JP2012036048A - Process of producing vanadium lithium phosphate carbon composite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process of producing a vanadium lithium phosphate carbon composite useful for a positive active material for lithium secondary batteries.SOLUTION: There is provided the process of producing the vanadium lithium phosphate carbon composite composed of a vanadium lithium phosphate having a NASICON structure and an electroconductive carbon material. The process comprises the first step of preparing a slurry wherein a vanadium source, a source of the electroconductive carbon material, and an Me source added as necessary, (Me donates a metal element or a transition metal element having an atomic number of not less than 11 except for V) are dispersed in an aqueous solution of lithium phosphate, the second step of obtaining a reaction precursor by spray-drying the slurry, and the third step of firing the reaction precursor at 600-1,300°C in an inert gas environment or in a reducing environment.

Description

  The present invention relates to a process for producing a lithium vanadium phosphate carbon composite comprising lithium vanadium phosphate useful as a positive electrode active material for a lithium secondary battery and a conductive carbon material.

Lithium ion batteries are used as batteries for portable devices, notebook computers, electric vehicles, and hybrid vehicles. Lithium ion batteries are generally said to be excellent in high capacity and high energy density. Currently, LiCoO ₂ is mainly used for the positive electrode, but LiMnO ₂ , LiNiO _2, etc. are also actively developed due to Co resource problems. Has been done.
Currently, LiFePO ₄ is attracting attention as a further alternative material, and research and development is progressing in each organization. Fe is excellent in resources, and LiFePO ₄ using this is expected to be a positive electrode material for a lithium ion battery for electric vehicles because it has a low energy density but is excellent in high temperature characteristics.
However, LiFePO ₄ has a slightly low 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 is proposed in which a lithium source, a vanadium source 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 solution is dried to obtain a precursor. And a method of obtaining a composite of Li ₃ V ₂ (PO ₄ ) ₃ and a conductive carbon material by heat-treating this precursor in an inert atmosphere has been proposed.

Special Table 2001-2001655 gazette Japanese translation of PCT publication No. 2002-530835 JP 2008-052970 A

Li ₃ V ₂ (PO ₄ ) ₃ is known to have a theoretical capacity as high as 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 the lithium secondary battery using Li ₃ V ₂ (PO ₄ ) ₃ as the positive electrode active material. In a battery, further improvement in discharge capacity is desired.

  Therefore, the object of the present invention is useful as a positive electrode active material of a lithium secondary battery, and when used as a positive electrode active material of a lithium secondary battery, imparts excellent battery performance such as a high discharge capacity to the lithium secondary battery. An object of the present invention is to provide a method for producing a lithium vanadium phosphate carbon composite that can be used.

 As a result of intensive research in view of the above problems, the present inventors have made lithium vanadium phosphate-carbon composites composed of a lithium vanadium phosphate and a conductive carbon material obtained through a specific process as a positive electrode active material. The secondary battery has been found to have a particularly high discharge capacity and excellent cycle characteristics, and the present invention has been completed.

That is, the present invention is a method for producing a lithium vanadium phosphate carbon composite comprising a lithium vanadium phosphate having a NASICON structure and a conductive carbon material,
A slurry is prepared in which a vanadium source, a conductive carbon material source, and a Me source added as necessary (Me represents a metal element having a atomic number of 11 or more or a transition metal element other than V) are dispersed in an aqueous lithium phosphate solution. A first step, then a second step in which the slurry is spray-dried to obtain a reaction precursor, and then a third step in which the reaction precursor is calcined at 600 to 1300 ° C. in an inert gas atmosphere or a reducing atmosphere. The present invention provides a method for producing a lithium vanadium phosphate carbon composite characterized by comprising:

  ADVANTAGE OF THE INVENTION According to this invention, the vanadium lithium phosphate carbon composite which consists of an electroconductive carbon material and lithium vanadium phosphate useful as a positive electrode active material of a lithium secondary battery by an industrially advantageous method can be provided. In addition, a lithium secondary battery using the vanadium phosphate lithium carbon composite obtained by the production method of the present invention as a positive electrode active material has a particularly high discharge capacity and excellent cycle characteristics.

