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

Abstract

To provide a method for obtaining X-ray diffractive single phase transition metal-containing lithium pyrophosphate of a single phase with a high yield by an industrially advantageous method.SOLUTION: A method for producing transition metal-containing lithium pyrophosphate represented by LixM1-yAyP2O7 (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-containing pyrophosphate useful as a positive electrode material for lithium secondary batteries, all-solid-state batteries, etc.

Background Art

[0002] Lithium-ion batteries are being utilized 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. They are also expected to be used in hybrid vehicles and electric vehicles.

[0003] Phosphates such as lithium cobalt pyrophosphate (Li2CoP2O7) have attracted attention as positive electrode active materials for lithium secondary batteries with high capacity and high energy density (for example, Patent Document 1, Patent Document 2), and positive electrode active materials for all-solid-state batteries with high battery capacity (for example, Patent Document 3, Patent Document 4).

[0004] As a method for producing lithium cobalt pyrophosphate, for example, Patent Document 1 discloses a method in which a lithium source, a cobalt source, and a phosphorus source are mixed by a ball mill, the resulting particle mixture is further pelletized, and the pelletized mixture is fired. Patent Document 3 discloses a method in which a lithium source, a cobalt source, and a phosphorus source are mixed, the resulting mixture is calcined in an air atmosphere, and then the calcined product obtained by the calcination is fired at 650 to 680 °C for 20 to 30 hours in an air atmosphere at a temperature higher than the calcination temperature.

[0005] In addition, the present inventors have also previously proposed a method for producing lithium cobalt pyrophosphate by an industrially advantageous method (Patent Document 5).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] However, in the method of dry-mixing each raw material as in Patent Documents 1 and 2, it is difficult to obtain single-phase cobalt lithium pyrophosphate in X-ray diffraction analysis.

[0008] Also, in the method of Patent Document 5, single-phase cobalt lithium pyrophosphate can be obtained by X-ray diffraction in an industrially advantageous method. However, in the method of Cited Document 5, 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 problem that the yield of cobalt lithium pyrophosphate becomes low.

[0009] In addition, cobalt lithium pyrophosphate has attracted attention as a safe cathode active material, and further development in a more industrially advantageous method is desired.

[0010] Lithium metaphosphate is a compound represented by LiPO3, 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 terms of the atomic molar ratio of Li and P, when used as a production raw material in the case of producing a compound containing 1:1, there are advantages such as being easy to prepare the composition. However, industrially available lithium metaphosphate has coarse particles and problems with reactivity, and has hardly been used as a production raw material for compounds containing Li and P in fields where the presence of heterogeneous phases is disliked by X-ray diffraction.

[0011] Therefore, an object of the present invention is to provide an industrially advantageous method for obtaining a transition metal-containing lithium pyrophosphate that is single-phase in terms of X-ray diffraction in high yield. [Means for solving the problem]

[0012] In view of the above circumstances, the present inventors have conducted extensive research and have found that a compound represented by the following general formula (1): Li x M 1-y A y P2O7(1) (In the formula, 1.7≦x≦2.2, 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.) The present inventors have discovered that in a method for producing a transition metal-containing lithium pyrophosphate represented by the formula (I), lithium metaphosphate is used as the phosphorus source and the lithium source, and the lithium metaphosphate and the M source are mixed in an aqueous solvent and wet-pulverized to produce a slurry that exhibits little adhesion to a spray dryer. Therefore, the present inventors have discovered that a transition metal-containing lithium pyrophosphate that is single-phase in terms of X-ray diffraction can be obtained in high yield by spray-drying a slurry containing the ground raw material obtained by wet-pulverization using a spray-drying method and then calcining the resulting spray-dried powder, thereby completing the present invention. Furthermore, the present inventors have discovered that a transition metal-containing lithium pyrophosphate having a uniform particle size can be obtained by pulverizing the transition metal-containing lithium pyrophosphate thus obtained.

[0013] That is, the present invention (1) relates to a compound represented by the following general formula (1): Li x M 1-y A y P2O7(1) (wherein 1.7 ≦ x ≦ 2.2 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 transition metal-containing lithium pyrophosphate 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; and provides a method for producing a transition metal-containing lithium pyrophosphate, characterized by having the above steps.

