Method for producing lithium vanadium phosphate

Abstract

To provide a method for industrially advantageously producing a lithium vanadium phosphate carbon composite containing lithium vanadium phosphate of high purity as determined by X-ray diffraction.SOLUTION: There is provided a method for producing lithium vanadium phosphate having a NASICON structure, the method comprising: a first step of adding vanadium pentoxide, phosphoric acid, and gluconic acid to a water solvent and performing a reduction reaction of vanadium pentoxide to prepare a reduction reaction solution; a second step of adding a lithium source to the reduction reaction solution to prepare a starting material mixed solution; a third step of subjecting the starting material mixed solution to spray-drying to obtain a reaction precursor; and a fourth step of firing the reaction precursor at 500-1300°C in an inert gas atmosphere or a reducing atmosphere to obtain lithium vanadium phosphate.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for producing lithium vanadium phosphate, which is useful as a positive electrode material for lithium secondary batteries and electrochemical capacitors. [Background technology]

[0002] Lithium-ion batteries are used in mobile devices, laptop computers, electric vehicles, and hybrid vehicles. Lithium-ion batteries are generally considered to have excellent capacity and energy density, and currently LiCoO2 is the main material used for the positive electrode. However, due to resource issues with Co, LiMnO2 and LiNiO 2、 Development of Li-Ni-Mn-Co systems and other materials is also underway.

[0003] Currently, LiFePO4 is attracting attention as an alternative material, and research and development is underway at various institutions. Fe is an excellent resource, and LiFePO4, which uses Fe, has a slightly lower energy density, but its excellent high-temperature properties make it a promising material for the positive electrode of lithium-ion batteries for electric vehicles.

[0004] However, LiFePO4 has a rather low operating voltage, so lithium vanadium phosphate (Li3V2(PO4)3) with a NASICON (Na Super Ionic Conductor) structure, which uses V instead of Fe, is attracting attention.

[0005] The present applicants previously proposed in Patent Document 1 listed below a method for producing a lithium vanadium phosphate carbon composite, which comprises: a first step of preparing a raw material mixture by mixing, in an aqueous solvent, a lithium source, a pentavalent or tetravalent vanadium compound, a phosphorus source, and a conductive carbon material source that generates carbon upon thermal decomposition; a second step of heating the raw material mixture to cause a precipitation reaction to obtain a reaction solution containing a precipitate product; a third step of wet-pulverizing the reaction solution containing the precipitate product using a media mill to obtain a slurry containing a pulverized product; a fourth step of spray-drying the slurry containing the pulverized product to obtain a reaction precursor; and a fourth step of firing the reaction precursor at 600 to 1300°C in an inert gas atmosphere or a reducing atmosphere. Furthermore, in Patent Document 2 listed below, the present applicant has proposed a method for producing lithium vanadium phosphate by heat-treating a vanadium compound, a phosphorus source, and a conductive carbon material source that generates carbon upon thermal decomposition in an aqueous solvent, preferably at 60 to 100°C, to carry out a reaction, adding a lithium source to the heat-treated liquid, carrying out a reaction, spray-drying the resulting reaction liquid to obtain a reaction precursor, and calcining the reaction precursor in an inert gas atmosphere or a reducing atmosphere. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2012 / 043367 Brochure [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-160107 Summary of the Invention [Problem to be solved by the invention]

[0007] Lithium vanadium phosphate is highly safe even at high temperatures and is therefore attracting attention as a positive electrode material for lithium secondary batteries for automotive applications, all-solid-state batteries, electrochemical capacitors, and the like. To commercialize this compound, it is desirable to develop a method for producing lithium vanadium phosphate at even lower cost by, for example, simplifying the process.

[0008] That is, an object of the present invention is to provide an industrially advantageous method for producing lithium vanadium phosphate containing lithium vanadium phosphate of high purity as measured by X-ray diffraction. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems, and as a result of investigating ways to simplify the steps in the methods for producing lithium vanadium phosphate described in Patent Documents 1 and 2, they have discovered that by using gluconic acid instead of reducing sugar in the step of preparing the reaction precursor, it is possible to carry out the reduction reaction of vanadium pentoxide without actively performing a heat treatment, and have thus completed the present invention.

[0010] That is, the present invention (1) is a method for producing lithium vanadium phosphate having a NASICON structure, a first step of adding vanadium pentoxide, phosphoric acid, and gluconic acid to an aqueous solvent and carrying out a reduction reaction of vanadium pentoxide to prepare a reduction reaction solution; a second step of adding a lithium source to the reduction reaction solution to prepare a raw material mixture; a third step of spray-drying the raw material mixture to obtain a reaction precursor; a fourth step of calcining the reaction precursor at 500 to 1300°C in an inert gas atmosphere or a reducing atmosphere to obtain lithium vanadium phosphate; The present invention provides a method for producing lithium vanadium phosphate, comprising the steps of:

[0011] The present invention (2) also provides the method for producing lithium vanadium phosphate according to (1), characterized in that the amount of gluconic acid added in the first step is such that the molar ratio (C / V) of C atoms in gluconic acid to V atoms in vanadium pentoxide is 0.9 to 6.0.

