Method for producing lithium vanadium phosphate

Abstract

To provide a method for producing lithium vanadium phosphate which is single phase in X-ray diffraction, has a low specific surface area that is a BET specific surface area of 10 m2 / g or less, and has a sharp particle distribution.SOLUTION: Disclosed is a method for producing lithium vanadium phosphate having a NASICON structure, which is characterized by comprising: a step A for preparing carbon source-attached particles in which lithium dihydrogen phosphate (LiH2PO4) and an organic compound in which carbon is generated by thermal decomposition are attached to the particle surface of a lithium vanadium phosphate complex oxide represented by general formula (1): LiVOPO4 xH2O (1) (where x is an integer of 0 to 2), in which the average particle diameter of the primary particles is 2.0 μm or less; a step B for obtaining a reaction precursor by heat-treating the carbon source-attached particles in an oxygen-containing atmosphere; and a step C for obtaining lithium vanadium phosphate by firing the reaction precursor at 500 to 1300°C in an inert gas atmosphere or a reducing atmosphere.SELECTED DRAWING: Figure 7

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 all-solid-state batteries. [Background technology]

[0002] Lithium-ion batteries are used in portable devices and laptop computers. They are generally considered to have excellent capacity and energy density. They are also expected to be used in hybrid and electric vehicles. However, when lithium-ion secondary batteries are used in automobiles, the conditions of temperature and charge / discharge current are severer than those of conventional batteries.

[0003] Nasicon-type phosphates such as lithium vanadium phosphate (Li3V2(PO4)3) are attracting attention as positive electrode active materials for lithium secondary batteries for automobiles and all-solid-state batteries because of their high safety even at high temperatures.

[0004] As a method for producing lithium vanadium phosphate, for example, a method has been proposed in which a lithium source, a vanadium compound, and a phosphorus source are pulverized and mixed, the resulting homogeneous mixture is formed into pellets, and then the formed product is fired (see, for example, Patent Documents 1 and 2). In addition, the following Patent Document 3 proposes a method in which vanadium oxide (V) is dissolved in an aqueous solution containing lithium hydroxide, a phosphorus source and carbon and / or a non-volatile organic compound are further added, the resulting raw material mixture solution is dried to obtain a precursor, and the precursor is heat-treated in an inert atmosphere to obtain a composite of Li3V2(PO4)3 and a conductive carbon material.

[0005] The present applicant also previously proposed in Patent Document 4 below a method for producing a lithium vanadium phosphate carbon composite, which comprises the steps of: a first step of preparing a raw material mixed solution by mixing a lithium source, a pentavalent or tetravalent vanadium compound, a phosphorus source, and a conductive carbon material source that generates carbon by thermal decomposition in an aqueous solvent; a second step of heating the raw material mixed solution to carry out a precipitation reaction to obtain a reaction solution containing a precipitation product; a third step of wet-pulverizing the reaction solution containing the precipitation 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 5 listed below, the present applicant has proposed a method of producing lithium vanadium phosphate by heat-treating a vanadium compound, a phosphorus source, and a conductive carbon material source that generates carbon by thermal decomposition in an aqueous solvent, preferably at 60 to 100° C., to which a lithium source is further added to the liquid after the heat treatment, and then spray-drying the resulting reaction liquid to obtain a reaction precursor, which is then calcined in an inert gas atmosphere or a reducing atmosphere. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2001-500665 [Patent Document 2] Special Publication No. 2002-530835 [Patent Document 3] JP 2008-052970 A [Patent Document 4] International Publication No. 2012 / 043367 Brochure [Patent Document 5] International Publication No. 2014 / 006948 Brochure Summary of the Invention [Problem to be solved by the invention]

[0007] When lithium vanadium phosphate is used as a positive electrode active material for lithium secondary batteries for automobiles, all-solid-state batteries, and the like, it is sometimes desired that the lithium vanadium phosphate has a low specific surface area and a sharp particle size distribution in order to improve battery performance or facilitate handling.

[0008] However, the conventional methods for producing lithium vanadium phosphate as described above tend to produce lithium vanadium phosphate with a high specific surface area. For example, the methods for producing lithium vanadium phosphate described in Patent Documents 4 and 5 produce lithium vanadium phosphate with a sharp particle size distribution and a BET specific surface area of ​​10 m 2 / g, but the BET specific surface area is less than 10 m 2 / g or less, it is difficult to obtain a sharp particle size distribution.

[0009] Therefore, the present invention is a single-phase quartz crystal having a BET specific surface area of ​​10 m 2 The present invention provides a method for producing lithium vanadium phosphate which can provide lithium vanadium phosphate having a low specific surface area of ​​0.1 to 1.0 μm / g or less and a sharp particle distribution. [Means for solving the problem]

[0010] The above problems are solved by the present invention described below. That is, the present invention (1) is a vanadium phosphate having a NASICON structure. A method for producing mulithium, comprising the steps of: The average particle size of the primary particles is 2.0 μm or less, and the formula (1) is as follows: LiVOPO4 xH2O (1) (wherein x is an integer of 0 to 2) A step A of preparing carbon source-attached particles having lithium dihydrogen phosphate (LiH2PO4) and an organic compound that generates carbon by thermal decomposition attached to the surface of a lithium vanadium phosphorus composite oxide particle represented by the formula: A step B of obtaining a reaction precursor by heat-treating the carbon source-attached particles in an oxygen-containing atmosphere; A step C of calcining the reaction precursor at 500 to 1300°C in an inert gas atmosphere or a reducing atmosphere to obtain lithium vanadium phosphate; Have The carbon content of the reaction precursor obtained in the step B is 0.3 to 0.6 in terms of the molar ratio of carbon atoms to vanadium atoms (C / V). The present invention provides a method for producing lithium vanadium phosphate, comprising the steps of:

[0011] The present invention (2) also provides a method for producing lithium vanadium phosphate according to (1), characterized in that the content of the organic compound that generates carbon upon thermal decomposition in the carbon source-attached particles is greater than 0.6 in terms of a molar ratio of carbon atoms to vanadium atoms (C / V).

[0013] In addition, the present invention ( 3 ) is characterized in that the step A includes a spray drying treatment for spraying and drying a slurry containing a lithium vanadium phosphorus composite oxide represented by the general formula (1) having an average particle size of primary particles of 2.0 μm or less, lithium dihydrogen phosphate (LiH2PO4), and the organic compound that generates carbon by thermal decomposition. Or (2) The present invention provides a method for producing lithium vanadium phosphate.

[0014] In addition, the present invention ( 4 ) is characterized in that in the step B, the temperature for heat-treating the carbon source-attached particles is 270 to 370° C. 3 The present invention provides a method for producing lithium vanadium phosphate.

