WO2017154690A1

WO2017154690A1 - Method for manufacturing vanadium lithium phosphate

Info

Publication number: WO2017154690A1
Application number: PCT/JP2017/008049
Authority: WO
Inventors: 純也深沢; 淳史 ▲高▼▲崎▼
Original assignee: 日本化学工業株式会社
Priority date: 2016-03-08
Filing date: 2017-03-01
Publication date: 2017-09-14

Abstract

In order to provide vanadium lithium phosphate which is single-phase by X-ray diffraction and useful particularly as a positive-electrode active material or the like for a lithium secondary cell by an industrially advantageous method, the present invention is a method for manufacturing vanadium lithium phosphate having a NASICON structure, the method for manufacturing vanadium lithium phosphate characterized by having a first step for mixing a tetravalent or pentavalent vanadium compound, a phosphorus source, and a reducing sugar in an aqueous medium and preparing a mixed slurry, a second step for then heating the mixed slurry and forming a solution, a third step for then adding a lithium source to the solution and preparing a starting material mixture, a fourth step for spray drying the starting material mixture and obtaining a reaction precursor, and a fifth step for then firing the reaction precursor at a temperature of 500-1300°C in an inert gas atmosphere or a reducing atmosphere.

Description

Method for producing lithium vanadium phosphate

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

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

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

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 uniform mixture is formed into a pellet, and then the molded product is fired ( For example, see Patent Documents 1 and 2). In Patent Document 3 below, vanadium oxide (V) is dissolved in an aqueous solution containing lithium hydroxide, a phosphorus source and carbon and / or a nonvolatile organic compound are added, and the resulting raw material mixture solution is dried. A method has been proposed in which a precursor is obtained, and the precursor is heat-treated in an inert atmosphere to obtain a composite of Li ₃ V ₂ (PO ₄ ) ₃ and a conductive carbon material.

In addition, the present applicant also previously mixed a lithium source, a pentavalent or tetravalent vanadium compound, a phosphorus source, and a conductive carbon material source in 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 perform a precipitation reaction to obtain a reaction solution containing a precipitation product, and a reaction solution containing the precipitation product as a media mill A third step of obtaining a slurry containing the pulverized product by spray-drying, a fourth step of obtaining a reaction precursor by spray drying the slurry containing the pulverized product, and a step of removing the reaction precursor. A method for producing a lithium vanadium phosphate carbon composite that is fired at 600 to 1300 ° C. in an active gas atmosphere or a reducing atmosphere has been proposed.

JP-T-2001-500665 Japanese translation of PCT publication No. 2002-530835 JP 2008-052970 A International Publication No. 2012/043367 Pamphlet

Li ₃ V ₂ (PO ₄ ) ₃ is known to have a high theoretical capacity of 197 mAhg ⁻¹ .
However, the conventional lithium secondary battery using Li ₃ V ₂ (PO ₄ ) ₃ as the positive electrode active material has a low discharge capacity, and according to the method for producing lithium vanadium phosphate disclosed in Patent Document 4, the discharge capacity is low. However, in order to obtain a reaction precursor having excellent reactivity, a precipitation reaction or a pulverization treatment with a media mill is required, and the production process becomes complicated, which is not industrially advantageous.

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

As a result of intensive studies in view of the above problems, the inventors of the present invention performed a reduction reaction of a vanadium compound by heat-treating a mixed slurry containing a tetravalent or pentavalent vanadium compound, a phosphorus source, and a reducing sugar. The reaction precursor obtained by spray-drying a raw material mixture prepared by adding a lithium source to a solution is excellent in reactivity, and single phase highly crystalline lithium vanadium phosphate is obtained even at a low temperature of about 600 ° C. Be done. In addition, the present inventors have 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 completed the present invention. It was.