[0014] Further, the present invention (2) provides a method for producing a transition metal-containing lithium pyrophosphate according to (1), characterized in that 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.

[0015] The present invention (3) provides a method for producing a transition metal-containing lithium pyrophosphate according to (1) or (2), characterized in that in the 2 above step, the wet grinding treatment is performed by a media mill.

[0016] Further, the present invention (4) provides a method for producing lithium transition metal pyrophosphate according to any one of (1) to (3), characterized in that in the second step, the average particle diameter of the solid content in the slurry containing the raw material pulverized product after wet pulverization treatment is 10.0 μm or less.

[0017] Further, the present invention (5) provides a method for producing lithium transition metal pyrophosphate according to any one of (1) to (4), characterized in that M in the general formula (1) is Co.

[0018] Further, the present invention (6) provides a method for producing lithium transition metal pyrophosphate according to any one of (1) to (5), characterized in that the M source is cobalt hydroxide.

[0019] Further, the present invention (7) provides a method for producing lithium transition metal pyrophosphate according to any one of (1) to (6), characterized in that the firing temperature in the fourth step is 600 °C or higher.

[0020] Further, the present invention (8) provides a method for producing lithium transition metal pyrophosphate according to any one of (1) to (6), characterized in that in the fourth step, the spray-dried powder is fired at 600 to 700 °C in an air atmosphere.

[0021] Further, the present invention (9) provides a method for producing lithium transition metal pyrophosphate according to any one of (1) to (8), characterized by further having a fifth step of pulverizing the lithium transition metal pyrophosphate obtained by performing the fourth step.

[0022] Further, the present invention (10) involves mixing lithium transition metal pyrophosphate obtained by performing the production method of lithium transition metal pyrophosphate according to any one of (1) to (9) with a conductive carbon material source in which carbon is deposited by thermal decomposition to obtain a mixture of the lithium transition metal pyrophosphate and the conductive carbon material source, and then heat-treating the mixture to thermally decompose the conductive carbon material source, thereby obtaining a lithium transition metal pyrophosphate-carbon composite. The present invention provides a method for producing a lithium transition metal pyrophosphate-carbon composite, which is characterized by having a first A step.

Advantages of the Invention

[0023] According to the method for producing lithium transition metal pyrophosphate of the present invention, it is possible to provide a method capable of obtaining single-phase lithium transition metal pyrophosphate by X-ray diffraction in a high yield by an industrially advantageous method.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0025] The method for producing lithium transition metal pyrophosphate of the present invention is represented by the following general formula (1): Li x M 1-y A y P2O7(1) (wherein 1.7 ≤ x ≤ 2.2 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 transition metal-containing lithium pyrophosphate 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 wet-milling the raw material mixture to obtain a slurry containing a raw material milled product; a third step of spray-drying the slurry containing the raw material milled 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 transition metal-containing lithium pyrophosphate, characterized by comprising the above steps.

[0026] The transition metal-containing lithium pyrophosphate obtained by the method for producing a transition metal-containing lithium pyrophosphate of the present invention has the following general formula (1): Li x M 1-y A y P2O7(1) (wherein 1.7 ≤ x ≤ 2.2 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 transition metal-containing lithium pyrophosphate represented by

[0027] In the formula of general formula (1), x is 1.7 or more and 2.2 or less, preferably 1.8 or more and 2.1 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 terms of obtaining a cathode active material for a lithium secondary battery or an all-solid-state battery having a high capacity and a high energy density. 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.

[0028] The first step according to the method for producing lithium transition metal pyrophosphate 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.

[0029] 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 having 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 particles of lithium metaphosphate can be used without problems.

[0030] Examples of the M source according to the first step include oxides, hydroxides, carbonates, organic acid salts, nitrates, and phosphates containing the M element. Oxides, hydroxides, and carbonates containing the M element are preferable from the viewpoints of industrial availability and ease of handling as the M source.

[0031] As the M source related to the first step, a compound containing Co, for example, an oxide, hydroxide, carbonate, organic acid salt, nitrate, or phosphate containing Co is 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.

