JP2022135546A - METHOD FOR MANUFACTURING Li3PO4 PARTICLE FOR OBTAINING OLIVINE TYPE LITHIUM PHOSPHATE SYSTEM POSITIVE ELECTRODE MATERIAL - Google Patents

Abstract

To provide a method for manufacturing a raw material effective for manufacturing a high performance olivine type lithium phosphate system positive electrode material.SOLUTION: A method for manufacturing Li3 PO4 particles for obtaining an olivine type lithium phosphate system positive electrode material includes the following steps of (I) to (IV): (I) a step of adding lithium carbonate and sulfuric acid or lithium carbonate, lithium sulfate and sulfuric acid to a solution X with a predetermined content of lithium ions to obtain a mixture A with a predetermined content of lithium ions and a predetermined content of sulfuric acid; (II) a step of subjecting the obtained mixture A to bubbling treatment with inert gas to obtain a mixture B; (III) a step of adding, to the obtained mixture B, an alkaline compound with an amount of alkali ions of 1.05-2.10 mol with respect to one mole of lithium ions in the mixture B to obtain a mixture C; and (IV) a step of, after adding a phosphate compound to the obtained mixture C to obtain a mixture D, obtaining Li3 PO4 particles by the solid-liquid separation of the mixture D.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a method for producing Li ₃ PO ₄ particles for obtaining an olivine-type lithium phosphate-based positive electrode material.

Lithium-ion secondary batteries have established themselves as high-capacity, lightweight power sources that are essential for mobile electronic terminals, electric vehicles, and the like. With the increase in power consumption due to the recent improvement in the performance of electronic devices, there is a demand for a lithium-ion secondary battery with a higher capacity. In order to improve the performance of such batteries, various positive electrode materials have been developed using lithium manganese phosphate, lithium iron phosphate, etc., having an olivine structure obtained by a process of hydrothermal reaction.

By the way, most lithium phosphate-based positive electrode materials having an olivine structure are obtained from a reaction mixture obtained by subjecting a raw material compound to a hydrothermal reaction, while the liquid phase separated from such a reaction mixture is disposed of as an unnecessary waste liquid. It is However, a large amount of lithium ions remain in the disposed liquid phase, and the lithium source, which is the most expensive raw material, is excessively consumed, leading to an increase in production costs. For these reasons, attempts have been made to recover and reuse the lithium ions remaining in the liquid phase after the hydrothermal reaction.

For example, in Patent Document 1, after adding a specific amount of phosphoric acid to a lithium salt aqueous solution containing a specific amount of lithium, the temperature is raised to 30 to 80 ° C., and sodium hydroxide is added while stirring so as to adjust the pH. An aqueous phase synthesis method of nano-lithium iron phosphate is disclosed in which an aqueous solution is added and the like to go through a lithium phosphate preparation step to obtain solid lithium phosphate. We are trying to reuse it. Further, in Patent Document 2, a step of adding an alkali to a solution in which lithium ions separated after a hydrothermal reaction remain until the pH reaches 10.5 or more and 11.8 or less to obtain a solution from which solidified matter is removed. , a method for producing an electrode material including a step of adding a lithium source to the obtained solution to produce lithium phosphate, etc., and removing unreacted lithium ions produced in the production process of the olivine-based electrode material. It is recovered as lithium phosphate.

JP 2016-528140 A JP 2020-47514 A

However, in the technique described in Patent Document 1, there is a risk of an excessive increase in processing time due to steps such as temperature raising that require a large-scale apparatus, as well as a large number of steps. However, it is not suitable for mass production. Moreover, even with the technique described in Patent Document 2, since the solution to which the lithium source is added has a high pH, part of the lithium source remains undissolved, and the efficiency of lithium ion recovery cannot be sufficiently improved. There is a possibility that it will not.
Therefore, even a lithium ion secondary battery manufactured using this material may still not be able to exhibit good battery characteristics, and there is ample room for improvement.

Therefore, an object of the present invention is to manufacture a high-performance olivine-type lithium phosphate-based positive electrode material while effectively reusing the lithium ion-containing solution discharged when manufacturing the olivine-type lithium phosphate-based positive electrode material. The object of the present invention is to provide a production method for obtaining Li ₃ PO ₄ (trilithium phosphate) particles, which are useful raw materials for manufacturing.

Therefore, the present inventor conducted various studies and found that a specific amount of lithium carbonate, lithium sulfate, and sulfuric acid were added to the lithium ion-containing solution discharged during the production of the olivine-type lithium phosphate-based positive electrode material, and an inert gas was added. After performing the bubbling treatment with , high-purity Li ₃ PO ₄ particles with a large specific surface area are efficiently obtained by a simple method by including a step of adding an alkali compound and a step of adding a phosphoric acid compound. I found a manufacturing method that can do this.

That is, the present invention is a method for producing Li ₃ PO ₄ particles using a solution X discharged when obtaining an olivine-type lithium phosphate-based positive electrode material from a reaction mixture obtained by subjecting a raw material compound to a hydrothermal reaction,
The following steps (I)-(IV):
(I) Lithium carbonate and sulfuric acid, or lithium carbonate, lithium sulfate, and sulfuric acid are added to solution X having a lithium ion content of 1000 mg/L to 20000 mg/L, so that the lithium ion content is 5000 mg/L. Step of obtaining a mixed solution A having a concentration of up to 40000 mg/L and a sulfuric acid content of 0.52 mol to 1.00 mol per 1 mol of lithium ions (II) Injecting an inert gas into the obtained mixed solution A (III) The amount of alkali ions in the mixed solution B is 1.05 mol to 2.10 mol per 1 mol of lithium ions in the mixed solution B. A step of adding an alkali compound to obtain a mixed liquid C (IV) A step of adding a phosphoric acid compound to the obtained mixed liquid C to obtain a mixed liquid D, followed by solid-liquid separation to obtain Li ₃ PO ₄ particles. A method for producing Li ₃ PO ₄ particles for obtaining an olivine-type lithium phosphate-based cathode material, comprising:

According to the production method of the present invention, in the process of producing an olivine-type lithium phosphate-based positive electrode material, after subjecting a predetermined raw material compound containing a lithium compound or the like to a hydrothermal reaction, it is separated from the reaction mixture and disposed of. While effectively reusing target lithium ion-containing waste liquid, it is a simple method that does not require a large-scale device such as a temperature raising process, and produces high-purity Li ₃ PO ₄ particles with a large specific surface area. It can be manufactured efficiently.
In this way, it is possible to obtain highly useful Li ₃ PO ₄ particles while using lithium, which is a rare and valuable substance, without waste. type lithium phosphate-based cathode material can be obtained.