[0012] The present invention (3) also provides the method for producing lithium vanadium phosphate according to (1), characterized in that the amount of gluconic acid added in the first step is 2.0 to 6.0 in terms of the molar ratio (C / V) of C atoms in gluconic acid to V atoms in vanadium pentoxide, and a raw material mixture in the form of a solution is obtained in the second step.

[0013] The present invention (4) also provides the method for producing lithium vanadium phosphate according to (1), characterized in that the amount of gluconic acid added in the first step is 0.9 to 1.9 in terms of the molar ratio (C / V) of C atoms in gluconic acid to V atoms in vanadium pentoxide, and a slurry-like raw material mixture is obtained in the second step.

[0014] The present invention (5) also provides a method for producing lithium vanadium phosphate according to (4), characterized in that it comprises a wet-pulverizing step of wet-pulverizing the slurry-like raw material mixture in a media mill after the second step.

[0015] The present invention (6) also provides a method for producing lithium vanadium phosphate according to (4) or (5), characterized in that in the first step, a dispersant is further added to the aqueous solvent to carry out the reduction reaction.

[0016] The present invention (7) also provides a method for producing lithium vanadium phosphate according to (6), wherein the dispersant is a polycarboxylic acid surfactant.

[0017] The present invention (8) also provides the method for producing lithium vanadium phosphate according to any one of (1) to (7), characterized in that in the first step, the reduction reaction is carried out at a temperature lower than 70°C.

[0018] The present invention (9) also provides a method for producing lithium vanadium phosphate according to any one of (1) to (8), characterized in that in the first step, a Me source (Me represents a metal element other than V having an atomic number of 11 or more or a transition metal element) is further contained in the reduction reaction solution.

[0019] The present invention (10) also provides a method for producing lithium vanadium phosphate according to (9), characterized in that the Me source is at least one selected from a Ti source and an Al source. [Effects of the Invention]

[0020] According to the present invention, the reduction reaction of vanadium pentoxide can be carried out without actively carrying out a heat treatment, and therefore lithium vanadium phosphate containing lithium vanadium phosphate that is highly pure as measured by X-ray diffraction can be produced industrially and advantageously. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is an X-ray diffraction pattern of the reaction precursor obtained in Example 1. [Figure 2] 1 is an SEM photograph of the reaction precursor obtained in Example 1. [Figure 3] 1 is an X-ray diffraction diagram of lithium vanadium phosphate obtained in Example 1. [Figure 4] 1 is an SEM photograph of the lithium vanadium phosphate sample obtained in Example 1. [Figure 5] 1 is an X-ray diffraction pattern of the reaction precursor obtained in Example 2. [Figure 6] 1 is an X-ray diffraction diagram of lithium vanadium phosphate obtained in Example 2. [Figure 7] 1 is an SEM photograph of lithium vanadium phosphate obtained in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described below based on preferred embodiments thereof. The method for producing lithium vanadium phosphate of the present invention is a method for producing lithium vanadium phosphate having a NASICON structure, a first step of adding vanadium pentoxide, phosphoric acid, and gluconic acid to an aqueous solvent and carrying out a reduction reaction of vanadium pentoxide to prepare a reduction reaction solution; a second step of adding a lithium source to the reduction reaction solution to prepare a raw material mixture; a third step of spray-drying the raw material mixture to obtain a reaction precursor; a fourth step of calcining the reaction precursor at 500 to 1300°C in an inert gas atmosphere or a reducing atmosphere to obtain lithium vanadium phosphate; 1. A method for producing a lithium vanadium phosphate carbon composite, comprising:

[0023] The method for producing a lithium vanadium phosphate carbon composite of the present invention is a method for producing a lithium vanadium phosphate carbon composite having a NASICON structure (hereinafter simply referred to as "lithium vanadium phosphate carbon composite").

[0024] The lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention is lithium vanadium phosphate of high purity as measured by X-ray diffraction. In the present invention, lithium vanadium phosphate of high purity as measured by X-ray diffraction means that the lithium vanadium phosphate is detected as single-phase lithium vanadium phosphate when analyzed by X-ray diffraction. The lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention contains carbon to an extent that is not detectable by X-ray diffraction analysis, or is free of carbon.

[0025] The lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention is represented by the following general formula (1): Li x V y (PO4)3(1) (In the formula, x is 2.5 or more and 3.5 or less, and y is 1.8 or more and 2.2 or less.) or lithium vanadium phosphate represented by general formula (1) doped with Me element (Me represents a metal element other than V having an atomic number of 11 or more or a transition metal element), as needed.

