WO2019035322A1

WO2019035322A1 - Method for producing lithium vanadium phosphate

Info

Publication number: WO2019035322A1
Application number: PCT/JP2018/027703
Authority: WO
Inventors: 純也深沢; 畠　透
Original assignee: 日本化学工業株式会社
Priority date: 2017-08-17
Filing date: 2018-07-24
Publication date: 2019-02-21
Also published as: AT522061A2; AT522061B1; AT522061A5

Abstract

Provided is a method for producing a lithium vanadium phosphate having a NASICON structure, the method comprising: a first step for mixing vanadium pentoxide, phosphoric acid, and a reducing sugar in an aqueous solvent to prepare an acidic mixed slurry; a second step for heating the mixed slurry into a solution to obtain a reduction reaction solution; a third step for adding a lithium hydroxide-containing solution to the reduction reaction solution while maintaining the reduction reaction solution at 35°C or lower to prepare a raw mixed solution; a fourth step for spray-drying the raw mixed solution to obtain a reaction precursor; and a fifth step for baking the reaction precursor at 500-1300°C in an inert gas atmosphere or reducing atmosphere to obtain the lithium vanadium phosphate. According to the present invention, a lithium vanadium phosphate, which is a single phase as analyzed by X-ray diffraction and useful especially as a positive electrode active material for lithium secondary batteries, can be provided in an industrially advantageous manner.

Description

Method for producing lithium vanadium phosphate

The present invention relates to a method for producing lithium vanadium phosphate which is particularly useful as a positive electrode active material of a lithium secondary battery.

Lithium ion batteries are used as batteries for portable devices, notebook computers, electric vehicles, and hybrid vehicles. Lithium-ion batteries are generally considered to be excellent in capacity and energy density. Currently, LiCoO ₂ is mainly used for the positive electrode, but development of LiMnO ₂ , LiNiO _{2 and the} like is also actively carried out due to resource problems of Co. ing.
At present, attention is focused on LiFePO ₄ as a further alternative material, and research and development is progressing in each organization. Fe is excellent in resources, and although LiFePO ₄ using this has a somewhat low energy density, it is expected as a positive electrode material for lithium ion batteries for electric vehicles because of its excellent high temperature characteristics.

However, LiFePO ₄ has a slightly lower operating voltage, and attention is focused on lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ) having a NASICON (Na Super Ionic Conductor) structure using V instead of Fe. There is.

As a method for producing lithium vanadium phosphate, for example, there has been proposed a method in which a lithium source, a vanadium compound and a phosphorus source are ground and mixed, the resulting uniform mixture is formed into a pile and then this molded product is fired ( See, for example, Patent Documents 1 and 2). Further, according to Patent Document 3 below, 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, and a raw material mixed solution obtained is dried. It has been proposed to obtain a precursor and heat-treat the precursor in an inert atmosphere to obtain a complex of Li ₃ V ₂ (PO ₄ ) ₃ and a conductive carbon material.

Also, the applicant of the present invention has previously made a mixture of a lithium source, a pentavalent or tetravalent vanadium compound, a phosphorus source and a conductive carbon material source from which carbon is generated by thermal decomposition in an aqueous solvent. A first step of preparing a raw material mixture, a second step of heating the raw material mixture to cause a precipitation reaction, and obtaining a reaction liquid containing the precipitation product, and a media mill for the reaction liquid containing the precipitation product Wet grinding treatment to obtain a slurry containing the ground product, spray drying treatment of the slurry containing the ground material to obtain a reaction precursor, and the reaction precursor A method for producing a lithium vanadium phosphate carbon composite, which is fired at 600 to 1300 ° C. in an active gas atmosphere or in a reducing atmosphere, has been proposed.

Further, in Patent Document 5 below, a vanadium compound, a phosphorus source, and a conductive carbon material source from which carbon is generated by thermal decomposition are reacted by heat treatment in an aqueous solvent, preferably at 60 to 100 ° C. After cooling down, the solution after heat treatment is further reacted by adding a lithium source, and the resulting reaction solution is spray-dried to obtain a reaction precursor, and the reaction precursor is subjected to an inert gas atmosphere or a reducing atmosphere It is disclosed to produce lithium vanadium phosphate by calcining in situ.

Japanese Patent Publication No. 2001-500665 Japanese Patent Publication No. 2002-530835 JP, 2008-052970, A International Publication No. 2012/043367 pamphlet International Publication No. 2014/006948 brochure

Li ₃ V ₂ (PO ₄ ) ₃ is known to have a theoretical capacity as high as 197 mAh g ⁻¹ .
However, the lithium secondary battery using the conventional Li ₃ V ₂ (PO ₄ ) ₃ as the positive electrode active material has a low discharge capacity, and according to the method of producing lithium vanadium phosphate described in Patent Document 4, the discharge capacity is However, in order to obtain a reactive precursor excellent in reactivity, a precipitation reaction and a grinding treatment with a media mill are required, and the production process becomes complicated, which is not industrially advantageous.
In addition, Patent Document 5 does not show any specific reaction conditions, and after cooling to room temperature, the reaction is carried out by simply adding a lithium source to the solution after the heat treatment. Even if a solution obtained by spray drying is used as a reaction precursor, it is difficult to obtain a solution having a high discharge capacity.

