阅读说明：本技术 焦磷酸钴锂的制造方法和焦磷酸钴锂碳复合体的制造方法 (Method for producing cobalt lithium pyrophosphate and method for producing cobalt lithium pyrophosphate-carbon composite ) 是由 深泽纯也 畠透 于 2019-07-24 设计创作，主要内容包括：本发明提供一种制造下述通式(1)：Li-xCo-(1－)-yM-yP-2O-7(1)所示的焦磷酸钴锂的制造方法(式中,1.7≤x≤2.2,0≤y≤0.5,M表示选自Mg、Zn、Cu、Fe、Cr、Mn、Ni、Al、B、Na、K、F、Cl、Br、I、Ca、Sr、Ba、Ti、Zr、Hf、Nb、Ta、Y、Yb、Si、S、Mo、W、V、Bi、Te、Pb、Ag、Cd、In、Sn、Sb、Ga、Ge、La、Ce、Nd、Sm、Eu、Tb、Dy和Ho中的1种或2种以上的金属元素。),该制造方法包括：第一工序,在水溶剂中添加有机酸和氢氧化钴,之后添加磷酸和氢氧化锂,制备水性原料浆料(1)；第二工序,利用介质磨对该水性原料浆料(1)进行湿式粉碎处理,得到含有原料粉碎处理物的浆料(2)；第三工序,对该含有原料粉碎处理物的浆料(2)进行喷雾干燥处理,得到反应前体；和第四工序,对该反应前体在600℃以上进行烧制。根据本发明,能够提供能够利用工业上有利的方法得到在X射线衍射中为单相的焦磷酸钴锂的方法。(The present invention provides a process for producing a compound represented by the following general formula (1): li x Co 1－ y M y P 2 O 7 (1) A method for producing lithium cobalt pyrophosphate is described (wherein x is 1.7. ltoreq. x.ltoreq.2.2, Y is 0. ltoreq. y.ltoreq.0.5, and M is selected from the group consisting of Mg, Zn, Cu, Fe, Cr, Mn, Ni, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ti, Zr, Ti,ce. 1 or more than 2 metal elements of Nd, Sm, Eu, Tb, Dy and Ho. ) The manufacturing method comprises the following steps: a first step of adding an organic acid and cobalt hydroxide to a water solvent, and then adding phosphoric acid and lithium hydroxide to prepare an aqueous raw material slurry (1); a second step of subjecting the aqueous raw material slurry (1) to wet grinding by means of a media mill to obtain a slurry (2) containing a raw material grinding product; a third step of subjecting the slurry (2) containing the pulverized material to spray drying to obtain a reaction precursor; and a fourth step of firing the reaction precursor at 600 ℃ or higher. According to the present invention, it is possible to provide a method capable of obtaining lithium cobalt pyrophosphate which is a single phase in X-ray diffraction by an industrially advantageous method.)

1. A method for producing lithium cobalt pyrophosphate represented by the following general formula (1),

Li_xCo_1－yM_yP₂O₇ (1)

in the formula (1), x is not less than 1.7 and not more than 2.2, Y is not less than 0 and not more than 0.5, M represents 1 or more than 2 metal elements selected from Mg, Zn, Cu, Fe, Cr, Mn, Ni, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy and Ho,

the manufacturing method is characterized by comprising:

a first step of adding an organic acid and cobalt hydroxide to a water solvent, and then adding phosphoric acid and lithium hydroxide to prepare an aqueous raw material slurry (1);

a second step of subjecting the aqueous raw material slurry (1) to wet grinding by means of a media mill to obtain a slurry (2) containing a raw material grinding product;

a third step of subjecting the slurry (2) containing the pulverized material to spray drying to obtain a reaction precursor; and

and a fourth step of firing the reaction precursor at 600 ℃ or higher.

2. The method for producing lithium cobalt pyrophosphate according to claim 1, characterized in that:

the aqueous raw material slurry (1) In the first step or the slurry (2) containing a raw material pulverized product In the second step further contains an M source, wherein M represents 1 or 2 or more metal elements selected from the group consisting of Mg, Zn, Cu, Fe, Cr, Mn, Ni, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy and Ho.

3. The method for producing lithium cobalt pyrophosphate according to any one of claims 1 and 2, characterized in that:

the average particle diameter of the solid content in the slurry (2) containing the crushed material of the raw material is 1.5 [ mu ] m or less.

4. The method for producing lithium cobalt pyrophosphate according to any one of claims 1 to 3, characterized in that:

the organic acid is a carboxylic acid.

5. The method for producing lithium cobalt pyrophosphate according to any one of claims 1 to 3, characterized in that:

the organic acid is oxalic acid.

6. The method for producing lithium cobalt pyrophosphate according to any one of claims 1 to 5, characterized in that:

the reaction precursor contains an organic acid salt of cobalt and a phosphate of lithium.

7. The method for producing lithium cobalt pyrophosphate according to any one of claims 1 to 6, further comprising:

and a fifth step (A) of heating the cobalt lithium pyrophosphate obtained in the fourth step.

8. The method for producing lithium cobalt pyrophosphate according to claim 7 wherein:

the heat treatment temperature in the fifth step (A) is 200-700 ℃.