[0026] In the general formula (1), x is 2.5 or more and 3.5 or less, preferably 2.8 or more and 3.2 or less, and y is 1.8 or more and 2.2 or less, preferably 1.9 or more and 2.1 or less. When lithium vanadium phosphate contains an Me element, the Me element to be doped may be one or more selected from Sr, Ba, Sc, Y, Hf, Ta, W, Ru, Os, Ag, Zn, Si, Ga, Ge, Sn, Bi, S, Se, Te, Cl, Br, I, Na, K, Mg, Ca, Al, Mn, Co, Ni, Fe, Ti, Zr, Bi, Cr, Nb, Mo, and Cu. Among these, the Me element is preferably Al and / or Ti.

[0027] The method for producing lithium vanadium phosphate of the present invention includes a first step, a second step, a third step, and a fourth step.

[0028] The first step is a step of adding vanadium pentoxide, phosphoric acid, and gluconic acid to an aqueous solvent to carry out a reduction reaction of vanadium pentoxide, thereby preparing a reduction reaction solution.

[0029] In conventional methods using reducing sugars as reducing agents, the reduction reaction of vanadium pentoxide usually needs to be carried out at temperatures between 60 and 100°C. However, by using gluconic acid as a reducing agent, the reduction reaction of vanadium pentoxide can be carried out at temperatures below 60°C.

[0030] In the first step, the amounts of vanadium pentoxide and phosphoric acid added are preferably such that the molar ratio (V / P) of V atoms in vanadium pentoxide to P atoms in phosphoric acid is 0.50 to 0.80, and preferably 0.55 to 0.75, in terms of atom conversion, since this makes it easier to obtain a single-phase lithium vanadium phosphate as a final product in X-ray diffraction analysis.

[0031] In the first step, gluconic acid promotes the reduction reaction of vanadium pentoxide. Furthermore, in the fourth step, gluconic acid is thermally decomposed in an inert or reducing atmosphere to isolate carbon, which serves as a component necessary for preventing the oxidation of vanadium. Furthermore, in the method for producing lithium vanadium phosphate of the present invention, gluconic acid can also function as a component of a conductive carbon source that imparts electrical conductivity to lithium vanadium phosphate.

[0032] In the first step, the amount of gluconic acid added is, in atomic terms, a molar ratio (C / V) of carbon atoms in gluconic acid to V atoms in vanadium pentoxide of preferably 0.9 to 6.0, particularly preferably 1.0 to 5.0, and even more preferably 1.5 to 4.5. If the amount of gluconic acid added is less than the above range, the reduction of vanadium pentoxide will be insufficient, while if it exceeds the above range, the amount of carbon will be excessive relative to lithium vanadium phosphate, which will tend to result in insufficient capacity as a positive electrode material, and this is not preferred.

[0033] In the first step, in order to appropriately adjust the viscosity of the slurry, a dispersant can be added to the water solvent to which vanadium pentoxide, phosphoric acid, and gluconic acid have been added.

[0034] As the dispersant, at least one anionic surfactant selected from carboxylates, sulfates, sulfonates, and phosphates is preferred, as it reduces the viscosity of the reduction reaction slurry and provides a reaction precursor with excellent reactivity. As the anionic surfactant, polycarboxylic acid surfactants or polyacrylic acid surfactants are preferred, and polycarboxylic acid surfactants are particularly preferred. As the polycarboxylic acid surfactant, ammonium salts of polycarboxylic acids are preferred.

[0035] The anionic surfactant may be a commercially available one, and examples of commercially available polycarboxylic acid surfactants include SN Dispersant 5020, SN Dispersant 5023, SN Dispersant 5027, SN Dispersant 5468, and Nopcosperse 5600 manufactured by San Nopco, and Poise 532A manufactured by KAO.

[0036] The concentration of the dispersant in the aqueous solvent is preferably 0.5 to 10% by mass, and more preferably 1 to 10% by mass, in order to obtain a sufficient dispersion effect.

[0037] The vanadium pentoxide, phosphoric acid, and gluconic acid used in the first step may have any production history, but in order to produce high-purity lithium vanadium phosphate, it is preferable that the impurity content be as low as possible.

[0038] The aqueous solvent used in the first step may be water, or a mixed solvent of water and a hydrophilic organic solvent.

[0039] In the first step, the order in which vanadium pentoxide, phosphoric acid, gluconic acid, and an optional dispersant are added to the aqueous solvent, and the means for mixing are not particularly limited.

[0040] In the first step, for example, vanadium pentoxide, phosphoric acid, and gluconic acid are added to an aqueous solvent, and then these are mixed by stirring to carry out a reduction reaction of vanadium pentoxide.