[0015] In addition, the present invention ( 5 ) is a process in which the step A is A step A1 of mixing vanadium pentoxide, phosphoric acid and a reducing sugar in an aqueous solvent to prepare a mixed slurry (1); A2 step of heating the mixed slurry to obtain a reduction reaction solution; A step A3 of adding a solution containing lithium hydroxide to the reduction reaction solution under heating to prepare a slurry (2) containing the lithium vanadium phosphorus composite oxide represented by the general formula (1), lithium dihydrogen phosphate (LiH2PO4), and the organic compound that generates carbon by thermal decomposition; A step A4 of wet-milling the slurry (2) using a media mill to prepare a wet-milled slurry (3); A5 step of spray-drying the wet-milled slurry (3) to obtain the carbon source-adhered particles; The process (1) to ( 4 The present invention provides a method for producing lithium vanadium phosphate.

[0016] In addition, the present invention ( 6 ) is characterized in that in the step A2, the temperature at which the mixed slurry (1) is heat-treated is 60 to 100°C. 5 The present invention provides a method for producing lithium vanadium phosphate of the formula (I).

[0017] In addition, the present invention ( 7 ) is characterized in that in the step A3, the heating temperature of the reduction reaction solution is 40 to 100°C ( 5 ) or ( 6 The present invention provides a method for producing lithium vanadium phosphate of the formula (I).

[0018] In addition, the present invention ( 8 ) is characterized in that in the step A1, the amount of the reducing sugar mixed is such that the molar ratio (C / V) of carbon atoms converted to vanadium atoms of vanadium pentoxide is greater than 0.6 and is not greater than 2.0 ( 5 )~( 7 The present invention provides a method for producing lithium vanadium phosphate.

[0019] In addition, the present invention ( 9 ) is characterized in that the average particle size of the solid content in the wet-milled slurry (3) obtained after the step A4 is 2.0 μm or less ( 5 )~(8 The present invention provides a method for producing lithium vanadium phosphate.

[0020] In addition, the present invention ( 10 ) is characterized in that the reaction precursor further contains an Me source (Me represents a metal element having an atomic number of 11 or more other than V or a transition metal element). 9 The present invention provides a method for producing lithium vanadium phosphate. Effect of the Invention

[0021] According to the method for producing lithium vanadium phosphate of the present invention, a lithium vanadium phosphate having a single phase in terms of X-ray diffraction and a BET specific surface area of ​​10 m 2 The present invention provides a method for producing lithium vanadium phosphate that can provide a lithium vanadium phosphate having a low specific surface area of ​​1 / g or less and a sharp particle distribution. [Brief description of the drawings]

[0022] [Figure 1] X-ray diffraction pattern of LiVOPO4·2H2O obtained in Step A3 of Example 1. [Diagram 2] SEM photograph (1000x) of LiVOPO4·2H2O obtained in step A3 of Example 1. [Diagram 3] SEM photograph (5000x) of LiVOPO4·2H2O obtained in step A3 of Example 1. [Figure 4] 1 is an X-ray diffraction pattern of the carbon source-adhered particles obtained in step A5 of Example 1. [Diagram 5] FIG. 2 is an X-ray diffraction diagram of the lithium vanadium phosphate sample obtained in Example 1. [Figure 6] FIG. 2 is an X-ray diffraction diagram of the lithium vanadium phosphate sample obtained in Example 2. [Figure 7] 1 is a SEM photograph of the lithium vanadium phosphate sample obtained in Example 1. [Figure 8] 1 is an SEM photograph of the lithium vanadium phosphate sample obtained in Comparative Example 1. [Figure 9]FIG. 2 is a particle size distribution diagram of the lithium vanadium phosphate sample obtained in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will now be described based on its preferred embodiments. The method for producing lithium vanadium phosphate of the present invention comprises the steps of: A method for producing lithium vanadium phosphate having a NASICON structure, comprising the steps of: The average particle size of the primary particles is 2.0 μm or less, and the formula (1) is as follows: LiVOPO4 xH2O (1) (wherein x is an integer of 0 to 2) A step A of preparing carbon source-attached particles having lithium dihydrogen phosphate (LiH2PO4) and an organic compound that generates carbon by thermal decomposition attached to the surface of a lithium vanadium phosphorus composite oxide particle represented by the formula: A step B of obtaining a reaction precursor by heat-treating the carbon source-attached particles in an oxygen-containing atmosphere; A step C 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 method for producing lithium vanadium phosphate is characterized by comprising the steps of:

[0024] The method for producing lithium vanadium phosphate of the present invention is a method for producing lithium vanadium phosphate having a NASICON structure (hereinafter simply referred to as "lithium vanadium phosphate").

[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 (2): Li x V y (PO4)3(2) (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 (2) doped with Me element (Me represents a metal element having an atomic number of 11 or more other than V or a transition metal element) as necessary.

[0026] In the general formula (2), 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.

[0027] 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 one or more selected from Mg, Ca, Al, Mn, Co, Ni, Fe, Ti, Zr, Bi, Cr, Nb, Mo, and Cu.

[0028] The method for producing lithium vanadium phosphate of the present invention includes steps A, B, and C.

[0029] (Process A) Step A in the method for producing lithium vanadium phosphate of the present invention is a step of preparing carbon source-attached particles in which lithium dihydrogen phosphate (LiH2PO4) and an organic compound that generates carbon upon thermal decomposition are attached to the particle surface of a lithium vanadium phosphorus composite oxide represented by general formula (1) and having an average primary particle size of 2.0 μm or less.

[0030] In the present invention, the carbon source-attached particles may be (i) monodispersed particles in which lithium vanadium phosphorus composite oxide particles represented by general formula (1) having an average primary particle size of 2.0 μm or less are monodispersed, and lithium dihydrogen phosphate (LiH2PO4) and an organic compound that generates carbon upon thermal decomposition are attached to the particle surfaces of the monodispersed particles; or (ii) secondary particles in which lithium vanadium phosphorus composite oxide represented by general formula (1) having an average primary particle size of 2.0 μm or less forms secondary particles, and lithium dihydrogen phosphate (LiH2PO4) and an organic compound that generates carbon upon thermal decomposition are attached to the particle surfaces of the secondary particles; or (iii) particles that include both of the forms (i) and (ii).