3 is an SEM photograph of the reaction precursor obtained in the second step of Example 1. FIG. 2 is an SEM photograph of the vanadium phosphate lithium carbon composite sample obtained in Example 1. FIG. The powder X-ray-diffraction figure of the vanadium-lithium-phosphate carbon composite sample obtained in Examples 1-2 and Comparative Examples 1-2.

Hereinafter, the present invention will be described based on preferred embodiments thereof.
The lithium vanadium phosphate carbon composite obtained by the production method of the present invention is composed of lithium vanadium phosphate having a NASICON structure (hereinafter simply referred to as “lithium vanadium phosphate”) and a conductive carbon material.
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 or more and 3.5 or less, y represents 1.8 or more and 2.2 or less), or lithium vanadium phosphate represented by the general formula (1), It contains lithium vanadium phosphate that 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.

  The method for producing the lithium vanadium phosphate carbon composite according to the present invention includes a vanadium source, a conductive carbon material source, and a Me source added as necessary to a lithium phosphate aqueous solution (Me is a metal having an atomic number of 11 or more other than V). A first step of preparing a slurry in which an element or a transition metal element is dispersed), then a second step of spray-drying the slurry to obtain a reaction precursor, and then the reaction precursor in an inert gas atmosphere It has the 3rd process baked at 600-1300 degreeC in inside or a reducing atmosphere, It is characterized by the above-mentioned.

  The first step according to the present invention is a step of preparing a slurry (C) in which a vanadium source, a conductive carbon material source, and a Me source added as necessary are uniformly dispersed in an aqueous lithium phosphate solution.

  The lithium phosphate aqueous solution may be prepared by dissolving commercially available lithium phosphate in water, or may be produced by itself. The concentration of the lithium phosphate aqueous solution is preferably 5 to 40% by weight, more preferably 20 to 40% by weight, from the viewpoint that precipitation of lithium phosphate crystals does not occur even at room temperature.

  As a method for producing a lithium phosphate aqueous solution, (1) a method in which lithium carbonate or lithium hydroxide is added to a phosphoric acid aqueous solution to carry out the reaction (for example, see JP-A-63-243965), or (2 ) A method of performing a reaction by adding an aqueous phosphoric acid solution to a solution containing lithium carbonate or lithium hydroxide (for example, see JP-A-2004-359538) can be used.

  In this production method, the method for preparing the lithium phosphate aqueous solution is particularly from the viewpoint that the use of the method (1) avoids the possibility of bumping due to rapid reaction heat generation and avoids the use of excess water. preferable.

Hereinafter, the method for preparing the lithium phosphate aqueous solution (1) will be described.
The reaction is carried out by preparing an aqueous phosphoric acid solution having a predetermined concentration and adding a predetermined amount of a lithium compound selected from lithium carbonate or lithium hydroxide to the aqueous phosphoric acid solution.
The concentration of the aqueous phosphoric acid solution is preferably 25% by weight or more, and preferably 35 to 85% by weight because energy required for handling and water removal is reduced.
Subsequently, a lithium compound is added to the phosphoric acid aqueous solution kept at 10 to 60 ° C., preferably 15 to 55 ° C.
The addition amount of the lithium compound is 0.70 to 1.30, preferably 0.83 to 1.17, in terms of the molar ratio (P / Li) of the lithium atom of the lithium compound to the P atom in the phosphoric acid aqueous solution. Addition enables efficient reaction, and facilitates obtaining single-phase lithium vanadium phosphate as a final product. A lithium secondary using the lithium vanadium phosphate composite as a positive electrode active material It is preferable from the viewpoint that the discharge capacity of the battery can be increased.
The reaction between the lithium compound and phosphoric acid can be easily obtained by carrying out the reaction for 30 minutes or longer, preferably 1 to 5 hours with stirring.

  As the vanadium source in the first step, vanadium pentoxide, vanadium trioxide, ammonium vanadate, vanadium oxyoxalate, or the like can be used. Among these, vanadium pentoxide is preferably used from the viewpoint that it is easy to handle, and that a fine and high-purity one is industrially available and has excellent reactivity with other raw materials. A preferable physical property of the vanadium source is that the average particle diameter is 100 μm or less, preferably 5 to 50 μm, from the viewpoint of easy uniform mixing.