9. A method for producing a cobalt lithium pyrophosphate-carbon composite, comprising:

a fifth step (B) of mixing the cobalt lithium pyrophosphate obtained by performing the method for producing cobalt lithium pyrophosphate according to any one of claims 1 to 6 with a conductive carbon material source from which carbon is precipitated by thermal decomposition to obtain a mixture of the cobalt lithium pyrophosphate and the conductive carbon material source, and then subjecting the mixture to a heat treatment to thermally decompose the conductive carbon material source to obtain a cobalt lithium pyrophosphate-carbon composite.

Technical Field

The present invention relates to a method for producing cobalt lithium pyrophosphate useful as a positive electrode material for lithium secondary batteries, all-solid batteries, and the like, and a method for producing a cobalt lithium pyrophosphate-carbon composite.

Background

As a battery for portable devices and notebook personal computers, a lithium ion battery is used. Lithium ion batteries are generally considered to have excellent capacity and energy density. Further, the present invention is expected to be used in hybrid vehicles and electric vehicles.

Lithium cobalt pyrophosphate (Li)₂CoP₂O₇) Isopyrophosphates have attracted attention as positive electrode active materials for lithium secondary batteries having high capacity characteristics and high energy density (see, for example, patent documents 1 to 2), and as positive electrode active materials for all-solid-state batteries having high potential and capacity (see, for example, patent documents 3 to 4).

As a method for producing lithium cobalt pyrophosphate, for example, patent document 1 proposes a method in which a lithium source, a cobalt source, and a phosphorus source are mixed by a ball mill, the obtained pellet mixture is further pelletized, and the pelletized mixture is fired; further, patent document 3 proposes a method in which a lithium source, a cobalt source, and a phosphorus source are mixed, the obtained mixture is pre-fired in an atmospheric atmosphere, and then the pre-fired product obtained by the pre-firing is fired at 650 to 680 ℃ for 20 to 30 hours in an atmospheric atmosphere at a temperature higher than that of the pre-firing.

Further, lithium cobalt pyrophosphate has attracted attention as a safe positive electrode active material, and is desired to be provided by an industrially advantageous method.

Documents of the prior art

Patent document

Patent document 1: japanese Kokai publication No. 2006-523930

Patent document 2: japanese patent laid-open publication No. 2016-38996

Patent document 3: japanese patent laid-open publication No. 2017-182949

Patent document 4: japanese patent laid-open publication No. 2017-228453

Disclosure of Invention

Technical problem to be solved by the invention

However, in the method of dry-mixing the raw materials as in patent documents 1 and 2, it is difficult to obtain lithium cobalt pyrophosphate which is a single phase in X-ray diffraction analysis.

Accordingly, an object of the present invention is to provide a method for obtaining lithium cobalt pyrophosphate which is a single phase in X-ray diffraction by an industrially advantageous method. Another object of the present invention is to provide a method for obtaining the complex of lithium cobalt pyrophosphate and carbon.

Technical solution for solving technical problem

The inventors of the present invention have made intensive studies in view of the above circumstances, and as a result, have found that: in a method of preparing a raw material mixture in a wet process using at least cobalt hydroxide, phosphoric acid, and lithium hydroxide as raw materials, when the raw material mixture is prepared in consideration of the order of addition of the raw materials in the presence of an organic acid, the raw materials can be uniformly dispersed, and an aqueous raw material slurry which is easy to handle can be obtained; the aqueous raw material slurry can be subjected to wet grinding treatment by a media mill; further, the reactivity of the reaction precursor obtained by wet-pulverizing the aqueous raw material slurry to obtain a slurry containing a pulverized product and then spray-drying the slurry containing the pulverized product is excellent; further, by firing the reaction precursor at a specific temperature or higher, cobalt lithium pyrophosphate which is a single phase in X-ray diffraction can be obtained, and the present invention has been completed.

That is, the present invention (1) provides a method for producing lithium cobalt pyrophosphate represented by the following general formula (1),

Li_xCo_1－yM_yP₂O₇ (1)

(wherein x is 1.7. ltoreq. x.ltoreq.2.2, Y is 0. ltoreq. y.ltoreq.0.5, M represents 1 or 2 or more metal elements selected from the group consisting of Mg, Zn, Cu, Fe, Cr, Mn, Ni, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy and Ho),

the manufacturing method is characterized by comprising:

a first step of adding an organic acid and cobalt hydroxide to a water solvent, and then adding phosphoric acid and lithium hydroxide to prepare an aqueous raw material slurry (1);

a second step of subjecting the aqueous raw material slurry (1) to wet grinding by means of a media mill to obtain a slurry (2) containing a raw material grinding product;

a third step of subjecting the slurry (2) containing the pulverized material to spray drying to obtain a reaction precursor; and

and a fourth step of firing the reaction precursor at 600 ℃ or higher.

The present invention also provides (2) the method for producing lithium cobalt pyrophosphate according to (1), wherein: the aqueous raw material slurry (1) In the first step or the slurry (2) containing a raw material pulverized product In the second step further contains an M source (M represents 1 or 2 or more metal elements selected from the group consisting of Mg, Zn, Cu, Fe, Cr, Mn, Ni, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho).

The present invention (3) provides the method for producing lithium cobalt pyrophosphate according to any one of (1) and (2), wherein: the slurry (2) containing the pulverized material has an average particle diameter of the solid content of 1.5 μm or less.

