JP6032410B2 - Method for producing ferric phosphate hydrate particles powder - Google Patents

Description

  The present invention relates to a crystalline ferric phosphate hydrate particle powder that is favorable as a precursor of olivine-type lithium iron phosphate particles and a method for producing the same.

In recent years, many efforts have been made to reduce carbon dioxide from the consideration of the global environment, and storage batteries that can store electrical energy as chemical energy are attracting attention as one approach. Among them, a lithium ion secondary battery having a high energy density has attracted attention. However, it is pointed out that lithium cobaltate, which is mainly used for the positive electrode material, is a rare metal and is expensive and has problems with supply stability, as well as safety issues such as reports of thermal runaway and ignition accidents, and high toxicity. ing.
On the other hand, olivine-type lithium iron phosphate, known as a positive electrode material, has a practical discharge capacity comparable to lithium cobaltate, has low toxicity, and consists of only abundant elements on the earth, so it can be supplied inexpensively and stably. There is a possibility and a promising material.
Since the lithium ion secondary battery has a thin film electrode structure, the electrode material is required to have a uniform particle size that improves the electrode density in addition to the material characteristics. When a material having a large particle size and a low specific surface area is used, there is a concern that a sufficient reaction area with the electrolytic solution cannot be secured, the output does not increase due to an increase in reaction resistance, and the separator performance is damaged and the battery performance deteriorates. In addition, if fine dust is contained, it may cause a handling problem and cause an abnormal reaction. For these reasons and further from the viewpoint of applicability, the electrode material is required to have as uniform a particle size distribution as possible.

As a method for producing lithium iron phosphate, there are a solid phase method (Patent Document 1, Patent Document 2), a hydrothermal method (Patent Document 3), a supercritical method (Patent Document 4), an atmospheric pressure wet method (Patent Document 5), and the like. It has been reported that ferric phosphate hydrate is known as an intermediate of lithium iron phosphate.
In Patent Document 6, iron (II) is obtained by reacting iron (II) or iron (III) or a mixture of iron (II) and iron (III) with 5 to 50% phosphoric acid and adding an oxidizing agent. Has been described, but the reaction requires vigorous stirring and the resulting iron (III) phosphate has a very fine primary particle size.
Patent Document 7 describes a method in which an aqueous solution of iron chloride or iron sulfate is used and a surfactant is added at the time of reaction with phosphoric acid, and nanoparticles are obtained.
Patent Document 8 describes that by using a buffer solution, iron phosphate powder having a small pH variation and a uniform particle size can be obtained.
Since these methods use iron sulfate or iron chloride as starting materials, they contain sulfates or chlorides that have an adverse effect on battery characteristics as impurities, and can be obtained as extremely fine powders. The fineness affects the conductivity of the positive electrode material, but in the manufacturing process, it is easy to cause filtration leakage, and the workability and efficiency are poor. Also, when lithium iron phosphate is used, it is difficult to generate dust and difficult to handle. Arise.

  On the other hand, in Patent Document 2, iron oxide or hydrous iron oxide and a phosphorus compound are reacted in a relatively thin aqueous solution, the reaction concentration is 0.1 to 3.0 mol / L (in terms of Fe concentration), and the P / Fe molar ratio. 1 to 10 and a pH of 3 or less, it is described that fine primary particles aggregate, ferric phosphate hydrates having a high specific surface area and very few impurities. Since the ferric phosphate hydrate obtained by this production method has fine primary particles, the battery performance when used as a positive electrode material is good, and because of the agglomerated secondary particles, the size is easy to handle. There are advantages.

The positive electrode material is required to have uniform quality and a uniform particle size distribution in order to produce a uniform electrode film, and the requirement is similarly required for ferric phosphate as a precursor. However, the method of Patent Document 2 has a drawback that it cannot be stably industrially produced with a uniform particle size distribution.
In Patent Document 2, since the raw material ferric phosphate hydrate particle size and the lithium iron phosphate particle size are substantially equal, the ferric phosphate hydrate hydrate particle size is good for producing lithium iron phosphate. Important things are shown. However, the relationship between the particle size of the iron raw material and the particle size of the ferric phosphate hydrate produced is not described, and the production method of the present invention is not specifically shown.
The method for producing good crystalline ferric phosphate hydrate particles according to the present invention is novel, characterized in that ferric phosphate hydrate particles having an appropriate particle size and uniform particle size distribution can be obtained. And

WO2005 / 041327 WO2011 / 030786 Special table 2007-511458 gazette JP 2004-095386 A WO2007 / 000251 Special table 2011-500492 Special table 2011-505332 WO2012 / 023439

Lithium ion secondary batteries are mounted on various devices, have higher discharge capacities, have low toxicity, can be supplied inexpensively and stably, and have high safety. Particularly for the positive electrode material, safety is required, and a new production method is desired.
The present invention provides a ferric phosphate hydrate having an appropriate particle size and a uniform particle size distribution that is useful as an intermediate for a highly safe positive electrode material that can be used in lithium ion secondary batteries and the like. It is another object of the present invention to establish a manufacturing method thereof.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the ferric phosphate hydrate hydrate particle size produced by the iron raw material particle size has a uniform particle size. A method for producing iron hydrates has been found.