[0041] The temperature at which the reduction reaction of vanadium pentoxide in the first step is carried out is not particularly limited, but the reduction reaction of vanadium pentoxide in the first step can be carried out at 80°C or lower. Since the reduction reaction of vanadium pentoxide in the first step proceeds sufficiently at temperatures below 60°C, the temperature at which the reduction reaction of vanadium pentoxide is carried out in the first step is below 60°C, preferably 20 to 50°C, and more preferably 25 to 45°C, in consideration of the advantages of the present invention. The reduction reaction of vanadium pentoxide is an exothermic reaction, which causes a slight rise in the temperature of the reaction system, but the reduction reaction and the next step can be carried out as is.

[0042] The reduction reaction solution obtained by carrying out the first step is in the form of a solution or a slurry. Note that the term "solution" refers to a state in which no solid matter is visually observed in the solution.

[0043] In the first step, the completion of the reduction reaction can be confirmed by visually confirming that the reduction reaction solution has turned deep green.

[0044] The reaction time for the reduction reaction in the first step is not particularly limited and is generally 0.5 hours or more, preferably 1 to 3 hours. If the reduction reaction is carried out for a reaction time within this range, a satisfactory reduction reaction slurry can be obtained.

[0045] The second step is a step of adding a lithium source to the reduction reaction solution obtained in the first step to prepare a raw material mixture solution.

[0046] Examples of the lithium source for the second step include lithium hydroxide and lithium carbonate. The lithium source is preferably added to the reduction reaction solution obtained in the first step as a solution in water or a suspension in which water is used as a dispersion solvent. The lithium source may have any manufacturing history, but in order to produce high-purity lithium vanadium phosphate, it is preferable that the lithium source have as little impurity content as possible.

[0047] In the second step, the amount of the lithium source added is, in atomic terms, 0.7 to 1.3, preferably 0.8 to 1.2, in terms of the molar ratio (Li / P) of Li atoms in the lithium source to P atoms in the phosphoric acid in the first step. When the amount of the lithium source added is within the above range, it is preferred from the viewpoint that the final product is easily obtained as lithium vanadium phosphate having high purity as measured by X-ray diffraction.

[0048] In the second step, the temperature at which the lithium source is added to the reduction reaction solution is not particularly limited, but is 80°C or lower, preferably less than 60°C, more preferably 15 to 50°C, and even more preferably 20 to 45°C.

[0049] In the second step, for example, a lithium source is added to the reduction reaction solution, and a mixing treatment such as stirring is carried out at 80°C or lower, preferably less than 60°C, more preferably 15 to 50°C, and even more preferably 20 to 45°C, for 30 minutes or more, preferably 60 minutes to 2 hours, to obtain a raw material mixture.

[0050] The raw material mixture obtained by carrying out the second step may be in the form of a solution or a slurry. Whether the raw material mixture is obtained in the form of a solution or a slurry can be selected by adjusting the amount of gluconic acid added in the first step, and therefore, by adjusting the amount of gluconic acid added in the first step, a raw material mixture in a desired form can be obtained in the second step.

[0051] The raw material mixture obtained by carrying out the second step is in the form of a solution or a slurry. The solution will be referred to as a "raw material mixture in the form of a solution," and the slurry will be referred to as a "raw material mixture in the form of a slurry." Furthermore, when simply referring to a "raw material mixture," it refers to both a raw material mixture in the form of a solution and a raw material mixture in the form of a slurry.

[0052] When obtaining a solution-like raw material mixture in the second step, the amount of gluconic acid added in the first step is set to an amount such that the molar ratio (C / V) of C atoms in gluconic acid to V atoms in vanadium pentoxide is 2.0 to 6.0, preferably 2.5 to 6.0, in atomic terms, thereby making it possible to obtain a solution-like raw material mixture in the second step.

[0053] Citric acid is added to an aqueous solvent containing vanadium pentoxide and phosphoric acid in an amount greater than that required for the reduction of vanadium pentoxide, with the expectation that it will also act as a vanadium chelating agent, and the reduction reaction of vanadium pentoxide is carried out. When a lithium source is added to the solution thus prepared, the solution is unstable at room temperature and the amount of precipitate gradually increases over time, making it difficult to handle industrially. In contrast, the raw material mixture solution obtained in the second step of the present invention is stable and easy to handle, with no precipitate even after 24 hours at room temperature, and allows the production of the target lithium vanadium phosphate in an industrially advantageous manner compared to a solution using citric acid.

[0054] When a slurry-like raw material mixture is obtained in the second step, the amount of gluconic acid added in the first step is set to an amount such that the molar ratio (C / V) of C atoms in gluconic acid to V atoms in vanadium pentoxide is 0.9 to 1.9, preferably 1.0 to 1.9, in atomic terms, so that a slurry-like raw material mixture can be obtained in the second step.