Accordingly, an object of the present invention is to provide lithium vanadium phosphate single phase in an industrially advantageous manner in an X-ray diffraction manner, which is particularly useful as a positive electrode active material of a lithium secondary battery.

As a result of intensive studies conducted in view of the above problems, the present inventors conducted a heat treatment of an acidic mixed slurry containing vanadium pentoxide, phosphoric acid and reducing sugar, thereby causing a reduction reaction of vanadium pentoxide and causing a solution. Be able to In addition, when a solution containing lithium hydroxide is added while maintaining the reduction reaction solution obtained by heat-treating an acidic mixed slurry containing vanadium pentoxide, phosphoric acid and reducing sugar at a certain temperature or lower, Being capable of maintaining the solution state for a while even after the addition while suppressing the reaction between the components of the present invention and lithium hydroxide. Moreover, the reaction precursor obtained by spray-drying the solution after the addition of the solution containing lithium hydroxide is excellent in reactivity, and single-phase highly crystalline lithium vanadium phosphate can be obtained even at a low temperature of about 600 ° C. about. In addition, it has been found that a lithium secondary battery using lithium vanadium phosphate obtained by using the reaction precursor as a positive electrode active material has excellent battery performance, and completes the present invention. The

That is, the present invention is a method for producing lithium vanadium phosphate having a NASICON structure,
A first step of mixing vanadium pentoxide, phosphoric acid and reducing sugar in an aqueous solvent to prepare an acidic mixed slurry, and then heating the mixed slurry to form a solution to obtain a reduced reaction solution Then, while maintaining the reduction reaction solution at 35 ° C. or less, a third step of preparing a raw material mixed solution by adding a solution containing lithium hydroxide to the reduction reaction solution, and then spray drying the raw material mixed solution It has a fourth step of processing to obtain a reaction precursor, and then a fifth 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 process for producing lithium vanadium phosphate.

According to the present invention, it is possible to provide, in an industrially advantageous manner, an X-ray diffraction single phase lithium vanadium phosphate useful as a positive electrode active material of a lithium secondary battery, etc. A lithium secondary battery using lithium vanadium oxide as a positive electrode active material has excellent battery performance.

The X-ray-diffraction diagram of the reaction precursor obtained by Example 1, the comparative example 1, and the comparative example 2. FIG. The SEM photograph of the reaction precursor obtained in Example 1. FIG. 2 is an X-ray diffraction diagram of a lithium vanadium phosphate sample obtained in Example 1 and Comparative Example 1. FIG. SEM photograph of lithium vanadium phosphate obtained in Example 1. SEM photograph of the reaction precursor obtained in Example 5. X-ray diffraction diagram of lithium vanadium phosphate sample obtained in Example 5. FIG. SEM photograph of lithium vanadium phosphate sample obtained in Example 5. The X-ray-diffraction figure of the reaction precursor obtained by the comparative example 3. FIG. X-ray diffraction pattern of lithium vanadium phosphate sample obtained in Comparative Example 3.

Hereinafter, the present invention will be described based on its preferred embodiments.
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").

The lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate according to the present invention has the following general formula (1):
Li _x V _y (PO ₄ ) ₃ (1)
(In the formula, x is 2.5 or more and 3.5 or less, y is 1.8 or more and 2.2 or less.)
In the lithium vanadium phosphate represented by the general formula (1) or the lithium vanadium phosphate represented by the general formula (1), the Me element (Me represents a metal element or transition metal element having an atomic number of 11 or more other than V). It is lithium vanadium phosphate which is doped and contained.

X in the general formula (1) is preferably 2.5 or more and 3.5 or less, and particularly preferably 2.8 or more and 3.2 or less. y is preferably 1.8 or more and 2.2 or less, and particularly preferably 1.9 or more and 2.1 or less.

When lithium vanadium phosphate contains a Me element, the Me element to be doped is 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 2 or more types are mentioned. Among them, Me element is preferably one or more selected from Mg, Ca, Al, Mn, Co, Ni, Fe, Ti, Zr, Bi, Cr, Nb, Mo and Cu. .

The process for producing lithium vanadium phosphate according to the present invention comprises the first step of mixing vanadium pentoxide, phosphoric acid and reducing sugar in an aqueous solvent to prepare an acidic mixed slurry, and then heating the mixed slurry A second step to obtain a reduction reaction solution, and then adding a solution containing lithium hydroxide to the reduction reaction solution while maintaining the reduction reaction solution at 35 ° C. or less to prepare a raw material mixed solution Three steps, and then a fourth step of spray-drying the raw material mixture solution to obtain a reaction precursor, and then calcining the reaction precursor at 500 to 1300 ° C. in an inert gas atmosphere or a reducing atmosphere to obtain phosphoric acid It has the 5th process of obtaining vanadium lithium.