1 shows an X-ray diffraction pattern of Li ₃ PO ₄ particles Z ¹ obtained in Example 1. FIG.

The present invention will be described in detail below.
The method for producing Li ₃ PO ₄ particles for obtaining an olivine-type lithium phosphate-based positive electrode material according to the present invention comprises: obtaining an olivine-type lithium phosphate-based positive electrode material from a reaction mixture obtained by subjecting a raw material compound to a hydrothermal reaction; A method for producing Li ₃ PO ₄ particles using discharged solution X, comprising:
The following steps (I)-(IV):
(I) Lithium carbonate and sulfuric acid, or lithium carbonate, lithium sulfate, and sulfuric acid are added to solution X having a lithium ion content of 1000 mg/L to 20000 mg/L, so that the lithium ion content is 5000 mg/L. Step of obtaining a mixed solution A having a concentration of up to 40000 mg/L and a sulfuric acid content of 0.52 mol to 1.00 mol per 1 mol of lithium ions (II) Injecting an inert gas into the obtained mixed solution A (III) The amount of alkali ions in the mixed solution B is 1.05 mol to 2.10 mol per 1 mol of lithium ions in the mixed solution B. A step of adding an alkali compound to obtain a mixed liquid C (IV) A step of adding a phosphoric acid compound to the obtained mixed liquid C to obtain a mixed liquid D, followed by solid-liquid separation to obtain Li ₃ PO ₄ particles. Prepare.

The solution X used in the present invention is an unreacted lithium ion-containing solution discharged when obtaining an olivine-type lithium phosphate-based positive electrode material from a reaction mixture obtained by subjecting a raw material compound to a hydrothermal reaction, which is a so-called waste disposal target. It is an effluent and has a lithium ion content of 1000 mg/L to 20000 mg/L. In the present invention, by using such a solution X, the lithium ion-containing waste liquid to be discarded, which was once discharged during the production of the olivine-type lithium phosphate-based positive electrode material, can be reused without waste, and the olivine-type A method for producing Li ₃ PO ₄ particles for obtaining lithium phosphate-based cathode materials is realized.

Here, the olivine-type lithium phosphate-based positive electrode material is a material that is produced by subjecting a predetermined raw material compound to a hydrothermal reaction, separating the solution X from the resulting reaction mixture, and recovering solid matter. More specifically, for example, it is represented by the following formula (X).
_{LiaMnbFecMxPO4 ( wherein M} is _Mg , Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb , Bi, La, Ce, Nd and Gd, a, b, c and x are 0<a≤1.2, 0.3≤b≤1.2 , 0.2 ≤ c ≤ 1.2, and 0 ≤ x ≤ 0.3, and a + (valence of Mn) x b + (valence of Fe) x c + (valence of M) x x = 3 indicates the number that satisfies

The olivine-type lithium phosphate-based positive electrode material represented by formula (X) contains at least both manganese (Mn) and iron (Fe) as transition metals. That is, in formula (X), M is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd One or more selected elements, preferably Mg or Zr. The value of a is preferably 0.6≦a≦1.2, more preferably 0.65≦a≦1.15, and still more preferably 0.7≦a≦1.1. b is preferably 0.3≦b≦0.8, more preferably 0.5≦b≦0.8, and still more preferably 0.7≦b≦0.8. As for c, 0.2≦c≦0.6 is preferable, 0.2≦c≦0.5 is more preferable, and 0.2≦c≦0.3 is still more preferable. x is preferably 0≤x≤0.2, more preferably 0≤x≤0.15, and still more preferably 0≤x≤0.1.

_{Specifically , for example , LiMn0.3Fe0.7PO4 , LiMn0.7Fe0.3PO4 , LiMn0.9Fe0.1PO4 , LiMn0.8Fe0.2PO4 , LiMn0.75Fe0.15Mg0.1PO4 , LiMn0.75Fe0.19Zr _ _ _ 4 , LiMn0.6Fe0.4PO4 , LiMn0.5Fe0.5PO4 , Li1.2Mn0.63Fe0.27PO4 , Li0.6Mn0.84Fe0.36PO4 and the like . _ _ Among them , LiMn0.3Fe0.7PO4 , LiMn0.7Fe0.3PO4 , LiMn0.8Fe0.2PO4 , LiMn0.6Fe0.4PO4 , Li1.2Mn0.63Fe0.27PO4 , or Li0.6Mn0.84Fe0.36 is preferable . _ _} .

In the production method of the present invention, as step (I), lithium carbonate and sulfuric acid, or lithium carbonate, lithium sulfate and sulfuric acid are added to solution X having a lithium ion content of 1000 mg/L to 20000 mg/L. , obtaining a mixed solution A having a lithium ion content of 5000 mg/L to 40000 mg/L and a sulfuric acid content of 0.52 mol to 1.00 mol per 1 mol of lithium ions.
Thus, in step (I), a solution X containing a certain amount of lithium ions is used as a starting material, and lithium carbonate or lithium carbonate and lithium sulfate are added as a lithium source together with sulfuric acid to temporarily The solution X, which is the lithium ion-containing waste liquid used in the production of the olivine-type lithium phosphate-based positive electrode material, can be effectively reused.

Contaminants need not be mixed in the solution X until it is subjected to the step (I) after the solution X is recovered, and no special storage environment is required. Further, in order to adjust the content of lithium ions in the solution X within the above range, a dilution operation or a concentration operation may be performed by a general method.
The content of lithium ions in the solution X is 1000 mg/L to 20000 mg/L from the viewpoint of increasing productivity when subjecting the obtained Li ₃ PO ₄ particles to the production of an olivine-type lithium phosphate-based positive electrode material. , preferably 2500 mg/L to 20000 mg/L, more preferably 4000 mg/L to 20000 mg/L.
In addition, the solution X may contain other sulfate ions. From the viewpoint of not inhibiting, it is preferably 3000 mg/L to 150000 mg/L, more preferably 6000 mg/L to 150000 mg/L, still more preferably 9000 mg/L to 150000 mg/L.

