JP2022135547A - METHOD FOR MANUFACTURING Li3PO4 PARTICLE FOR OBTAINING OLIVINE TYPE LITHIUM PHOSPHATE SYSTEM POSITIVE ELECTRODE MATERIAL - Google Patents

Abstract

To provide a manufacturing method for obtaining a raw material effective for manufacturing a high performance olivine type lithium phosphate system positive electrode material.SOLUTION: A manufacturing method for obtaining an olivine type lithium phosphate system positive electrode material is a method for manufacturing Li3 PO4 particles using a solution X that is exhausted when an olivine type lithium phosphate system positive electrode material is obtained from a reaction mixture in accordance with of a raw material compound with a hydrothermal reaction, the method including the following steps of (I) to (IV): (I) a step of obtaining 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 a mixture C to the mixture B to obtain a mixture D with a predetermined content of lithium and a predetermined content of an alkaline compound; and (IV) a step of obtaining Li3 PO4 particles by the solid-liquid separation of the obtained mixture D.SELECTED DRAWING: Figure 1

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, an alkali is added 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 substances are removed. and a step of adding a lithium source to the resulting solution to generate lithium phosphate. Ions are recovered as high-purity lithium phosphate.

JP 2020-47514 A

However, in the technique described in Patent Document 1, since the solution to which the lithium source is added has a high pH, part of the lithium source remains undissolved, and there is a possibility that the efficiency of lithium ion recovery cannot be sufficiently improved. There is In addition, the generated Li ₃ PO ₄ particles tend to have a coarse particle size, and there is a possibility that an excessive amount of time may be required to obtain such particles by solid-liquid separation.
As a result, the particle size of the positive electrode active material is also coarsened, and there is a risk that the lithium ion secondary battery manufactured using this material cannot exhibit good battery characteristics, and there is still 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. Li ₃ PO having a unique shape that makes it possible to improve the efficiency of solid-liquid separation by including a step of dropping a mixed solution containing a phosphoric acid compound and an alkali compound after performing a bubbling treatment with We found a manufacturing method that can obtain ₄ particles.

That is, the present invention is a method for producing Li ₃ PO ₄ particles using 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, comprising: Steps (I) to (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 30000 mg/L and a sulfuric acid content of 0.52 mol to 1.00 mol per 1 mol of lithium ions (II) Add an inert gas to the obtained mixed solution A (III) A mixed solution C containing a phosphoric acid compound and an alkaline compound is added dropwise to the obtained mixed solution B, and the content of lithium per 1 mol of phosphorus step of obtaining a mixture D in which the content is 2.7 mol to 3.3 mol and the content of the alkaline compound is 1.6 mol to 2.2 mol per 1 mol of sulfuric acid (IV) the obtained mixture The present invention provides a method for producing Li ₃ PO ₄ particles for obtaining an olivine-type lithium phosphate-based positive electrode material, comprising a step of solid-liquid separation of liquid D to obtain Li ₃ PO ₄ particles.

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. To easily produce Li ₃ PO ₄ particles containing many rod-shaped particles, which are peculiar to solid-liquid separation, while effectively reusing target lithium ion-containing waste liquid. be able to.
In this way, it is possible not only to obtain Li ₃ PO ₄ particles capable of improving the efficiency of solid-liquid separation while using lithium, which is a rare and valuable substance, without waste, but also to use such particles as a raw material to obtain favorable It is possible to obtain an olivine-type lithium phosphate-based positive electrode material that also enables expression of battery characteristics.

1 shows an SEM image of Li ₃ PO ₄ particles obtained in Example 1. FIG. 4 shows an SEM image of Li ₃ PO ₄ particles obtained in Comparative Example 2. 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 30000 mg/L and a sulfuric acid content of 0.52 mol to 1.00 mol per 1 mol of lithium ions (II) Add an inert gas to the obtained mixed solution A (III) A mixed solution C containing a phosphoric acid compound and an alkaline compound is added dropwise to the obtained mixed solution B, and the content of lithium per 1 mol of phosphorus step of obtaining a mixture D in which the content is 2.7 mol to 3.3 mol and the content of the alkaline compound is 1.6 mol to 2.2 mol per 1 mol of sulfuric acid (IV) the obtained mixture A step of solid-liquid separating the liquid D to obtain Li ₃ PO ₄ particles is provided.