The first step of the method for producing lithium vanadium phosphate according to the present invention is a step of mixing vanadium pentoxide, phosphoric acid and reducing sugar in an aqueous solvent to obtain an acidic mixed slurry in which each raw material is mixed.

In the first step, the mixing amount of vanadium pentoxide and phosphoric acid is preferably 0.50 to 0.80, preferably 0.5 to 0.80, as the molar ratio (V / P) of V atom in vanadium pentoxide to P atom in phosphoric acid. It is preferable that the ratio is 0.60 to 0.73, from the viewpoint of easily obtaining a single phase lithium vanadium phosphate as a final product.

The reducing sugar in the first step is thermally decomposed in an inert gas atmosphere or a reducing atmosphere at least in the fifth step, and carbon which is isolated, that is, converted into carbon, is used. The reducing sugar accelerates the reduction reaction of vanadium pentoxide in the second step, and, in addition to the reaction solution having the good viscosity that can be stirred in the second step, the fifth step It becomes a component necessary for preventing the oxidation of vanadium in the process. The excess reducing sugar is converted to conductive carbon by the baking of the fifth step, so in the method for producing lithium vanadium phosphate of the present invention, the reducing sugar is added in excess to impart conductivity to lithium vanadium phosphate It can also function as a component of a conductive carbon source.

Examples of the reducing sugar according to the first step include glucose, fructose, lactose, maltose, sucrose and the like, among which lactose and sucrose are preferable from the viewpoint of obtaining a reactive precursor having excellent reactivity.

In the first step, it is preferable that the mixing amount of reducing sugars is 0.3 to 40 parts by mass in terms of C atom with respect to 100 parts by mass of lithium vanadium phosphate to be produced. In the firing in the fifth step, the amount of C atoms contained in the reducing sugar tends to decrease after firing as compared to before firing. Therefore, in the first step, the reducing sugar is converted from the reducing sugar to a mixing amount of 0.3 to 40 parts by mass in terms of C atom with respect to 100 parts by mass of lithium vanadium phosphate to be produced. The content of the conductive carbon is likely to be 0 to 20 parts by mass in terms of C atom with respect to 100 parts by mass of lithium vanadium phosphate to be produced. When the mixing amount of reducing sugar with respect to 100 parts by mass of lithium vanadium phosphate to be formed is in the above range, lithium vanadium phosphate is excellent for a lithium secondary battery when it is used as a positive electrode active material of a lithium secondary battery Performance can be provided. In particular, in the first step, the mixing amount of reducing sugar is 0.5 to 40 parts by mass, preferably 5 to 30 parts by mass, in terms of C atom, with respect to 100 parts by mass of lithium vanadium phosphate to be produced. The content of conductive carbon converted from reducing sugar is 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight with respect to 100 parts by weight of lithium vanadium phosphate to be produced. Since sufficient conductivity can be imparted by carbon carbon, the internal resistance of the lithium secondary battery can be lowered, and the discharge capacity per mass or volume can be increased. On the other hand, if the mixing amount of the reducing sugar with respect to 100 parts by mass of lithium vanadium phosphate to be produced is less than the above range, it tends to be difficult to obtain single phase lithium vanadium phosphate, and if it exceeds the above range The discharge capacity per mass or volume tends to be low. In the first step, the amount of lithium vanadium phosphate to be produced is calculated from the amounts of vanadium pentoxide and phosphoric acid added as raw materials.

Although the production history of vanadium pentoxide, phosphoric acid and reducing sugar in the first step does not matter, in order to produce lithium vanadium phosphate having high purity, it is preferable that the content of impurities be as low as possible. .

Examples of the water solvent used in the first step include water and a mixed solvent of water and a hydrophilic organic solvent.

In the first step, the order in which vanadium oxide, phosphoric acid and reducing sugar are added to the water solvent, and the mixing means are not particularly limited, and the lines are mixed so as to form an acidic mixed slurry in which the above respective materials are uniformly dispersed. It will be.

In the second step of the method for producing lithium vanadium phosphate according to the present invention, the acidic mixed slurry obtained in the first step is heat-treated to perform at least a reduction reaction of vanadium pentoxide, and each component is mixed It is a step of converting into a dissolved solution to obtain a reduction reaction solution. The temperature of the heat treatment in the second step is 60 to 100 ° C., preferably 80 to 100 ° C. The reason for this is that the temperature of the heat treatment is lower than 60 ° C., which is industrially disadvantageous because the reaction time is prolonged, and a pressure vessel must be used to raise the temperature of the heat treatment to more than 100 ° C. It is not industrially advantageous. Thus, the second step can be carried out under atmospheric pressure.

The time of the heat treatment in the second step is not particularly limited, and generally, heat treatment is performed for 0.2 hours or more, preferably 0.5 to 4 hours, particularly preferably 0.5 to 2 hours to obtain a reduction reaction solution. be able to.