That is, the present invention relates to the following.
1) In a method of producing ferric phosphate hydrate by reacting iron oxide particle powder or hydrous iron oxide particle powder with a phosphorus compound in solution, oxidation with a maximum particle size of 30 μm or less in particle size distribution measurement The present invention relates to a method for producing ferric phosphate hydrate comprising using iron particle powder or hydrous iron oxide particle powder as an iron raw material.
2) In the production method described above, the iron oxide particle powder or the hydrous iron oxide particle powder having a D90 (90 minute fraction under sieving) in the particle size distribution measurement of 10 μm or less is used as the iron raw material. This relates to a method for producing ferric phosphate hydrate.
3) The method for producing ferric phosphate hydrate according to 1) or 2) above, wherein the ferric phosphate hydrate has a particle content of 30% or more and 2% or less. Is.
4) The ferric phosphate hydrate according to any one of 1) to 3) above, wherein the ferric phosphate hydrate is free of aggregated particles of 40 μm or more as observed with a scanning electron microscope. It is related with the manufacturing method.
5) The method for producing a ferric phosphate hydrate according to any one of 1) to 4) above, wherein an iron raw material whose particle size is adjusted by dry pulverization is used.
6) The above-mentioned 5), wherein the particles of ferric phosphate hydrate having a particle size of 5 μm or less are 10% or less under sieving and the particles of 30 μm or less are 90% or more under sieving. It relates to a method for producing the described ferric phosphate hydrate.
7) It relates to a ferric phosphate hydrate produced by any one of 1) to 6).

Hereinafter, the present invention will be described in detail.
The composition of the ferric phosphate hydrate produced in the present invention is FePO4 · nH2O (0 <n ≦ 2, n is the amount of hydrated water), and the dihydrate is the most stable. However, the amount of hydration water varies depending on the drying conditions. Further, the crystal structure of the ferric phosphate hydrate includes one or both of a strengite structure and a metastrength structure.

  As the iron oxide particle powder or the hydrous iron oxide particle powder of the present invention, it is particularly desirable to use a fine goethite powder (α-FeOOH) having a large BET specific surface area, and orthophosphoric acid, metaphosphoric acid, phosphorus pentoxide as the phosphorus compound. Etc., and orthophosphoric acid is particularly desirable.

The ferric phosphate hydrate of the present invention can be produced by mixing a fine iron oxide particle powder or hydrated iron oxide particle powder having a BET specific surface area of 50 m 2 / g or more and a secondary particle size and a phosphorus compound in a solution. While stirring in a temperature range of ˜100 ° C., it is desirable to react at a P / Fe ratio in the range of 1 to 10 in terms of mole, pH 3 or less, and a reaction concentration of 0.1 to 3.0 mol / L (Fe concentration) .
The particle size of the iron raw material used for the reaction is closely related to the particle size of the ferric phosphate hydrate, and the median diameter D90 of the iron oxide particle powder or the hydrated iron oxide particle powder is preferably 10 μm or less, and Dmax is 30 μm. The following is desirable. When particles larger than these are used as raw materials, coarse ferric phosphate hydrates are produced, and homogeneous ferric phosphate hydrates cannot be obtained.
Uniformly pulverize and mix ball mills, vibration mills, planetary ball mills, paint shakers, high-speed rotary blade mills, jet mills, etc. There is no limit to the device if it can be used. In particular, when a dry pulverized raw material is used, depending on the pulverization conditions, for example, particles of 5 μm or less are 10% or less of the total sieve sieve, and ferrous phosphate whose particles of 30 μm or less are 90% or more of the sieve sieve accumulated. It is more preferable because a hydrate is generated and the proportion of fine and coarse substances is suppressed and becomes more homogeneous.

After completion of the reaction, excess moisture may be removed using a ventilating dryer, a freeze vacuum dryer, a spray dryer, a filter press, a vacuum filter, a filter thickener, or the like.
The ferric phosphate hydrate produced according to the present invention has an average secondary particle size in the range of 8 to 20 μm depending on the production conditions, and a desirable particle size as a precursor of lithium iron phosphate. The ferric phosphate hydrate produced is composed of secondary particles formed by agglomeration of plate-like primary particles, and when observed with a scanning electron microscope, a particle size at which aggregated particles of 40 μm or more cannot be seen. It becomes a well-organized powder.