[0031] In the present invention, in step A, carbon source-attached particles are prepared by attaching lithium dihydrogen phosphate (LiH2PO4) and an organic compound that generates carbon upon thermal decomposition to the particle surfaces of a lithium vanadium phosphorus composite oxide represented by general formula (1) and having an average primary particle size of 2.0 μm or less. This makes it easier to obtain lithium vanadium phosphate that is single-phase as measured by X-ray diffraction with a small amount of carbon by firing in step C, and also makes it easier to obtain lithium vanadium phosphate with a sharp particle distribution.

[0032] The lithium vanadium phosphorus composite oxide represented by general formula (1) in the step A has an average particle size of 2.0 μm or less, preferably 0.1 to 1.5 μm. When the average particle size of the primary particles of the lithium vanadium phosphorus composite oxide represented by general formula (1) is within the above range, the lithium vanadium phosphate produced is less likely to have coarse particles, and it is easy to obtain lithium vanadium phosphate with a sharp particle size distribution, and it is easy to obtain lithium vanadium phosphate with a single phase in terms of X-ray diffraction with a small amount of carbon. On the other hand, when the average particle size of the primary particles of the lithium vanadium phosphorus composite oxide represented by general formula (1) exceeds the above range, the lithium vanadium phosphate produced is more likely to be mixed with coarse particles, and it is difficult to obtain lithium vanadium phosphate with a sharp particle size distribution. The average particle size of the primary particles of the lithium vanadium phosphorus composite oxide is determined as the average particle size (long diameter in Heywood diameter) of 200 particles randomly selected from scanning electron microscope (SEM) observation.

[0033] The lithium vanadium phosphorus composite oxide represented by the general formula (1) is a known compound, and examples of the method include a method in which vanadium pentoxide, a phosphorus source, and an organic compound having a reducing action are subjected to a reduction reaction of vanadium pentoxide in an aqueous solvent at 60 to 100°C, and then lithium hydroxide is added to the reduction solution and a reaction is carried out at 60 to 100°C; and a method in which phosphoric acid, vanadium pentoxide, lithium hydroxide, and an organic compound having a reducing action are used as raw materials for hydrothermal synthesis (see, for example, JP 2010-218829 A). Furthermore, by performing a pulverization treatment as necessary, it is possible to obtain the lithium vanadium phosphorus composite oxide represented by the general formula (1) having an average primary particle size of 2.0 μm or less.

[0034] In the carbon source-attached particles prepared in step A, lithium dihydrogen phosphate (LiH2PO4) is attached to the particle surface of the lithium vanadium phosphorus composite oxide represented by general formula (1). In step B, a part or all of the lithium dihydrogen phosphate (LiH2PO4) attached to the particle surface of the lithium vanadium phosphorus composite oxide represented by general formula (1) becomes an amorphous phosphorus compound (LiH2PO4, LiPO3, etc.) or lithium phosphate (Li3PO4), and further in step C, the lithium dihydrogen phosphate (LiH2PO4) and the amorphous phosphorus compound and / or lithium phosphate produced in step B react with the lithium vanadium phosphorus composite oxide represented by general formula (1) to produce lithium vanadium phosphate represented by general formula (2).

[0035] In the carbon source-attached particles prepared in step A, in addition to lithium dihydrogen phosphate (LiH2PO4), an organic compound that generates carbon upon thermal decomposition is attached to the particle surface of the lithium vanadium phosphorus composite oxide represented by general formula (1). The organic compound that generates carbon upon thermal decomposition is one that is partially removed from the system or the carbon is isolated when the carbon source-attached particles are heat-treated in step B, or is thermally decomposed when the reaction precursor is fired in step C, and the carbon is isolated and converted to carbon. In addition, this isolated carbon is a component necessary for preventing the oxidation of vanadium during firing in step C.

[0036] The organic compound that generates carbon by thermal decomposition is not particularly limited as long as it is converted to carbon through steps B and C, but it is preferable that it dissolves in water solvent because it can be uniformly attached to the particle surface of the lithium vanadium phosphorus composite oxide represented by general formula (1), and reducing sugar is particularly preferable. Examples of reducing sugar include glucose, fructose, lactose, maltose, sucrose, etc., and among these, lactose and sucrose are preferable because they can obtain a reaction precursor with excellent reactivity.

[0037] Among organic compounds that generate carbon by thermal decomposition, an organic compound having a reducing ability for vanadium pentoxide, for example, a reducing sugar, may also be used as a reducing agent for vanadium pentoxide in a preferred embodiment of step A having steps A1 to A5 described below. In this case, in step A having steps A1 to A5, a reaction conversion product generated when an "organic compound having a reducing ability for vanadium pentoxide and generating carbon by thermal decomposition" is used in the reduction reaction of vanadium pentoxide, for example, a reducing sugar, is used as a reducing agent in the reduction reaction of vanadium pentoxide, may be attached to the carbon source-attached particles. In other words, when Step A is a process including Steps A1 to A5, the carbon source-attached particles are carrying thereon organic compounds that produce carbon upon thermal decomposition, including "organic compounds that have the reducing properties of vanadium pentoxide, such as reducing sugars, and that produce carbon upon thermal decomposition" that were not used in the reduction of vanadium pentoxide, and "organic compounds that have the reducing properties of vanadium pentoxide, such as reducing sugars, and that produce carbon upon thermal decomposition" that were produced by using the organic compound as a reducing agent in the reduction reaction of vanadium pentoxide.

[0038] The amount of the organic compound that generates carbon by thermal decomposition in the carbon source-attached particles prepared in step A is preferably greater than 0.6 in terms of the molar ratio of carbon atoms in terms of carbon atoms to vanadium atoms in the carbon source-attached particles (C / V), in order to uniformly attach the organic compound that generates carbon by thermal decomposition to the particle surface of the lithium vanadium phosphorus composite oxide represented by general formula (1) and to suppress oxidation of vanadium in the firing in step C. On the other hand, the amount of the organic compound that generates carbon by thermal decomposition in the carbon source-attached particles prepared in step A is preferably greater than 0.6 and less than 2.0, particularly preferably 0.7 or more and less than 1.7, in terms of the molar ratio of carbon atoms in terms of carbon atoms to vanadium atoms in the carbon source-attached particles (C / V), in order to efficiently reduce carbon derived from the organic compound that generates carbon by thermal decomposition by heating in an oxygen-containing atmosphere in step B and to facilitate adjustment of the content.

[0039] Step A is preferably a step including a spray drying treatment for spray-drying a slurry containing a lithium vanadium phosphorus composite oxide represented by general formula (1) having an average primary particle size of 2.0 μm or less, lithium dihydrogen phosphate (LiH2PO4), and an organic compound that generates carbon when decomposed by heating, in that the lithium dihydrogen phosphate (LiH2PO4) and the organic compound that generates carbon when decomposed by heating can be uniformly attached to the particle surfaces of the lithium vanadium phosphorus composite oxide represented by general formula (1).