After completion of the second step, if the reduction reaction solution is kept at a temperature exceeding 35 ° C. for 4 hours or more, the reaction proceeds, and precipitates such as (VO) (HPO ₄ ) (H ₂ O) ₄ are easily generated Therefore, it is preferable from the viewpoint of preparation of a uniform raw material mixed solution that the temperature of the reduction reaction solution be rapidly cooled to 35 ° C. or less after the completion of the second step. Usually, after completion of the second step, the reduction reaction solution is cooled to 35 ° C. or less, preferably 5 to 35 ° C., particularly preferably 10 to 25 ° C. within 4 hours. More preferably, after completion of the second step, the reduction reaction solution is cooled to 35 ° C. or less, preferably 5 to 35 ° C., particularly preferably 10 to 25 ° C. within 3 hours.

The third step of the method for producing lithium vanadium phosphate of the present invention is a step of adding a solution containing lithium hydroxide to the reduction reaction solution capable of obtaining the second step to obtain a raw material mixed solution.

The solution containing lithium hydroxide is a solution in which lithium hydroxide is dissolved in water.

The concentration of lithium hydroxide in the solution containing lithium hydroxide is 5 to 20% by mass, preferably 10 to 15% by mass. When the concentration of lithium hydroxide in the solution containing lithium hydroxide is in the above range, it is preferable from the viewpoint of controlling the heat generation associated with the preparation of the uniform raw material mixed solution and the addition of the solution containing lithium hydroxide to improve the production efficiency.

The addition amount of the solution containing lithium hydroxide is 0.70 to 1.30, preferably 0.83 to 1., as the molar ratio of Li atoms in the lithium source to P atoms in the phosphorus source (Li / P). The addition amount is 17. When the addition amount of the solution containing lithium hydroxide is in the above-mentioned range, it is preferable from the viewpoint that single phase lithium vanadium phosphate is easily obtained as a final product. In the third step, it is uniform to add a solution containing lithium hydroxide so that the pH of the raw material mixed solution is 3 to 7, preferably 4 to 6, particularly preferably 4 to 5. It is particularly preferable from the viewpoint of preparation of the raw material mixed solution.

In the third step of the method for producing lithium vanadium phosphate according to the present invention, although the production history of lithium hydroxide is not limited, the content of impurities is as small as possible in order to produce lithium vanadium phosphate having high purity. It is preferred that

When a solution containing lithium hydroxide is added to the reduction reaction solution obtained by performing the second step, heat is generated. Therefore, in the third step, the solution containing lithium hydroxide is added to the reduction reaction solution while maintaining the reduction reaction solution obtained by the second step at 35 ° C. or lower. In the third step, a solution containing lithium hydroxide is added to the reduction reaction solution while maintaining the reduction reaction solution at 35 ° C. or less, whereby a reaction precursor having uniform composition distribution and excellent reactivity is obtained. It becomes easy to obtain. Further, the addition temperature of the solution containing lithium hydroxide in the third step is preferably 5 to 35 ° C., and more preferably 10 to 25 ° C., from the viewpoint of obtaining a reaction precursor which is particularly uniform and excellent in reactivity. Is particularly preferred. On the other hand, in the third step, when the addition temperature of the solution containing lithium hydroxide exceeds 35 ° C., the components in the reduction reaction solution react with lithium hydroxide to form a precipitate, which is spray-dried as it is It is not preferable from the viewpoint of becoming a reaction precursor in which each component is unevenly distributed.

In the third step, addition of a solution containing lithium hydroxide is preferably performed at a constant rate from the viewpoint of obtaining stable quality.

Further, in the third step, after the addition of the solution containing lithium hydroxide, the reaction between the components in the reduction reaction solution and lithium hydroxide proceeds extremely slowly at 35 ° C. or lower, for example, the raw material mixed solution is At a temperature of 35 ° C., a dark blue solution is maintained without precipitate for about 200 minutes, but a precipitate is gradually observed after 200 minutes, and the color of the solution is also from dark blue to light blue to green. Change. The raw material mixed solution obtained by performing the third step is a dark blue solution, and in the fourth step to be described later, it is possible to spray dry the raw raw material mixed solution as it is, having a uniform composition distribution. It is preferable from the viewpoint of obtaining a reaction precursor excellent in reactivity.

The 4th process concerning the manufacturing method of lithium vanadium phosphate of the present invention is a process of carrying out spray drying of the materials mixed solution obtained by performing the 3rd process, and obtaining a reaction precursor.

Although methods other than spray drying are also known as methods for drying a liquid, in the present invention, this drying method is adopted based on the finding that it is advantageous to select the spray drying method. In detail, since the spray drying method uniformly disperses the respective components and tightly packed particles are obtained, the particles are used as a reaction precursor in the method of producing lithium vanadium phosphate of the present invention. By firing the reaction precursor in the fifth step described later, it is possible to obtain lithium vanadium phosphate single phase in an X-ray diffraction manner.

In the spray drying method, the reaction precursor is obtained by atomizing the liquid by a predetermined means and drying the fine droplets generated thereby. There are, for example, a method using a rotary disk and a method using a pressure nozzle for atomizing the liquid. Any method can be used in the fifth step.

In the spray drying method, the size of droplets of the atomized liquid affects the stable drying and the properties of the resulting dried powder. From this point of view, the size of the atomized droplets is preferably 5 to 100 μm, particularly preferably 10 to 50 μm. In spray drying, it is desirable to determine the amount of liquid feed to the spray dryer taking this aspect into consideration.