[0032] The aqueous solvent related to the first step may be water alone or a mixed solvent of water and a hydrophilic solvent.

[0033] 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.

[0034] 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 15.0 to 30.0 parts by mass with respect to 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 grinding efficiency can be increased or the increase in the slurry viscosity after grinding can be suppressed.

[0035] 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 0.30 to 0.70, particularly preferably 0.40 to 0.60. 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 single-phase transition metal-containing lithium pyrophosphate by X-ray diffraction.

[0036] In this way, a raw material mixture is obtained in the first step. However, in the method for producing lithium transition metal pyrophosphate of the present invention, if necessary, in the first step, to the aqueous solvent, 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. That is, in the method for producing lithium transition metal pyrophosphate of the present invention, in addition to lithium metaphosphate and the M source in the aqueous solvent, if necessary, an A source is added, 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 according to the first step.

[0037] Examples of the A source include oxides, hydroxides, carbonates, organic acid salts, nitrates, and phosphates containing the A element.

[0038] 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 and M atoms in the M source (A / (A + M)) is preferably 0.10 to 0.20.

[0039] It should be noted that lithium metaphosphate, the M source, and the A source to be mixed as necessary in the first step are preferably high-purity products in terms of obtaining high-purity lithium transition metal pyrophosphate.

[0040] The second step in the method for producing lithium transition metal pyrophosphate according to 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.

[0041] In the second step, when performing wet grinding, 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 process can be carried out 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 carried out.

[0042] And in the second step, the raw material mixture is subjected to wet grinding. The wet grinding process in the second step can be carried out 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 process using a media mill. By subjecting the raw material mixture to wet grinding 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.

[0043] 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.

[0044] From the viewpoint of performing the wet grinding process 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.

[0045] In the second step, the wet grinding process is carried out until 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. 50This is preferably carried out until the average particle diameter becomes 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 easier to obtain a spray-dried powder having excellent reactivity. Note that D 50 refers to, for example, the particle diameter at 50% in volume integration in the particle size distribution curve obtained by the laser scattering / diffraction method using MT3300 manufactured by Microtrac Bell Co., Ltd.

[0046] In this way, by performing the second step, a slurry containing the raw material pulverized product can be obtained.

[0047] In the method for producing lithium transition metal pyrophosphate of the present invention, the first step of mixing lithium metaphosphate, an M source, and, if necessary, an 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.

[0048] Further, in the method for producing lithium transition metal pyrophosphate of the present invention, in the wet pulverization treatment device for performing the second step, the first step of mixing lithium metaphosphate, an M source, and, if necessary, an 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, an M source, and, if necessary, an A source, and an aqueous solvent are added to the media mill for performing the second step, and then lithium metaphosphate, an M source, an aqueous solvent, and, if necessary, an 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, an M source, and, if necessary, an 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 to mix lithium metaphosphate, an M source, an A source, if necessary, and an aqueous solvent and perform wet pulverization treatment of the obtained raw material mixture.

[0049] The third step in the method for producing lithium transition metal pyrophosphate according to 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.

[0050] Although methods other than the spray-dry method are known as slurry drying methods, based on the finding that it is advantageous to select the spray-dry method in the method for producing lithium transition metal pyrophosphate 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 lithium transition metal pyrophosphate can be obtained by X-ray diffraction.

[0051] 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. Either method can be used in the third step.

[0052] 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 with respect 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.

[0053] 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 pyrophosphate 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 pyrophosphate, 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.

[0054] In the spray drying method of the third step, it is preferable to adjust the hot air inlet temperature of the spray dryer to 170 to 320 °C, preferably 190 to 300 °C, and to adjust the hot air outlet temperature to 80 to 140 °C, because it can prevent the powder from absorbing moisture and facilitate the recovery of the powder.

[0055] In this way, by performing the third step, a spray-dried powder to be subjected to firing in the fourth step is obtained.

[0056] The fourth step according to the method for producing lithium transition metal pyrophosphate of the present invention is a step of firing the spray-dried powder obtained by performing the third step to obtain an X-ray single-phase lithium transition metal pyrophosphate.