  The addition amount of the vanadium source is 0.50 to 0.80 in terms of the molar ratio (V / P) of the V atom in the vanadium source and the P atom in the lithium phosphate when the Me source added as necessary is not added. It is easy to obtain a single-phase lithium vanadium phosphate as the final product, preferably 0.60 to 0.73, and a lithium secondary using the lithium vanadium phosphate composite as a positive electrode active material. It is preferable from the viewpoint that the discharge capacity of the battery can be increased.

In the present invention, the Me source is added as necessary for the purpose of stabilizing the crystal structure of lithium vanadium phosphate and further improving battery performance such as cycle characteristics, and is represented by the general formula (1) as a Me element. It is added to lithium vanadium phosphate. 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 represents a metal element or a transition metal element having an atomic number of 11 or more other than V, and preferred Me includes Mg, Ca, Al, Mn, Co, Ni, Fe, Ti, Zr, Bi, Cr, Nb, Mo, Cu etc. are mentioned, These are used by 1 type (s) or 2 or more types.
Examples of the Me source that can be used include Me-containing oxides, hydroxides, halides, carbonates, nitrates, carbonates, and organic acid salts.
When a solid source is used as the Me source, the average particle size is preferably 100 μm or less, and preferably 0.1 to 50 μm from the viewpoint of easy uniform mixing.

  When adding the Me source, depending on the type of Me element to be doped, in many cases, the sum of V in the vanadium source and the Me atom in the Me source (V + Me = M) and the P atom in the phosphorus source The molar ratio (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 and not larger than 0.45, preferably larger than 0 and 0.00. It is preferable to add the Me source so that it becomes 1 or less.

  Examples of the conductive carbon material source that can be used include natural graphite such as scaly graphite, scaly graphite, and earthy graphite, and graphite such as artificial graphite; carbon black, acetylene black, ketjen black, channel black, furnace black Carbon blacks such as lamp black and thermal black; and carbon materials such as carbon fiber. In addition, an organic compound in which carbon is precipitated by firing in the third step can also be used as a conductive carbon material source. Examples of the organic compound from which carbon is precipitated include coal tar pitch from soft pitch to hard pitch; heavy coal oil such as dry distillation liquefied oil, normal pressure residual oil, DC heavy oil of reduced pressure residual oil, crude oil Petroleum heavy oils of cracked heavy oils such as ethylene tar produced as a by-product during thermal decomposition of naphtha, etc .; aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, phenanthrene; polyphenylenes such as phenazine, biphenyl, terphenyl; Polyvinyl chloride; water-soluble polymers such as polyvinyl alcohol, polyvinyl butyral, and polyethylene glycol, and insolubilized products thereof; nitrogen-containing polyacrylonitrile; organic polymers such as polypyrrole; organic compounds such as sulfur-containing polythiophene and polystyrene Molecule: Starch, cellulose, lignin, mannan, polygalactose Natural polymers such as saccharides such as acid, chitin, chitosan, saccharose and sucrose; thermoplastic resins such as polyphenylene sulfide and polyphenylene oxide, and one or more thermosetting resins such as phenol-formaldehyde resin and imide resin Is mentioned.

  In this production method, the conductive carbon material source may be one type or a combination of two or more types. Of these, carbon materials are preferred, and carbon black and ketjen black are particularly easily available in the form of fine particles, and the lithium vanadium lithium carbon composite obtained is used as a positive electrode active material. The secondary battery is also preferable from the viewpoint of increasing the discharge capacity.

  The average particle diameter of the carbon material that can be used in this production method is 1 μm or less, preferably 0.1 μm or less, and particularly preferably 0.01 to 0.1 μm. When the carbon material is fibrous, the average fiber diameter of the carbon material is 1 μm or less, preferably 0.1 μm or less, and particularly preferably 0.01 to 0.1 μm. When the average particle diameter or the average fiber diameter of the carbon material is within the above range, the conductive carbon material is easily highly dispersed in the lithium vanadium phosphate particles. In the present invention, the average particle diameter or the average fiber diameter of the conductive carbon material is an average particle diameter or an average fiber diameter determined from a scanning electron micrograph (SEM). The average value of the particle diameters of the 20 particles extracted or the fiber diameters of the fibers.