[0055] When a slurry-like raw material mixture is obtained in the second step, the product obtained by adding a lithium source to the slurry-like reduction reaction solution in the second step has a solid content represented by the following general formula (2): LiVOPO4·xH2O (2) (wherein x is 0 to 2) The slurry contains a lithium vanadium phosphorus composite oxide represented by the formula (I) and also lithium dihydrogen phosphate (LiH2PO4) and gluconic acid.

[0056] Furthermore, when a slurry-like raw material mixture is obtained in the second step, it is preferable to carry out a wet-pulverization step in which the slurry-like raw material mixture is wet-pulverized in a media mill after the second step, since this allows a reaction precursor having even better reactivity to be obtained.

[0057] Examples of media mills include bead mills, ball mills, paint shakers, attritors, sand mills, etc., with bead mills being preferred. When using a bead mill, the operating conditions and the type and size of the beads may be appropriately selected depending on the size of the apparatus and the processing amount.

[0058] The wet grinding treatment using a media mill is preferably carried out until the average particle size of the solid content reaches 2.0 μm or less, preferably 0.1 to 1.5 μm, and particularly preferably 0.2 to 0.5 μm, as measured by a laser scattering / diffraction method, in order to obtain a reaction precursor having excellent reactivity. The average particle size is determined by measuring the volume frequency particle size distribution using the laser diffraction scattering method. 50 ) refers to the particle size.

[0059] In the case where a slurry raw material mixture is obtained in the second step and then a wet-grinding step is carried out in which the slurry raw material mixture obtained by carrying out the second step is wet-grinded, the slurry raw material mixture obtained by carrying out the wet-grinding step after the wet-grinding treatment is used as the raw material mixture to be subjected to the third step.

[0060] The third step is a step of spray-drying the raw material mixture obtained in the second step to obtain a reaction precursor.

[0061] When the raw material mixture solution obtained in the second step is subjected to the third step, the reaction precursor obtained by carrying out the third step is an amorphous reaction precursor in terms of X-ray diffraction.

[0062] Furthermore, when the slurry-like raw material mixed solution obtained in the second step is subjected to the third step, the reaction precursor obtained by carrying out the third step is a reaction precursor in which lithium dihydrogen phosphate (LiH2PO4) and gluconic acid are attached to the particle surfaces of the lithium vanadium phosphorus composite oxide represented by the general formula (2). The average particle size of the primary particles of the lithium vanadium phosphorus composite oxide represented by the general formula (2) constituting the reaction precursor is approximately the same as the average particle size of the primary particles of the solid content in the wet-milled slurry obtained by carrying out, for example, the second step.

[0063] Although methods other than spray drying are known for drying the liquid, the present invention employs spray drying based on the finding that it is advantageous to select this drying method. Specifically, when spray drying is used, densely packed granules in which each component is uniformly dispersed can be obtained, and these granules are used as a reaction precursor in the method for producing lithium vanadium phosphate of the present invention, and by calcining this reaction precursor in the third step described below, lithium vanadium phosphate of high purity as measured by X-ray diffraction can be obtained.

[0064] In the spray drying method, a liquid is atomized by a predetermined means, and the resulting fine droplets are dried to obtain granules. For example, the liquid can be atomized using a rotating disk or a pressure nozzle. Either method can be used in the third step.

[0065] In spray drying, the relationship between the size of the atomized slurry droplets and the size of the pulverized material particles contained therein affects stable drying and the properties of the resulting dried powder. Specifically, if the size of the pulverized material raw material particles is too small compared to the size of the droplets, the droplets become unstable, making it difficult to successfully dry. From this perspective, the size of the atomized droplets is preferably 5 to 100 μm, and particularly preferably 10 to 50 μm. It is desirable to determine the amount of slurry to be supplied to the spray drying apparatus taking this into consideration.

[0066] The drying temperature in the spray dryer is preferably adjusted so that the hot air inlet temperature is 180 to 250°C, preferably 200 to 240°C, and the powder temperature is 90 to 150°C, preferably 100 to 130°C, as this prevents the powder from absorbing moisture and makes it easier to recover the powder.

[0067] The fourth step is a step in which the reaction precursor obtained by carrying out the third step is fired at 500 to 1300° C. to obtain lithium vanadium phosphate that is highly pure as measured by X-ray diffraction.

[0068] The firing temperature in the fourth step is 500 to 1300° C., preferably 600 to 1100° C. If the firing temperature in the fourth step is below the above range, the firing time until lithium vanadium phosphate is produced becomes long, and if the firing temperature exceeds the above range, lithium vanadium phosphate melts.