[0040] The solvent used in the slurry containing the lithium vanadium phosphorus composite oxide represented by general formula (1) having an average primary particle size of 2.0 μm or less, lithium dihydrogen phosphate (LiH2PO4), and an organic compound that generates carbon when decomposed by heating is not particularly limited as long as it is inert to the lithium vanadium phosphorus composite oxide represented by general formula (1), insoluble or poorly soluble, and can dissolve lithium dihydrogen phosphate (LiH2PO4) and the organic compound that generates carbon when decomposed by heating. However, from the viewpoint of industrial advantage, water or a mixed solvent of water and a hydrophilic organic solvent is preferred.

[0041] In addition, when the carbon source-attached particles prepared in step A are in the form of (ii) or (iii), the lithium vanadium phosphorus composite oxide represented by general formula (1) having an average particle size of 2.0 μm or less of primary particles forms secondary particles, and the average particle size (secondary particle size) of the carbon source-attached particles having lithium dihydrogen phosphate (LiH2PO4) and an organic compound that generates carbon by thermal decomposition attached to the particle surface of the secondary particles is 5 to 100 μm, preferably 10 to 50 μm as determined by SEM observation, from the viewpoint of easy handling and excellent reactivity as a reaction precursor. The average particle size (secondary particle size) of the carbon source-attached particles is determined as the average particle size (long diameter in Heywood diameter) of 200 particles randomly selected from SEM observation.

[0042] Step A is preferably a process including the following steps A1 to A5, in that a reaction precursor having excellent reactivity can be obtained which is industrially advantageous. A step A1 of mixing vanadium pentoxide, phosphoric acid and a reducing sugar in an aqueous solvent to prepare a mixed slurry (1); A2 step of heating the mixed slurry to obtain a reduction reaction solution; A step A3 of adding a solution containing lithium hydroxide to the reduction reaction solution under heating to prepare a slurry (2) containing a lithium vanadium phosphorus composite oxide represented by the general formula (1), lithium dihydrogen phosphate (LiH2PO4), and an organic compound that generates carbon by thermal decomposition; A step A4 of wet-milling the slurry (2) using a media mill to prepare a wet-milled slurry (3); A5 step of spray-drying the wet-milled slurry (3) to obtain carbon source-adhered particles; It is preferable that the process has the following steps.

[0043] Step A1 is a step of mixing vanadium pentoxide, phosphoric acid and a reducing sugar in an aqueous solvent to prepare a mixed slurry (1).

[0044] In the step A1, the mixing amounts of vanadium pentoxide and phosphoric acid are preferably 0.50 to 0.80, and more preferably 0.60 to 0.73, in terms of the molar ratio (V / P) of V atoms in vanadium pentoxide to P atoms in phosphoric acid, in order to facilitate the production of a single-phase lithium vanadium phosphate as the final product.

[0045] The reducing sugar in step A1 is a component that promotes the reduction reaction of vanadium pentoxide in step A2, and is also a component necessary for making the reduction reaction solution obtained in step A2 have a good viscosity that allows it to be stirred. In addition, the carbon source derived from the reducing sugar that was not used in the reduction in step A2 is a component that suppresses the oxidation of vanadium during the firing in step C.

[0046] Reducing sugars for step A1 include the reducing sugars mentioned above, such as glucose, fructose, lactose, maltose, sucrose, etc., and of these, lactose and sucrose are preferred because they give reaction precursors with excellent reactivity.

[0047] In step A1, the amount of reducing sugar mixed is preferably more than 0.6 and not more than 2.0, particularly preferably 0.7 or more and not more than 1.7, in terms of the molar ratio of carbon atoms converted to carbon atoms to V atoms in vanadium pentoxide (C / V). By having the amount of reducing sugar mixed in step A1 within the above range, it is economically advantageous, the reduction reaction solution can be dissolved in step A2, and carbon source-attached particles with reducing sugar uniformly attached thereto can be obtained. On the other hand, if the amount of reducing sugar mixed in step A1 is less than the above range, it is difficult to obtain vanadium pentoxide reduced and dissolved in step A2, and the amount of reducing sugar tends to be insufficient in step A5, making it difficult to obtain carbon source-attached particles with reducing sugar uniformly attached thereto. Furthermore, if the amount of reducing sugar mixed in step A1 exceeds the above range, it takes a long time to prepare the amount of reducing sugar in step B, which is not industrially advantageous.

[0048] In step A1, the vanadium pentoxide, phosphoric acid, and reducing sugar may have any manufacturing history, but in order to produce high-purity lithium vanadium phosphate, it is preferable that the impurity content is as low as possible.

[0049] The aqueous solvent used in step A1 may be water or a mixed solvent of water and a hydrophilic organic solvent.

[0050] In the step A1, the order in which vanadium pentoxide, phosphoric acid and reducing sugar are added to the aqueous solvent and the mixing means are not particularly limited, and the mixing is carried out so as to obtain a mixed slurry (1) in which the above-mentioned raw materials are uniformly dispersed.

[0051] Step A2 is a step of heating the mixed slurry (1) obtained in step A1 to form a solution, and then performing a reduction reaction of at least vanadium pentoxide to form a solution, thereby obtaining a reduction reaction solution. The present inventors have discovered that vanadium pentoxide and phosphoric acid react in the presence of reducing sugar to produce VOPO4 or a hydrate thereof (see, for example, JP 2011-96640 A, JP 2011-96641 A, JP 2019-34877 A, etc.), and therefore the reduction reaction solution obtained in step A2 contains VOPO4 or a hydrate thereof, excess reducing sugar, and dihydrogen phosphate ions (H2PO4 - It is believed that these ions originating from phosphoric acid, such as phosphate ions, are dissolved in the aqueous solvent.

[0052] The temperature of the heat treatment in step A2 is 60 to 100° C., preferably 80 to 100° C. When the temperature of the heat treatment in step A is within the above range, it can be advantageously carried out under atmospheric pressure. On the other hand, if the temperature of the heat treatment in step A is below the above range, the reaction time becomes long, which is industrially disadvantageous, and if it exceeds the above range, a pressurized container must be used, which is industrially disadvantageous.

[0053] In step A2, the completion of the reduction reaction can be confirmed by visually observing that the solution becomes a dark blue, transparent liquid.

[0054] The time for the heat treatment in step A2 is not particularly limited and is generally 0.2 hours or more, preferably 0.5 to 4 hours. If the heat treatment is carried out for a time within the above range, a satisfactory reduction reaction solution can be obtained.