That is, the present invention is a method for producing lithium vanadium phosphate having a NASICON structure, in which a tetravalent or pentavalent vanadium compound, a phosphorus source, and a reducing sugar are mixed in an aqueous solvent to form a mixed slurry. A first step to prepare, a second step in which the mixed slurry is heated to form a solution, a third step in which a lithium source is added to the solution to prepare a raw material mixture, and then the raw material mixture Vanadium phosphate, characterized in that it has a fourth step of obtaining a reaction precursor by spray-drying and then a fifth step of calcining the reaction precursor at 500 to 1300 ° C. in an inert gas atmosphere or a reducing atmosphere. A method for producing lithium is provided.

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

The X-ray diffraction pattern of the reaction precursor obtained in Example 1, Comparative Example 1, and Comparative Example 2. FIG. 2 is an SEM photograph of the reaction precursor obtained in Example 1. The X-ray-diffraction figure of the lithium vanadium phosphate sample obtained in Example 1 and Comparative Example 1. FIG. 2 is an SEM photograph of lithium vanadium phosphate obtained in Example 1. FIG. 4 is an SEM photograph of the reaction precursor obtained in Example 5. The X-ray-diffraction figure of the lithium vanadium phosphate sample obtained in Example 5. FIG. 4 is an SEM photograph of a lithium vanadium phosphate sample obtained in Example 5. FIG. The X-ray-diffraction figure of the lithium vanadium phosphate sample obtained in Example 6. FIG. The SEM photograph of the lithium vanadium phosphate sample obtained in Example 6.

Hereinafter, the present invention will be described based on preferred embodiments thereof.
The lithium vanadium phosphate obtained by the production method of the present invention is a lithium vanadium phosphate having a NASICON structure (hereinafter, simply referred to as “vanadium lithium phosphate”).

In the present invention, the lithium vanadium phosphate is represented by the following general formula (1):
Li _x V _y (PO ₄ ) ₃ (1)
(Wherein x represents 2.5 to 3.5 and y represents 1.8 to 2.2), or lithium vanadium phosphate represented by the general formula (1) Further, it is lithium vanadium phosphate which is doped with a Me element (Me represents a metal element or a transition metal element having an atomic number of 11 or more other than V) as necessary.
X in the formula (1) is preferably 2.5 or more and 3.5 or less, 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.
The Me element to be doped is preferably one or more selected from Mg, Ca, Al, Mn, Co, Ni, Fe, Ti, Zr, Bi, Cr, Nb, Mo, and Cu.

The method for producing lithium vanadium phosphate according to the present invention comprises mixing a tetravalent or pentavalent vanadium compound (hereinafter sometimes simply referred to as “vanadium compound”), a phosphorus source and a reducing sugar in an aqueous solvent. The first step for preparing the mixed slurry, the second step for heat-treating the obtained mixed slurry, and the third step for preparing the raw material mixture by adding a lithium source to the next solution. Next, a fourth step of obtaining a reaction precursor by subjecting the obtained raw material mixture to spray drying, and then a step of baking the obtained reaction precursor at 500 to 1300 ° C. in an inert gas atmosphere or a reducing atmosphere. It has the process, It is characterized by the above-mentioned.

The first step according to the present invention is a step of obtaining a mixed slurry in which each raw material is mixed by mixing a vanadium compound, a phosphorus source, and a reducing sugar in an aqueous solvent.

As the vanadium compound, vanadium pentoxide, vanadium trioxide, ammonium vanadate, vanadium oxyoxalate, or the like can be used. Among these, vanadium pentoxide is preferable from the viewpoint of being industrially available at a low cost and having excellent reactivity.

As the phosphorus source, phosphoric acid, polyphosphoric acid, anhydrous phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, and the like can be used. Among these, phosphoric acid is preferable from the viewpoint of being industrially available at low cost and obtaining a reaction precursor having excellent reactivity.

The addition amount of the vanadium compound and the phosphorus source is such that the addition amount of the vanadium compound is 0.50 to 0.80 in terms of the molar ratio (V / P) of the V atom in the vanadium compound to the P atom in the phosphorus source, preferably A value of 0.60 to 0.73 is preferable from the viewpoint of easily obtaining single-phase lithium vanadium phosphate as the final product.