  The amount of the conductive carbon material source added is preferably 0.1 to 20% by mass in terms of C atoms with respect to the generated lithium vanadium phosphate.

  There is a tendency for the amount of C atoms contained in the conductive carbon material to decrease after firing compared to before firing. Therefore, in the first step, the compounding amount of the conductive carbon material source with respect to 100 parts by mass of lithium vanadium phosphate to be generated is 0.5 to 40 parts by mass, preferably 5 to 30 parts by mass in terms of C atoms. The blending amount of the conductive carbon material with respect to 100 parts by mass of vanadium phosphate lithium in the lithium vanadium phosphate carbon composite actually obtained is 0.1 to 20 parts by mass, preferably 1 to 15 parts by mass in terms of C atoms. It is easy to become. When the compounding amount of the conductive carbon material source with respect to 100 parts by mass of the generated lithium vanadium phosphate is within the above range, the lithium vanadium phosphate carbon composite is used as the positive electrode active material of the lithium secondary battery. Since sufficient conductivity can be imparted, 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, when the blending amount of the conductive carbon material source with respect to 100 parts by mass of the generated lithium vanadium phosphate is less than the above range, the lithium vanadium phosphate carbon composite is used as the positive electrode active material of the lithium secondary battery. Since sufficient conductivity cannot be imparted, the internal resistance of the lithium secondary battery tends to be high, and when the above range is exceeded, the discharge capacity per mass or volume tends to be low.

  Further, when a carbon material is used as the conductive carbon material source, alcohol is added to the slurry during the mixing treatment of the carbon material into the lithium phosphate aqueous solution, and the carbon material mixing treatment is performed in the presence of the alcohol. Since the carbon material can be highly dispersed in the slurry in a short time, the mixing process can be advantageously performed.

  As the alcohol that can be used, for example, one or more of lower alcohols such as methanol, ethanol, propanol, and butanol are used, and among these, ethanol is particularly preferable in that the effect of highly dispersing the carbon material is high. Used.

  The addition amount of the alcohol is 2 to 30 parts by mass, preferably 5 to 20 parts by mass with respect to 100 parts by mass of the carbon material. By adding the alcohol to the slurry in this range, the carbon material is easily highly dispersed. The prepared slurry can be prepared.

  Means for dispersing the vanadium source, the conductive carbon material source and the Me source added if necessary in the lithium phosphate aqueous solution is not particularly limited, and the vanadium source, the conductive carbon material source and the lithium phosphate aqueous solution A method of adding a Me source added if necessary and mixing with stirring with a powerful stirrer or the like can be applied. However, a slurry in which a vanadium source and a Me source added if necessary are dispersed in a lithium phosphate aqueous solution is used. Phosphoric acid obtained by having a step A for preparing a slurry containing a pulverized product and a conductive carbon material source that has been wet pulverized by a media mill until the average particle size of the solid content is 10 μm or less, preferably 1 μm or less In lithium secondary batteries using vanadium lithium-carbon composite as the positive electrode active material, the discharge capacity is particularly high, and the cycle characteristics Is preferable from the viewpoint of obtaining an excellent product.

  The step A according to the present invention includes (a) a step of preparing a slurry (B) that has been wet pulverized by a media mill, and (b) a step of mixing a conductive carbon material source.

  In the operation related to the step (a), the slurry (A) obtained by adding a predetermined amount of the vanadium source and the Me source added as necessary to the lithium phosphate aqueous solution is subjected to a wet pulverization treatment by a media mill. By adopting this method, the vanadium source and the Me source added if necessary can be finely pulverized, so that the reaction precursor obtained in the second step described later has even better reactivity. become.