The reaction precursor obtained by the spray drying method is subjected to calcination in the fifth step, but the powder characteristics such as the average particle diameter of secondary particles of lithium vanadium phosphate obtained by the fifth step are the reaction precursor You will generally take over your body. For this reason, spray drying is performed such that the secondary particles of the reaction precursor are 5 to 100 μm, in particular 10 to 50 μm, in terms of the particle size determined by scanning electron microscope (SEM) observation. It is preferable from the point of control of the particle size of lithium vanadium oxide. As for the drying temperature in the spray dryer, the hot air inlet temperature is adjusted to 180 to 250 ° C., preferably 200 to 240 ° C., and the powder temperature is 90 to 150 ° C., preferably 100 to 130 ° C. Adjustment is preferable because it prevents moisture absorption of the powder and facilitates recovery of the powder.

While the reaction precursor used in Patent Document 4 contains a crystalline substance, the reaction precursor obtained by performing the fourth step of the method for producing lithium vanadium phosphate of the present invention is amorphous. It is quality. Since the reaction precursor is amorphous, the present inventors speculate that the reaction precursor is excellent in reactivity, sintered at a low temperature, and further the crystallinity is higher than that of the reaction precursor of Patent Document 4 There is. In addition, it is confirmed by X-ray diffraction analysis that the reaction precursor is amorphous.

In the fifth step of the method for producing lithium vanadium phosphate according to the present invention, the reaction precursor obtained in the fourth step is calcined at 500 to 1300 ° C. to obtain single phase lithium vanadium phosphate in X-ray diffraction manner. It is a process.

The calcination temperature in the fifth step is 500 to 1300 ° C., preferably 600 to 1000 ° C. The reason for this is that when the firing temperature is lower than 500 ° C., the firing time until the single phase is prolonged, while when the firing temperature is higher than 1300 ° C., lithium vanadium phosphate melts.

The firing atmosphere in the fifth step is an inert gas atmosphere or a reducing atmosphere because it prevents the oxidation of vanadium and the melting thereof. There is no restriction | limiting in particular as an inert gas which can be used at a 5th process, For example, nitrogen gas, helium gas, argon gas etc. are mentioned.

In the fifth step, the baking time is not particularly limited, and generally, when baked for 2 hours or more, particularly 3 to 24 hours, it is possible to obtain single phase lithium vanadium phosphate in X-ray diffraction.

In the fifth step, lithium vanadium phosphate obtained by firing may be subjected to firing several times, if necessary.

In the method of producing lithium vanadium phosphate according to the present invention, a Me source (Me is other than V, if necessary, for the purpose of stabilizing the crystal structure of lithium vanadium phosphate and further improving the battery performance such as cycle characteristics. Metal element or transition metal element having an atomic number of 11 or more) is mixed with the acidic mixed slurry in the first step of the method for producing lithium vanadium phosphate of the present invention, and subsequently, the vanadium phosphate of the present invention By performing the second to fifth steps according to the method for producing lithium, lithium vanadium phosphate represented by the general formula (1) can be obtained by doping it with Me element. In the present invention, the Me element is present as being substituted at the Li site and / or V site of lithium vanadium phosphate represented by the above general formula (1).

Me in the Me source is a metal element or transition metal element having an atomic number of 11 or more other than V, and preferable 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, etc. may be mentioned, and these may be used alone or in combination of two or more.

Examples of the Me source include oxides having a Me element, hydroxides, halides, carbonates, nitrates, carbonates, organic acid salts and the like. In the first step, when the Me source is mixed, the Me source may be dissolved and present in the mixed slurry, or may be present as a solid. When a source of Me is present as a solid in the mixed slurry, using one having an average particle diameter of 100 μm or less, preferably 0.1 to 50 μm is preferable from the viewpoint of obtaining a reaction precursor having excellent reactivity. preferable. Also, in the first step, when mixing the Me source, the mixing amount of the Me source depends on the kind of Me element to be doped, but in many cases, the V atom of the vanadium compound relative to P atom in the phosphorus source The molar ratio (M / P) of the total (V + Me = M) of Me atoms in the source and the Me source is 0.50 to 0.80, preferably 0.60 to 0.73, and the molar ratio of Me / V is A mixing amount of more than 0 and 0.45 or less, preferably more than 0 and 0.1 or less is preferable.

Moreover, in the method for producing lithium vanadium phosphate according to the present invention, the lithium vanadium phosphate obtained in the fifth step is further subjected to a heat treatment to adjust the amount of conductive carbon contained in lithium vanadium phosphate. Step 6 can be performed. A specific operation of the sixth step is performed by subjecting lithium vanadium phosphate containing conductive carbon obtained in the fifth step to a heat treatment to oxidize the conductive carbon.