The present invention (4) provides the method for producing lithium cobalt pyrophosphate according to any one of (1) to (3), wherein: the organic acid is a carboxylic acid.

Further, the present invention (5) provides the method for producing lithium cobalt pyrophosphate according to any one of (1) to (3), wherein: the organic acid is oxalic acid.

Further, the present invention (6) provides the method for producing lithium cobalt pyrophosphate according to any one of (1) to (5), wherein: the reaction precursor contains an organic acid salt of cobalt and a phosphate of lithium.

Further, the present invention (7) provides the method for producing lithium cobalt pyrophosphate according to any one of (1) to (6), further comprising: and a fifth step (A) of heating the cobalt lithium pyrophosphate obtained in the fourth step.

Further, the present invention (8) provides the method for producing lithium cobalt pyrophosphate according to (7), wherein: the heat treatment temperature in the fifth step (A) is 200 to 700 ℃.

Further, the present invention (9) provides a method for producing a cobalt lithium pyrophosphate-carbon composite, comprising: a fifth step (B) of mixing the cobalt lithium pyrophosphate obtained by performing the method for producing cobalt lithium pyrophosphate according to any one of the (1) to (6) of the present invention with a conductive carbon material source from which carbon is precipitated by thermal decomposition to obtain a mixture of the cobalt lithium pyrophosphate and the conductive carbon material source, and then subjecting the mixture to a heat treatment to thermally decompose the conductive carbon material source to obtain a cobalt lithium pyrophosphate-carbon composite.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a method capable of obtaining lithium cobalt pyrophosphate which is a single phase in X-ray diffraction by an industrially advantageous method. Further, according to the present invention, a composite of the lithium cobalt pyrophosphate and carbon can be provided.

Drawings

FIG. 1 is an X-ray diffraction chart of the reaction precursor obtained in the third step of example 1.

FIG. 2 is an X-ray diffraction chart of lithium cobalt pyrophosphate obtained in example 1.

FIG. 3 is an X-ray diffraction chart of the calcined product obtained in comparative example 1.

FIG. 4 is an X-ray diffraction chart of the solid content obtained in comparative example 2.

Fig. 5 is an SEM photograph of lithium cobalt pyrophosphate obtained in example 1.

FIG. 6 is an X-ray diffraction chart of lithium cobalt pyrophosphate obtained in example 4.

Detailed Description

The method for producing lithium cobalt pyrophosphate of the present invention is a method for producing lithium cobalt pyrophosphate represented by the following general formula (1),

Li_xCo_1－yM_yP₂O₇ (1)

(wherein x is 1.7. ltoreq. x.ltoreq.2.2, Y is 0. ltoreq. y.ltoreq.0.5, and M represents 1 or 2 or more metal elements selected from the group consisting of Mg, Zn, Cu, Fe, Cr, Mn, Ni, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy and Ho.)

The manufacturing method is characterized by comprising:

a first step of adding an organic acid and cobalt hydroxide to a water solvent, and then adding phosphoric acid and lithium hydroxide to prepare an aqueous raw material slurry (1);

a second step of subjecting the aqueous raw material slurry (1) to wet grinding by means of a media mill to obtain a slurry (2) containing a raw material grinding product;

a third step of subjecting the slurry (2) containing the pulverized material to spray drying to obtain a reaction precursor; and

and a fourth step of firing the reaction precursor at 600 ℃ or higher.

The cobalt lithium pyrophosphate obtained by the method for producing cobalt lithium pyrophosphate of the present invention is a cobalt lithium pyrophosphate represented by the following general formula (1),

Li_xCo_1－yM_yP₂O₇ (1)

(wherein x is 1.7. ltoreq. x.ltoreq.2.2, Y is 0. ltoreq. y.ltoreq.0.5, and M represents 1 or 2 or more metal elements selected from the group consisting of Mg, Zn, Cu, Fe, Cr, Mn, Ni, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy and Ho.).

X in the formula of the general formula (1) is 1.7 to 2.2, preferably 1.8 to 2.1. y is 0 to 0.5, preferably 0 to 0.4. M is a metal element that is contained as necessary to improve battery characteristics. M represents 1 or 2 or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Mn, Ni, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy and Ho, preferably 1 or 2 or more metal elements selected from Fe, Ni and Mn.

The first step of the method for producing lithium cobalt pyrophosphate of the present invention is a step of preparing an aqueous raw material slurry (1) by adding an organic acid and cobalt hydroxide to a water solvent and then adding phosphoric acid and lithium hydroxide.

When cobalt hydroxide, phosphoric acid and lithium hydroxide are added to the aqueous solvent, the slurry is formed into a cake (cake) and stirring or the like cannot be performed. The inventors of the present invention found that: when an organic acid and cobalt hydroxide are added to a water solvent, and then phosphoric acid and lithium hydroxide are added, the respective raw materials are uniformly dispersed, and an aqueous raw material slurry (1) which is easy to handle can be obtained; the aqueous raw material slurry (1) can be subjected to wet grinding treatment by a media mill.

In the first step, first, an organic acid and cobalt hydroxide are added to a water solvent, and the cobalt hydroxide and the organic acid react with each other to form an organic acid salt of cobalt. Then, phosphoric acid and lithium hydroxide are added to the aqueous slurry (a) containing the organic acid salt of cobalt, and the phosphoric acid and lithium hydroxide are further reacted with each other to form a lithium phosphate. Therefore, the aqueous raw material slurry (1) obtained by performing the first step contains at least an organic acid salt of cobalt and a phosphate of lithium.