  As the media mill, a bead mill, a ball mill, a paint shaker, an attritor, a sand mill, or the like can be used. It is particularly preferable to use a bead mill. In that case, the operating conditions and the type and size of the beads may be appropriately selected according to the size of the apparatus and the processing amount.

  From the viewpoint of more efficiently performing the treatment using the media mill, a dispersant may be added to the slurry (A). What is necessary is just to select a suitable dispersing agent to use according to the kind of dispersion medium. When the dispersion medium is water, for example, various surfactants, polycarboxylic acid ammonium salts, and the like can be used as the dispersant. The concentration of the dispersant in the slurry is preferably 0.01 to 10% by weight, particularly 0.1 to 5% by weight, from the viewpoint of a sufficient dispersion effect.

  The pulverization treatment using the media mill is excellent in reactivity when it is carried out until the average particle size of the solid content obtained by the laser scattering / diffraction method is 5 μm or less, preferably 1 μm or less, particularly 0.2 to 1 μm. It is preferable from the viewpoint of obtaining a reaction precursor. By doing so, a slurry (B) containing a pulverized product can be prepared.

  (B) The step of mixing the conductive carbon material source may be (i) before or after the wet pulverization treatment by the media mill. That is, the conductive carbon material source may be added to the slurry (A) and mixed, or the conductive carbon material source may be added to the slurry (B) and mixed.

  In the present production method, when the carbon material is used as the conductive carbon material source, in particular, (i) the conductive carbon material source is added to the slurry (B) after the wet pulverization treatment by the media mill, B) Providing the step of mixing the conductive carbon material source can reduce the burden on the pulverizer, and the lithium secondary battery using the obtained vanadium lithium phosphate carbon composite as the positive electrode active material has a discharge capacity. Is also preferable from the viewpoint of further improvement.

  In addition, when using as an electroconductive carbon material source the organic compound which carbon precipitates by baking in a 3rd process, it is preferable to use what can be melt | dissolved in the dispersion medium used for a grinding | pulverization process. The organic compound may be added to the slurry (A), or the organic compound may be added to the slurry (B). Which method is to be adopted may be appropriately selected from industrially advantageous methods in consideration of the apparatus to be used.

  In this way, a slurry (C) in which a vanadium source, a conductive carbon material source, and a Me source added as needed are highly dispersed in the lithium phosphate aqueous solution can be obtained, and the slurry (C) is used in the second step. As a result, a reaction precursor is obtained.

  In the second step according to the present invention, the slurry (C) in which the vanadium source, the conductive carbon material source, and the Me source added as necessary are highly dispersed in the lithium phosphate aqueous solution obtained in the first step is spray-dried. In this process, a reaction precursor comprising a lithium phosphate having excellent reactivity, a vanadium source, a conductive carbon material source, and a Me source added as necessary is obtained.

  Although methods other than the spray drying method are known as the drying method of the slurry (C), this drying method is adopted based on the knowledge that it is advantageous to select the spray drying method in this production method. ing. Specifically, when the spray drying method is used, a granulated product containing lithium phosphate, a vanadium source, and a conductive carbon material source uniformly and packed with raw material particles is obtained. In the present invention, the product is used as a reaction precursor and calcined in the third step to be described later using the reaction precursor, so that, for powder X-ray diffraction, single-phase lithium vanadium phosphate and a conductive carbon material are used. And a complex can be obtained.

  In the spray drying method, the reaction precursor is obtained by atomizing the slurry (C) by a predetermined means and drying fine droplets generated thereby. The atomization of the slurry (C) includes, for example, 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 relationship between the size of the droplets of the atomized slurry and the size of the raw material particles contained therein affects stable drying and the properties of the obtained reaction precursor. Specifically, if the size of the solid material particles is too small with respect to the size of the droplets, the droplets become unstable, making it difficult to dry successfully. From this point of view, the size of the atomized droplets is 0.5 to 30 μm, particularly 1 to 20 μm, provided that the size of the solid particles in the slurry (C) is in the above-mentioned range. It is preferable that It is desirable to determine the supply amount of the slurry (C) to the spray drying apparatus in consideration of this viewpoint.
The drying temperature in the spray dryer is adjusted so that the hot air inlet temperature is 200 to 250 ° C., preferably 210 to 240 ° C., and the powder temperature is 100 to 150 ° C., preferably 105 to 130 ° C. It is preferable to prevent the powder from absorbing moisture and facilitate the recovery of the powder.