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 0.4≦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. , a step of obtaining a mixed solution A having a lithium ion content of 5000 mg/L to 30000 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.
The temperature of solution X is preferably 5°C to 25°C, more preferably 10°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 30000 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 the removal of dissolved carbonic acid from the solution, and it is possible to improve the efficiency of solid-liquid separation containing many rod-shaped particles. Li ₃ PO ₄ particles having a unique shape can be obtained. 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 unique shape 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 liquid mixture A obtained in step (I) is 5000 mg/L to 30000 mg/L, preferably 7500 mg/L to 27500 mg/L, from the viewpoint of increasing the productivity of Li ₃ PO ₄ particles. L, more preferably 10000 mg/L to 25000 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 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 50°C, more preferably 30°C to 50°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 effectively removed. Therefore, it is possible to efficiently obtain Li ₃ PO ₄ particles having a unique shape that can improve the efficiency of solid-liquid separation while simplifying the manufacturing process.

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 to 5, and still more preferably 1.5. 5-5.
The temperature of the mixed liquid B is preferably 20°C or higher, more preferably 25°C to 50°C.

In the production method of the present invention, as step (III), a mixture C containing a phosphoric acid compound and an alkali compound is added dropwise to the mixture B obtained in step (II), and the lithium content is 1 mol of phosphorus. 2.7 mol to 3.3 mol per 1 mol of sulfuric acid, and the content of the alkaline compound is 1.6 mol to 2.2 mol per 1 mol of sulfuric acid. That is, in the present invention, in step (I), lithium carbonate or lithium sulfate and sulfuric acid are added without adding a phosphoric acid compound, while in step (III), a mixed solution C containing a phosphoric acid compound is added dropwise. .

In this way, by dropping the mixed liquid C containing the alkaline compound together with the phosphoric acid compound, the acidic mixed liquid B is neutralized while the Li ions and PO ₄ ions in the mixed liquid appropriately generate Li ₃ PO ₄ . By controlling the particle nucleation reaction, it is possible to form Li ₃ PO ₄ particles having a unique shape, which includes many rod-shaped particles and which can improve the efficiency of solid-liquid separation. Also, it is possible to prevent the Li ₃ PO ₄ particles from being degraded in purity or contaminated by impurities such as SO ₄ ^2- ions in the solution X used in step (I).

Mixed liquid C dropped into mixed liquid B contains a phosphoric acid compound and an alkali compound.
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 enabling an appropriate nucleation reaction for obtaining Li ₃ PO ₄ particles exhibiting a unique shape, it is preferably used as an aqueous solution having a concentration of 40 to 90% by mass. .
Examples of the alkali compound 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.

The content of the phosphoric acid compound in the mixture C may be such that the phosphorus content in the mixture C is 10000 ppm to 60000 ppm, more preferably 15000 ppm to 55000 ppm.
The content of the alkaline compound in the mixed solution C may be an amount such that the alkaline compound is 2.7 mol to 3.6 mol per 1 mol of phosphoric acid in the mixed solution C, and is 2.9 mol to 3.5 mol. It is more preferable if the amount becomes 3 mol.

In preparing such a mixed solution C, specifically, from the viewpoint of inhibiting the precipitation of alkali phosphate due to the buffering action, it is preferable to add the alkali solution dropwise to the phosphate compound and then stir the mixture.
The dropping rate of the alkaline solution is preferably 2 minutes to 50 minutes, more preferably 5 minutes to 30 minutes, in terms of the time required to drop the total amount of the alkaline solution onto the phosphoric acid compound. In addition, it is preferable to stir the phosphoric acid compound while dropping the alkaline solution.
The stirring time of the phosphoric acid compound when dropping the alkaline solution is preferably 5 minutes to 120 minutes, more preferably 10 minutes to 60 minutes.

The temperature of the mixed liquid C is preferably 40°C to 70°C, more preferably 45°C to 65°C.
The pH of the mixture C at 25° C. is preferably 12-14, more preferably 12-13.5, still more preferably 12-13.

Next, in step (III), the obtained mixed liquid C is added dropwise to the mixed liquid B to obtain a mixed liquid D. By dropping the mixed liquid C containing the phosphoric acid compound and the alkali compound into the mixed liquid B, the nucleation reaction of the Li ₃ PO ₄ particles is appropriately controlled, the purity is high, and the efficiency of solid-liquid separation is improved. Li ₃ PO ₄ particles exhibiting a unique shape that can be produced can be efficiently produced.

From the viewpoint of appropriately controlling the nucleation reaction of the Li ₃ PO ₄ particles exhibiting a unique shape, the dropping rate of the mixed liquid C is preferably in terms of the time required to drop the entire amount of the mixed liquid C into the mixed liquid B. is 10 to 100 minutes, more preferably 10 to 30 minutes. In addition, it is preferable to stir the mixed liquid B while the mixed liquid C is dripped.
Further, after the mixed liquid C is added dropwise to the mixed liquid B, it is preferable to stir. Specifically, the stirring time is preferably 10 minutes to 60 minutes, more preferably 10 minutes to 30 minutes. .