The pH of solution X at 25° C. is preferably 6 to 9, more preferably 6 to 8.5, and more preferably 6 to 8.5, from the viewpoint of good dissolution or dispersion of subsequently added lithium carbonate, lithium sulfate, and sulfuric acid. Preferably 6-8.
Also, the temperature of the solution X is preferably 5°C to 25°C, more preferably 15°C to 25°C.

In step (I), lithium carbonate and sulfuric acid, or lithium carbonate, lithium sulfate, and sulfuric acid are added to the solution X, and the lithium ion content is reduced from 5000 mg/L to 40000 mg/L without adding a phosphoric acid compound. L and a sulfuric acid content of 0.52 mol to 1.00 mol per 1 mol of lithium ions, that is, a mixed solution A in which lithium carbonate or lithium carbonate and lithium sulfate are completely dissolved. get As described above, in obtaining the mixed liquid A, as the lithium source to be added to the solution X, lithium carbonate is used either alone or in combination with lithium carbonate and lithium sulfate, and lithium carbonate is always used.
As a result, it is possible to adjust the pH environment to a low range, while promoting the dissolution of lithium carbonate and lithium sulfate, while gasifying carbonic acid derived from the added lithium carbonate (dissolved carbonic acid) that is excessively dissolved in the solution. Alternatively, it is insolubilized and combined with bubbling treatment in step ₍ II) described later to facilitate removal of dissolved carbonic acid from the solution and effectively increase the specific surface area of the resulting Li _PO particles. Further, the addition of sulfuric acid to the solution X makes it easier to dispose of the waste liquid than the case of adding nitric acid, organic acid, hydrochloric acid, etc., and can effectively avoid the formation of repellent components. Then, without adding a phosphoric acid compound in the step (I), by adding a phosphoric acid compound in the step (IV) described later, it is possible to produce Li ₃ PO ₄ particles efficiently and simply. can do.
Thus, in the present invention, Li ₃ PO ₄ particles having a large specific surface area can be efficiently obtained through carbonic acid derived from lithium carbonate.

In this specification, "lithium carbonate, or a mixture of lithium carbonate and lithium sulfate completely dissolved" means that the added lithium carbonate or lithium sulfate is completely dissolved in the solvent, and suspended matter in the mixture is It means that it is a liquid substance different from a highly transparent mixed liquid, a so-called slurry, without generating any sediment. "Lithium carbonate-derived carbonic acid (dissolved carbonic acid)" is carbonic acid present in a dissolved state in the mixed liquid, and includes ions such as CO ₃ ^2- and HCO ₃ ^- , and dissolved carbon dioxide gas (CO ₂ ). is a generic term for

The amount of sulfuric acid added to the solution X is such that the content of sulfuric acid in the resulting mixed solution A is 0.52 mol to 1.00 mol per 1 mol of lithium ions in the mixed solution A. From the viewpoint of efficiently removing dissolved carbonic acid, it is preferably 0.52 mol to 0.95 mol, more preferably 0.52 mol to 0.90 mol.
Further, the mass ratio of the amount of sulfuric acid added to the amount of lithium carbonate added to solution X (sulfuric acid/lithium carbonate) is preferably 1.2 to 4.8 from the viewpoint of efficiently removing dissolved carbonic acid. , more preferably 1.2 to 4.0, more preferably 1.2 to 3.2.
In the total amount of lithium carbonate and lithium sulfate added, which is 100% by mass, the amount of lithium carbonate added is preferably 50% by mass or more, more preferably 75% by mass or more, from the viewpoint of efficiently removing dissolved carbonic acid. , and more preferably 100% by mass.

The content of lithium ions in the mixed solution A obtained in step (I) is 5000 mg/L to 40000 mg/L, preferably 7500 mg/L to 40000 mg/L, from the viewpoint of increasing the productivity of Li ₃ PO ₄ particles. L, more preferably 10000 mg/L to 40000 mg/L.
That is, the content of lithium ions in the mixed solution A is greater than the content of lithium ions in the solution X, and when lithium carbonate is used alone as a lithium source so as to achieve such an amount, such lithium carbonate Considering the amount of lithium ions released from, when using lithium carbonate and lithium sulfate together as a lithium source, considering the amount of lithium ions released from both lithium carbonate and lithium sulfate, These lithium sources may be added.

The order of addition of lithium carbonate and sulfuric acid, or of lithium carbonate, lithium sulfate, and sulfuric acid to solution X is, from the viewpoint of sufficiently and effectively promoting the dissolution of lithium carbonate, after addition of lithium carbonate, or lithium carbonate and lithium sulfate. The sulfuric acid is preferably added after the addition of and.
Here, before adding sulfuric acid, the solution X after adding lithium carbonate or lithium carbonate and lithium sulfate in advance may be stirred. The stirring time is preferably 5 minutes to 300 minutes, more preferably 10 minutes to 180 minutes.

The pH of the mixed liquid A obtained in step (I) at 25° C. is effectively and efficiently adjusted by bubbling with an inert gas in the following step (II) while leaving the dissolved carbonic acid in the form of H ₂ CO ₃ . It is preferably 0.5 to 5, more preferably 1.0 to 5, still more preferably 1.5 to 5, from the viewpoint of effectively removing dissolved carbonic acid from the mixed liquid.
The temperature of the mixed liquid A is preferably 25°C to 40°C.

The production method of the present invention includes, as step (II), a step of obtaining a mixed liquid B by subjecting the mixed liquid A obtained in the step (I) to bubbling treatment with an inert gas. By performing the bubbling treatment with an inert gas in this way, the inert gas is blown into the mixed liquid A to effectively and efficiently remove the dissolved carbonic acid remaining in the mixed liquid A, especially the dissolved carbonic acid remaining in the form of CO ₂ . can be removed

The inert gas that can be used is preferably nitrogen, argon or helium, more preferably nitrogen.
From the viewpoint of sufficiently and effectively removing dissolved carbonic acid, the total amount of inert gas blown in the bubbling process is the ratio of the total volume of the blown inert gas to the volume of the mixed liquid A (total volume of inert gas/mixed volume of liquid A), preferably 0.5 to 15, more preferably 1 to 15, still more preferably 2 to 15.
From the same point of view, the duration of the bubbling treatment is preferably 10 minutes to 300 minutes, more preferably 20 minutes to 240 minutes, and even more preferably 30 minutes to 180 minutes.