  The reaction precursor obtained by the spray drying method is subjected to firing in the next step, and the powder properties such as the average particle diameter of the obtained vanadium lithium phosphate carbon composite generally inherit the properties of the reaction precursor. Become. For this reason, spray drying is performed such that the secondary particles of the reaction precursor are 0.5 to 30 μm, particularly 1 to 20 μm, in terms of the particle diameter determined by observation with a scanning electron microscope (SEM). From the viewpoint of controlling the particle size of the lithium vanadium phosphate carbon composite.

  The reaction precursor thus obtained is then subjected to a third step of firing at 600 to 1300 ° C. in an inert gas atmosphere or a reducing atmosphere to obtain the target lithium vanadium phosphate carbon composite. obtain.

  In the third step according to the present invention, the reaction precursor obtained in the second step is calcined at 600 to 1300 ° C., and from powder X-ray diffraction single phase lithium vanadium phosphate and a conductive carbon material. This is a step of obtaining a lithium vanadium phosphate carbon composite.

  The firing temperature according to the third step is 600 to 1300 ° C, preferably 800 to 1000 ° C. The reason for this is that if the calcination temperature is lower than 600 ° C., the reduction calcination is insufficient and there is a high possibility that the final product does not become a single phase. This is because it affects the quality characteristics of the product.

  The firing atmosphere is performed in an inert gas atmosphere or a reducing atmosphere for the purpose of preventing vanadium oxidation and preventing phosphate melting.

  The firing time is not critical in this production method. In general, if it is baked for 1 hour or longer, particularly 2 to 12 hours, a composite composed of single-phase lithium vanadium phosphate and a conductive carbon material can be obtained by powder X-ray diffraction.

The lithium vanadium lithium carbon composite thus obtained may be subjected to a plurality of firing steps as necessary.
After firing, the obtained lithium vanadium carbon composite may be crushed and / or pulverized as necessary, and further classified.

The lithium vanadium phosphate carbon composite thus obtained is a lithium vanadium phosphate carbon composite composed of a single-phase lithium vanadium phosphate and a conductive carbon material in terms of powder X-ray diffraction. Is aggregated lithium vanadium phosphate in which a large number of primary particles are aggregated, preferably 0.01 μm or more and 10 μm or less to form secondary particles having an average particle diameter of 1 μm or more and 50 μm or less, preferably 2 to 20 μm. In addition, a high discharge capacity when used as a positive electrode active material of a lithium secondary battery is that a conductive carbon material having an average particle size of 1 μm or less, preferably 0.01 to 0.1 μm is contained. It is preferable at the point obtained.
Further, when the BET specific surface area of the lithium vanadium phosphate carbon composite is 15 to 50 m ² / g, preferably 20 to 45 m ² / g, the paste characteristics when formed into a paint are good, and the lithium vanadium phosphate has Since a composite is formed in a state where the carbon content is well dispersed, it is preferable because it exhibits good electron conductivity.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.
{Example 1}
<First step>
Add 3 L of ion-exchanged water to a 10 L beaker, add 1,729 g of 85 wt% phosphoric acid to this, stir, add 554.2 g of lithium carbonate (average particle size 10 μm), and react at 25 ° C. with stirring for 1 hour This was used as an aqueous lithium phosphate solution.
Next, under stirring, 909.4 g of vanadium pentoxide (average particle size 12 μm) was added to the lithium phosphate aqueous solution and stirred for 1 hour to obtain a slurry. To this slurry, 204 g of ketjen black (average particle size 0.04 μm) and 20 g of ethanol were added and mixed by stirring to prepare slurry (C).
<Second step>
Next, the slurry (C) was supplied to a spray drying apparatus in which the temperature of the hot air inlet was set to 230 ° C. at a supply rate of 50 g / min to obtain a reaction precursor. As a result of SEM observation of the reaction precursor, the reaction precursor had a secondary particle size of 2 to 25 μm.
An electron micrograph (SEM image) of the reaction precursor is shown in FIG.
<Third step>
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 coarsely pulverized to 0.5 mm or less in an alumina mortar and crushed by a jet mill to obtain a lithium vanadium phosphate carbon composite sample.
An electron micrograph (SEM image) of the obtained lithium vanadium phosphate carbon composite sample is shown in FIG.