[0069] The firing atmosphere in the fourth step is an inert gas atmosphere or a reducing atmosphere to prevent oxidation of vanadium and melting. The inert gas used in the fourth step is not particularly limited, and examples thereof include nitrogen gas, helium gas, and argon gas.

[0070] In the fourth step, the calcination time is not particularly limited, and calcination for generally 2 hours or more, particularly 3 to 24 hours, will yield lithium vanadium phosphate of high purity as measured by X-ray diffraction.

[0071] In the fourth step, the lithium vanadium phosphate obtained by calcination may be subjected to multiple calcinations, if necessary. When multiple calcinations are performed, the calcined product may be crushed or disintegrated and then calcined.

[0072] In the method for producing lithium vanadium phosphate of the present invention, for the purpose of stabilizing the crystal structure of lithium vanadium phosphate and further improving battery performance, an Me source (Me represents a metal element other than V having an atomic number of 11 or more or a transition metal element) is added to the reduction reaction slurry in the first step as needed, and then the second to fourth steps of the method for producing lithium vanadium phosphate of the present invention are carried out, thereby obtaining lithium vanadium phosphate doped with Me element.

[0073] The Me element is present as a substitute at the Li site and / or V site of the lithium vanadium phosphate represented by the general formula (2).

[0074] Me in the Me source is a metal element or transition metal element having an atomic number of 11 or more other than V. Preferred Me elements include Sr, Ba, Sc, Y, Hf, Ta, W, Ru, Os, Ag, Zn, Si, Ga, Ge, Sn, Bi, S, Se, Te, Cl, Br, I, Na, K, Mg, Ca, Al, Mn, Co, Ni, Fe, Ti, Zr, Bi, Cr, Nb, Mo, and Cu, which may be used alone or in combination of two or more. In the present invention, Me in the Me source is preferably Ti and / or Al, and particularly preferably Al.

[0075] Examples of Me sources include oxides, hydroxides, halides, carbonates, nitrates, phosphates, biphosphates, and organic acid salts containing Me. The Me source can be incorporated into the reduction reaction slurry in the first step by adding the Me source during the first step or before adding the lithium source in the second step. The Me source may be present in the reduction reaction slurry in the form of a solution or a solid. When the Me source is present in the slurry as a solid, it is preferable to use a Me source having an average particle size of 100 μm or less, preferably 0.1 to 50 μm, in order to obtain a reaction precursor with excellent reactivity. A Ti source and / or an Al source is preferable as the Me source in order to further improve battery performance.

[0076] Furthermore, when a Me source is mixed, the amount of the Me source to be mixed depends on the type of Me element to be doped, but in many cases, the amount is such that the molar ratio of the total of V atoms and Me atoms to P atoms in the reduction reaction solution ((Me+V) / P) is 0.50 to 0.80, preferably 0.60 to 0.73, in atomic terms, and the molar ratio of Me atoms to V atoms (Me / V) is greater than 0 and less than 0.45, preferably greater than 0 and less than 0.10.

[0077] When a phosphate or biphosphate is used as the Me source, the phosphorus atoms in the phosphate or biphosphate also serve as a phosphorus source in the production method of the present invention, similar to phosphoric acid. Therefore, when a phosphate or biphosphate is used as the Me source, the amount of the phosphate or biphosphate mixed is preferably adjusted so that the total molar ratio of P atoms derived from the phosphate or biphosphate to P atoms derived from the phosphoric acid in the first step falls within the range of the molar ratio of V atoms and Me atoms to P atoms in the reaction precursor ((Me+V) / P).

[0078] In the method for producing lithium vanadium phosphate of the present invention, the obtained lithium vanadium phosphate may be subjected to a crushing treatment or a pulverization treatment, and may further be classified, if necessary.

[0079] The lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention is highly pure as measured by X-ray diffraction. Furthermore, the lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention contains carbon to an extent that it is not detectable by X-ray diffraction analysis, or contains no carbon at all. When the lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention contains carbon, the carbon contained in the lithium vanadium phosphate becomes conductive carbon. Therefore, when the lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention contains carbon, the carbon content is preferably 1 to 20 mass %, and more preferably 2 to 15 mass %, calculated as C atoms, from the viewpoint of being usable as a positive electrode material for lithium secondary batteries, electrochemical capacitors, and the like.

[0080] Furthermore, when the lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention contains carbon, the carbon content of the lithium vanadium phosphate can be reduced and used as a cathode material for all-solid-state batteries. Examples of methods for reducing the carbon content of the lithium vanadium phosphate include a method in which the reaction precursor obtained by performing the third step is heat-treated in an oxygen-containing atmosphere with an oxygen concentration of 5% by volume or more, preferably 10 to 30% by volume, at 270 to 370°C, preferably 290 to 360°C, until the molar ratio of carbon atoms to vanadium atoms in the reaction precursor becomes 0.3 to 0.6, preferably 0.35 to 0.55, to reduce the carbon content, and then the fourth step is subsequently performed. Alternatively, the lithium vanadium phosphate obtained in the fourth step is heat-treated in an oxygen-containing atmosphere with an oxygen concentration of 5% by volume or more, preferably 10 to 30% by volume, at 250 to 450°C, preferably 300 to 400°C, to reduce the carbon content.