Examples of the organic acid in the first step include: monocarboxylic acids such as formic acid, acetic acid, glycolic acid, lactic acid, and gluconic acid; dicarboxylic acids such as oxalic acid, maleic acid, malonic acid, malic acid, tartaric acid, and succinic acid; and a carboxylic acid such as citric acid having 3 carboxyl groups. Among these, oxalic acid is preferred as the organic acid from the viewpoint of excellent reactivity with cobalt hydroxide.

The organic acid is added in an amount such that the molar ratio (C/Co) of carbon atoms in the organic acid to cobalt atoms in the cobalt hydroxide is 1.5 or more. When the molar ratio (C/Co) of carbon atoms in the organic acid to cobalt atoms in the cobalt hydroxide is less than the above range, Co is formed₃(PO₄)₂·8H₂O, the slurry tends to be cake-like and cannot be stirred. In addition, the amount of the organic acid added is preferably such that the molar ratio (C/Co) of carbon atoms in the organic acid to cobalt atoms in the cobalt hydroxide is 1.5 to 2.5, and particularly preferably 1.7 to 2.3, from the viewpoint of stabilizing the viscosity of the slurry.

The amount of cobalt hydroxide added to the aqueous solvent is 5 to 30 parts by mass, preferably 7 to 25 parts by mass, per 100 parts by mass of the aqueous solvent. When the amount of cobalt hydroxide added to the aqueous solvent is in the above range, the viscosity of the slurry becomes stable.

After adding the organic acid and the cobalt hydroxide to the aqueous solvent, the mixture is preferably stirred at 15 to 90 ℃ and more preferably 20 to 80 ℃ for 30 minutes or more, and still more preferably 30 minutes to 2 hours, in order to react the organic acid and the cobalt hydroxide. Further, by reacting an organic acid with cobalt hydroxide, an aqueous slurry (a) of an organic acid salt containing at least cobalt can be obtained.

In the preparation of the aqueous slurry (a) containing the organic acid salt of cobalt, the order of addition of the organic acid and cobalt hydroxide is not particularly limited, and from the viewpoint of stabilization of the viscosity of the slurry, it is preferable to add the organic acid to the aqueous solvent and then add the cobalt hydroxide.

In the first step, phosphoric acid and lithium hydroxide are then added to the aqueous slurry (a) containing the cobalt organic acid salt.

The amount of phosphoric acid added to the aqueous slurry (A) of an organic acid salt containing cobalt is such that the molar ratio (P/Co) of phosphorus atoms in the phosphoric acid to cobalt atoms in the aqueous slurry (A) is preferably 1.7 to 2.2, particularly preferably 1.8 to 2.1. When the molar ratio (P/Co) of phosphorus atoms in phosphoric acid to cobalt atoms in the aqueous slurry (a) is in the above range, lithium cobalt pyrophosphate which is a single phase in X-ray diffraction can be easily obtained.

The amount of lithium hydroxide added to the aqueous slurry (a) containing an organic acid salt of cobalt is such that the molar ratio (Li/P) of lithium atoms in the lithium hydroxide to phosphorus atoms in the phosphoric acid is preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. When the molar ratio (Li/P) of lithium atoms in lithium hydroxide to phosphorus atoms in phosphoric acid is in the above range, lithium cobalt pyrophosphate which is a single phase in X-ray diffraction can be easily obtained.

In the first step, when phosphoric acid and lithium hydroxide are added to the aqueous slurry (a) containing an organic acid salt of cobalt, the phosphoric acid and lithium hydroxide react with each other to produce a lithium phosphate. The aqueous raw material slurry (1) in the first step preferably contains a lithium phosphate. In the first step, in order to react phosphoric acid with lithium hydroxide, the reaction mixture is preferably stirred at 15 to 90 ℃, more preferably 20 to 80 ℃ for 30 minutes or more, and still more preferably 30 minutes to 2 hours.

When the aqueous raw material slurry (1) is prepared from the aqueous slurry (a) containing the organic acid salt of cobalt, the order of adding phosphoric acid and lithium hydroxide to the aqueous slurry (a) containing the organic acid salt of cobalt is not particularly limited, but from the viewpoint of maintaining the pH of the slurry in an acidic region and stabilizing the viscosity of the slurry, it is preferable to add phosphoric acid to the aqueous slurry (a) containing the organic acid salt of cobalt and then add lithium hydroxide.

As described above, In the first step, the aqueous raw material slurry (1) can be obtained, but In the method for producing cobalt lithium pyrophosphate of the present invention, In the first step, the aqueous raw material slurry (1) may further contain an M source (M represents 1 or 2 or more metal elements selected from Mg, Zn, Cu, Fe, Cr, Mn, Ni, Al, B, Na, K, F, Cl, Br, I, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, Mo, W, V, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho) as necessary).

Examples of the M source include an oxide, a hydroxide, a carbonate, an organic acid salt, a nitrate, and a phosphate containing an M element.