{Example 2}
<First step>
Add 3 L of ion-exchanged water to a 10 L beaker, add 1,729 g of 85 wt% phosphoric acid to this, stir, add 554.2 g of lithium carbonate (average particle size 10 μm), and react at 23 ° C. with stirring for 1 hour. To prepare an aqueous lithium phosphate solution. Subsequently, 909.4 g of vanadium pentoxide (average particle size 12 μm) was added to the aqueous lithium phosphate solution with stirring, and the mixture was stirred for 1 hour to obtain a slurry (A).
A zirconia ball having a major axis of 0.5 mm is charged into a wet pulverizer, and this slurry (A) is introduced into the wet pulverizer, and the average particle diameter (D ₅₀ ) determined by a laser scattering / diffraction method (manufactured by Nikkiso, model 9320-X100). The slurry (B) was prepared by pulverization by a wet method for 5 hours using a bead mill until the slag was 1.0 μm or less. 204 g of ketjen black and 20 g of ethanol were added to this slurry (B) and mixed by stirring to prepare slurry (C).
<Second step>
Next, the slurry (C) was supplied to a spray drying apparatus in which the temperature of the hot air inlet was set to 230 ° C. at a supply rate of 50 g / min to obtain a reaction precursor. As a result of SEM observation of the reaction precursor, the reaction precursor had a secondary particle diameter of 2 to 30 μm.
<Third step>
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 coarsely pulverized to 0.5 mm or less in an alumina mortar and pulverized by a jet mill to obtain a lithium vanadium phosphate carbon composite sample.

{Comparative Example 1}
1 L of ion-exchanged water was put into a 2 L beaker, and 125.9 g of lithium hydroxide (Li: 3 mol) was added and dissolved therein. To this solution, 181.9 g (V: 2 mol) of vanadium pentoxide was added and stirred for 1 h. Glucose (glucose) 36.0 g (0.2 mol) and 85% phosphoric acid 345.9 g (P: 3 mol) were added to this solution and stirred for 1 hour to obtain a mixed solution.
Subsequently, the liquid mixture was supplied to the spray drying apparatus in which the temperature of the hot air inlet was set to 230 ° C. at a supply rate of 50 g / min to obtain a reaction precursor. As a result of SEM observation of the reaction precursor, the reaction precursor had a secondary particle diameter of 2 to 30 μm.
The obtained reaction precursor was put in a mullite slag and baked for 1 minute in a nitrogen atmosphere at 600. The heat-treated product was roughly crushed to 0.5 mm or less to obtain a lithium vanadium phosphate carbon composite sample.

{Comparative Example 2}
1 L of ion exchange water was put into a 2 L beaker, and 125.9 g of lithium hydroxide was added and dissolved therein. To this solution, 181.9 g of vanadium pentoxide was added and stirred for 1 h. To this solution, 10 g of ketjen black (average particle size 0.04 μm) and 345.9 g of 85% phosphoric acid were added to prepare a mixed solution. An alumina ball having a diameter of 2 mm is charged in a pod for ball mill, and the average particle diameter (D ₅₀ ) of the pulverized product in the slurry obtained by a laser scattering / diffraction method (manufactured by Nikkiso, model 9320-X100) is 1.0 μm or less. The slurry (C) was prepared by processing by a wet method until 24 hours.
Next, the slurry (C) was supplied to a spray drying apparatus in which the temperature of the hot air inlet was set to 230 ° C. at a supply rate of 50 g / min to obtain a reaction precursor. As a result of SEM observation of the reaction precursor, the reaction precursor had a secondary particle diameter of 2 to 30 μm.
The obtained precursor compound was baked at 600 ° C. for 1 hour in a nitrogen atmosphere to obtain a lithium vanadium phosphate carbon composite sample.