The pH of the mixture B obtained in step (II) at 25° C. is acidic, specifically preferably 0.5 to 5, more preferably 1.0 to 5, still more preferably 1.5-5.
The temperature of the mixed liquid B is preferably 20°C or higher, more preferably 25°C to 40°C.

In the production method of the present invention, as the step (III), the mixture B obtained in the step (II) is added in an amount of 1.05 mol to 2.10 mol of alkali ions per 1 mol of lithium ions in the mixture B. and adding an alkali compound to obtain a mixed liquid C. As a result, heat is generated by the neutralization reaction of the acidic mixed solution B, so that the specific surface area of the Li ₃ PO ₄ particles can be effectively increased without heating or raising the temperature. It is also possible to prevent a decrease in purity and contamination of the Li ₃ PO ₄ particles due to impurities such as SO ₄ ^2- ions in the solution X used in I).

The amount of the alkali compound to be added is determined from the viewpoint of adjusting the temperature of the mixed liquid C, and from the viewpoint of prioritizing the nucleation reaction over the nucleation reaction of the Li PO particles in the step _{( IV} ). The amount of alkali ion per 1 mol is 1.05 mol to 2.10 mol, preferably 1.05 mol to 2.00 mol, more preferably 1.05 mol to 1.90 mol. .
Examples of usable alkali compounds include one or more selected from sodium hydroxide (alkali ion=sodium ion) and potassium hydroxide (alkali ion=potassium ion). Among them, from the viewpoint of improving the recovery rate of Li ₃ PO ₄ particles and the battery characteristics of lithium ion batteries obtained by using the olivine-type lithium phosphate-based positive electrode material produced from the recovered Li ₃ PO ₄ particles, hydroxylation is used. Preference is given to using sodium. As such an alkaline compound, a solid (granular or flaky) may be used, an alkaline solution such as an aqueous solution may be used, and an alkaline aqueous solution is preferable.

Thus, when adding the alkaline compound to the mixed liquid B, specifically, it is preferable to make the alkaline compound into an alkaline solution using a solvent, add the alkaline solution dropwise to the mixed liquid B, and then stir the mixture.
In addition, it is preferable to stir the mixed solution B while dropping the alkaline solution.
Further, the stirring time of the mixed liquid C after dropping the alkaline solution is preferably 5 minutes to 180 minutes, more preferably 10 minutes to 120 minutes.

The temperature of the mixture C obtained in step (III) is preferably 40°C to 80°C, more preferably 40°C to 70°C.
The pH of the mixture C at 25° C. is preferably 12-14, more preferably 12.5-14, still more preferably 13-14.

In the production method of the present invention, as step (IV), a phosphoric acid compound is added to the mixed liquid C obtained in step (III) to obtain a mixed liquid D, and then solid-liquid separation is performed to obtain Li ₃ PO ₄ particles. A step of obtaining That is, in the present invention, lithium carbonate or lithium sulfate and sulfuric acid are added without adding a phosphoric acid compound in step (I), while a phosphoric acid compound is added in step (IV). By setting the addition order of the raw material compounds in this way, the waste liquid containing lithium ions to be disposed of can be reused without waste, and Li ₃ PO ₄ particles with a large specific surface area can be obtained by a simple method. An efficient method of manufacturing can be realized.

From the viewpoint of effectively promoting the nucleation reaction of the Li ₃ PO ₄ particles, the amount of the phosphoric acid compound added is preferably 0.30 mol to 0.36 mol per 1 mol of lithium ions in the mixed liquid C. , more preferably 0.31 mol to 0.35 mol, more preferably 0.32 mol to 0.35 mol.
Usable phosphoric acid compounds include orthophosphoric acid (H ₃ PO ₄ , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. Among them, phosphoric acid is preferably used, and from the viewpoint of promoting the nucleation reaction of Li ₃ PO ₄ particles, it is preferably used as an aqueous solution having a concentration of 40 to 90 mass %.

Specifically, in adding the phosphoric acid compound to the mixed liquid C, it is preferable to add the phosphoric acid compound dropwise to the mixed liquid C and then stir the mixture. Such dropwise addition of the phosphoric acid compound effectively accelerates the nucleation reaction of the Li ₃ PO ₄ particles and efficiently produces Li ₃ PO ₄ particles of high purity and large specific surface area.

From the viewpoint of effectively promoting the nucleation reaction of the Li ₃ PO ₄ particles, the dropping rate of the phosphoric acid compound is preferably 0.3 minutes or more in terms of the time required to drop the entire amount of the phosphoric acid compound into the mixed liquid C. 5 minutes, more preferably 0.3 to 4 minutes.
In addition, it is preferable to stir the mixed solution C while dropping the phosphoric acid compound.
Further, the stirring time of the mixed solution D after the phosphoric acid compound is added dropwise is preferably 1 minute to 30 minutes, more preferably 5 minutes to 15 minutes.

Although the step (IV) does not particularly require heating or raising the temperature, the temperature of the mixed liquid D obtained in the step (IV) is preferably 40° C. to 80° C., more preferably 40° C. to 70° C. °C.
The pH of the mixture D at 25° C. is preferably 10.0 to 13.0, more preferably 11.0 to 13.0.

Then, the liquid mixture D is subjected to solid-liquid separation to precipitate and recover Li ₃ PO ₄ particles. Apparatuses used for solid-liquid separation include, for example, a filter press, a centrifugal filter, and a vacuum filter. Among them, it is preferable to use a filter press from the viewpoint of obtaining Li ₃ PO ₄ particles efficiently.

The Li ₃ PO ₄ particles (cake) obtained are preferably further dried. As such a drying means, constant temperature drying, freeze drying or vacuum drying is preferable.

The Li ₃ PO ₄ particles obtained by the production method of the present invention, that is, the production method via a so-called liquid-liquid reaction using the mixed liquids A to D, have a large specific surface area and a very small particle diameter, and therefore have high performance. It is a useful raw material for producing an olivine-type lithium phosphate-based positive electrode material.

Specifically, the BET specific surface area of the obtained Li ₃ PO ₄ particles is preferably 19 m ² /g or more from the viewpoint of improving reactivity when used as a raw material for obtaining an olivine-type lithium phosphate-based positive electrode material. more preferably 22 m ² /g or more, preferably 200 m ² /g or less.
The average particle size (D ₅₀ ) of the obtained Li ₃ PO ₄ particles is preferably 1 μm to 10 μm, more preferably 1 μm to 9 μm, still more preferably 1 μm to 8 μm.
The average particle size (D ₅₀ ) of the Li ₃ PO ₄ particles means the volume-based cumulative 50% particle size measured by a laser diffraction/scattering method.