[0055] Step A3 is a step of adding a solution containing lithium hydroxide to the reduction reaction solution obtained in Step A2 while keeping the reduction reaction solution obtained in Step A2 in a heated state, thereby preparing a slurry (2) containing a lithium vanadium phosphorus composite oxide represented by general formula (1), lithium dihydrogen phosphate (LiH2PO4), and an organic compound that generates carbon by thermal decomposition.

[0056] In step A3, the lithium vanadium phosphorus composite oxide represented by general formula (1) precipitated by adding a solution containing lithium hydroxide to the reduction reaction solution has plate-like primary particles forming an aggregate of secondary particles, and the average thickness of the plate-like primary particles as determined by SEM observation is 1 to 20 nm, preferably 3 to 15 nm, and the average particle size of the secondary particles as determined by SEM observation is 0.5 to 20 μm, preferably 1 to 15 μm. The average thickness of the plate-like primary particles and the average particle size of the secondary particles of the lithium vanadium phosphorus composite oxide represented by general formula (1) are determined as the average values ​​of 200 particles randomly selected from SEM observation.

[0057] The lithium vanadium phosphorus composite oxide represented by general formula (1) produced in step A3 is easily pulverized into fine lithium vanadium phosphorus composite oxide represented by general formula (1) by wet pulverization using a media mill in step A4, thereby obtaining a slurry (2) containing the fine lithium vanadium phosphorus composite oxide represented by general formula (1).

[0058] The solution containing lithium hydroxide in step A3 is a solution in which lithium hydroxide is dissolved in water.

[0059] The lithium hydroxide concentration in the solution containing lithium hydroxide is 5 to 20% by mass, preferably 10 to 15% by mass. The lithium hydroxide concentration in the solution containing lithium hydroxide in the above range is preferable in that the operation of adding the lithium hydroxide to the reduction reaction solution is easy and the production efficiency can be improved while controlling the heat generation accompanying the addition of the solution containing lithium hydroxide.

[0060] The amount of the solution containing lithium hydroxide added is such that the molar ratio (Li / P) of Li atoms in the solution containing lithium hydroxide to P atoms in the reduction reaction solution obtained by carrying out the step A2 is 0.70 to 1.30, preferably 0.83 to 1.17. The amount of the solution containing lithium hydroxide added is within the above range, which is preferable in that it is easy to obtain a single-phase lithium vanadium phosphate as the final product. In addition, in the step A3, it is preferable to add the solution containing lithium hydroxide so that the pH of the "slurry (2) containing the lithium vanadium phosphorus composite oxide represented by the general formula (1), lithium dihydrogen phosphate (LiH2PO4), and an organic compound that generates carbon by thermal decomposition" after the addition of the solution containing lithium hydroxide is 3 to 7, preferably 4 to 6, particularly preferably 4 to 5, which is preferable in that it is easy to obtain a single-phase lithium vanadium phosphate as the final product.

[0061] In step A3, the lithium hydroxide may have any manufacturing history, but in order to produce high-purity lithium vanadium phosphate, it is preferable that the impurity content is as low as possible.

[0062] In step A3, a solution containing lithium hydroxide is added to the reduction reaction solution obtained by carrying out step A2 while maintaining the reduction reaction solution at 40 to 100° C., preferably 60 to 100° C. In step A3, if the temperature at which the solution containing lithium hydroxide is added is below the above range, precipitation becomes non-uniform, whereas if it exceeds the above range, operability tends to deteriorate due to boiling of the solution containing lithium hydroxide.

[0063] In step A3, the solution containing lithium hydroxide is preferably added at a constant rate in order to obtain a solution of stable quality.

[0064] In addition, after the solution containing lithium hydroxide is added in step A3, in order to complete the reaction between the reduction reaction solution and lithium hydroxide, an aging reaction can be carried out subsequently, if necessary.

[0065] The temperature at which the aging reaction is carried out is preferably 40 to 100° C., and more preferably 60 to 100° C., in terms of obtaining particles with a uniform composition. The aging reaction time is not particularly limited, but a satisfactory slurry (2) can usually be obtained by carrying out the aging reaction for 0.5 hours or more.

[0066] Step A4 is a step of wet-pulverizing the slurry (2) obtained in step A3 using a media mill to prepare a wet-pulverized slurry (3).

[0067] By carrying out step A4, it is possible to obtain a wet-milled slurry (3) containing a fine lithium vanadium phosphorus composite oxide represented by general formula (1). The reaction precursor obtained from this fine lithium vanadium phosphorus composite oxide represented by general formula (1) has excellent reactivity, and by firing in step C, a lithium vanadium phosphate that is single-phase in terms of X-ray diffraction is generated, making it easy to obtain one with a sharp particle distribution.

[0068] In step A4, the solid content of the slurry (2) to be wet-pulverized by the media mill is preferably 10 to 40% by mass, more preferably 15 to 30% by mass, from the viewpoints of good operability and efficient pulverization. Therefore, after step A3, it is desirable to adjust the solid content of the slurry (2) to the above range as necessary, and then wet-pulverize the slurry (2) in step A4.

[0069] In step A4, the slurry (2) is wet-pulverized in a media mill. By using this method, the lithium vanadium phosphorus composite oxide represented by the general formula (1) can be more finely pulverized, and therefore a reaction precursor having even better reactivity can be obtained.

[0070] Examples of media mills include bead mills, ball mills, paint shakers, attritors, sand mills, etc., and bead mills are 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 device and the processing amount.

[0071] In order to perform the treatment using the media mill more efficiently, a dispersant may be added to the slurry (2) to be wet-milled. Examples of the dispersant include various surfactants and ammonium polycarboxylates. The concentration of the dispersant in the slurry (2) to be wet-milled is preferably 0.01 to 10% by mass, and more preferably 0.1 to 5% by mass, in order to obtain a sufficient dispersion effect.

[0072] In step A4, it is preferable to carry out the wet grinding treatment using a media mill 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.

[0073] Step A5 is a step of spray-drying the wet-milled slurry (3) obtained in step A4 to obtain carbon source-adhered particles.

[0074] The carbon source-adhered particles obtained by carrying out step A5 are preferably carbon source-adhered particles in the form (ii) or (iii) above, in that they serve as a reaction precursor with excellent reactivity.

[0075] The average particle size of the primary particles of the lithium vanadium phosphorus composite oxide represented by general formula (1) constituting the carbon source-adhered particles is approximately the same as the average particle size of the primary particles of the solid content in the wet-milled slurry (3) obtained by carrying out step A4.

