary.

[0067] Also, in the method for producing a transition metal-containing lithium phosphate of the present invention, in the fourth step, firing is performed at a temperature exceeding 700°C, preferably 750 to 850°C, particularly preferably 800 to 850°C, and grain growth is performed so that the average particle diameter of the obtained transition metal-containing lithium phosphate becomes 2 μm or more. Then, the sintering of the transition metal-containing lithium phosphate proceeds, and then, a pulverization treatment is performed in the fifth step. However, when chipping is performed, there may be many fine particle components. Therefore, after performing the fifth step, in order to reduce the fine particle component, it is preferable to perform a sixth step of re-firing the pulverized product obtained by performing the fifth step. For example, in the method for producing a transition metal-containing lithium phosphate of the present invention, a fourth step of firing the spray-dried powder obtained by performing the third step at a temperature exceeding 700°C, preferably 750 to 850°C, particularly preferably 800 to 850°C is performed. Then, a fifth step of pulverizing the transition metal-containing lithium phosphate obtained by performing the fourth step is performed. Then, a sixth step of re-firing the pulverized product obtained by performing the fifth step can be performed.

[0068] By performing the re-firing in this sixth step, fine particles of the transition metal-containing lithium phosphate can be incorporated into larger particles of the transition metal-containing lithium phosphate, and the amount of fine particles can be reduced.

[0069] The re-firing temperature in the sixth step is 400 to 800 °C, preferably 500 to 700 °C. If the firing temperature is less than the above range, the effect of reducing fine particles will be low. On the other hand, if the re-firing temperature exceeds the above range, sintering will proceed excessively and the tendency for coarse particles to increase will occur.

[0070] The re-firing atmosphere in the sixth step is an oxidizing atmosphere such as an air atmosphere or an oxygen gas atmosphere, or an inert gas atmosphere. In the sixth step, it is preferable to perform the firing in an oxidizing atmosphere because the fine particles of the transition metal-containing lithium phosphate are more likely to be incorporated into the larger particles of the transition metal-containing lithium phosphate. Further, when the M source or A source that needs to prevent oxidation is included during the firing in the sixth step, it is preferable to use an inert gas atmosphere as the firing atmosphere.

[0071] The re-firing time in the sixth step is not particularly limited and is 2 hours or more, preferably 4 to 10 hours. In the sixth step, if firing is performed for 2 hours or more, preferably 4 to 10 hours, cobalt lithium phosphate having satisfactory physical properties can be obtained.

[0072] After the completion of the sixth step, the transition metal-containing lithium phosphate obtained by performing the sixth step can be crushed, classified, etc. as necessary.

[0073] The transition metal-containing lithium phosphate obtained by the method for producing a transition metal-containing lithium phosphate of the present invention in this way is, in addition to being a single-phase transition metal-containing lithium phosphate by X-ray diffraction, preferably has an average particle diameter of 0.1 to 10 μm, particularly preferably 0.5 to 5.0 μm, as determined by SEM observation, and a BET specific surface area of preferably 0.5 to 10.0 m 2 / g, particularly preferably 1.0 to 8.0 m 2 / g.

[0074] In addition, in the method for producing a transition metal-containing lithium phosphate of the present invention, if necessary, the following Step A can be performed on the transition metal-containing lithium phosphate obtained by performing any one of Step 4, Step 5, and Step 6.

[0075] Step A is a step of mixing the transition metal-containing lithium phosphate obtained by performing any one of Step 4, Step 5, and Step 6 with a conductive carbon material source in which carbon is deposited by thermal decomposition (hereinafter, also simply referred to as "conductive carbon material source") to obtain a mixture of the transition metal-containing lithium phosphate and the conductive carbon material source, and then heat-treating the mixture to thermally decompose the conductive carbon material source to obtain a transition metal-containing lithium phosphate-carbon composite.

[0076] As the conductive carbon material source, at least one that is thermally decomposed by heat treatment in Step A to deposit carbon is used. The conductive carbon material source is a component that imparts conductivity to the transition metal-containing lithium phosphate. By forming a composite of conductive carbon and the transition metal-containing lithium phosphate, a lithium secondary battery using the transition metal-containing lithium phosphate-carbon composite as a positive electrode active material can be expected to have improved discharge capacity and cycle characteristics.