The heat treatment according to the sixth step is preferably performed in an oxygen-containing atmosphere. The oxygen concentration in the atmosphere of the heat treatment in the sixth step is preferably 5 vol% or more, particularly preferably 10 to 30 vol%, from the viewpoint of oxidizing the conductive carbon with high efficiency. The temperature of the heat treatment according to the sixth step is preferably 250 to 450 ° C., preferably 300 to 400 ° C. from the viewpoint of oxidizing the conductive carbon with high efficiency. The time of the heat treatment according to the sixth step is not particularly limited, and the content of conductive carbon contained in lithium vanadium phosphate decreases as the heat treatment time increases. In the heat treatment according to the sixth step, it is preferable to carry out by appropriately setting suitable conditions in advance so as to obtain a desired content of conductive carbon.

Thus, the lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention is single phase lithium vanadium phosphate in X-ray diffraction, and the average primary particle diameter is preferably 10 μm or less, preferably It is preferable to use lithium vanadium phosphate in the form of agglomerates in which a large number of primary particles of 0.01 to 5 μm gather to form secondary particles having an average particle diameter of 5 to 100 μm, preferably 10 to 50 μm.

In the method for producing lithium vanadium phosphate of the present invention, the obtained lithium vanadium phosphate may be further subjected to crushing treatment or grinding treatment as required, and further classification.

The lithium vanadium phosphate obtained by the method for producing lithium vanadium phosphate of the present invention may be a lithium vanadium phosphate carbon composite in which particles are coated with conductive carbon derived from reducing sugar. The lithium secondary battery of higher discharge capacity can be obtained by using the lithium vanadium phosphate complex obtained by the method of the present invention for producing lithium vanadium phosphate as the positive electrode active material.
Further, lithium vanadium phosphate obtained by the method for manufacturing lithium vanadium phosphate of the present invention is also used for applications in a solid electrolyte.

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to these examples.
Example 1
<First step>
Add 2 L of ion-exchanged water to a 5 L beaker, add 605 g of 85% phosphoric acid, 320 g of vanadium pentoxide and 170 g of sucrose (sucrose) to this, and stir at room temperature (25 ° C) to mix the yellowish acid mixed slurry Obtained (pH 0.9).
Second step
The obtained mixed slurry was heated at 95 ° C. for 1 hour under stirring to conduct a reduction reaction to obtain a dark blue reduction reaction solution (pH 1.7).
<Third step>
The reduction reaction solution was cooled to room temperature (25 ° C.) for 2 hours. Next, a lithium hydroxide solution was prepared by dissolving 220 g of lithium hydroxide monohydrate in 1.5 L of ion-exchanged water. The jacketed reaction vessel was cooled by a cooler, and while maintaining the reaction solution in a temperature range of 22 ° C., a lithium hydroxide solution was added to the reaction solution at a constant rate in 60 minutes to obtain a dark blue raw material mixed solution (PH 4.6).
<The 4th process>
Then, the dark blue raw material mixed solution was supplied to a spray dryer whose outlet temperature was set to 120 ° C. to obtain a reaction precursor. The average secondary particle size determined by SEM observation of the reaction precursor was 12 μm.
When the obtained reaction precursor was subjected to X-ray diffraction measurement using CuKα radiation as a radiation source, it could be confirmed that the reaction precursor was amorphous. Also, an X-ray diffraction diagram of the reaction precursor is shown in FIG. Moreover, the electron micrograph (SEM image) of the reaction precursor is shown in FIG.
<Fifth step>
The obtained reaction precursor was placed in a mullite-made mortar and fired at 600 ° C. for 10 hours under a nitrogen atmosphere. As a result of X-ray diffraction analysis of the obtained lithium vanadium phosphate sample, it was confirmed to be single-phase lithium vanadium phosphate. The X-ray diffraction pattern of the obtained lithium vanadium phosphate sample is shown in FIG. Moreover, the electron micrograph (SEM image) of the obtained lithium vanadium phosphate sample is shown in FIG.
Further, the residual carbon content of the obtained lithium vanadium phosphate sample was determined as a content of C atom by measuring with a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation).

(Examples 2 to 4)
In the fifth step, a reaction was performed in the same manner as in Example 1 except that the firing temperature was set to 700 to 900 ° C., to obtain a lithium vanadium phosphate sample.
Further, as a result of X-ray diffraction analysis of the obtained lithium vanadium phosphate sample, it was confirmed that all were single phase lithium vanadium phosphate. Further, the amount of residual carbon was determined in the same manner as in Example 1.

Note) 1) The “V / P molar ratio” in the first step indicates the molar ratio of V atom in vanadium pentoxide to P atom in the added phosphoric acid.
2) The “molar ratio of Li / P” in the third step indicates the molar ratio of Li atoms in lithium hydroxide added in the third step to P atoms in phosphoric acid added in the first step.
3) The “pH after addition” in the third step indicates the pH of the reaction solution after the addition of the solution containing lithium hydroxide.