The amount of the M source added is such that the molar ratio of M atoms in the M source to the total molar ratio of cobalt atoms in the cobalt hydroxide and M atoms in the M source (M/(M + Co)) is preferably 0 to 0.5. In the first step, when the M source is further added to the aqueous solvent, the amount of phosphoric acid added to the aqueous slurry (a) containing the organic acid salt of cobalt is preferably 1.8 to 2.2, more preferably 1.9 to 2.1, in terms of the molar ratio (P/(Co + M)) of phosphorus atoms in phosphoric acid to the total moles of cobalt atoms in the aqueous slurry (1) and M atoms in the M source, from the viewpoint of obtaining cobalt lithium pyrophosphate which is a single phase in X-ray diffraction.

The timing of adding the M source in the first step is not particularly limited, and the M source may be added to the aqueous raw material slurry (1) at any timing before the second step.

In the method for producing cobalt lithium pyrophosphate of the present invention, in the first step, the organic acid and cobalt hydroxide are added to the aqueous solvent, and then phosphoric acid and lithium hydroxide are added, whereby the raw materials are uniformly dispersed, and an aqueous raw material slurry (1) which is easy to handle and can be subjected to wet grinding treatment by a media mill can be obtained.

The second step of the method for producing lithium cobalt pyrophosphate of the present invention is a step of wet-grinding the aqueous raw material slurry (1) obtained by the first step by means of a media mill to obtain a slurry (2) containing a ground product.

In the second step, the solid content concentration in the aqueous raw material slurry (1) when wet-ground by the media mill is 5 to 40 mass%, particularly preferably 10 to 35 mass%. When the aqueous raw material slurry (1) is wet-pulverized by a media mill, the solid content concentration is in the above range, the operability is good, and the pulverization treatment can be efficiently performed. Therefore, after the first step, it is preferable to adjust the solid content concentration of the aqueous raw material slurry (1) as necessary so as to achieve the above solid content concentration, and then perform wet grinding treatment in the second step.

In the second step, the aqueous raw material slurry (1) is subjected to wet grinding treatment by a media mill. In the second step, the aqueous raw material slurry (1) is subjected to wet pulverization treatment by a media mill, whereby the solid content contained in the aqueous raw material slurry (1) can be finely pulverized, and thus a reaction precursor having excellent reactivity can be obtained.

Examples of the media mill include a bead mill, a ball mill, a paint shaker (paint shaker), an attritor, and a sand mill, and a bead mill is preferable. In the case of using a bead mill, the operating conditions, the kind and size of beads may be appropriately selected depending on the size and throughput of the apparatus.

From the viewpoint of more efficient treatment by the media mill, a dispersant may be added to the aqueous slurry (a) containing the cobalt organic acid salt or the aqueous raw material slurry (1). The dispersant may be appropriately selected depending on the kind and characteristics of the slurry. Examples of the dispersant include various surfactants and polycarboxylic acid ammonium salts. The concentration of the dispersant in the slurry is preferably 0.01 to 10% by mass, and particularly preferably 0.1 to 5% by mass, from the viewpoint of obtaining a sufficient dispersing effect.

In the second step, wet pulverization treatment is carried out by a media mill until the average particle diameter of the solid content in the slurry (2) containing the pulverized material is preferably 1.5 μm or less, particularly preferably 0.1 to 1.2 μm, as measured by D50 obtained by a laser scattering diffraction method. When the average particle diameter of the solid content in the slurry (2) containing the pulverized product is in the above range, a reaction precursor having excellent reactivity can be easily obtained. Among them, D50 obtained by the laser scattering diffraction method means a particle diameter of 50% in volume accumulation in a particle size distribution curve obtained by the laser scattering diffraction method using MT3300 manufactured by microtrac bel corp.

Thus, by performing the second step, the slurry (2) containing the pulverized material can be obtained.

By performing the second step as described above, the slurry (2) containing the pulverized product can be obtained, but in the method for producing lithium cobalt pyrophosphate of the present invention, the slurry containing the pulverized product in the second step may further contain an M source, if necessary. The type of M source and the amount of M source added in the second step are the same as those in the first step.

The timing of adding the M source in the second step is not particularly limited, and the M source may be added to the slurry (2) containing the pulverized product at any timing before the third step.

The third step of the method for producing lithium cobalt pyrophosphate of the present invention is a step of spray-drying the slurry (2) containing the pulverized product obtained in the second step to obtain a reaction precursor.

As a method for drying the slurry, a method other than the spray drying method is also known, but in the method for producing cobalt lithium pyrophosphate of the present invention, the drying method is adopted based on the knowledge that the selection of the spray drying method is advantageous.

Specifically, since a granulated substance containing each raw material component uniformly and having raw material particles densely packed can be obtained when drying by a spray drying method, in the method for producing cobalt lithium pyrophosphate of the present invention, cobalt lithium pyrophosphate which is a single phase in X-ray diffraction can be obtained by firing the reaction precursor in the fourth step using the granulated substance as a reaction precursor.

In the spray drying in the third step, the slurry is atomized by a predetermined method, and the resulting fine droplets are dried to obtain a reaction precursor. Examples of the method of atomizing the slurry include a method using a rotating disk and a method using a pressure nozzle. Any method may be used in the third step.

In the spray drying method in the third step, the relationship between the size of the droplets of the atomized slurry and the size of the particles of the ground product contained therein affects stable drying and the properties of the resulting dried powder. Specifically, when the size of the raw material particles of the ground product is too small relative to the size of the droplets, the droplets become unstable and smooth drying becomes difficult. From this viewpoint, the size of the atomized droplets is preferably 1 to 50 μm, and particularly preferably 10 to 40 μm. In view of this, the supply amount of the slurry to the spray drying apparatus is preferably determined.