As the reducing sugar, one in which carbon is isolated by heat decomposition in an inert or reducing atmosphere at least in the baking in the fifth step is used. The reducing sugar promotes the reduction reaction of the vanadium compound in the second step, and in addition to making the obtained solution a reaction solution having a good viscosity that can be stirred, it prevents the oxidation of vanadium in the fifth step. It becomes a necessary ingredient. Excess reducing sugar is converted to conductive carbon by firing in the fifth step. Therefore, in this production method, excessive reducing sugar is added as a component of a conductive carbon source that imparts conductivity of lithium vanadium phosphate. It can also function.

Examples of reducing sugars that can be used include glucose, fructose, lactose, maltose, sucrose, and the like. Among these, lactose and sucrose are preferable from the viewpoint of obtaining a reaction precursor having excellent reactivity.

The amount of reducing sugar added is preferably 0 to 20% by mass in terms of C atoms with respect to the lithium vanadium phosphate produced.
There is a tendency for the amount of C atoms contained in the reducing sugar to decrease after baking as compared to before baking. Therefore, in the first step, when the reducing sugar is added in an amount of 0.3 to 40 parts by mass in terms of C atoms with respect to 100 parts by mass of lithium vanadium phosphate produced, The compounding amount of conductive carbon converted from reducing sugar tends to be 0 to 20 parts by mass in terms of C atoms. When the amount of reducing sugar compounded with respect to 100 parts by mass of lithium vanadium phosphate is within the above range, when lithium vanadium phosphate is used as the positive electrode active material of a lithium secondary battery, the lithium secondary battery Excellent performance can be imparted. In particular, 100 parts by mass of lithium vanadium phosphate is added by adding a reducing sugar to 100 to 40 parts by mass of lithium vanadium phosphate so that the amount of C is 0.5 to 40 parts by mass, preferably 5 to 30 parts by mass. The amount of conductive carbon converted from the reducing sugar is 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight, and sufficient conductivity can be imparted by the conductive carbon. Therefore, the internal resistance of the lithium secondary battery can be lowered, and the discharge capacity per mass or volume is increased. On the other hand, if the amount of reducing sugar added to 100 parts by mass of lithium vanadium phosphate is less than the above range, it is difficult to obtain single-phase lithium vanadium phosphate, which is not preferable. Further, when the amount of reducing sugar added exceeds the above range, the discharge capacity per mass or volume tends to be low.

In the first step according to the present invention, the production history of the vanadium compound, the phosphorus source, and the reducing sugar is not limited. However, in order to produce high purity lithium vanadium phosphate, the content of impurities is as small as possible. It is preferable.

The aqueous solvent used in the first step according to the present invention is not limited to water and may be a mixed solvent of water and a hydrophilic organic solvent.

The order in which the vanadium compound, the phosphorus source, and the reducing sugar are added to the aqueous solvent, and the mixing means are not particularly limited, and are performed so as to obtain a mixed slurry in which the respective raw materials are uniformly dispersed.

The second step according to the present invention is a step in which the mixed slurry obtained in the first step is heat-treated and at least a reduction reaction of the vanadium compound is performed to convert the mixed slurry into a solution in which each component is dissolved. The temperature of the heat treatment according to the second step is 60 to 100 ° C., preferably 80 to 100 ° C. The reason is that if the temperature of the heat treatment is lower than 60 ° C., the reaction time becomes longer, which is industrially disadvantageous, and a pressure vessel must be used to raise the temperature of the heat treatment higher than 100 ° C. It is not industrially advantageous. Therefore, the second step can be performed under atmospheric pressure.

The time for the reduction reaction is not critical in this production method. In general, a satisfactory solution can be obtained by heat treatment for 0.2 hours or more, particularly 0.5 to 2 hours.

The third step according to the present invention is a step of obtaining a raw material mixture by adding a lithium source to the solution obtained in the second step.
Note that the raw material mixture may be a solution or a slurry.