(Comparative example 1)
In a 5 L beaker, put 3.5 L of ion-exchanged water, add 220 g of lithium hydroxide monohydrate, 320 g of vanadium pentoxide, 605 g of 85% phosphoric acid and 170 g of sucrose, and stir at 95 ° C. for 1 hour Heating gave a green slurry. Then, the slurry was supplied to a spray dryer whose outlet temperature was set to 120 ° C. to obtain a reaction precursor. When the obtained reaction precursor was subjected to X-ray diffraction analysis, a clear diffraction peak could be confirmed for the reaction precursor. Also, the X-ray diffraction pattern of the reaction precursor is shown in FIG.
The obtained reaction precursor was placed in a mullite-made mortar and fired at 600 ° C. for 10 hours under a nitrogen atmosphere to obtain a lithium vanadium phosphate sample.
The X-ray diffraction analysis of the obtained lithium vanadium phosphate sample is also shown in FIG. As a result of X-ray diffraction analysis, the presence of a heterophase other than lithium vanadium phosphate was confirmed. Further, the amount of remaining carbon was determined in the same manner as in Example 1. As a result, the amount of remaining carbon was 1.9% by mass.

(Comparative example 2)
In a 5 L beaker, 2 L of ion exchanged water was placed, and 252 g of lithium hydroxide monohydrate was added and dissolved therein. To this solution was added 364 g of vanadium pentoxide and stirred for 1 h. To this solution were added 72 g of glucose (dextrose) and 692 g of 85% phosphoric acid, and the mixture was stirred for 1 hour to obtain a raw material mixed solution. Next, the raw material mixture was supplied to a spray drying apparatus in which the outlet temperature was set to 120 ° C. to obtain a reaction precursor. Also, the X-ray diffraction pattern of the reaction precursor is shown in FIG.
The obtained reaction precursor was placed in a mullite-made mortar and fired at 900 ° C. for 12 hours under a nitrogen atmosphere. The fired product was crushed by a jet mill to obtain a lithium vanadium phosphate sample. As a result of X-ray diffraction analysis of the obtained lithium vanadium phosphate sample, it was confirmed to be single phase lithium vanadium phosphate. Further, when the amount of remaining carbon was determined in the same manner as in Example 1, the amount of remaining carbon was 0.1% by mass.

(Example 5)
<First step>
Put 2.5L of ion-exchanged water in a 5L beaker, and add 864.7g of 85% phosphoric acid, 457.7g of vanadium pentoxide and 156.6g of lactose monohydrate to this and stir at room temperature (25 ° C) As a result, an ocher colored acidic mixed slurry was obtained (pH 0.9).
Second step
The obtained mixed slurry was heated at 95 ° C. for 1 hour under stirring to conduct a reduction reaction to obtain a dark blue reduction reaction solution (pH 1.7).
<Third step>
The reduction reaction solution was cooled to room temperature (25 ° C.) for 2 hours. Next, a lithium hydroxide solution was prepared by dissolving 314.7 g of lithium hydroxide monohydrate in 1.5 L of ion-exchanged water. The jacketed reaction vessel was cooled by a cooler, and while maintaining the reaction solution in a temperature range of 22 ° C., a lithium hydroxide solution was added to the reaction solution at a constant rate in 60 minutes to obtain a dark blue raw material mixed solution (PH 4.6).
<The 4th process>
Then, the dark blue raw material mixed solution was supplied to a spray dryer whose outlet temperature was set to 120 ° C. to obtain a reaction precursor. When the obtained reaction precursor was subjected to X-ray diffraction measurement using CuKα radiation as a radiation source, it could be confirmed that the reaction precursor was amorphous. Moreover, the electron micrograph (SEM image) of the reaction precursor is shown in FIG.
<Fifth step>
The obtained reaction precursor was placed in a mullite-made mortar and fired at 800 ° C. for 10 hours under a nitrogen atmosphere. As a result of X-ray diffraction analysis of the obtained lithium vanadium phosphate sample, it was confirmed to be single-phase lithium vanadium phosphate. Also, an X-ray diffraction diagram of a lithium vanadium phosphate sample is shown in FIG. The electron micrograph (SEM image) of the obtained lithium vanadium phosphate sample is shown in FIG.
In addition, the amount of remaining carbon of the obtained lithium vanadium phosphate sample was measured with a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corp.) and found to be 1.5% by mass. Further, the BET specific surface area was 9.8 m ² / g.

(Comparative example 3)
After completion of the second step, the reaction solution was cooled to room temperature (25 ° C.) for 2 hours, and in the third step, the lithium hydroxide solution was added as it was at a constant rate for 15 minutes without cooling the reaction vessel with a cooler. The reaction was carried out in the same manner as in Example 1 except for using a lithium vanadium phosphate sample. The temperature of the reaction solution during the addition of the lithium hydroxide solution rose from 25 ° C. to 40 ° C. Moreover, the raw material mixed solution after the 3rd process was a blue slurry (pH 4.7).
Next, in the fourth step, the blue slurry was supplied to a spray drying apparatus whose outlet temperature was set to 120 ° C. to obtain a reaction precursor. When the obtained reaction precursor was subjected to X-ray diffraction measurement, a clear diffraction peak could be confirmed for the reaction precursor. Moreover, the X-ray diffraction pattern of the reaction precursor is shown in FIG.
Next, the obtained reaction precursor was placed in a mullite-made mortar and fired at 600 ° C. for 10 hours under a nitrogen atmosphere to obtain a lithium vanadium phosphate sample.
The X-ray diffraction analysis of the obtained lithium vanadium phosphate sample is shown in FIG. As a result of X-ray diffraction analysis, the presence of a heterophase other than lithium vanadium phosphate was confirmed. Further, the amount of remaining carbon was determined in the same manner as in Example 1. As a result, the amount of remaining carbon was 1.8% by mass.