[0057] The firing temperature in the fourth step is 600 °C or higher, preferably 600 to 700 °C, and particularly preferably 650 to 700 °C. When the firing temperature is within the above range, an X-ray diffraction single-phase lithium transition metal pyrophosphate can be obtained. On the other hand, when the firing temperature is less than the above range, the reaction is difficult to complete, and lithium transition metal pyrophosphate tends not to be obtained.

[0058] The firing atmosphere in the fourth step is an air atmosphere or an inert gas atmosphere. In the fourth step, when firing is performed at a high temperature exceeding 700°C, if firing is performed in an air atmosphere, a molten product is obtained and a powdery product cannot be obtained. Therefore, when firing is performed at a temperature exceeding 700°C, it is preferable to perform firing in an inert gas atmosphere. Examples of the inert gas include argon gas, helium gas, nitrogen gas, etc. Among these, nitrogen gas is preferable from the viewpoint of being inexpensive and industrially advantageous.

[0059] In the method for producing lithium transition metal pyrophosphate of the present invention, from the viewpoint of being industrially advantageous, in the fourth step, it is preferable to bake the spray-dried powder at 600 to 700°C in an air 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 lithium transition metal pyrophosphate can be obtained by X-ray diffraction.

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

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

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

[0064] Further, in the method for producing lithium transition metal pyrophosphate of the present invention, a fifth step of pulverizing the lithium transition metal pyrophosphate obtained by performing the fourth step can be performed as necessary. In the method for producing lithium transition metal pyrophosphate of the present invention, performing a pulverization treatment on the lithium transition metal pyrophosphate obtained by performing the fourth step is preferable in that a lithium transition metal pyrophosphate 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 device include a ball mill and a bead mill. Examples of the dry pulverization device include known pulverization devices 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 lithium transition metal pyrophosphate obtained by performing the fifth step may be further classified as necessary.

[0067] The lithium transition metal pyrophosphate obtained by the method for producing lithium transition metal pyrophosphate of the present invention in this way is a single-phase lithium transition metal pyrophosphate by X-ray diffraction. In addition, the average particle diameter determined by SEM observation is preferably 10.0 μm or less, particularly preferably 1.0 to 5. *0 μm, and the BET specific surface area is preferably 1.0 m 2 / g or more, particularly preferably 2.0 to 10.0 m 2 / g.

[0068] Further, in the method for producing lithium transition metal pyrophosphate of the present invention, the following step A can be performed on the lithium transition metal pyrophosphate obtained by performing either the fourth step or the fifth step as necessary.

[0069] In the first step A, the lithium transition metal-containing pyrophosphate obtained by performing either the fourth step or the fifth step is mixed with a conductive carbon material source that deposits carbon by thermal decomposition (hereinafter, also simply referred to as "conductive carbon material source") to obtain a mixture of the lithium transition metal-containing pyrophosphate and the conductive carbon material source. Subsequently, the mixture is heat-treated to thermally decompose the conductive carbon material source to obtain a lithium transition metal-containing pyrophosphate carbon composite.

[0070] As the conductive carbon material source, at least one that thermally decomposes by heat treatment in the first step A to deposit carbon is used. The conductive carbon material source is a component that imparts conductivity to the lithium transition metal-containing pyrophosphate. By forming a composite of conductive carbon and the lithium transition metal-containing pyrophosphate, a lithium secondary battery using the lithium transition metal-containing pyrophosphate carbon composite as a positive electrode active material can be expected to have improved discharge capacity and cycle characteristics.

[0071] Examples of the conductive carbon material source include coal tar pitch from soft pitch to hard pitch; coal-based heavy oils such as retorted liquefied oil, straight-run heavy oils of atmospheric residue, vacuum residue, crude oil, and naphtha, and decomposition-based heavy oils such as ethylene tar by-produced during thermal decomposition, which are petroleum-based 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 such as 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 lithium transition metal-containing phosphate carbon composite as a positive electrode active material.

[0072] The blending ratio of the conductive carbon material source is 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 pyrophosphate. Adding the conductive carbon material source in this way is preferable from the viewpoint of improving the discharge capacity and cycle characteristics of a lithium secondary battery using the transition metal-containing lithium pyrophosphate-carbon composite as a positive electrode active material.