Examples of the lithium source include lithium carbonate, lithium hydroxide, lithium oxide, lithium nitrate, and organic acid lithium such as lithium oxalate. These may be hydrated or anhydrous. Among these, lithium carbonate and lithium hydroxide are preferred from the viewpoint of being industrially available at low cost and obtaining a reaction precursor having excellent reactivity.
These lithium sources may be added to the solution obtained in the second step as a solution dissolved in an aqueous solvent.

The addition amount of the lithium source is 0.70 to 1.30, preferably 0.83 to 1.17 in terms of a molar ratio (Li / P) of Li atoms in the lithium source to P atoms in the phosphorus source. Is preferable from the viewpoint of easily obtaining single-phase lithium vanadium phosphate as the final product.

In the third step according to the present invention, the production history of the lithium source described above is not limited, but in order to produce high purity lithium vanadium phosphate, it is preferable that the impurity content is as low as possible.

The addition temperature of the lithium source is not particularly limited, but a precipitate is observed when it exceeds 35 ° C., and in this production method, a slurry-like raw material mixture containing this precipitate is subjected to a fourth step described later. However, the raw material mixture obtained in the third step is preferably in the form of a solution from the viewpoint of obtaining a reaction precursor that is more uniform and excellent in reactivity. From this point of view, the addition temperature of the lithium source is less than 35 ° C., preferably 30 ° C. or less, particularly preferably 0 to 30 ° C.

After the addition of the lithium source, an aging reaction can be performed as necessary for the purpose of obtaining a reaction precursor having further improved physical properties such as powder characteristics such as particle size distribution.
The raw material mixture after the aging reaction can be obtained as a slurry in which each component is uniformly mixed. However, unlike Patent Document 4, the slurry contains finer particles. Instead, in this production method, the spray precursor is spray-dried in the fourth step of the next step as it is, and a reaction precursor having excellent reactivity can be obtained.
The temperature of the ripening reaction is 60 to 100 ° C., preferably 80 to 100 ° C. The aging time is 0.5 hours or more, preferably 0.5 to 10 hours.

The fourth step according to the present invention is a step of obtaining a reaction precursor by spray drying the raw material mixture obtained in the third step.

Although methods other than the spray drying method are known as the liquid drying method, this drying method is adopted based on the knowledge that it is advantageous to select the spray drying method in this production method.
In detail, when the spray drying method is used, each component is uniformly dispersed and a densely packed granular material is obtained. This granular material is used as a reaction precursor in the present invention, and will be described later using the reaction precursor. By firing in the fifth step, single-phase lithium vanadium phosphate can be obtained in X-ray diffraction.

In the spray drying method, the reaction precursor is obtained by atomizing the liquid by a predetermined means and drying fine droplets generated thereby. For example, the liquid atomization includes a method using a rotating disk and a method using a pressure nozzle. Any method can be used in this step.

In the spray drying method, the size of the droplets of the atomized liquid affects stable drying and the properties of the resulting dry powder. From this point of view, the size of the atomized droplet is preferably 5 to 100 μm, particularly 10 to 50 μm. It is desirable to determine the supply amount of the liquid to the spray drying apparatus in consideration of this viewpoint.

The reaction precursor obtained by the spray drying method is subjected to calcination in the next step, but the powder properties such as the average particle diameter of the secondary particles of lithium vanadium phosphate obtained generally take over the reaction precursor. . For this reason, spray drying is performed so that the secondary particles of the reaction precursor have a particle diameter of 5 to 100 μm, particularly 10 to 50 μm, as determined by observation with a scanning electron microscope (SEM). This is preferable from the viewpoint of controlling the particle size of lithium vanadium oxide.
The drying temperature in the spray drying apparatus is 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. Adjustment is preferable because it prevents moisture absorption of the powder and facilitates collection of the powder.

One feature is that the reaction precursor used in Patent Document 4 contains a crystalline substance, whereas the reaction precursor used in the present invention is amorphous. The present inventors presume that since the reaction precursor is amorphous, the reaction precursor is superior in reactivity, sintered at a low temperature, and has higher crystallinity than the reaction precursor of Patent Document 4. Yes.