[0081] Furthermore, the lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention has a BET specific surface area of ​​15 m 2 / g or more, preferably 20 to 70m 2 / g. The lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention has an average particle size of 1 to 30 μm, preferably 2 to 25 μm, as measured by laser diffraction scattering. The average particle size is determined by measuring the volume frequency particle size distribution using the laser diffraction scattering method. 50 ) refers to the particle size. Furthermore, the lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention has a cumulative particle size distribution of 90% (D 90 ) particle size and D 50 The particle size ratio (D 90 / D 50 ) is 3.0 or less, preferably 1.2 to 2.8.

[0082] The lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention is used as a cathode material for lithium secondary batteries, all-solid-state batteries, and electrochemical capacitors.

[0083] In the method for producing lithium vanadium phosphate of the present invention, by using gluconic acid as a reducing agent for reducing vanadium pentoxide in the first step, it is possible to reduce vanadium pentoxide without actively heating it, and therefore it is possible to produce lithium vanadium phosphate of high purity as measured by X-ray diffraction in an industrially advantageous manner. [Example]

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0085] Example 1 <First step> 2.4 L of ion-exchanged water was placed in a 10 L beaker, and 94.2 g of ammonium polycarboxylate salt as a dispersant, 450.0 g of vanadium pentoxide, 291.2 g of 50 wt% gluconic acid solution, and 852.5 g of 85 wt% phosphoric acid were added in that order at room temperature (25°C). The reduction reaction was carried out at 25 to 45°C for 40 minutes with stirring, yielding a greenish-blue slurry-like reduction reaction solution. Note that the reduction reaction was exothermic, so the temperature of the reaction system rose from 25°C to 45°C.

[0086] <Second process> A lithium carbonate-containing suspension was prepared by adding 274.2 g of lithium carbonate to 1.3 L of ion-exchanged water. The entire amount of the lithium carbonate-containing suspension was added to the slurry reduction reaction liquid obtained in the first step at 40°C over 30 minutes, and stirring was continued for 60 minutes to obtain a greenish-blue slurry raw material mixture liquid. Next, the obtained slurry-like raw material mixture was fed to a media-agitated bead mill containing zirconia beads with a diameter of 0.5 mm while stirring, and wet-pulverized to obtain a slurry-like raw material mixture after wet-pulverization. The average particle diameter (D 50 ) was 0.8 μm.

[0087] <Third step> The slurry-like raw material mixture after wet grinding was fed into a spray dryer with the outlet temperature set to 120°C to obtain a reaction precursor. X-ray diffraction analysis of the reaction precursor showed that it contained LiVOPO4·2H2O and LiH2PO4 (see Figure 1). Figure 2 shows an electron microscope (SEM) image of the reaction precursor.

[0088] <Fourth process> The resulting reaction precursor was placed in a mullite sagger and fired at 750°C for 4 hours in a nitrogen atmosphere. X-ray diffraction analysis of the resulting lithium vanadium phosphate revealed that it was a single-phase lithium vanadium phosphate (see Figure 3). This was designated the lithium vanadium phosphate sample. An SEM photograph of the resulting lithium vanadium phosphate sample is shown in Figure 4. The average particle diameter (D 50 ) is 19.2 μm, and D 90 The BET specific surface area was 12.4 m 2 / g. Furthermore, the amount of residual carbon in the obtained lithium vanadium phosphate sample was measured using a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation) to determine the content of C atoms, and the amount of residual carbon was found to be 2.2 mass%.

[0089] Example 2 <First step> 2.4 L of ion-exchanged water was placed in a 10 L beaker, and 450.0 g of vanadium pentoxide, 1294.2 g of 50 wt % gluconic acid solution, and 852.5 g of 85 wt % phosphoric acid were added to the beaker at room temperature (25°C), in that order. The reduction reaction was carried out at 25 to 45°C for 40 minutes with stirring, yielding a greenish-blue slurry-like reduction reaction solution. Note that the reduction reaction was exothermic, so the temperature of the reaction system rose from 25°C to 45°C.

[0090] <Second process> A lithium carbonate-containing suspension was prepared by adding 274.2 g of lithium carbonate to 1.3 L of ion-exchanged water. The entire amount of the lithium carbonate-containing suspension was added to the slurry reduction reaction solution obtained in the first step at 40° C. over 30 minutes, and stirring was continued for 60 minutes to obtain a raw material mixture solution that was a deep blue color. No precipitate was observed visually in the solution-state raw material mixture, and even after the solution-state raw material mixture was left standing at 25°C for 24 hours, no precipitate was observed, and the solution was stable.