[0076] Although methods other than spray drying are known as a method for drying the liquid, the present invention employs the spray drying method based on the knowledge that it is advantageous to select this drying method. In detail, by using the spray drying method in the step A5, reducing sugar and lithium dihydrogen phosphate (LiH2PO4) are uniformly attached to the particle surface of the lithium vanadium phosphorus composite oxide represented by the general formula (1), and a granulated product in which the particles of the lithium vanadium phosphorus composite oxide represented by the general formula (1) are densely packed is obtained, so that in the firing step C, lithium vanadium phosphate that is single-phase in terms of X-ray diffraction can be easily produced with a small amount of carbon.

[0077] In the spray drying method, a liquid is atomized by a predetermined means, and the resulting fine droplets are dried to obtain a granulated product. For example, a rotating disk or a pressure nozzle can be used to atomize the liquid. Either method can be used in the A5 step.

[0078] In the spray drying method, the relationship between the size of the droplets of the atomized slurry and the size of the particles of the pulverized material contained therein affects stable drying and the properties of the resulting dried powder. In detail, if the size of the raw material particles of the pulverized material is too small compared 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 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 device taking this viewpoint into consideration.

[0079] 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, since this prevents the powder from absorbing moisture and makes it easier to recover the powder.

[0080] The carbon source-adhered particles obtained by carrying out step A5 may be dried to produce a mixture of lithium vanadium phosphorus composite oxide represented by general formula (1) in which x is 2 and lithium vanadium phosphorus composite oxide in which the water of crystallization has been partially removed, as determined by X-ray diffraction analysis. In the present invention, such a mixture is also preferably used.

[0081] (B process) Step B in the method for producing lithium vanadium phosphate of the present invention is a step of obtaining a reaction precursor by heat-treating the carbon source-attached particles prepared in step A in an oxygen atmosphere.

[0082] In the present invention, by carrying out step B and adjusting the amount of carbon atoms attached to the particle surfaces of the carbon source-attached particles, it is possible to produce lithium vanadium phosphate having a low specific surface area and a sharp particle distribution through step C.

[0083] In step B, it is preferable to carry out the heat treatment until the carbon content of the reaction precursor reaches 0.3 to 0.6, preferably 0.35 to 0.55, in terms of the molar ratio (C / V) of carbon atoms to V atoms in the reaction precursor. When the carbon content of the reaction precursor is within the above range, the reduction in step C occurs sufficiently, and the BET specific surface area of ​​lithium vanadium phosphate decreases because the carbon content is appropriate. On the other hand, if the carbon content of the reaction precursor is less than the above range, the reduction in step C becomes incomplete, and if it exceeds the above range, the carbon content becomes excessive, tending to increase the BET specific surface area of ​​lithium vanadium phosphate.

[0084] In step B, the heat treatment is carried out in an oxygen-containing atmosphere. In step B, the oxygen concentration in the atmosphere during the heat treatment is preferably 5 vol% or more, particularly preferably 10 to 30 vol%, in order to efficiently oxidize organic compounds that generate carbon by thermal decomposition and to easily adjust the carbon content to the above range.

[0085] In step B, the temperature of the heat treatment is preferably 270 to 370° C., particularly preferably 290 to 360° C., in that the carbon content can be easily controlled. If the heat treatment temperature is below the above range, it becomes difficult to reduce the carbon content, and if it exceeds the above range, the carbon content decreases suddenly, so that it tends to become difficult to adjust the carbon content.

[0086] In step B, the carbon content can be reduced as the heat treatment time is longer, so it is preferable to perform the heat treatment for a sufficient time so that the carbon content falls within the above range, but if the heat treatment time is 8 hours or more, the lithium vanadium phosphate obtained after step C becomes a hard sintered body, making it difficult to recover it as a powder. In step B, a satisfactory reaction precursor can usually be obtained with a heat treatment time of 1 hour or more and less than 8 hours, preferably 2 to 5 hours.

[0087] In addition, the reaction precursor obtained by carrying out step B may contain, in addition to the lithium vanadium phosphorus composite oxide represented by general formula (1) in X-ray diffraction analysis, a part or all of lithium dihydrogen phosphate (LiH2PO4) in the form of amorphous phosphorus compounds (LiH2PO4, LiPO3, etc.) and / or lithium phosphate (Li3PO4) due to the heat treatment in step B. However, in the present invention, even such compounds can be used without any problems.

[0088] (C process) Step C in the method for producing lithium vanadium phosphate of the present invention is a step in which the reaction precursor obtained by carrying out step B is fired at 500 to 1300° C. to obtain lithium vanadium phosphate that is single-phase in terms of X-ray diffraction.

[0089] The firing temperature in step C is 500 to 1300° C., and preferably 600 to 1000° C. If the firing temperature in step C is below the above range, the firing time required to reach a single phase becomes long, and if it exceeds the above range, the lithium vanadium phosphate melts.

[0090] The firing atmosphere in step C is an inert gas atmosphere or a reducing atmosphere in order to prevent the oxidation of vanadium and to prevent melting. The inert gas used in step C is not particularly limited, and examples thereof include nitrogen gas, helium gas, and argon gas.

[0091] In step C, the calcination time is not particularly limited, and calcination for generally 2 hours or more, particularly 3 to 24 hours, can provide lithium vanadium phosphate that is single-phase in terms of X-ray diffraction.

[0092] In step C, the lithium vanadium phosphate obtained by calcination may be subjected to multiple calcinations, if necessary.

[0093] 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 as necessary in step A of the method for producing lithium vanadium phosphate of the present invention, or a mixture containing carbon source-attached particles and an Me source is prepared, and step B is carried out using the mixture to incorporate the Me source into the reaction precursor, and then step C is carried out to obtain lithium vanadium phosphate represented by general formula (1) doped with Me element. Specifically, as a method for incorporating an Me source into the carbon source-attached particles, a method of adding an Me source at any time between step A1 and before spray drying in step A5 is carried out can be mentioned.

[0094] The Me element is present as a substitute on the Li site and / or the V site of the lithium vanadium phosphate represented by the general formula (2).

[0095] 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, Cu, and the like, which may be used alone or in combination of two or more.

[0096] Examples of the Me source include oxides, hydroxides, halides, carbonates, nitrates, carbonates, organic acid salts, etc. having the Me element. When the Me source is mixed during the period from step A1 to before the spray drying in step A5, the Me source may be present in the slurry in a dissolved form or as a solid.