In the Li ₃ PO ₄ particles obtained by the production method of the present invention, lithium carbonate and lithium sulfate, which were not sufficiently dissolved in the step (I), are added from the viewpoint of realizing finer particles and sharper particle size distribution. It is preferred that no carbon derived from carbon or carbon derived from dissolved carbonic acid that could not be sufficiently removed during the process remain. Specifically, the residual amount of carbon in the Li ₃ PO ₄ particles is preferably 0.3% by mass or less, more preferably 0.2% by mass or less.
The amount of carbon remaining in such Li ₃ PO ₄ particles can be confirmed using a carbon-sulfur analyzer (EMIA-220V2, manufactured by Horiba, Ltd.).

When Li ₃ PO ₄ particles obtained by the production method of the present invention are used as a raw material to obtain, for example, the olivine-type lithium phosphate-based positive electrode material represented by the above formula (X), the following steps (i) to (ii) are performed. :
(i) The obtained Li ₃ PO ₄ particles contain an iron compound and a manganese compound, and a metal (M) compound (M is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, one or more elements selected from Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd. (ii) separating a solution containing unreacted Li ions from the reaction mixture obtained in step (i) to obtain an olivine-type lithium phosphate-based positive electrode material; can be obtained by

In the above step (i), the Li ₃ PO ₄ particles obtained by the production method of the present invention contain an iron compound and a manganese compound, and a metal (M) compound (M is Mg, Al, Ti, Cu, Zn, one or more elements selected from Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd). After addition and mixing, it is subjected to a hydrothermal reaction to obtain a reaction mixture.

Iron compounds that can be used include divalent iron compounds and hydrates thereof. Examples include halides such as iron halides; sulfates such as iron sulfate; organic compounds such as iron oxalate and iron acetate; acid salts; and hydrates thereof. Among them, iron sulfate or a hydrate thereof is preferably used from the viewpoint of improving the physical properties of the battery or effectively utilizing the waste liquid obtained in the step (i) in the production method of the present invention.

Manganese compounds that can be used include divalent manganese compounds and hydrates thereof. Examples include halides such as manganese halides; sulfates such as manganese sulfate; organic acids such as manganese oxalate and manganese acetate; salts; and hydrates thereof. Among them, manganese sulfate or a hydrate thereof is preferably used from the viewpoint of improving the physical properties of the battery or effectively utilizing the waste liquid obtained in the step (i) as part of the solution X in the production method of the present invention. preferable.

As metal compounds other than iron compounds and manganese compounds, M (M is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, one or more elements selected from Ba, Pb, Bi, La, Ce, Nd, and Gd.), as well as iron compounds and manganese compounds, such as halides, sulfuric acid Salts, organic acid salts, hydrates thereof, and the like are included. Among them, from the viewpoint of improving the physical properties of the battery, it is preferable to use sulfates or hydrates thereof, and it is more preferable to use metal (M) sulfates in which M is Mg or Zr.

The molar ratio of the iron compound and the manganese compound (manganese compound:iron compound) is preferably 99:1 to 30:70, more preferably 95:5 to 40:60, still more preferably 90:10 to It is 50:50.

The Li ₃ PO ₄ particles obtained by the production method of the present invention are mixed with water to form a Li ₃ PO ₄ -containing mixture, to which a metal source such as a metal compound containing the iron compound and manganese compound is added and mixed. A mixture is prepared for hydrothermal reaction. The order of addition of such metal sources is not particularly limited.
Prior to mixing the Li ₃ PO ₄ -containing mixture with the metal source, it is preferred to previously stir the Li ₃ PO ₄ -containing mixture. The stirring time of the Li ₃ PO ₄ -containing mixture is preferably 1 minute to 10 minutes, more preferably 2 minutes to 8 minutes. By this stirring, a Li ₃ PO ₄ -containing mixture with ensured symmetry can be obtained.

A metal source is then added and mixed into the Li ₃ PO ₄ -containing mixture. Mixing of the metal source is performed while stirring the Li ₃ PO ₄ -containing mixture. The pH of such mixtures is preferably 3.5-8, more preferably 4-7. The total amount of these metal sources added is preferably 0.90 to 1.10 mol, more preferably 0.95 to 1.05 mol, per 1 mol of Li ₃ PO ₄ contained in the mixture. be.

The resulting mixture containing Li ₃ PO ₄ and metal source is subjected to a hydrothermal reaction. As a result, a compound that becomes an olivine-type lithium phosphate-based positive electrode material can be produced, and a reaction mixture containing the compound can be obtained. The amount of water used in producing the mixture containing Li ₃ PO ₄ and the metal source is determined from the viewpoint of the solubility of the metal source, the ease of stirring, the efficiency of synthesis, etc. It is preferably 10 to 90 mol, more preferably 20 to 70 mol, per 1 mol of Li ₃ PO ₄ .
Moreover, an antioxidant may be added to the mixture to be subjected to the hydrothermal reaction, if necessary. Examples of such antioxidants include sodium sulfite (Na ₂ SO ₃ ), sodium hydrosulfite (Na ₂ S ₂ O ₄ ), aqueous ammonia, and the like. The amount of the antioxidant added is preferably 0.1 to 1 mol of the metal source, from the viewpoint of preventing suppression of the production of the compound that becomes the olivine-type lithium phosphate-based positive electrode material due to excessive addition. 01 mol to 1 mol, more preferably 0.03 mol to 0.5 mol.

The hydrothermal reaction may be carried out at 100°C or higher, preferably from 130°C to 180°C. Such a hydrothermal reaction is preferably carried out in a pressure vessel, and when the reaction is carried out at 130° C. to 180° C., the pressure at this time is preferably 0.3 MPa to 0.9 MPa, and the reaction is carried out at 140° C. to 160° C. is preferably 0.3 MPa to 0.6 MPa. The hydrothermal reaction time is preferably 0.5 hours to 24 hours, more preferably 3 hours to 12 hours.