[0073] In the first A step, the mixing of the transition metal-containing lithium pyrophosphate and the conductive carbon material source can be carried out either dry or wet.

[0074] In the first A step, as a method of performing the mixing treatment dry, it is preferable to perform it by mechanical means in terms of obtaining a uniform mixture. The apparatus used for dry mixing is not particularly limited as long as a uniform mixture can be obtained. For example, a high-speed mixer, a super mixer, a turbo sphere mixer, an Ehrlich mixer, a Henschel mixer, a Nauta mixer, a ribbon blender, a V-type mixer, a conical blender, a jet mill, a cosmosizer, a paint shaker, a bead mill, a ball mill, etc. can be mentioned. At the laboratory level, a household mixer is sufficient.

[0075] Also, in the first A step, as a method of performing the mixing treatment wet, the transition metal-containing lithium pyrophosphate and the 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 mixture of the transition metal-containing lithium pyrophosphate and the conductive carbon material source can be obtained by drying the slurry in a stationary state or by spray-drying the slurry.

[0076] The device used for wet mixing is not particularly limited as long as a uniform slurry can be obtained. For example, devices such as stirrers, agitators with stirring blades, three-roll mills, ball mills, disper mills, homogenizers, vibration mills, sand grind mills, attritors, and high-intensity stirrers can be mentioned. The wet mixing process is not limited to the mixing process by the mechanical means exemplified above. In addition, a surfactant may be added to the slurry for the wet mixing process.

[0077] Next, the mixture of the lithium transition metal-containing pyrophosphate prepared as described above and the conductive carbon material source is heat-treated. The heat treatment needs to be carried out at a temperature at which the conductive carbon material source is thermally decomposed to deposit carbon, and 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 0.5 to 5 hours. The atmosphere of 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 the lithium transition metal-containing pyrophosphate of the present invention, it is preferable to heat 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-treat within the above range to deposit carbon from the conductive carbon material source, in that carbon can be uniformly coated on the particle surface.

[0078] The lithium transition metal-containing pyrophosphate and the lithium transition metal-containing pyrophosphate-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-state battery, and the like.

Examples

[0079] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0080] (Example 1) <First step · Second step> Into a 2.4 L polypropylene pot, 2.3 kg of φ5 mm zirconia balls, 181.5 g of high-purity lithium metaphosphate (average particle size 300 μm, manufactured by Nippon Chemical Industry Co., Ltd.), 100.0 g of cobalt hydroxide (average particle size 0.24 μm), 950 g of pure water, and 19 g of a dispersant (ammonium polycarboxylate) were added. The mill was started at a rotation speed of 200 rpm, and a grinding treatment was performed 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 size (D 50 ) of the solid content in the slurry containing the raw material ground product determined by the laser scattering / diffraction method was 6.0 μm. <Third step> 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 280 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 96.7% based on the solid content. <Fourth step and Fifth step> 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 ground with a lab jet mill to obtain a ground product. When the obtained ground product was analyzed by X-ray diffraction, the ground product was single-phase Li 1.86 CoP2O7. This was used as a transition metal-containing lithium pyrophosphate sample. Also, the X-ray diffraction pattern of the obtained transition metal-containing lithium pyrophosphate sample is shown in FIG. 1.

[0081] (Example 2) <First step and Second step> Into a 2.4 L polypropylene pot, 2.3 kg of φ5 mm zirconia balls, 154.8 g of high-purity lithium metaphosphate (average particle size 300 μm, manufactured by Nippon Chemical Industry Co., Ltd.), 110.0 g of manganese carbonate (average particle size 17.8 μm), 882 g of pure water, and 16 g of a dispersant (ammonium polycarboxylate) were added. The mill was started at a rotation speed of 200 rpm, and a grinding treatment was performed 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 size (D 50 ) of the solid content in the slurry containing the raw material pulverized product determined by the laser scattering / diffraction method was 4.1 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, and 261 g of spray-dried powder was obtained. Further, when the inside of the spray dryer after spray drying was visually observed, there was little internal adhesion, and the recovery rate was 96.4% 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. Then, 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 Li2MnP2O7. This was used as a transition metal-containing lithium pyrophosphate sample. The X-ray diffraction pattern of the obtained transition metal-containing lithium pyrophosphate sample is shown in Figure 2.