[0077] Examples of the conductive carbon material source include coal tar pitch from soft pitch to hard pitch; coal-based heavy oils such as dry distillation liquefied oil, straight-run heavy oils of atmospheric residue, vacuum residue, crude oil, and pyrolysis by-products such as ethylene tar during naphtha pyrolysis; petroleum-based heavy oils such as cracked heavy oils; 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; nitrogen-containing polyacrylonitrile; organic polymers such as polypyrrole; sulfur-containing organic polymers such as polythiophene and polystyrene; natural polymers such as saccharides including glucose, fructose, lactose, maltose, and sucrose; thermoplastic resins such as polyphenylene sulfide and polyphenylene oxide, and thermosetting resins such as phenol-formaldehyde resin and imide resin. Among these, saccharides are industrially available at low cost and are preferable from the viewpoint of improving the discharge capacity and cycle characteristics of a lithium secondary battery using the finally obtained transition metal-containing lithium phosphate carbon composite as a positive electrode active material.

[0078] The blending ratio of the conductive carbon material source is preferably such that the carbon atoms in the conductive carbon material source are 0.1 to 20.0% by mass, preferably 0.5 to 15.0% by mass, with respect to the transition metal-containing lithium phosphate, from the viewpoint of improving the discharge capacity and cycle characteristics of a lithium secondary battery using the transition metal-containing lithium phosphate carbon composite as a positive electrode active material.

[0079] In the first A step, the mixing of the transition metal-containing lithium phosphate and the conductive carbon material source can be carried out either dry or wet.

[0080] In the first step A, as a method of performing dry mixing treatment, it is preferable to perform it by mechanical means in terms of obtaining a uniform mixture. The device used for dry mixing is not particularly limited as long as it can obtain a uniform mixture. For example, high-speed mixers, super mixers, turbo-sphere mixers, Erie mixers, Henschel mixers, Nauta mixers, ribbon blenders, V-type mixers, conical blenders, jet mills, cosmomisers, paint shakers, bead mills, ball mills, etc. can be mentioned. In addition, at the laboratory level, a household mixer is sufficient.

[0081] In addition, in the first step A, as a method of performing wet mixing treatment, a transition metal-containing lithium phosphate and a conductive carbon material source are added to an aqueous solvent so that the solid content is 10 to 80% by mass, preferably 20 to 70% by mass, and this is mixed by mechanical means to prepare a slurry. Then, the slurry is dried in a static state or spray-dried to obtain a mixture of the transition metal-containing lithium phosphate and the conductive carbon material source.

[0082] The device used for wet mixing is not particularly limited as long as it can obtain a uniform slurry. For example, stirrers, agitators with stirring blades, three-roll mills, ball mills, disper mills, homogenizers, vibration mills, sand grind mills, attritors, and high-power agitators can be mentioned. The wet mixing treatment is not limited to the mixing treatment by the mechanical means exemplified above. In addition, a surfactant may be added to the slurry during wet mixing for the mixing treatment.

[0083] Next, the mixture of the transition metal-containing lithium phosphate and the conductive carbon material source prepared as described above is heat-treated. It is necessary to perform the heat treatment at a temperature at which the conductive carbon material source is thermally decomposed to deposit carbon. The heating temperature is 180 to 900 °C, preferably 210 to 800 °C. By having the heating temperature of the heat treatment within the above range, aggregation can be suppressed while uniformly coating the particles with carbon. The heating time of the heat treatment is 0.2 hours or more, preferably It is 0.5 to 5 hours. The atmosphere for the heat treatment is preferably an inert gas atmosphere in that it can suppress the oxidation of carbon. Further, in the heat treatment in the method for producing lithium transition metal phosphate of the present invention, the conductive carbon material source is heated once to a temperature equal to or higher than the melting point of the used conductive carbon material source to melt the conductive carbon material source, and then heat-treated within the above range to precipitate carbon from the conductive carbon material source, which is preferable in that carbon can be uniformly coated on the particle surface.

[0084] The lithium transition metal phosphate and the lithium transition metal phosphate-carbon composite obtainable by carrying out the production method of the present invention are suitably used as a positive electrode material for a lithium secondary battery, an all-solid battery, or the like.

Examples

[0085] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to these examples.