In the step (ii), a solution containing unreacted Li ions is separated from the reaction mixture containing the olivine-type lithium phosphate-based positive electrode material obtained in the step (i) to obtain an olivine-type lithium phosphate-based positive electrode material. is the process of obtaining As an apparatus used for so-called solid-liquid separation, which separates a solution containing unreacted Li ions from such a reaction mixture, the same apparatus as described above can be used, and from the viewpoint of efficiently obtaining a positive electrode material, a filter press It is preferred to use a machine.
Furthermore, it is preferable to wash the obtained positive electrode material with water. When washing the positive electrode material with water, it is preferable to use 3 to 20 parts by mass, more preferably 5 to 15 parts by mass, of water per 1 part by mass of the positive electrode material.
Since the washed water contains unreacted Li ions that have been washed away from the positive electrode material, the entire amount of the washed water is recovered and used as solution X in step (I) of the present invention together with the solution obtained by solid-liquid separation. can do. In order to efficiently collect the washing water, it is preferable to use a filter press for washing and solid-liquid separation. The recovered water obtained does not need to be contaminated with contaminants until it is used in step (I), and does not require a special storage environment. Moreover, for adjustment of the Li ion concentration in this recovered water, a dilution operation or a concentration operation can be performed by a general method.

The olivine-type lithium phosphate-based positive electrode material separated and recovered in step (ii) is dried if necessary. Drying means include spray drying, vacuum drying, freeze drying and the like.

The average particle size of such an olivine-type lithium phosphate positive electrode material is preferably 10 nm to 200 nm, more preferably 30 nm to 150 nm.

The obtained olivine-type lithium phosphate-based positive electrode material is preferably made into a positive electrode active material by supporting carbon and then firing. Carbon support is carried out by adding a carbon source such as glucose, fructose, polyethylene glycol, polyvinyl alcohol, carboxymethylcellulose, saccharose, starch, dextrin, citric acid, and water to an olivine-type lithium phosphate-based positive electrode material by a conventional method, followed by calcination. do it. The firing conditions are preferably 400° C. or higher, preferably 400° C. to 800° C., in an inert gas atmosphere or under reducing conditions for 10 minutes to 3 hours, preferably 0.5 hours to 1.5 hours. Through such treatment, a positive electrode active material in which carbon is supported on the particle surfaces of the positive electrode material can be obtained. The amount of the carbon source used is preferably 3 to 15 parts by mass as carbon contained in the carbon source, more preferably 5 to 10 parts by mass as carbon contained in the carbon source, with respect to 100 parts by mass of the positive electrode material.

In addition to the above treatment, as a treatment for supporting carbon on the surface of the particles, for example, a method of pulverizing/compositing/mixing the obtained mixture containing the obtained olivine-type lithium phosphate-based positive electrode material and the conductive carbon material. may be used. By performing such a treatment, a positive electrode active material in which the positive electrode material and the conductive carbon material are combined can be formed, and the conductivity can be further improved.

As the conductive carbon material used in the pulverization/compositing/mixing process, carbon black is preferable, and among them, acetylene black and ketjen black are more preferable. The amount of the conductive carbon material added is preferably 0.5 parts by mass to 15 parts by mass in terms of carbon atoms with respect to 100 parts by mass of the positive electrode material, from the viewpoint of good discharge capacity and economy, and 2 parts by mass. parts to 10 parts by mass is more preferable.

A mixture of the olivine-type lithium phosphate-based positive electrode material and the conductive carbon material is subjected to dry pulverization/compositing/mixing treatment. At this time, a small amount of diethylene glycol, ethanol, or the like may be added as an auxiliary agent.

As a device for pulverizing / compounding / mixing treatment, a normal ball mill may be used, but a planetary ball mill (manufactured by Fritsch Co., Ltd.) that can rotate and revolve is preferable. ), or a hybridizer (manufactured by Nara Machinery Co., Ltd.), as long as it can perform mechanochemical action/composite treatment on the object to be treated.

Containers used in planetary ball mills include those made of steel, stainless steel, or nylon, and inner walls made of alumina brick, magnetic material, natural silica stone, rubber, urethane, or the like. As the balls, alumina balls, natural silica stones, iron balls, zirconia balls and the like are used. The size of the ball is preferably 0.1 mm to 20 mm, more preferably 0.5 mm to 5 mm. The ball filling volume is preferably such that the ball filling volume accounts for 5 to 50% of the internal volume of the mill used.
Mixing using a planetary ball mill, for example, under the conditions of revolution 50 rpm to 800 rpm and rotation 100 rpm to 1,600 rpm, is preferably 5 minutes to 24 hours, more preferably 0.5 hours to 6 hours, and still more preferably 1 hour to 3 hours. conduct.

The positive electrode active material obtained by compounding carbon on the surface of the olivine-type lithium phosphate-based positive electrode material as described above is preferably heated at 500° C. to 800° C. for 10 minutes to 24 hours under an inert gas atmosphere or under reducing conditions. More preferably, it is fired at 600° C. to 700° C. for 0.5 hour to 3 hours. Through such treatment, a positive electrode active material in which carbon is further firmly supported on the surface of the positive electrode material can be obtained. The apparatus used for firing is not particularly limited as long as the firing atmosphere and temperature can be adjusted, and any of batch type, continuous type, and heating method (indirect or direct) can be used. . Examples of such devices include tubular electric furnaces such as externally heated kilns and roller hearths.

Next, a lithium ion secondary battery containing the obtained olivine-type lithium phosphate-based positive electrode material will be described.
A lithium-ion secondary battery to which such a positive electrode material can be applied is not particularly limited as long as it essentially comprises a positive electrode, a negative electrode, an electrolytic solution, and a separator.

Here, as for the negative electrode, as long as it can absorb lithium ions during charging and release lithium ions during discharging, the material composition is not particularly limited, and a known material composition can be used. Examples include carbon materials such as lithium metal, graphite, and amorphous carbon. It is preferable to use an electrode made of an intercalate material capable of electrochemically intercalating and deintercalating lithium, particularly a carbon material.

The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent that is usually used in the electrolytic solution of a lithium ion secondary battery. Examples include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, and lactones , oxolane compounds and the like can be used.

The type of supporting salt is not particularly limited, but inorganic salts selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , derivatives of the inorganic salts, LiSO ₃ CF ₃ , LiC(SO ₃ CF ₃ ) ₂ and LiN(SO ₃ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ and LiN(SO ₂ CF ₃ )(SO ₂ C ₄ F ₉ ), and derivatives of said organic salts. is preferably at least one of

The separator serves to electrically insulate the positive electrode and the negative electrode and retain the electrolyte. For example, a porous synthetic resin film, particularly a porous film of polyolefin polymer (polyethylene, polypropylene) may be used.