[0082]

Table 1

[0083] (Reference Example 1) To 11 L of pure water at room temperature (25°C), 1604.5 g of oxalic acid dihydrate was added and stirred for 30 minutes using a three-one motor stirrer, and 228 g of a dispersant (ammonium polycarboxylate) was added. Next, 1200 g of cobalt hydroxide was added and stirred for 30 minutes. Next, 2922.4 g of 85 mass% phosphoric acid was added and stirred for 30 minutes. Next, 1068.8 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, it was supplied to a media stirring type bead mill charged with zirconia beads having a diameter of 0.5 mm and mixed for 3 hours to perform wet pulverization. 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 2590 g of a reaction precursor. Further, when the inside of the spray dryer after spray drying was visually observed, there were many internal deposits, and the recovery rate was 44.8% based on the solid content. Next, the obtained reaction precursor was calcined in an air atmosphere at 650°C for 4 hours to obtain a calcined product. Next, the calcined product was pulverized with a jet mill to obtain a pulverized product. When the obtained pulverized product was analyzed by X-ray diffraction, the pulverized product was single-phase Li 1.86 CoP2O7. This was used as a transition metal-containing lithium pyrophosphate sample.

[0084] (Comparative Example 1) A calcined product was prepared in the same manner as in Example 1, except that the slurry containing the pulverized product obtained after the second step was dried at 120°C for 5 hours without drying by the spray drying method. Next, the calcined 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 had heterogeneous phases such as Li 1.86 CoP2O7 and LiCoPO4. This was used as a transition metal-containing lithium pyrophosphate sample. Further, the X-ray diffraction pattern of the obtained transition metal-containing lithium pyrophosphate sample is shown in FIG. 3.

[0085] <Evaluation of Various Physical Properties> For the transition metal-containing lithium pyrophosphate samples obtained in the examples, reference examples, and comparative examples, the average particle diameter, BET specific surface area, and particle size distribution were measured. Regarding the measurement of the average particle diameter, observations were made with a scanning electron microscope at a magnification of 10,000 times, and the average value of 50 or more arbitrarily extracted particles was determined as the average particle diameter. The particle size distribution was evaluated as follows. (Particle Size Distribution) For the transition metal-containing lithium pyrophosphate samples obtained in the examples, reference examples, and comparative examples, D 50 , D 90was measured. In addition, D 50 and D 90 The smaller the difference between them indicates that the particle sizes are more uniform.

[0086]

Table 2

[0087] (Example 3) <The first step A> 10 g of Li2CoP2O7 obtained in Example 1 and 2 g of lactose were mixed (in a rotating and revolving mixer at 100 rpm for 1 minute). After heat-treating the mixture at 220 °C for 2 hours under a nitrogen atmosphere, the temperature was raised to 700 °C and held for 4 hours to obtain a Li2CoP2O7-carbon composite. Further, as a result of observing the Li2CoP2O7-carbon composite by (SEM-EDX), it was confirmed that the particle surface of Li2CoP2O7 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 P 2 O 7 (1) (In the formula, 1.7 ≤ x ≤ 2.2, 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.) A method for producing lithium transition metal pyrophosphate 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 lithium transition metal pyrophosphate, characterized by comprising the above steps.

2. In the first step, further, 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 lithium transition metal pyrophosphate 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 lithium transition metal pyrophosphate 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 lithium transition metal pyrophosphate according to any one of Claims 1 to 3, characterized by this.

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

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

7. The method for producing lithium transition metal pyrophosphate according to any one of claims 1 to 6, characterized in that the firing temperature in the fourth step is 600 ° C or higher.

8. The method for producing lithium transition metal pyrophosphate according to any one of claims 1 to 6, characterized in that in the fourth step, the spray-dried powder is fired at 600 to 700 ° C in an air atmosphere.

9. Furthermore, the method for producing lithium transition metal pyrophosphate according to any one of claims 1 to 8, characterized by having a fifth step of pulverizing the lithium transition metal pyrophosphate obtained by performing the fourth step.

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

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