The content of lithium in the mixed solution D is 2.7 mol to 3.3 mol, preferably 2.7 mol to 3.2 mol, more preferably 1 mol of phosphorus in the mixed solution D. is 2.7 mol to 3.1 mol.
The content of the alkali compound in the mixed solution D is 1.6 mol to 2.2 mol, preferably 1.7 mol to 2.1 mol, per 1 mol of sulfuric acid in the mixed solution D, and more It is preferably 1.8 mol to 2.0 mol.
The mixture C containing the phosphoric acid compound and the alkali compound may be added dropwise to the mixture B so that the content of lithium and the content of the alkali compound in the mixture D are such amounts.

The temperature of the mixture D obtained in step (III) is preferably 30°C to 70°C, more preferably 40°C to 60°C.
The pH of the mixture D at 25° C. is preferably 9-12, more preferably 9-11.5.

The production method of the present invention includes, as step (IV), a step of solid-liquid separation of the mixture D obtained in step (III) to obtain Li ₃ PO ₄ particles. In the mixed solution D, Li ₃ PO ₄ particles having a high purity and a peculiar shape that can improve the efficiency of solid-liquid separation are precipitated. Just do it. 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 production method of the present invention appropriately controls the nucleation reaction of Li ₃ PO ₄ particles and produces fine Li ₃ PO 4 containing many particles exhibiting a unique shape, that is, a rod shape, which can improve the efficiency of solid-liquid separation. ₄ particles can be obtained, and such Li ₃ PO ₄ particles exhibit high filterability that can effectively reduce the amount of water used for washing, so it is possible to shorten the washing time and solid-liquid separation. efficiency can be effectively achieved. In addition, since the Li ₃ PO ₄ particles obtained by the production method of the present invention can exhibit good battery characteristics, they are useful raw materials for producing high-performance olivine-type lithium phosphate-based positive electrode materials.

Specifically, the average aspect ratio of the obtained Li ₃ PO ₄ particles is preferably 3 to 6, more preferably 3 to 5.5, from the viewpoint of containing many rod-shaped particles and enhancing filterability. Yes, more preferably 3-5.
The average aspect ratio of the Li ₃ PO ₄ particles is defined as the maximum span length in the major axis direction and the maximum span length in the direction perpendicular to the major axis direction of arbitrarily extracted 200 Li ₃ PO ₄ particles. is measured and the average value thereof is obtained, and the ratio of the length of the long side to the length of the short side is defined as the aspect ratio, and the average value is meant.

The average particle size (D ₅₀ ) of the obtained Li ₃ PO ₄ particles is preferably 1 μm to 20 μm, more preferably 4 μm to 20 μm, still more preferably 7 μm to 20 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.
The BET specific surface area of the obtained Li ₃ PO ₄ particles is preferably 1 m ² /g or more, more preferably 3 m ² /g or more, and preferably 15 m ² / or less.

Li ₃ PO ₄ particles obtained by the production method of the present invention contain lithium carbonate and sulfuric acid, which were not sufficiently dissolved in the step (I), from the viewpoint of making it possible to impart a unique shape and make the particles finer. It is preferable that no carbon derived from lithium 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, but the present invention is not limited to these examples.

[Example 1]
Li ₃ PO ₄ particles were produced according to the conditions shown in Tables 1 and 2.
Specifically, Li ₂ CO ₃ was added to 10 L of solution X ¹ having a lithium ion content of 10000 mg/L and a sulfate ion content of 69000 mg/L (pH=7.2 at 25° C., temperature 20° C.). (manufactured by FMC Co., purity 99%) and 0.98 kg of sulfuric acid (manufactured by Kurita Co., Ltd., purity 95%) were added to obtain a mixture A ¹ (the ratio of sulfuric acid to 1 mol of Li ions in the mixture A ¹ ). content = 0.55 mol, Li ion content = 20000 mg/L, pH at 25°C = 4.2, 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 = 4) to obtain mixed solution B. ¹ (pH=4.2 at 25° C., temperature 25° C.) was obtained.
Separately, 5 L of water and 1.35 kg of phosphoric acid (manufactured by Shimonoseki Mitsui Chemicals, Inc., 75%) were mixed, and then 2.75 kg of NaOH solution (manufactured by Kurita Co., Ltd., purity 48%) was added dropwise while stirring and mixing. , and further stirred for 10 minutes to obtain a mixed solution C ¹ (NaOH content per 1 mol of phosphoric acid=3.2 mol, pH at 25° C.=13, temperature 60° C.).