<Evaluation of battery performance>
<Battery performance test>
(I) Preparation of lithium secondary battery;
91% by mass of each sample of lithium vanadium phosphate of Example 1, Example 4, Example 5, Comparative Example 2 and Comparative Example 3 manufactured as described above, 6% by mass of graphite powder, 3% by mass of polyvinylidene fluoride The mixture was mixed to form a positive electrode agent, and this was dispersed in N-methyl-2-pyrrolidinone to prepare a kneading paste. The obtained kneaded paste was applied onto an aluminum foil, dried, pressed and punched out into a disk having a diameter of 15 mm to obtain a positive electrode plate.
Using this positive electrode plate, a lithium secondary battery was manufactured using each member such as a separator, a negative electrode, a positive electrode, a current collecting plate, a mounting bracket, an external terminal, and an electrolytic solution. Among them, a metal lithium foil was used for the negative electrode, and an electrolyte was prepared by dissolving 1 mol of LiPF _{6 in} 1 liter of a 1: 1 mixed solution of ethylene carbonate and methyl ethyl carbonate.

(2) Performance Evaluation of Battery The prepared lithium secondary battery was operated under the following conditions to evaluate the battery performance.
<Evaluation of cycle characteristics>
Charge by constant current constant voltage (CCCV) charge for 5 hours with full charge time to charge to 4.2V at 0.5C, and then hold to 4.2V constant to discharge to 2.0V at 0.1C Current (CC) discharge was performed, and the discharge capacity was measured every cycle with these operations as one cycle. This cycle was repeated 20 cycles, and the capacity retention rate was calculated from the discharge capacity of each of the first cycle and the 20th cycle according to the following equation. The discharge capacity at the first cycle was taken as the initial discharge capacity.

Capacity retention rate (%) = ((20th cycle discharge capacity) / (1st cycle discharge capacity)) × 100

(Example 6)
<Step 6>
The lithium vanadium phosphate sample (residue carbon content: 1.6% by mass) obtained in Example 3 was subjected to heat treatment at 350 ° C. for 15 hours in an air atmosphere (oxygen concentration: 20 Vol%) in an electric furnace.
As a result of X-ray diffraction analysis of the obtained lithium vanadium phosphate sample, it was confirmed to be single-phase lithium vanadium phosphate. In addition, the amount of remaining carbon of the obtained lithium vanadium phosphate sample was measured with a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corp.) and found to be 0.1 mass%. Moreover, the BET specific surface area was 7.1 m < ² > / g.

Claims

A method for producing lithium vanadium phosphate having a NASICON structure, comprising:
A first step of mixing vanadium pentoxide, phosphoric acid and reducing sugar in an aqueous solvent to prepare an acidic mixed slurry, and then heating the mixed slurry to form a solution to obtain a reduced reaction solution Then, while maintaining the reduction reaction solution at 35 ° C. or less, a third step of preparing a raw material mixed solution by adding a solution containing lithium hydroxide to the reduction reaction solution, and then spray drying the raw material mixed solution It has a fourth step of processing to obtain a reaction precursor, and then a fifth 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. And a method of producing lithium vanadium phosphate.
The method for producing lithium vanadium phosphate according to claim 1, wherein the temperature of the heating treatment in the second step is 60 to 100 ° C.
The method for producing lithium vanadium phosphate according to any one of claims 1 and 2, wherein the reducing sugar is one or two selected from sucrose and lactose.
The method for producing lithium vanadium phosphate according to any one of claims 1 to 3, wherein the concentration of lithium hydroxide in the solution containing lithium hydroxide is 5 to 20% by mass.
The raw material mixed solution obtained by performing the third step is a dark blue solution, and the deep blue solution is spray-dried in the fourth step. Method for producing lithium vanadium phosphate.
The lithium vanadium phosphate according to any one of claims 1 to 5, wherein the lithium hydroxide solution is added such that the pH of the raw material mixed solution is 3 to 7 in the third step. Manufacturing method.
7. The method according to claim 1, wherein in the first step, a Me source (Me represents a metal element having an atomic number of 11 or more other than V or a transition metal element other than V) is further mixed into the acidic mixed slurry. The manufacturing method of vanadium vanadium phosphate of any one statement.
The method for producing lithium vanadium phosphate according to any one of claims 1 to 7, further comprising a sixth step of heat-treating lithium vanadium phosphate obtained in the fifth step.
9. The method according to claim 8, wherein the heat treatment is performed in an oxygen-containing atmosphere in the sixth step.
The method for producing lithium vanadium phosphate according to any one of claims 8 or 9, wherein the heat treatment temperature in the sixth step is 250 to 450 属 C.