The reaction precursor thus obtained is then subjected to a fifth step of baking at 500 to 1300 ° C. in an inert gas atmosphere or a reducing atmosphere to obtain the target lithium vanadium phosphate.

The fifth step according to the present invention is a step in which the reaction precursor obtained in the fourth step is fired at 500 to 1300 ° C. to obtain single-phase lithium vanadium phosphate by X-ray diffraction.

The firing temperature in the fifth step is 500 to 1300 ° C., preferably 600 to 1000 ° C. This is because if the firing temperature is lower than 500 ° C., the firing time until it becomes a single phase becomes longer, while if the firing temperature is higher than 1300 ° C., lithium vanadium phosphate is melted.

The firing atmosphere is performed in an inert gas atmosphere or a reducing atmosphere because vanadium is prevented from being oxidized and melted.
The inert gas that can be used in the fifth step is not particularly limited, and examples thereof include nitrogen gas, helium gas, and argon gas.

Calcination time is not critical in this production method. In general, by baking for 2 hours or more, particularly 3 to 24 hours, single-phase lithium vanadium phosphate can be obtained by X-ray diffraction.

The lithium vanadium phosphate thus obtained may be subjected to a plurality of firing steps as necessary.

In the present invention, for the purpose of stabilizing the crystal structure of lithium vanadium phosphate and further improving battery performance such as cycle characteristics, a Me source (Me is a metal element having an atomic number of 11 or more other than V or a transition, if necessary) Metal element) is mixed with the mixed slurry of the first step according to the production method of the present invention, and then the second to fifth steps of the production method of the present invention are performed, whereby the general formula (1) It is possible to obtain the lithium vanadium phosphate shown by doping with Me element. In the present invention, the Me element is substituted for the Li site or / and the V site of lithium vanadium phosphate represented by the general formula (1).
Me in the Me source is a metal element or a transition metal element having an atomic number of 11 or more other than V, and preferable Me elements include Mg, Ca, Al, Mn, Co, Ni, Fe, Ti, Zr, Bi, Cr, Nb, Mo, Cu, etc. are mentioned, These may be single 1 type or the combination of 2 or more types.
Examples of the Me source include oxides, hydroxides, halides, carbonates, nitrates, carbonates, and organic acid salts having the Me element. Note that the Me source may be dissolved in the mixed slurry in the first step or may be present as a solid. In the case where the Me source is present as a solid in the mixed slurry, it is preferable from the viewpoint of obtaining a reaction precursor having excellent reactivity that an average particle size of 100 μm or less, preferably 0.1 to 50 μm is used. .
When mixing the Me source, the mixing amount of the Me source depends on the type of Me element to be doped, but in many cases, the sum of the V atom of the vanadium compound and the Me atom in the Me source (V + Me = The molar ratio of M) to the P atom in the phosphorus source (M / P) is 0.5 to 0.80, preferably 0.60 to 0.73, and the molar ratio of Me / V is larger than 0 to 0.45. Hereinafter, an amount that is preferably greater than 0 and less than or equal to 0.1 is preferred.

In this production method, the sixth step of adjusting the amount of conductive carbon contained in the lithium vanadium phosphate by further heat-treating the lithium vanadium phosphate obtained in the fifth step is performed. it can.
The specific operation of the sixth step is performed by subjecting the lithium vanadium phosphate containing the 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 is preferably 5 Vol% or more, and 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., more preferably 300 to 400 ° C., from the viewpoint of oxidizing the conductive carbon with high efficiency.
The time for the heat treatment according to the sixth step is not critical in this production method. The longer the heat treatment time, the lower the conductive carbon content contained in the lithium vanadium phosphate. It is preferable to carry out by appropriately setting suitable conditions in advance so as to obtain a desired conductive carbon content.

The lithium vanadium phosphate thus obtained is a single-phase lithium vanadium phosphate in terms of X-ray diffraction, and as a preferred physical property, a large number of primary particles having an average primary particle diameter of 10 μm or less, preferably 0.01 to 5 μm are aggregated. Thus, it is preferable to use agglomerated lithium vanadium phosphate that forms secondary particles having an average particle diameter of 5 to 100 μm, preferably 10 to 50 μm.
In this production method, the obtained lithium vanadium phosphate may be further crushed or crushed as necessary, and further classified.