[0086] (Example 1) <First step · Second step> In a 2.4 L polypropylene pot, 2.3 kg of φ5 mm zirconia balls, 81.1 g of high-purity lithium metaphosphate (average particle size 300 μm, manufactured by Nippon Chemical Industry Co., Ltd.), 90 g of cobalt hydroxide (average particle size 0.24 μm), 855 g of pure water, and 11 g of a dispersant (ammonium polycarboxylate) were put in, the operation of the mill was started at a rotation speed of 200 rpm, and a pulverization treatment was performed for 20 hours. After pulverization, the zirconia balls were separated with a 1 mm sieve to obtain a slurry containing the raw material pulverized product. The average particle size (D ) of the solid content in the slurry containing the raw material pulverized product determined by the laser scattering / diffraction method was 5.5 μm. 50 <Third step> The slurry containing the raw material pulverized product was supplied to a spray dryer with the temperature of the hot air inlet set at 220°C at a supply rate of 2.4 L / h to obtain 170 g of a spray-dried powder. Further, when the inside of the spray dryer after spray drying was visually observed, there were few internal deposits, and the recovery rate was 95.5% based on the solid content. <Step 4 and Step 5> Next, the obtained spray-dried powder was fired in an air atmosphere at 650°C for 4 hours to obtain a fired product. Next, the fired product was pulverized using a lab jet mill to obtain a pulverized product. When the obtained pulverized product was subjected to X-ray diffraction analysis, the pulverized product was single-phase LiCoPO4. This was used as a transition metal-containing lithium phosphate sample. Also, the X-ray diffraction pattern of the obtained transition metal-containing lithium phosphate sample is shown in FIG. 1.

[0087] (Example 2) <Step 1 and Step 2> Into a 2.4 L polypropylene pot, 2.3 kg of φ5 mm zirconia balls, 110.8 g of high-purity lithium metaphosphate (average particle size 300 μm, manufactured by Nippon Chemical Industry Co., Ltd.), 155 g of manganese carbonate (average particle size 17.8 μm), 949 g of pure water, and 15 g of a dispersant (ammonium polycarboxylate) were added. The mill was started at a rotation speed of 200 rpm, and a pulverization treatment was performed for 20 hours. After pulverization, the zirconia balls were separated with a 1 mm sieve to obtain a slurry containing a raw material pulverized product. The average particle size (D 50 ) of the solid content in the slurry containing the raw material pulverized product determined by the laser scattering / diffraction method was 3.3 μm. <Step 3> The slurry containing the raw material pulverized product was supplied to a spray dryer with the temperature of the hot air inlet set at 220°C at a supply rate of 2.4 L / h to obtain 254 g of spray-dried powder. Also, when the inside of the spray dryer after spray drying was visually observed, there were few internal deposits, and the recovery rate was 95.6% based on the solid content. When the inside of the spray dryer after spray drying was visually observed, there were few internal deposits, and the recovery rate was 95.6% based on the solid content. <Step 4 and Step 5> Next, the obtained spray-dried powder was fired in an air atmosphere at 650°C for 4 hours to obtain a fired product. Next, the fired product was pulverized using a lab jet mill to obtain a pulverized product. When the obtained pulverized product was subjected to X-ray diffraction analysis, the pulverized product was single-phase LiMnPO4. This was used as a transition metal-containing lithium phosphate sample. Also, the X-ray diffraction pattern of the obtained transition metal-containing lithium phosphate sample is shown in FIG. 2.

[0088] (Example 3) <First process · Second process> Into a 2.4 L polypropylene pot, 2.3 kg of φ5 mm zirconia balls, 131.7 g of high-purity lithium metaphosphate (average particle diameter: 300 μm, manufactured by Nippon Chemical Industry Co., Ltd.), 145 g of nickel hydroxide (average particle diameter: 22.7 μm), 922 g of pure water, and 18 g of a dispersant (ammonium polycarboxylate) were placed, and the mill was started at a rotation speed of 200 rpm for a grinding treatment for 20 hours. After grinding, the zirconia balls were separated with a 1 mm sieve to obtain a slurry containing the raw material ground product. The average particle diameter (D 50 ) of the solid content in the slurry containing the raw material ground product determined by the laser scattering / diffraction method was 5.1 μm. <Third process> The slurry containing the raw material ground product was supplied to a spray dryer with the temperature of the hot air inlet set at 220°C at a supply rate of 2.4 L / h to obtain 279 g of spray-dried powder. Further, when the inside of the spray dryer after spray drying was visually observed, there were few internal deposits, and the recovery rate was 96.1% based on the solid content. <Fourth process · Fifth process> Next, the obtained spray-dried powder was fired in an air atmosphere at 700°C for 4 hours to obtain a fired product. Next, the fired product was ground with a lab jet mill to obtain a ground product. When the obtained ground product was subjected to X-ray diffraction analysis, the ground product was single-phase LiNiPO4. This was used as a transition metal-containing lithium phosphate sample. Further, the X-ray diffraction pattern of the obtained transition metal-containing lithium phosphate sample is shown in FIG. 3.