The manufacturing method of the ferric phosphate hydrate of the present invention confirmed that uniform particles were obtained compared to the case where the iron raw material particle size was not controlled.
The method for producing a ferric phosphate hydrate according to the present invention can produce a ferric phosphate hydrate having a uniform and appropriate particle size, and is useful as an intermediate of lithium iron phosphate. An iron hydrate can be provided.

2 is a powder X-ray diffraction pattern of the powder of ferric phosphate hydrate particles obtained in Example 1, Comparative Example 1, and Comparative Example 2. FIG. 2 is a scanning electron micrograph of the ferric phosphate hydrate particles obtained in Example 1. FIG. 4 is a powder X-ray diffraction pattern of the ferric phosphate hydrate particles obtained in Example 2 and Example 3. FIG. 2 is a scanning electron micrograph of the ferric phosphate hydrate particles obtained in Example 2. FIG. 4 is a scanning electron micrograph of the ferric phosphate hydrate particles obtained in Example 3. FIG. 2 is a scanning electron micrograph of the ferric phosphate hydrate particles obtained in Comparative Example 1. 2 is a scanning electron micrograph of ferric phosphate hydrate particles obtained in Comparative Example 2.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to these.
The average secondary particle diameter was measured using a laser diffraction / scattering particle size distribution analyzer Microtrac MT330EXII (Nikkiso Co., Ltd.), and the median diameters D50, D90, and Dmax were measured.
The crystal structure of the particles was measured with an X-ray diffractometer RINT2200 (manufactured by Rigaku Corporation) using Cu-Kα, 40 kV, 20 mA.
The shape of the particles was observed using a scanning electron microscope JSM-5310 (manufactured by JEOL).

<Example 1>
The hydrous iron oxide particles were dry-ground using a dynamic mill (manufactured by Nippon Coke).
In a heating type mixing stirrer, 71 g of hydrous iron oxide particles having a D90 of 10 μm and a Dmax of 26 μm were suspended in 1280 g of pure water. 344 g of 85% orthophosphoric acid solution was added, the temperature was raised to 85 ° C., and the reaction was carried out for 6 hours. The reaction mixture was allowed to cool, then the solvent was removed, washed with water, and dried at 110 ° C. for 24 hours to obtain 133 g of milky white powder.
Powder X-ray diffraction was performed to confirm that it was a metastrophite structure, and no strengite structure or impurity phase was confirmed. The obtained powder X-ray diffraction results are shown in FIG.
The secondary particle shape obtained by scanning electron microscope photography is a rounded square columnar secondary particle in which thin plate-like particles are densely aggregated. There is no giant aggregate. The result of particle size measurement by laser diffraction method is D50. Was 16 μm. A scanning electron micrograph of the obtained powder is shown in FIG.

<Example 2>
The hydrous iron oxide particles were dry-ground using a cyclone mill 150W (manufactured by Tsukishima Kikai).
In a heating type mixing stirrer, 29 kg of hydrous iron oxide particles subjected to dry pulverization with D90 of 6 μm and Dmax of 19 μm were suspended in 511 kg of pure water. 138 kg of 85% orthophosphoric acid solution was added, the temperature was raised to 85 ° C., and the reaction was carried out for 6 hours. The reaction mixture was allowed to cool, then the solvent was removed, washed with water, and dried at 110 ° C. to obtain 51 kg of milky white powder.
Powder X-ray diffraction was performed to confirm that it was a metastrophite structure, and no strengite structure or impurity phase was confirmed. The obtained X-ray diffraction is shown in FIG.
The secondary particle shape obtained by scanning electron microscope photography is a rounded square columnar secondary particle in which thin plate-like particles are densely agglomerated, and there is no giant aggregate. Was 12 μm. A scanning electron micrograph of the obtained powder is shown in FIG.

<Example 3>
The hydrous iron oxide particles were wet pulverized in an aqueous solution using 3 mmφ zirconia balls.
In a heating type mixing stirrer, 29 kg of hydrous iron oxide particles subjected to wet pulverization with D90 of 7 μm and Dmax of 22 μm were suspended in 511 kg of pure water. 138 kg of 85% orthophosphoric acid solution was added, the temperature was raised to 85 ° C., and the reaction was carried out for 6 hours. The reaction mixture was allowed to cool, then the solvent was removed, washed with water, and dried at 110 ° C. to obtain 54 kg of milky white powder.
Powder X-ray diffraction was performed to confirm that it was a metastrophite structure, and no strengite structure or impurity phase was confirmed. The obtained X-ray diffraction is shown in FIG.
The secondary particle shape obtained by scanning electron microscope photography is a rounded square columnar secondary particle in which thin plate-like particles are densely aggregated. There is no giant aggregate. The result of particle size measurement by laser diffraction method is D50. Was 16 μm. A scanning electron micrograph of the obtained powder is shown in FIG.