[0091] <Third step> 60 minutes after the second step was completed, the solution-like raw material mixture was fed into a spray dryer with the outlet temperature set to 120°C to obtain a reaction precursor. X-ray diffraction analysis of the reaction precursor showed that it was amorphous (see Figure 5).

[0092] <Fourth process> The resulting reaction precursor was placed in a mullite sagger and fired at 750°C for 4 hours in a nitrogen atmosphere. X-ray diffraction analysis of the resulting lithium vanadium phosphate revealed that it was a single-phase lithium vanadium phosphate (see Figure 6). This was designated the lithium vanadium phosphate sample. An SEM photograph of the resulting lithium vanadium phosphate sample is shown in Figure 7. The average particle diameter (D 50 ) is 14.0 μm, and D 90 The BET specific surface area was 34.7 m 2 / g. Furthermore, the amount of residual carbon in the obtained lithium vanadium phosphate sample was measured using a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation) to determine the content of C atoms, and the amount of residual carbon was found to be 8.1% by mass.

[0093] (Reference example 1) 2.8 ml of ion-exchanged water was placed in a 10 L beaker, and 500 g of vanadium pentoxide, 818.4 g of citric acid monohydrate, and 947.2 g of 85 wt% phosphoric acid were added in that order at room temperature (25°C). The reduction reaction was carried out at 25-45°C for 40 minutes with stirring, yielding a greenish-blue slurry-like reduction reaction solution. Note that the reduction reaction is exothermic, so the temperature of the reaction system rose from 25°C to 45°C. Next, 304.7 g of lithium carbonate was added to 1.5 L of ion-exchanged water to prepare a lithium carbonate-containing suspension. Next, the entire amount of the lithium carbonate-containing suspension was added to the slurry-like reduction reaction solution at 40°C over 30 minutes, and stirring was continued for 60 minutes to obtain a dark blue solution-like raw material mixture. When the raw material mixture was kept under stirring at 25°C for 24 hours, it became a slurry and a green precipitate was observed.

Claims

1. A method for producing lithium vanadium phosphate having a NASICON structure, comprising: a first step of adding vanadium pentoxide, phosphoric acid, and gluconic acid to an aqueous solvent and carrying out a reduction reaction of vanadium pentoxide to prepare a reduction reaction solution; a second step of adding a lithium source to the reduction reaction solution to prepare a raw material mixture; a third step of spray-drying the raw material mixture to obtain a reaction precursor; a fourth step of calcining the reaction precursor at 500 to 1300°C in an inert gas atmosphere or a reducing atmosphere to obtain lithium vanadium phosphate; 2. A method for producing lithium vanadium phosphate, comprising:

2. 2. The method for producing lithium vanadium phosphate according to claim 1, wherein the amount of gluconic acid added in the first step is such that the molar ratio (C / V) of C atoms in gluconic acid to V atoms in vanadium pentoxide is 0.9 to 6.

0.

3. 2. The method for producing lithium vanadium phosphate according to claim 1, wherein the amount of gluconic acid added in the first step is such that the molar ratio (C / V) of C atoms in gluconic acid to V atoms in vanadium pentoxide is 2.0 to 6.0, and a raw material mixture in the form of a solution is obtained in the second step.

4. 2. The method for producing lithium vanadium phosphate according to claim 1, wherein the amount of gluconic acid added in the first step is 0.9 to 1.9 in terms of a molar ratio (C / V) of C atoms in gluconic acid to V atoms in vanadium pentoxide, and a slurry-like raw material mixture is obtained in the second step.

5. 5. The method for producing lithium vanadium phosphate according to claim 4, further comprising a wet-pulverizing step of wet-pulverizing the slurry-like raw material mixture in a media mill after the second step.

6. 5. The method for producing lithium vanadium phosphate according to claim 4, wherein in the first step, a dispersant is further added to the aqueous solvent to carry out the reduction reaction.

7. 7. The method for producing lithium vanadium phosphate according to claim 6, wherein the dispersant is a polycarboxylic acid surfactant.

8. 2. The method for producing lithium vanadium phosphate according to claim 1, wherein the reduction reaction in the first step is carried out at a temperature lower than 70°C.

9. 2. The method for producing lithium vanadium phosphate according to claim 1, wherein in the first step, a Me source (Me represents a metal element other than V having an atomic number of 11 or more or a transition metal element) is further contained in the reduction reaction solution.

10. 10. The method for producing lithium vanadium phosphate according to claim 9, wherein the Me source is at least one selected from a Ti source and an Al source.

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