EXAMPLES The present invention will be specifically described below based on examples. In addition, unless otherwise indicated in the table, the content of each component indicates % by mass.

[Example 1]
Li ₃ PO ₄ particles Z ¹ were produced according to the conditions shown in Tables 1 and 2.
Specifically _, Li ² CO ₃ (manufactured by FMC Co., purity 99%) and 1.27 kg of sulfuric acid (manufactured by Kurita Co., Ltd., purity 95%) were added to mix liquid A ¹ (sulfuric acid per mole of Li ions in mixed liquid A ¹ ). content=0.57 mol, Li ion content=24000 mg/L, pH at 25° C.=3.9, temperature 30° C.). The resulting mixed solution A ¹ was stirred for 10 minutes, and then the mixed solution A ¹ was subjected to bubbling treatment with nitrogen for 30 minutes while stirring (total volume of nitrogen/volume of mixed solution A ¹ = 5) to obtain a mixed solution B ¹ (pH=3.9 at 25° C., temperature 25° C.) was obtained.
While dropping 4.29 kg of NaOH solution (manufactured by Kurita Co., Ltd., purity 48%) to the obtained mixed solution B ¹ (addition amount of Na ions per 1 mol of lithium ions in the mixed solution B ¹ = 1.4 mol, ) was stirred and mixed, and further stirred for 10 minutes to obtain a mixed solution C ¹ (pH at 25° C.=14, not measurable, temperature 45° C.).

Next, while stirring the mixed solution C ¹ , 1.60 kg of phosphoric acid (manufactured by Shimonoseki Mitsui Chemicals, Inc., 75%) (addition of H ₃ PO ₄ to ¹ mol of Li ions in the mixed solution C ¹ amount = 0.33 mol) (dripping rate = time required to drop the total amount of the phosphoric acid compound into the mixture C ¹ was 2 minutes) while stirring and mixing, and further stirring for 10 minutes to mix the mixture D ¹ (pH=12.5 at 25° C., temperature 50° C.) was obtained.
The obtained mixture D ¹ was filtered using a vacuum filter, and then the obtained solid content was washed with 10 parts by mass of water per 1 part by mass of the solid content to obtain a Li ₃ PO ₄ cake. After that, it was freeze-dried to obtain Li ₃ PO ₄ particles. The obtained Li ₃ PO ₄ particles had a BET specific surface area of 25 m ² /g, an average particle size (D ₅₀ ) of 6 μm, and a carbon content below the detection limit.
The obtained Li ₃ PO ₄ particles were a single phase exhibiting an X-ray diffraction pattern corresponding to the space group Pmnbs. The physical properties of the Li ₃ PO ₄ particles are shown in Table 3, and the X-ray diffraction pattern is shown in FIG.

[Example 2]
Under the conditions shown in Tables 1 and 2, 0.73 kg of Li ₂ CO ₃ and 1.16 kg of sulfuric acid were added to the solution X ¹ to obtain a mixed solution A ² (the ratio of sulfuric acid to 1 mol of Li ions in the mixed solution A ² ). Content = 0.54 mol, Li ion content = 24000 mg/L, pH at 25°C = 4.5, temperature 30°C), Li ₃ PO ₄ was prepared in the same manner as in Example 1. Particles were obtained.

[Example 3]
Stirring under the conditions shown in Tables 1 and 2 while adding 3.37 kg of NaOH solution dropwise to mixed solution B ¹ (addition amount of Na ions per 1 mol of lithium ions in mixed solution B ¹ = 1.1 mol) Li ₃ PO ₄ particles were obtained in the same manner as in Example 1, except that the mixture was mixed and further stirred for 10 minutes to obtain a mixed liquid C ³ (pH at 25° C.=13, temperature 40° C.).

[Example 4]
Under the conditions shown in Tables 1 and 2, while adding 1.68 kg of phosphoric acid (addition amount of H ₃ PO ₄ to 1 mol of Li ions in the mixed solution C ¹ =0.35 mol) dropwise to the mixed solution C ¹ . Li ₃ PO ₄ particles were obtained in the same manner as in Example 1, except that a mixture D ⁴ (pH=11.5 at 25° C., temperature 50° C.) was obtained by stirring and mixing for 10 minutes. Obtained.

[Comparative Example 1]
According to the conditions shown in Tables 1 and 2, 0.73 kg of Li ₂ CO ₃ and 1.01 kg of sulfuric acid were added to the solution X ¹ to prepare a mixed solution A ^x1 (the ratio of sulfuric acid to 1 mol of Li ions in the mixed solution A ^x1 ). Content = 0.50 mol, Li ion content = 24000 mg/L, pH at 25°C = 5.8, temperature 30°C), Li ₃ PO ₄ was prepared in the same manner as in Example 1. Particles were obtained.

[Comparative Example 2]
Stirring under the conditions shown in Tables 1 and 2 while dropping 2.76 kg of NaOH solution into mixed solution B ¹ (addition amount of Na ions per 1 mol of lithium ions in mixed solution B ¹ = 0.9 mol) Li ₃ PO ₄ particles were obtained in the same manner as in Example 1, except that the mixture was mixed and further stirred for 10 minutes to obtain a mixed liquid C ^x2 (pH=11 at 25° C., temperature 35° C.).

[Comparative Example 3]
0.73 kg of Li ₂ CO ₃ and 1.01 kg of sulfuric acid were added to the solution X ¹ to obtain a mixed solution A ^x3 (content of sulfuric acid per 1 mol of Li ions in the mixed solution A ^x3 = 0.50 mol, amount of Li ions content = 24000 mg / L, pH at 25 ° C. = 5.8, temperature 30 ° C.), and the mixture A ^x3 was bubbled with nitrogen (total volume of nitrogen / volume of the mixture A ^x1 = 5) for 30 minutes to give a mixture B ^x3 (pH=5.8 at 25° C., temperature 25° C.).
While 4.29 kg of NaOH solution was added dropwise to the obtained mixed solution B ^x3 (addition amount of Na ions per 1 mol of lithium ions in the mixed solution B ^x3 = 1.4 mol), the mixture was stirred and mixed, and further stirred for 10 minutes. A mixed solution C ^x3 (pH at 25° C.=14, not measurable, temperature 35° C.) was obtained.
Next, 1.83 kg of phosphoric acid (the amount of H ₃ PO ₄ added to 1 mol of Li ions in the mixed solution C ^x3 = 0.38 mol) of phosphoric acid was added dropwise to the mixed solution C ^x3 while stirring and mixing, followed by further stirring for 10 minutes. Li ₃ PO ₄ particles were obtained in the same manner as in Example 1 under the conditions shown in Tables 1 and 2, except that a mixed solution D ^x3 (pH at 25° C.=9, temperature 40° C.) was obtained. rice field.