Further, the lithium vanadium phosphate obtained by the present production method may be a vanadium lithium phosphate carbon composite in which the particles are coated with conductive carbon resulting from a reducing sugar, and the vanadium lithium lithium carbon composite By using as a positive electrode active material, a lithium secondary battery having a higher discharge capacity can be obtained.
Moreover, the lithium vanadium phosphate obtained by this manufacturing method can be used also for the use with a solid electrolyte.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.
{Example 1}
<First step>
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 170 g of sucrose (sucrose) were added thereto and stirred at room temperature (25 ° C.) to obtain an ocher mixed slurry. .
<Second step>
The obtained mixed slurry was heated with stirring at 95 ° C. for 1 hour to carry out a reduction reaction to obtain a dark blue reaction solution.
<Third step>
The reaction solution was cooled to room temperature (25 ° C.). Next, a solution in which 220 g of lithium hydroxide monohydrate was dissolved in 1.5 L of ion-exchanged water was prepared, and this solution was added to the reaction solution at room temperature to obtain a dark blue raw material mixture solution.
<4th process>
Subsequently, the liquid was supplied to the spray drying apparatus which set outlet temperature to 120 degreeC, and the reaction precursor was obtained. The average secondary particle diameter obtained by the SEM observation method of the reaction precursor was 12 μm.
When the obtained reaction precursor was used as a radiation source and X-ray diffraction measurement was performed using CuKα rays, it was confirmed that the reaction precursor was amorphous. An X-ray diffraction pattern of the reaction precursor is shown in FIG. Further, an electron micrograph (SEM image) of the reaction precursor is shown in FIG.
<5th process>
The obtained reaction precursor was placed in a mullite slag and baked at 600 ° C. for 10 hours in a nitrogen atmosphere. As a result of X-ray diffraction analysis of the obtained lithium vanadium phosphate sample, it was confirmed to be a single-phase lithium vanadium phosphate. FIG. 3 shows an X-ray diffraction pattern of the obtained lithium vanadium phosphate sample. 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 measured as a C atom content 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 carried out in the same manner as in Example 1 except that the firing temperature was 700 to 900 ° C. to obtain a lithium vanadium phosphate sample.
Moreover, 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) “Molar ratio of V / P” in the first step indicates the molar ratio of V atom in vanadium pentoxide to P atom in added phosphoric acid.
2) “Molar ratio of Li / P” in the third step indicates a molar ratio of Li atoms in lithium hydroxide added in the third step to P atoms in phosphoric acid added in the first step.

{Comparative Example 1}
Into a 5 L beaker, 3.5 L of ion-exchanged water was added, 220 g of lithium hydroxide monohydrate, 320 g of vanadium pentoxide, 605 g of 85% phosphoric acid, and 170 g of sucrose were added, and the mixture was stirred at 95 ° C. for 1 hour. A green slurry was obtained upon heating. Next, the 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 analysis, a clear diffraction peak could be confirmed for the reaction precursor. The X-ray diffraction pattern of the reaction precursor is also shown in FIG.
The obtained reaction precursor was put in a mullite slag and baked at 600 ° C. for 10 hours in a nitrogen atmosphere to obtain a lithium vanadium phosphate sample.
The X-ray diffraction analysis diagram of the obtained lithium vanadium phosphate sample is also shown in FIG. As a result of X-ray diffraction analysis, the presence of a different phase other than lithium vanadium phosphate was confirmed. Moreover, when the amount of residual carbon was calculated | required like Example 1, the amount of residual carbon was 1.9 mass%.