The reaction precursor obtained by the spray drying in the third step is subjected to firing in the fourth step, but the powder characteristics such as the average particle diameter of the obtained cobalt lithium pyrophosphate basically continue the characteristics of the reaction precursor. Therefore, in the spray drying in the third step, from the viewpoint of controlling the particle size of the target cobalt lithium pyrophosphate, it is preferable to perform the spray drying so that the size of the secondary particles of the reaction precursor becomes 1 to 50 μm, particularly preferably 10 to 40 μm, in terms of the particle size determined by the observation with a Scanning Electron Microscope (SEM).

In the third step, the drying temperature in the spray drying device is preferably adjusted so that the hot air inlet temperature is 150 to 350 ℃, preferably 200 to 330 ℃, and the hot air outlet temperature is 80 to 200 ℃, preferably 100 to 170 ℃, in order to prevent moisture absorption of the powder and facilitate recovery of the powder.

The reaction precursor obtained by performing the third step preferably contains at least an organic acid salt of cobalt and a lithium phosphate. By X-ray diffraction analysis of the reaction precursor, the organic acid salt of cobalt and the phosphate salt of lithium in the reaction precursor were confirmed. The lithium phosphate contained in the reaction precursor is preferably Li (H)₂PO₄) The organic acid salt of cobalt varies depending on the type of the organic acid used, and for example, when oxalic acid is used, an oxalate of cobalt (Co (C) is mentioned₂O₄)(H₂O)₂). Further, an organic acid salt of cobalt produced as a by-product in the reaction may be contained as long as the effect of the present invention is not impaired. When oxalic acid is used as the organic acid salt of cobalt produced as a by-product, for example, cobalt formate (co (hcoo)₂(H₂O)₂) And the like. The reaction precursor containing the M source may be a double salt with cobalt and an organic acid of M.

By performing the third step as described above, the reaction precursor to be used for firing in the fourth step is obtained.

The fourth step of the method for producing cobalt lithium pyrophosphate of the present invention is a step of firing the reaction precursor obtained in the third step to obtain cobalt lithium pyrophosphate which is a single phase in X-ray.

The firing temperature in the fourth step is 600 ℃ or higher, preferably 600 to 730 ℃. When the firing temperature is in the above range, lithium cobalt pyrophosphate which is a single phase in X-ray can be obtained. On the other hand, when the firing temperature is lower than the above range, the reaction cannot be completed, and lithium cobalt pyrophosphate cannot be obtained.

The firing atmosphere in the fourth step is an atmospheric atmosphere or an inert gas atmosphere. When firing is performed at a high temperature of 700 ℃ or higher, a molten material is obtained when firing is performed in an atmospheric atmosphere, and a powdery material is not obtained, so that when firing is performed at 700 ℃ or higher, firing is preferably performed in an inert gas atmosphere. Examples of the inert gas include argon, helium, and nitrogen, and among these, nitrogen is preferable from the viewpoint of low cost and industrial advantage.

The firing time in the fourth step is not particularly limited, but is 0.5 hours or more, preferably 2 to 20 hours. When firing is performed in the fourth step for 0.5 hour or more, preferably 2 to 20 hours, lithium cobalt pyrophosphate which is a single phase in X-ray diffraction can be obtained.

In the fourth step, the cobalt lithium pyrophosphate obtained by the primary firing may be fired a plurality of times as needed.

The cobalt lithium pyrophosphate obtained in the fourth step may be subjected to crushing treatment or pulverization treatment as necessary, or may be subjected to classification.

In the method for producing cobalt lithium pyrophosphate of the present invention, the cobalt lithium pyrophosphate obtained by the fourth step may be subjected to the following fifth step (a) or fifth step (B) as needed.

The fifth step (a) is a step of further heating the cobalt lithium pyrophosphate obtained in the fourth step to adjust the amount of carbon contained in the cobalt lithium pyrophosphate. Specifically, in the fifth step (a), the cobalt lithium pyrophosphate obtained in the fourth step is subjected to a heat treatment to oxidize carbon in the cobalt lithium pyrophosphate. The heat treatment in the fifth step (a) is preferably performed in an oxygen-containing atmosphere. In the fifth step (a), the oxygen concentration of the atmosphere is preferably 5 vol% or more, and more preferably 10 to 30 vol%, from the viewpoint of efficiently oxidizing carbon. The temperature of the heat treatment in the fifth step (A) is 200 to 700 ℃, preferably 250 to 600 ℃. When the heating temperature in the fifth step (a) is in the above range, the oxidation treatment of the remaining carbon can be efficiently performed. The time of the heat treatment in the fifth step (a) is not critical in the method for producing cobalt lithium pyrophosphate of the present invention. The longer the time of the heat treatment in the fifth step, the lower the carbon content contained in the cobalt lithium pyrophosphate. In the fifth step (a), it is preferable to heat-treat the carbon to a desired carbon content by appropriately setting appropriate conditions in advance.