[0089]

Table 1

[0090] (Reference Example 1) To 11 L of pure water at room temperature (25°C), 1597.7 g of oxalic acid dihydrate was added to make a three-way Stirred for 30 minutes using a N-motor stirrer, and 227 g of a dispersant (ammonium polycarboxylate) was added. Next, 1200 g of cobalt hydroxide was added and stirred for 30 minutes. Next, 1455.6 g of 85% by mass phosphoric acid was added and stirred for 30 minutes. Next, 532.5 g of lithium hydroxide monohydrate was added and stirred for 1 hour to obtain an aqueous raw material slurry. Next, while stirring this aqueous raw material slurry, zirconia beads with a diameter of 0.5 mm were charged into a media stirring type bead mill and mixed for 3 hours for wet grinding. Next, the slurry was supplied to a spray dryer with the temperature of the hot air inlet set at 220°C at a supply rate of 2.4 L / h to obtain 2960 g of a reaction precursor. Also, when the inside of the spray dryer after spray drying was visually observed, there were many internal deposits, and the recovery rate was 79.7% based on the solid content. Next, the obtained reaction precursor was fired in an air atmosphere at 550°C for 4 hours to obtain a fired product. Next, the fired product was ground with a jet mill to obtain a ground product. When the obtained ground product was analyzed by X-ray diffraction, the ground product was single-phase LiCoPO4. This was used as a transition metal-containing lithium phosphate sample.

[0091] (Comparative Example 1) A fired product was prepared in the same manner as in Example 1, except that the slurry containing the ground product obtained after the second step was dried at 120°C for 5 hours without drying by the spray drying method. Next, the fired product was ground with a lab jet mill to obtain a ground product. When the obtained ground product was analyzed by X-ray diffraction, there were heterogeneous phases in addition to LiCoPO4 in the ground product. This was used as a transition metal-containing lithium phosphate sample. Also, the X-ray diffraction pattern of the obtained transition metal-containing lithium phosphate sample is shown in FIG. 4.

[0092] <Evaluation of Physical Properties> The average particle size, BET specific surface area, and particle size distribution of the transition metal-containing lithium phosphate samples obtained in the Examples, Reference Examples, and Comparative Examples were measured. The average particle size was measured by observing the samples at a magnification of 10,000 times using a scanning electron microscope, and the average value of the diameters of 50 or more randomly selected particles was calculated as the average particle size. The particle size distribution was evaluated as follows. (particle size distribution) The transition metal-containing lithium phosphate samples obtained in the examples, reference examples, and comparative examples were analyzed by a laser diffraction / scattering method (manufactured by Nikkiso, product name: Microtrac MT3300EXII particle size analyzer, model: MTEX-SDU). 50 , D 90 was measured. In addition, D 50 and D 90 The smaller the difference, the more uniform the particle size.

[0093] [Table 2] From the results in Table 2, comparing Example 1 and Comparative Example 1, Example 1 has a higher D 50 and D 90 It can be seen that the difference is small and that particles with uniform particle size are obtained.

[0094] Example 4 <1st process / 2nd process> In a 2.4L polypropylene pot, 2.3kg of φ5mm zirconia balls and high-purity 81.1 g of lithium metaphosphate (average particle size 300 μm, manufactured by Nippon Chemical Industry Co., Ltd.), hydroxypropyl 90 g of baltic (average particle size 0.24 μm), 855 g of pure water, and 11 g of dispersant (ammonium polycarboxylate) were added, and the mill was started at 200 rpm and pulverized for 20 hours. After pulverization, the zirconia balls were separated using a 1 mm sieve to obtain a slurry containing the pulverized raw material. The average particle size (D50) of the solid matter in the slurry containing the ground raw material, determined by laser scattering and diffraction, was 5.5 μm. <3rd process> A slurry containing the raw material pulverized product was supplied to a spray dryer with the temperature of the hot air inlet set at 220°C at a supply rate of 2.4 L / h, and 170 g of dry powder was obtained. Also, when the inside of the spray dryer after spray drying was visually observed, there was little internal adhesion, and the recovery rate was 95.6% based on the solid content. <Fourth Step and Fifth Step> Next, the obtained dry powder was fired in an air atmosphere at 820°C for 4 hours to obtain a fired product. Next, the fired product was pulverized with a lab jet mill to obtain a pulverized product. When the obtained pulverized product was analyzed by X-ray diffraction, the pulverized product was single-phase LiCoPO4. Also, for the obtained lithium transition metal phosphate, the maximum particle diameter and the cumulative frequency of fine particles of 1.0 μm or less were measured by the laser scattering / diffraction method. <Sixth Step> The lithium transition metal phosphate after pulverization obtained in the fifth step was re-fired in an air atmosphere at 600°C for 4 hours. For the obtained lithium transition metal phosphate after re-firing, the maximum particle diameter and the cumulative frequency of particles of 1.0 μm or less were determined by the laser scattering / diffraction method. Also, in the same manner as in Example 1, the average particle diameter, BET specific surface area, and particle size distribution were measured.