[0097] In the case where a Me source is present as a solid in the slurry (2) containing the lithium vanadium phosphorus composite oxide represented by the general formula (1), lithium dihydrogen phosphate (LiH2PO4), and an organic compound that generates carbon by thermal decomposition, 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 having excellent reactivity. In addition, in the case where a Me source is mixed before the spray drying in the steps A1 to A5, the amount of the Me source to be mixed depends on the type of Me element to be doped, but in many cases, it is preferable to mix the amount of the Me source such that the molar ratio of the sum of V atoms and Me atoms to P atoms in the slurry (2) ((Me+V) / P) is 0.5 to 0.80, preferably 0.60 to 0.73, and the molar ratio of Me atoms to V atoms (Me / V) is more than 0 and 0.45 or less, preferably more than 0 and 0.1 or less.

[0098] The lithium vanadium phosphate obtained by carrying out the method for producing lithium vanadium phosphate of the present invention is a lithium vanadium phosphate having a single phase as determined by X-ray diffraction and a BET specific surface area of ​​10.0 m 2 / g or less, preferably 3.0 to 8.0m 2 / g. Furthermore, it is preferable that the lithium vanadium phosphate obtained by carrying out the method for producing lithium vanadium phosphate of the present invention has an average primary particle size of 0.3 to 1.5 μm, preferably 0.4 to 1.2 μm, as determined by SEM observation, and has a sharp particle size distribution.

[0099] The carbon content of the lithium vanadium phosphate obtained by carrying out the method for producing lithium vanadium phosphate of the present invention is 0.01 to 1.0 mass %, preferably 0.01 to 0.5 mass %.

[0100] In the method for producing lithium vanadium phosphate of the present invention, the obtained lithium vanadium phosphate may be further subjected to a crushing treatment or a pulverization treatment, and may further be subjected to classification, if necessary.

[0101] In the method for producing lithium vanadium phosphate of the present invention, if necessary, after completion of step C, the resultant product can be mixed with conductive carbon or the particle surfaces can be coated with conductive carbon to be used as a lithium vanadium phosphate carbon composite.

[0102] Furthermore, the lithium vanadium phosphate obtained by carrying out the method for producing lithium vanadium phosphate of the present invention is used as a positive electrode active material for lithium secondary batteries, all-solid-state batteries, and the like.

[0103] In the method for producing lithium vanadium phosphate of the present invention, by performing the B step, the carbon adhering to the surface of the lithium vanadium phosphorus composite oxide represented by the general formula (1) can be reduced, and the molar ratio of carbon atoms to vanadium atoms (C / V) can be made appropriate. Therefore, in the method for producing lithium vanadium phosphate of the present invention, the lithium vanadium phosphate obtained through the C step has a shape with a rounded particle surface. Due to these reasons, in the method for producing lithium vanadium phosphate of the present invention, the specific surface area of lithium vanadium phosphate can be lowered. Further, in the method for producing lithium vanadium phosphate of the present invention, in the A step, the average particle diameter of the primary particles of the lithium vanadium phosphorus composite oxide to which lithium dihydrogen phosphate (LiH2PO4) and an organic compound that generates carbon by thermal decomposition adhere is set to 2.0 μm or less, preferably 0.1 to 1.5 μm. As a result, the presence of coarse particles is extremely reduced, and the particle distribution of the lithium vanadium phosphate obtained through the B step and the C step can be sharpened.

[0104] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Examples

[0105] (Example 1) <Step A1> 2 L of ion-exchanged water was placed in a 5 L beaker, and 605 g of 85% phosphoric acid, 320 g of vanadium pentoxide, and 96 g of lactose were added thereto, and the mixture was stirred at room temperature (25 °C) to obtain a yellowish-brown mixed slurry (1).

[0106] <Step A2> The obtained mixed slurry (1) was heated with stirring at 80 °C for 3 hours to perform a reduction reaction, and a dark blue transparent reaction solution was obtained.

[0107] <Step A3> While maintaining the reaction solution at 80 °C, a lithium hydroxide solution was then prepared by dissolving 220 g of lithium hydroxide monohydrate in 1.5 L of ion-exchanged water. While maintaining the reaction solution within the temperature range of 70 - 80 °C, the lithium hydroxide solution was added to the reaction solution at a constant rate over 40 minutes to obtain a slurry (2) containing a precipitate. Subsequently, the slurry was allowed to cool to room temperature (25 °C). After sampling the precipitate, it was filtered, dried, and subjected to XRD measurement, which showed agreement with the peaks of LiVOPO4·2H2O. The obtained LiVOPO4·2H2O had an average thickness of 5 nm for the plate-like primary particles determined by SEM observation and an average particle diameter of 6 μm for the secondary particles determined from SEM observation. The X-ray diffraction pattern of the obtained LiVOPO4·2H2O is shown in Fig. 1, and the SEM photographs are shown in Figs. 2 (1000 times) and 3 (5000 times). Note that the average thickness of the primary particles of LiVOPO4·2H2O and the average particle diameter of the secondary particles were determined as the average values of 200 arbitrarily extracted particles in the SEM observation.

[0108] <A4 process> Next, 27 g of ammonium polycarboxylate salt was charged as a dispersant, and while stirring the slurry, it was supplied to a media stirring type bead mill charged with zirconia beads having a diameter of 0.5 mm, and wet grinding was performed. The average particle diameter of the solid content in the slurry (3) after wet grinding determined by the laser diffraction / scattering method was 0.5 μm. Also, for the solid content, the average particle diameter of the primary particles determined from SEM observation was 0.5 μm. Note that the average particle diameter of the primary particles of the solid content was determined as the average value of 200 arbitrarily extracted particles in the SEM observation.

[0109] <A5 process> The slurry (3) after wet grinding was supplied to a spray dryer with the outlet temperature set at 120 °C to obtain carbon source-attached particles. The average particle diameter (secondary particle diameter) determined from SEM observation of the carbon source-attached particles was 20 μm. When X-ray diffraction measurement was performed using CuKα rays with the obtained carbon source-attached particles as the radiation source, the carbon source-attached particles were found to contain LiVOPO4·2H2O and LiH2PO4 (see Fig. 4). In addition, the residual carbon content of the obtained carbon source-attached particles was determined as the content of C atoms by measuring with a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation). The residual carbon content was 4.1% by mass. The average particle diameter (secondary particle diameter) of the carbon source-attached particles was determined as the average value of 200 arbitrarily extracted particles in SEM observation.

[0110] <Step B> The obtained carbon source-attached particles were placed in a mullite crucible and heat-treated at 300 °C for 4 hours in an air atmosphere (oxygen concentration 20 Vol%) to obtain a reaction precursor. As a result of X-ray diffraction analysis of the obtained reaction precursor, it was found to contain LiVOPO4 and a trace amount of Li3PO4 peaks. Although a distinct peak of LiH2PO4 was not detected by X-ray diffraction analysis, it is considered that LiH2PO4 became an amorphous phosphorus compound (LiH2PO4, LiPO3). In addition, the residual carbon content of the obtained reaction precursor was determined as the content of C atoms by measuring with a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation). The residual carbon content was 3.0% by mass.