The fifth step (B) is a step of mixing the cobalt lithium pyrophosphate obtained in the fourth step with a conductive carbon material source from which carbon is precipitated by thermal decomposition (hereinafter also referred to simply as "conductive carbon material source") to obtain a mixture of the cobalt lithium pyrophosphate and the conductive carbon material source, and then subjecting the mixture to a heat treatment to thermally decompose the conductive carbon material source to obtain a cobalt lithium pyrophosphate-carbon composite.

As the conductive carbon material source, at least a material that is thermally decomposed by the heat treatment in the fifth step (B) to deposit carbon is used. The conductive carbon material source is a component that imparts conductivity to lithium cobalt pyrophosphate, and by forming a composite of conductive carbon and lithium cobalt pyrophosphate, it is possible to expect improvement in the discharge capacity and cycle characteristics of a lithium secondary battery using the lithium cobalt pyrophosphate-carbon composite as a positive electrode active material.

Examples of the conductive carbon material include: coal tar pitches ranging from soft to hard pitches; petroleum-based heavy oils such as coal-based heavy oils such as dry distillation liquefied oil, direct-current heavy oils such as atmospheric residue and vacuum residue, crude oils and petroleum-based heavy oils such as decomposition-based heavy oils such as ethylene tar, which are generated as by-products during thermal decomposition, e.g., crude oil and naphtha; aromatic hydrocarbons such as acenaphthylene, decacycloolefin, anthracene, phenanthrene, and the like; polyphenyls such as phenazine, biphenyl, terphenyl, and the like; 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 polymers such as sulfur-containing polythiophene and polystyrene; natural polymers such as sugars including glucose, fructose, lactose, maltose, and sucrose; among thermoplastic resins such as polyphenylene sulfide and polyphenylene ether, and thermosetting resins such as phenol resins and imide resins, saccharides are preferable from the viewpoint of being industrially available at low cost and improving the discharge capacity and cycle characteristics of a lithium secondary battery using the finally obtained cobalt lithium pyrophosphate carbon composite as a positive electrode active material.

The proportion of the conductive carbon material source is preferably such that the carbon atoms in the conductive carbon material source are 0.1 to 20.0 mass%, preferably 0.5 to 15.0 mass%, based on the cobalt lithium pyrophosphate, from the viewpoint of improving the discharge capacity and cycle characteristics of a lithium secondary battery using a cobalt lithium pyrophosphate-carbon composite as a positive electrode active material.

In the fifth step (B), the mixing of the cobalt lithium pyrophosphate and the conductive carbon material source may be performed in a dry or wet manner.

In the fifth step (B), the mixing treatment is preferably performed mechanically from the viewpoint of obtaining a uniform mixture as a method of performing the mixing treatment in a dry manner. The apparatus used for dry mixing is not particularly limited as long as a uniform mixture can be obtained, and examples thereof include a high-speed mixer, a super mixer, a turbo-ball mixer, an ebull mixer (Eirich mixer), a henschel mixer, a nauta mixer, a ribbon blender, a V-blender, a cone blender, a jet mill, a micro-pulverizer (cosmomizer), a paint mixer, a bead mill, and a ball mill. In the laboratory scale, a mixer for household use is used.

In the fifth step (B), the following methods can be mentioned as a method of performing the mixing treatment in a wet manner: the method for producing the conductive carbon material source includes the steps of adding cobalt lithium pyrophosphate and the conductive carbon material source to a water solvent so that the solid content is 10 to 80 mass%, preferably 20 to 70 mass%, mechanically mixing the materials to prepare a slurry, and then drying the slurry in a still state or drying the slurry by spray drying or the like to obtain a mixture of the cobalt lithium pyrophosphate and the conductive carbon material source.

The apparatus used for the wet mixing is not particularly limited as long as a uniform slurry can be obtained, and examples thereof include apparatuses such as a stirring bar (stirer), a stirrer with stirring blades, a three-roll mill, a ball mill, a dispersion mill, a homogenizer, a vibration mill, a sand grinding mill, an attritor, and a powerful stirrer. The wet mixing process is not limited to the above-described mechanical mixing process. In the wet mixing, a surfactant may be added to the slurry to perform a mixing treatment.

Next, the mixture of the lithium cobalt pyrophosphate and the conductive carbon material source prepared as described above was subjected to a heat treatment. The heating treatment is carried out at a temperature at which the conductive carbon material source is decomposed by heating to precipitate carbon, and the heating temperature is 180 to 900 ℃, preferably 210 to 800 ℃. When the heating temperature of the heating treatment is in the above range, the carbon can be uniformly coated on the particle surface and the aggregation can be suppressed. The heating time of the heat treatment is 0.2 hours or more, preferably 0.5 to 5 hours. From the viewpoint of suppressing the oxidation of carbon, the atmosphere of the heat treatment is preferably an inert gas atmosphere. In the heat treatment in the method for producing cobalt lithium pyrophosphate of the present invention, it is preferable that the conductive carbon material source is first heated to a temperature equal to or higher than the melting point of the conductive carbon material source to be used to melt the conductive carbon material source, and then the heat treatment is performed in the above-described range to precipitate carbon from the conductive carbon material source, from the viewpoint of uniformly covering the particle surface with carbon.