[0095] (Example 6) In the fourth step, lithium transition metal phosphate was obtained in the same manner as in Example 5, except that the firing temperature was 850°C for 4 hours.

[0096]

Table 3

[0097] From the results in Table 3, it can be seen that by performing the re-firing in the sixth step, the proportion of fine particles of 1.0 μm or less is reduced.

[0098]

Table 4

[0099] (Example 7) <Step A> 10 g of LiCoPO4 obtained in Example 1 and 2 g of lactose were mixed in a rotary and revolving mixer at 100 rpm for 1 minute. The mixture was heat-treated at 220°C for 2 hours under a nitrogen atmosphere, then heated to 700°C and held for 4 hours to obtain a LiCoPO4-carbon composite. Also, As a result of observing the LiCoPO4-carbon composite by (SEM-EDX), it was confirmed that the surface of the LiCoPO4 particles was uniformly coated with carbon. Also, when the carbon amount was measured by TOC, the carbon content was 3% by mass. ​

Claims

1. The following general formula (1): Li x M 1-y A y PO 4 (1) (In the formula, 0.8 ≦ x ≦ 1.2 and 0.0 ≦ y ≦ 0.

5. M represents one or more transition metal elements selected from Co, Mn, and Ni. A represents one or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.) A method for producing a lithium transition metal phosphate represented by the formula: A first step of mixing at least lithium metaphosphate and an M source with an aqueous solvent to obtain a raw material mixture; A second step of subjecting the raw material mixture to wet grinding treatment to obtain a slurry containing a raw material ground product; A third step of spray-drying the slurry containing the raw material ground product by a spray-drying method to obtain a spray-dried powder; A fourth step of firing the spray-dried powder; A method for producing a lithium transition metal phosphate, characterized by comprising the above steps.

2. In the first step, an A source (A represents one or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho) is added to the aqueous solvent. The method for producing a lithium transition metal phosphate according to Claim 1, characterized by this.

3. In the second step, the wet grinding treatment is performed using a media mill. The method for producing a lithium transition metal phosphate according to Claim 1 or 2, characterized by this.

4. In the second step, the average particle diameter of the solid content in the slurry containing the raw material ground product after the wet grinding treatment is 10.0 μm or less. The method for producing a lithium transition metal phosphate according to any one of Claims 1 to 3, characterized by this.

5. M in the general formula (1) is Co. The method for producing a lithium transition metal phosphate according to any one of Claims 1 to 4, characterized by this.

6. The M source is cobalt hydroxide. The method for producing a lithium transition metal phosphate according to any one of Claims 1 to 5, characterized by this.

7. The method for producing a transition metal-containing lithium phosphate according to any one of claims 1 to 6, wherein the firing temperature in the fourth step is 600 to 900 °C.

8. The method for producing a transition metal-containing lithium phosphate according to any one of claims 1 to 7, further comprising a fifth step of pulverizing the transition metal-containing lithium phosphate obtained by performing the fourth step.

9. The method for producing a transition metal-containing lithium phosphate according to any one of claims 1 to 7, further comprising a fifth step of pulverizing the transition metal-containing lithium phosphate obtained by performing the fourth step, and a sixth step of re-firing the pulverized product obtained by performing the fifth step.

10. A method for producing a transition metal-containing lithium phosphate-carbon composite, comprising: mixing the transition metal-containing lithium phosphate obtained by performing the method for producing a transition metal-containing lithium phosphate according to any one of claims 1 to 9 with a conductive carbon material source in which carbon is deposited by thermal decomposition to obtain a mixture of the transition metal-containing lithium phosphate and the conductive carbon material source; and then heat-treating the mixture to thermally decompose the conductive carbon material source to obtain a transition metal-containing lithium phosphate-carbon composite, characterized by having a step A.

Images