<Comparative Example 1>
In a heating type mixing stirrer, 71 g of hydrous iron oxide particles having a D90 of 51 μm and a Dmax of 104 μm were suspended in 1280 g of pure water. 344 g of 85% orthophosphoric acid solution was added, the temperature was raised to 85 ° C., and the reaction was carried out for 6 hours. The reaction mixture was allowed to cool, then the solvent was removed, washed with water, and dried at 110 ° C. for 24 hours to obtain 128 g of milky white powder.
Powder X-ray diffraction was performed to confirm that it was a metastrophite structure, and no strengite structure or impurity phase was confirmed. The obtained powder X-ray diffraction results are shown in FIG.
The secondary particle shape obtained by scanning electron microscope photography was a series of large particles with poor lamination and fine particles with poor development, and the uniformity was poor. As a result of measuring the particle diameter by the laser diffraction method, D50 was 17 μm. A scanning electron micrograph of the obtained powder is shown in FIG.

<Comparative example 2>
The hydrous iron oxide particles were dry-ground using a dynamic mill (manufactured by Nippon Coke).
In a heating type mixing stirrer, 71 g of hydrous iron oxide particles having a D90 of 28 μm and a Dmax of 56 μm were suspended in 1280 g of pure water. 344 g of 85% orthophosphoric acid solution was added, the temperature was raised to 85 ° C., and the reaction was carried out for 6 hours. The reaction mixture was allowed to cool, then the solvent was removed, washed with water, and dried at 110 ° C. for 24 hours to obtain 128 g of milky white powder.
Powder X-ray diffraction was performed to confirm that it was a metastrophite structure, and no strengite structure or impurity phase was confirmed. The obtained powder X-ray diffraction results are shown in FIG.
Further, according to scanning electron micrographs, although a series of large aggregates as seen in Comparative Example 1 are not observed, large particles in which secondary particles are further agglomerated and bonded are formed, and 40 μm is contained therein. There were also some large particles. As a result of measuring the particle diameter by the laser diffraction method, D50 was 16 μm. A scanning electron micrograph of the obtained powder is shown in FIG.

The manufacturing method of the ferric phosphate hydrate particles according to the present invention is simple, excellent in filterability, and suitable for industrial production.
The ferric phosphate hydrate particle powder according to the present invention has a high specific surface area and is easy to handle because it has a uniform and appropriate particle size, and is a precursor of an olivine type lithium iron phosphate particle powder. It is suitable as a raw material for lithium transition metal phosphate containing iron as a transition metal species. By using the ferric phosphate hydrate particles powder obtained in the present invention as a raw material, this can be easily and uniformly industrially produced, contributing to the production of a thin film positive electrode having good coating properties and high uniformity. .

Claims (6)

A method for producing a ferric hydrous phosphate dihydrate reacts with iron oxide particles or iron oxide hydroxide particles and phosphorus compound in solution, the particle size to 30μm below the maximum particle size in particle size distribution measurement by milling A manufacturing method characterized by using adjusted iron oxide particle powder or hydrous iron oxide particle powder as an iron raw material, comprising secondary particles obtained by aggregating plate-like primary particles, and having an average secondary particle size of 8 to A method for producing 20 μm ferric phosphate hydrate. 2. The phosphorus according to claim 1, wherein in the manufacturing method, an iron oxide particle powder or a hydrous iron oxide particle powder having a D90 (90 minute fraction under sieving) in a particle size distribution measurement of 10 μm or less is used as an iron raw material. A method for producing ferric acid hydrate. Method for producing a ferric phosphate hydrous hydrate according to claim 1 or 2, characterized in that the ferric phosphate hydrous sum thereof is 30μm or more particle content of not more than 2%. The method for producing ferric phosphate hydrate according to any one of claims 1 to 3, wherein the ferric phosphate hydrate is free of aggregated particles of 40 µm or more as observed with a scanning electron microscope. The method for producing ferric phosphate hydrate according to any one of claims 1 to 4, wherein an iron raw material whose particle size is adjusted by dry grinding is used. The ferric hydrous sum product phosphoric acid is not more than the particles less than 10% cumulative undersize fraction 5 [mu] m, and, 30 [mu] m or less of the particles according to claim 5, characterized in that a cumulative under sieve 90% A method for producing ferric phosphate hydrate.