As described above, the cobalt lithium pyrophosphate obtained by the method for producing cobalt lithium pyrophosphate of the present invention and the cobalt lithium pyrophosphate carbonThe composite is a lithium cobalt pyrophosphate which is a single phase in X-ray diffraction, and has an average particle diameter of preferably 10 μm or less, particularly preferably 0.05 to 5 μm as determined by SEM observation, and a BET specific surface area of preferably 0.1m²More than g, particularly preferably 0.5 to 15m²/g。

The cobalt lithium pyrophosphate and the cobalt lithium pyrophosphate-carbon composite obtained by performing the method for producing cobalt lithium pyrophosphate of the present invention are suitably used as a positive electrode material for a lithium secondary battery, an all-solid battery, or the like.

Examples

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

(example 1)

< first step >

1604.5g of oxalic acid dihydrate was added to 11L of pure water at room temperature (25 ℃), and stirred for 30 minutes using a Three-one motor stirrer, and 228g of a dispersant (ammonium polycarboxylate) was added. Then, 1200g of cobalt hydroxide was added thereto and stirred for 30 minutes. Subsequently, 2922.4g of 85 mass% phosphoric acid was added thereto and stirred for 30 minutes. Next, 1068.8g of lithium hydroxide monohydrate was added thereto and stirred for 1 hour to obtain an aqueous raw material slurry.

< second step >

Subsequently, the aqueous raw material slurry was supplied to a media-stirring type bead mill containing zirconia beads having a diameter of 0.5mm while stirring, and wet-pulverized by mixing for 3 hours. The average particle size of the solid content in the slurry after wet grinding, which was determined by the laser light scattering diffraction method, was 0.5 μm.

< third Process step >

Next, the slurry was supplied to a spray dryer in which the temperature of the hot air inlet was set to 220 ℃ at a supply rate of 2.4L/h, to obtain a reaction precursor. The obtained reaction precursor was analyzed by X-ray diffraction to confirm that Co (C) was present₂O₄)(H₂O)₂，Li(H₂PO₄) A mixture of (a). An X-ray diffraction pattern of the reaction precursor is shown in fig. 1.

< fourth step >

Thereafter, the obtained reaction precursor was fired at 650 ℃ for 4 hours in a nitrogen atmosphere to obtain a black fired product.

The obtained fired product was analyzed by X-ray diffraction and found to be single-phase Li_1.86CoP₂O₇. An X-ray diffraction pattern of the fired product is shown in fig. 2.

(example 2)

The same procedure as in example 1 was repeated except that firing was carried out at 700 ℃ for 4 hours in a nitrogen atmosphere in the fourth step, to obtain a black fired product.

The obtained fired product was analyzed by X-ray diffraction and found to be single-phase Li_1.86CoP₂O₇. An X-ray diffraction pattern of the fired product is shown in fig. 3.

Comparative example 1

The procedure of example 1 was repeated except that firing was carried out at 550 ℃ for 4 hours in an atmospheric air atmosphere in the fourth step, to obtain a purple fired product.

The X-ray diffraction analysis of the obtained fired product revealed that the fired product was Li_1.86CoP₂O₇With LiCoPO₄A mixture of (a).

Comparative example 2

1200g of cobalt hydroxide was added to 1L of pure water at room temperature (25 ℃ C.), stirred for 30 minutes using a Three-one motor stirrer, and 228g of a dispersant (ammonium polycarboxylate) was added thereto. Subsequently, 2922.4g of 85 mass% phosphoric acid was added to the mixture, and a purple cake was formed, which was not stirred. The subsequent steps could not be performed. The obtained solid was analyzed by X-ray diffraction and found to be Co₃(PO₄)₂·8H₂And O. The results are shown in FIG. 4.

[ Table 1]

(example 3)

The cobalt lithium pyrophosphate obtained in example 1 was subjected to a heat treatment at 350 ℃ for 4 hours in an atmospheric air atmosphere (oxygen concentration: 20 vol%).

The obtained heat-treated product was analyzed by X-ray diffraction and found to be single-phase Li_1.86CoP₂O₇。

(example 4)

The cobalt lithium pyrophosphate obtained in example 1 was subjected to a heat treatment at 700 ℃ for 4 hours in an atmospheric air atmosphere (oxygen concentration: 20 vol%).

The obtained heat-treated product was analyzed by X-ray diffraction and found to be single-phase Li_1.86CoP₂O₇。

(example 5)

In the same manner as in example 4 except that 218g of aluminum nitrate hydrate 9 was added to the slurry in the media-agitation type bead mill after the aqueous raw material slurry was pulverized in the second step by the media-agitation type bead mill, and the slurry was agitated in the media-agitation type bead mill to obtain a slurry to be supplied to the third step, the above-mentioned was repeated to obtain a slurry of Li in the second step_1.86CoP₂O₇A heat-treated product of lithium cobalt pyrophosphate containing 0.04 of Al in terms of molar ratio Al/Co.

As a result of X-ray diffraction analysis of the obtained heat-treated product, no hetero-phase was observed, and it was confirmed that the heat-treated product was single-phase Li_1.86CoP₂O₇(FIG. 6).

< evaluation of physical Properties >

The average particle diameter and BET specific surface area of the lithium cobalt pyrophosphate obtained in the examples were measured, and the results are shown in table 2. Fig. 5 shows an SEM photograph of the cobalt lithium pyrophosphate obtained in example 1.

The average particle size was measured by observing the particles at a magnification of 1 ten thousand times using a scanning electron microscope, and the average of arbitrarily selected 50 or more particles was determined as the average particle size.

[ Table 2]