[Comparative Example 4]
Example except that a mixture B ^x4 (pH at 25° C.=4.5, temperature 30° C.) was obtained according to the conditions shown in Tables 1 and 2 and without subjecting the mixture A ² to bubbling treatment with nitrogen. Li ₃ PO ₄ particles were obtained by the same operation as in 2.

[Comparative Example 5]
Under the conditions shown in Tables 1 and 2, 0.73 kg of Li ₂ CO ₃ and 1.01 kg of sulfuric acid were added to the solution X ¹ to obtain a mixed solution A ^x5 (the amount of sulfuric acid per mole of Li ions in the mixed solution A ^x5 ). content = 0.50 mol, Li ion content = 24000 mg / L, pH at 25 ° C. = 5.8, temperature 30 ° C.), and the mixture A ^x5 was mixed without bubbling with nitrogen. Li ₃ PO ₄ particles were obtained in the same manner as in Example 1 except that a liquid B ^x5 (pH=5.8 at 25° C., temperature 30° C.) was obtained.

<<Evaluation of charge/discharge characteristics>>
Using each Li ₃ PO ₄ particle shown in Table 3 as a raw material, an olivine-type lithium phosphate-based positive electrode material was produced by a conventional method to prepare a positive electrode for a lithium ion secondary battery. Specifically, an olivine-type lithium phosphate-based positive electrode material, acetylene black, and polyvinylidene fluoride were mixed at a weight ratio of 90:5:5, and N-methyl-2-pyrrolidone was added thereto and thoroughly kneaded. , to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of aluminum foil having a thickness of 20 μm using a coating machine, and vacuum-dried at 80° C. for 12 hours. After that, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.
Next, a coin-type lithium ion secondary battery was constructed using the above positive electrode. A lithium foil punched into a diameter of φ15 mm was used as the negative electrode. The electrolytic solution used was obtained by dissolving LiPF ₆ at a concentration of 1 mol/L in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1:1. A known separator such as a polymer porous film such as polypropylene was used. These battery parts were incorporated and housed in an atmosphere with a dew point of −50° C. or lower by a conventional method to produce a coin-type lithium ion secondary battery (CR-2032).
A charge/discharge test at a constant current density was performed using the manufactured lithium ion secondary battery. The charging conditions at this time were constant current charging with a current of 0.2 CA (34 mAh/g) and a voltage of 4.5V. The discharge conditions were a current of 0.2 CA or 3 CA, and a constant current discharge with a final voltage of 2.0V. All temperatures were 30°C.
Table 3 shows the results.

Claims (7)

A method for producing Li ₃ PO ₄ particles using a solution X discharged when an olivine-type lithium phosphate-based positive electrode material is obtained from a reaction mixture obtained by subjecting a raw material compound to a hydrothermal reaction,
The following steps (I)-(IV):
(I) Lithium carbonate and sulfuric acid, or lithium carbonate, lithium sulfate, and sulfuric acid are added to solution X having a lithium ion content of 1000 mg/L to 20000 mg/L, so that the lithium ion content is 5000 mg/L. Step of obtaining a mixed solution A having a concentration of up to 40000 mg/L and a sulfuric acid content of 0.52 mol to 1.00 mol per 1 mol of lithium ions (II) Injecting an inert gas into the obtained mixed solution A (III) The amount of alkali ions in the mixed solution B is 1.05 mol to 2.10 mol per 1 mol of lithium ions in the mixed solution B. A step of adding an alkali compound to obtain a mixed liquid C (IV) A step of adding a phosphoric acid compound to the obtained mixed liquid C to obtain a mixed liquid D, followed by solid-liquid separation to obtain Li ₃ PO ₄ particles. A method for producing _Li3PO4 particles for obtaining an olivine _- type lithium phosphate-based cathode material, comprising: 2. The method for producing Li ₃ PO ₄ particles according to claim 1, wherein the amount of the phosphoric acid compound added in step (IV) is 0.30 mol to 0.36 mol per 1 mol of lithium ions in the mixed liquid C. . _3. The method for producing _Li3PO4 particles according to claim 1 or 2, wherein the inert gas in the bubbling treatment of step (II) is nitrogen, argon, or helium. The total amount of inert gas blown in the bubbling treatment in step (II) is the ratio of the total volume of the blown inert gas to the volume of mixed liquid A (total volume of inert gas / volume of mixed liquid A), 0 .5 to 15. The method for producing Li ₃ PO ₄ particles according to any one of claims 1 to 3. The temperature of solution X used in step (I) is 5° C. to 25° C., the pH at 25° C. is 6 to 9, and the temperature of mixed solution C used in step (IV) is 40° C. to 80° C., 25 5. The method for producing Li ₃ PO ₄ particles according to any one of claims 1 to 4, wherein the pH is 12 to 14 at °C. _{Li3PO4 particles} have the formula _{( X} ) _{: LiaMnbFecMxPO4 (} where M is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr , Mo, Ba, Pb, Bi, La, Ce, Nd and Gd, a, b, c and x are 0<a≤1.2, 0.3 ≤ b ≤ 1.2, 0.2 ≤ c ≤ 1.2, and 0 ≤ x ≤ 0.3, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M The Li ₃ PO ₄ according to any one of claims 1 to 5, which is a particle for obtaining an olivine-type lithium phosphate-based positive electrode material represented by the number)×x=3. Particle production method. The solution X used in step (I) is subjected to the following steps (i)-(ii):
(i) Li ₃ PO ₄ particles containing an iron compound and a manganese compound, and a metal (M) compound (M is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr , Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd) are added and mixed, and subjected to a hydrothermal reaction. Step of obtaining a reaction mixture (ii) Separating a solution containing unreacted Li ions from the reaction mixture obtained in step (i) to obtain an olivine-type lithium phosphate-based positive electrode material of the formula (X ) is a solution containing unreacted Li ions separated in step ₍ ii) when the olivine _- type lithium phosphate-based positive electrode material represented by ) is obtained. Method.

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