{Comparative Example 2}
2 L of ion-exchanged water was put into a 5 L beaker, and 252 g of lithium hydroxide monohydrate was added thereto and dissolved. To this solution, 364 g of vanadium pentoxide was added and stirred for 1 h. To this solution, 72 g of glucose (glucose) and 692 g of 85% phosphoric acid were added and stirred for 1 hour to obtain a raw material mixture. Next, the raw material mixture was supplied to a spray drying apparatus in which the hot air inlet temperature was set to 230 ° C. and the outlet temperature set to 120 ° C. to obtain a reaction precursor. The X-ray diffraction pattern of the reaction precursor is also shown in FIG.
The obtained reaction precursor was placed in a mullite slag and baked at 900 ° C. for 12 hours in a nitrogen atmosphere. The fired product was pulverized 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 a single-phase lithium vanadium phosphate. Moreover, when the amount of residual carbon was calculated | required like Example 1, the amount of residual carbon was 0.1 mass%.

{Example 5}
<First step>
Put 2.5 L of ion-exchanged water in a 5 L beaker, add 854.7 g of 85% phosphoric acid, 457.7 g of vanadium pentoxide and 156.6 g of lactose monohydrate, and stir at room temperature (25 ° C.). As a result, an ocher mixed slurry was obtained.
<Second step>
The obtained mixed slurry was heated with stirring at 95 ° C. for 1 hour to carry out a reduction reaction to obtain a dark blue reaction solution.
<Third step>
The reaction solution was cooled to room temperature (25 ° C.). Next, a solution in which 314.7 g of lithium hydroxide monohydrate was dissolved in 1.5 L of ion-exchanged water was prepared, and this solution was added to the reaction solution at room temperature to obtain a dark blue raw material mixture solution.
<4th process>
Subsequently, the liquid was supplied to the spray drying apparatus which set outlet temperature to 120 degreeC, and the reaction precursor was obtained. When the obtained reaction precursor was used as a radiation source and X-ray diffraction measurement was performed using CuKα rays, it was confirmed that the reaction precursor was amorphous. An electron micrograph (SEM image) of the reaction precursor is shown in FIG.
<5th process>
The obtained reaction precursor was placed in a mullite slag and baked at 800 ° C. for 10 hours in a nitrogen atmosphere. As a result of X-ray diffraction analysis of the obtained lithium vanadium phosphate sample, it was confirmed to be a single-phase lithium vanadium phosphate. Moreover, the X-ray-diffraction figure of a lithium vanadium phosphate sample is shown in FIG. An electron micrograph (SEM image) of the obtained lithium vanadium phosphate sample is shown in FIG.
Further, when the residual carbon content of the obtained lithium vanadium phosphate sample was measured with a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation), it was 1.5% by mass. The BET specific surface area was 9.8 m ² / g.

{Example 6}
<First step>
Put 2.5 L of ion-exchanged water in a 5 L beaker, add 854.7 g of 85% phosphoric acid, 457.7 g of vanadium pentoxide and 156.6 g of lactose monohydrate, and stir at room temperature (25 ° C.). As a result, an ocher mixed slurry was obtained.
<Second step>
The obtained mixed slurry was heated with stirring at 95 ° C. for 1 hour to carry out a reduction reaction to obtain a dark blue reaction solution.
<Third step>
The reaction solution was cooled to room temperature (25 ° C.). Next, a solution in which 277.1 g of lithium carbonate was dissolved in 1.5 L of ion-exchanged water was prepared, and this solution was added to the reaction solution at room temperature to obtain a dark blue raw material mixture solution.
<4th process>
Subsequently, the liquid was supplied to the spray drying apparatus which set outlet temperature to 120 degreeC, and the reaction precursor was obtained. When the obtained reaction precursor was used as a radiation source and X-ray diffraction measurement was performed using CuKα rays, it was confirmed that the reaction precursor was amorphous.
<5th process>
The obtained reaction precursor was placed in a mullite slag and baked at 800 ° C. for 10 hours in a nitrogen atmosphere. As a result of X-ray diffraction analysis of the obtained lithium vanadium phosphate sample, it was confirmed to be a single-phase lithium vanadium phosphate. Moreover, the X-ray-diffraction figure of a lithium vanadium phosphate sample is shown in FIG. An electron micrograph (SEM image) of the obtained lithium vanadium phosphate sample is shown in FIG.
Further, when the residual carbon content of the obtained lithium vanadium phosphate sample was measured with a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation), it was 1.2% by mass. The BET specific surface area was 9.2 m ² / g.