[0111] <Step C> The obtained reaction precursor was calcined at 750 °C for 4 hours in a N2 atmosphere. Next, the calcined product was pulverized with an air jet mill to obtain a pulverized product. As a result of X-ray diffraction analysis, it was confirmed that it was single-phase lithium vanadium phosphate (Li3V2(PO4)3) (see Fig. 5). This was used as a lithium vanadium phosphate sample.

[0112] (Example 2) In Step B, a lithium vanadium phosphate sample was obtained by performing the reaction in the same manner as in Example 1 except that the heat treatment time was 2.5 hours. Furthermore, X-ray diffraction analysis of the obtained lithium vanadium phosphate samples confirmed that all were single-phase lithium vanadium phosphate (Li3V2(PO4)3) (see FIG. 6). These were used as lithium vanadium phosphate samples.

[0113] Comparative Example 1 A lithium vanadium phosphate sample was obtained by carrying out the reaction in the same manner as in Example 1, except that step B was not carried out. In addition, X-ray diffraction analysis of the obtained lithium vanadium phosphate samples confirmed that all were single-phase lithium vanadium phosphate (Li3V2(PO4)3), which were used as lithium vanadium phosphate samples.

[0114] In Table 1, the carbon content indicates the molar ratio of carbon atoms, calculated as carbon atoms, to V atoms in the carbon source-attached particles, and the molar ratio of carbon atoms, calculated as carbon atoms, to V atoms in the reaction precursor.

[0115] [Table 1]

[0116] <Physical property evaluation of lithium vanadium phosphate (LVP) sample> The lithium vanadium phosphate samples obtained in the Examples and Comparative Examples were measured for BET specific surface area, average particle size of primary particles, average particle size of secondary particles, and residual carbon amount. The average particle size of primary particles, average particle size of secondary particles, and residual carbon amount were measured as follows. (Average particle size of primary particles) In the SEM observation, the average particle size of the primary particles was calculated as the average value of 200 particles randomly selected. SEM photographs of the lithium vanadium phosphate samples obtained in Example 1 and Comparative Example 1 are shown in Figures 7 and 8, respectively. (Average particle size of secondary particles) Laser scattering and diffraction method 50 In addition, D 90The particle size distribution of the lithium vanadium phosphate sample obtained in Example 1 is shown in FIG. (Residual carbon content) Measurements were made using a TOC total organic carbon meter (Shimadzu TOC-5000A).

[0117] [Table 2]

[0118] From Table 2, the BET specific surface area of ​​the embodiment is smaller than that of the comparative example 1, and D 50 and D 90 It can be seen that the difference is small and the particle size distribution is sharp.

Claims

1. A method for producing lithium vanadium phosphate having a NASICON structure, comprising the steps of: The average particle size of the primary particles is 2.0 μm or less, and the average particle size of the primary particles is represented by the following general formula (1): 2019 ４ ・xH ２ O (1) (wherein x is an integer from 0 to 2) The lithium vanadium phosphorus composite oxide represented by the formula (I) is formed on the surface of the particles thereof. ２ P.O. ４ A step A of preparing carbon source-attached particles having attached thereto an organic compound that generates carbon upon thermal decomposition; A step B of obtaining a reaction precursor by heat-treating the carbon source-attached particles in an oxygen-containing atmosphere; A process C of calcining the reaction precursor at 500 to 1300° C. in an inert gas atmosphere or a reducing atmosphere to obtain lithium vanadium phosphate; having The method for producing lithium vanadium phosphate, wherein the carbon content of the reaction precursor is 0.3 to 0.6 in terms of a molar ratio of carbon atoms to vanadium atoms (C / V).

2. 2. The method for producing lithium vanadium phosphate according to claim 1, wherein the content of the organic compound that generates carbon upon thermal decomposition in the carbon source-attached particles is greater than 0.6 in terms of a molar ratio of carbon atoms to vanadium atoms (C / V).

3. The step A is a process for producing a lithium vanadium phosphorus composite oxide represented by the general formula (1) having an average primary particle size of 2.0 μm or less, and a lithium dihydrogen phosphate (LiH ２ P.O. ４ 3. The method for producing lithium vanadium phosphate according to claim 1, further comprising a spray drying process for spray drying a slurry containing the organic compound which generates carbon by thermal decomposition.

4. 4. The method for producing lithium vanadium phosphate according to claim 1, wherein the temperature for heat-treating the carbon source-attached particles in step B is 270 to 370° C.

5. The step A comprises: A step A1 of mixing vanadium pentoxide, phosphoric acid and a reducing sugar in an aqueous solvent to prepare a mixed slurry (1); A2 step of heating the mixed slurry to obtain a reduction reaction solution; A solution containing lithium hydroxide is added to the reduction reaction solution under heating to obtain a lithium vanadium phosphorus composite oxide represented by the general formula (1), lithium dihydrogen phosphate (LiH ２ P.O. ４ and a step A3 of preparing a slurry (2) containing the organic compound that generates carbon by thermal decomposition; A step A4 of wet-grinding the slurry (2) using a media mill to prepare a wet-grinded slurry (3); A5 step of spray-drying the wet-milled slurry (3) to obtain the carbon source-adhered particles; The method for producing lithium vanadium phosphate according to any one of claims 1 to 4, characterized in that the method comprises the steps of:

6. The method for producing lithium vanadium phosphate according to claim 5, characterized in that in the step A2, the mixed slurry (1) is heated at a temperature of 60 to 100°C.

7. The method for producing lithium vanadium phosphate according to claim 5 or 6, characterized in that in the step A3, the heating temperature of the reduction reaction solution is 40 to 100°C.

8. The method for producing lithium vanadium phosphate according to any one of claims 5 to 7, characterized in that in step A1, the amount of the reducing sugar mixed is greater than 0.6 and not more than 2.0 in terms of a molar ratio (C / V) of carbon atoms converted to vanadium atoms of vanadium pentoxide.

9. The method for producing lithium vanadium phosphate according to any one of claims 5 to 8, characterized in that the average particle size of the solid content in the wet-milled slurry (3) obtained after the step A4 is 2.0 μm or less.

10. The method for producing lithium vanadium phosphate according to any one of claims 1 to 9, characterized in that the reaction precursor further contains a Me source (Me represents a metal element having an atomic number of 11 or more other than V or a transition metal element).

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