<Property evaluation of lithium vanadium phosphate carbon composite>
For the vanadium phosphate carbon composites obtained in Examples 1 and 2 and Comparative Examples 1 and 2, the average particle size, BET specific surface area, and conductive carbon material content of the vanadium lithium phosphate composites were measured. In addition, powder X-ray diffraction measurement was performed. The obtained results are shown in Table 2. Moreover, the powder X-ray-diffraction figure of the vanadium phosphate lithium carbon composite_body | complex obtained in Examples 1-2 and Comparative Examples 1-2 is shown in FIG. In addition, the average secondary particle diameter of lithium vanadium phosphate was measured by a laser scattering / diffraction method (manufactured by Nikkiso, 9320-X100 type). The content of the conductive carbon material was determined as the content of C atoms by measuring the carbon atom content with a TOC total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation).

<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 vanadium lithium phosphate carbon composites of Examples 1 and 2 and Comparative Examples 1 and 2 manufactured as described above, 6% by mass of graphite powder, and 3% by mass of polyvinylidene fluoride. Was dispersed in N-methyl-2-pyrrolidinone to prepare a kneaded paste. 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 at room temperature under the following conditions, and the following battery performance was evaluated.
<Evaluation of cycle characteristics>
After charging the positive electrode to 4.4V at 1.0C for 5 hours by constant current voltage (CCCV) charging, charging / discharging to discharge to 2.7V at a discharge rate of 0.2C is performed. The discharge capacity was measured every cycle as one 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.

ADVANTAGE OF THE INVENTION According to this invention, the vanadium lithium phosphate carbon composite which consists of an electroconductive carbon material and lithium vanadium phosphate useful as a positive electrode active material of a lithium secondary battery by an industrially advantageous method can be provided. In addition, a lithium secondary battery using the vanadium phosphate lithium carbon composite obtained by the production method of the present invention as a positive electrode active material has a particularly high discharge capacity and excellent cycle characteristics.

Claims (7)

A method for producing a lithium vanadium phosphate carbon composite comprising a lithium vanadium phosphate having a NASICON structure and a conductive carbon material,
A slurry is prepared in which a vanadium source, a conductive carbon material source, and a Me source added as necessary (Me represents a metal element having a atomic number of 11 or more or a transition metal element other than V) are dispersed in an aqueous lithium phosphate solution. A first step, then a second step in which the slurry is spray-dried to obtain a reaction precursor, and then a third step in which the reaction precursor is calcined at 600 to 1300 ° C. in an inert gas atmosphere or a reducing atmosphere. A method for producing a lithium vanadium phosphate carbon composite, characterized by comprising:   2. The vanadium lithium phosphate carbon composite according to claim 1, wherein the addition amount of the conductive carbon material source is 0.1 to 20% by mass in terms of C atom with respect to lithium vanadium phosphate to be generated. Production method.   The method for producing a lithium vanadium phosphate carbon composite according to claim 1 or 2, wherein the conductive carbon material source is a carbon material.   4. The method for producing a lithium vanadium phosphate carbon composite according to claim 3, wherein the carbon material is dispersed in the presence of alcohol.   The method for producing a lithium vanadium phosphate carbon composite according to claim 3, wherein the carbon material is selected from carbon black and ketjen black.   In the first step, a slurry in which a vanadium source and an optional Me source are dispersed in a lithium phosphate aqueous solution is subjected to a wet pulverization treatment with a media mill until the average particle size of solids becomes 1 μm or less, and a conductive product. A method for producing a lithium vanadium phosphate carbon composite according to claim 1, further comprising an A step of preparing a slurry containing a carbonaceous material source. Step A is a step in which a slurry in which a vanadium source and an optional Me source are dispersed in a lithium phosphate aqueous solution is subjected to a wet pulverization treatment with a media mill until the average particle size of solids becomes 1 μm or less, and then wet pulverization 7. The method for producing a lithium vanadium phosphate carbon composite according to claim 6, further comprising a step of adding a carbon material as a conductive carbon material source to the slurry after the treatment and mixing the slurry.