<Evaluation of battery performance>
<Battery performance test>
(I) Production of lithium secondary battery;
The positive electrode agent was prepared by mixing 91% by mass of the lithium vanadium phosphate sample of Example 4, Example 5 and Comparative Example 2 manufactured as described above, 6% by mass of graphite powder, and 3% by mass of polyvinylidene fluoride. A kneaded paste was prepared by dispersing in -methyl-2-pyrrolidinone. The obtained kneaded paste was applied to an aluminum foil, dried, pressed and punched 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 collector plate, a mounting bracket, an external terminal, and an electrolytic solution. Among these, a metal lithium foil was used for the negative electrode, and 1 mol of LiPF ₆ dissolved in 1 liter of a 1: 1 kneaded solution of ethylene carbonate and methyl ethyl carbonate was used for the electrolyte.

(2) Battery performance evaluation The produced lithium secondary battery was operated on the following conditions, and battery performance was evaluated.
<Evaluation of cycle characteristics>
After charging with constant current and constant voltage (CCCV) charging for 5 hours with a total charging time of 5 hours, charging to 4.2 V at 0.5 C, and then holding at 4.2 V, discharging to 2.0 V at 0.1 C Current (CC) discharge was performed, and these operations were regarded as one cycle, and the discharge capacity was measured every cycle. This cycle was repeated 20 times, and the capacity retention rate was calculated from the discharge capacity of the first cycle and the 20th cycle according to the following formula. The discharge capacity at the first cycle was defined as the initial discharge capacity.

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

{Example 7}
<6th process>
The lithium vanadium phosphate sample (residual carbon content 1.6 mass%) obtained in Example 3 was heat-treated at 350 ° C. for 15 hours in an electric furnace in an air atmosphere (oxygen concentration 20 Vol%).
As a result of X-ray diffraction analysis of the obtained lithium vanadium phosphate sample, it was confirmed to be a single-phase lithium vanadium phosphate. Further, when the residual carbon content of the obtained lithium vanadium phosphate sample was measured with a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation), it was 0.1% by mass. The BET specific surface area was 7.1 m ² / g.

Claims

A method for producing lithium vanadium phosphate having a NASICON structure,
A first step of preparing a mixed slurry by mixing a tetravalent or pentavalent vanadium compound, a phosphorus source and a reducing sugar in an aqueous solvent, and then a second step of heating the mixed slurry to form a solution; Next, a third step of preparing a raw material mixture by adding a lithium source to the solution, then a fourth step of obtaining a reaction precursor by spray drying the raw material mixture, and then removing the reaction precursor. A method for producing lithium vanadium phosphate, comprising a fifth step of firing at 500 to 1300 ° C. in an active gas atmosphere or a reducing atmosphere.
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 claim 1, wherein the lithium source is lithium hydroxide or lithium carbonate.
The method for producing lithium vanadium phosphate according to claim 1, wherein the vanadium compound is vanadium pentoxide.
The method for producing lithium vanadium phosphate according to claim 1, wherein the phosphorus source is phosphoric acid.
The method for producing lithium vanadium phosphate according to claim 1, wherein the reducing sugar is selected from sucrose and lactose.
2. The vanadium phosphate according to claim 1, wherein in the first step, a Me source (Me represents a metal element or a transition metal element other than V having an atomic number of 11 or more) is further mixed with the mixed slurry. Method for producing lithium.
Furthermore, the 6th process of heat-processing lithium vanadium phosphate obtained after a 5th process is provided, The manufacturing method of the lithium vanadium phosphate as described in any one of Claim 1 thru | or 7 characterized by the above-mentioned.
The method for producing lithium vanadium phosphate according to claim 8, wherein the heat treatment is performed in an oxygen-containing atmosphere.
The method for producing lithium vanadium phosphate according to any one of claims 8 and 9, wherein the heat treatment temperature is 250 to 450 ° C.