Next, while dropping the mixed liquid C ¹ into the mixed liquid B ¹ (dropping speed = the time required to drop the entire amount of the mixed liquid C ¹ into the mixed liquid B ¹ is 12.5 minutes). After stirring for a minute, a mixed solution D ¹ (Li content per ¹ mol of P = 2.94 mol, NaOH content per 1 mol of sulfuric acid = 2.0 mol) was obtained. The particle size distribution D ₅₀ of the Li ₃ PO ₄ aggregates contained in the mixture D ¹ was 9 μm.
10 L of the resulting mixture D ¹ was filtered using a vacuum filter to remove the filtrate. Next, 500 ml of washing water was added to the obtained solid content, and the time until filtration was completed was measured. The conductivity of the filtrate after filtration was measured and then collected in another container. This washing operation was repeated until the conductivity of the filtrate after filtration became 8 mS/cm or less.
After washing, the resulting Li ₃ PO ₄ cake was lyophilized to obtain Li ₃ PO ₄ particles. The carbon content of the obtained Li ₃ PO ₄ particles Z ¹ was 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. FIG. 1 shows an SEM image of the obtained Li ₃ PO ₄ particles, and Table 3 shows the physical properties of the Li ₃ PO ₄ particles.

[Example 2]
According to the conditions shown in Tables 1 and 2, 0.59 kg of Li ₂ CO ₃ and 0.88 kg of sulfuric acid were added to 10 L of solution X ¹ (pH at 25° C.=7.2, temperature of 20° C.) to form a mixed solution. A ² (sulfuric acid content per 1 mol of Li ions in mixed solution A ² =0.52 mol, pH at 25°C = 4.8, temperature 30°C) was prepared in the same manner as in Example 1. to obtain Li ₃ PO ₄ particles.

[Example 3]
According to the conditions shown in Tables 1 and 2, 5 L of water and 1.41 kg of phosphoric acid were mixed, followed by stirring and mixing while dropping 2.75 kg of NaOH solution, and then stirring for 10 minutes to obtain a mixed solution C ³ ( Li ₃ PO ₄ particles were obtained in the same manner as in Example 1 except that the content of NaOH to 1 mol of phosphoric acid=3.05 mol, pH at 25° C.=12, and temperature of 60° C.).

[Example 4]
According to the conditions shown in Tables 1 and 2, 5 L of water and 1.35 kg of phosphoric acid were mixed, followed by stirring and mixing while dropping 2.49 kg of NaOH solution, and then stirring for 10 minutes to obtain a mixed solution C ⁴ ( Li ₃ PO ₄ particles were obtained in the same manner as in Example 1, except that the content of NaOH to 1 mol of phosphoric acid=2.9 mol, pH at 25° C.=12, and temperature of 55° C.).

[Comparative Example 1]
Without preparing the mixed solution C containing the phosphoric acid compound and the alkaline compound in advance, the alkaline compound and the phosphoric acid compound are sequentially added to the mixed solution B to prepare the mixed solution D under the conditions shown in Tables 1 and 2. Li ₃ PO ₄ particles were obtained according to
Specifically _, Li ² CO ₃ (manufactured by FMC, purity 99%) 0.73 kg and sulfuric acid (manufactured by Kurita Co., Ltd., purity 95%) 1.27 kg were added to mix liquid A ^x1 (the amount of sulfuric acid per mole of Li ions in the mixed liquid A ^x1 ). content=0.57 mol, Li ion content=24000 mg/L, pH at 25° C.=3.9, temperature 30° C.). The obtained mixed solution A ^x1 was stirred for 10 minutes, and then the mixed solution A ^x1 was subjected to bubbling treatment with nitrogen for 30 minutes while stirring (total volume of nitrogen/volume of mixed solution A ¹ = 5), and mixed solution B ^x1 (pH=3.9 at 25°C, temperature 25°C) was obtained.
While 4.29 kg of NaOH solution (manufactured by Kurita Co., Ltd., purity 48%) was added dropwise to the obtained mixed solution B ^x1 (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 liquid C ^x1 (pH at 25° C.=14, not measurable, temperature 45° C.).

Next, while stirring the mixed solution C ^x1 , 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) was added dropwise and stirred and mixed, and further stirred for 10 minutes to obtain a mixed solution D ^x1 (pH at 25°C = 12.5, temperature 50°C).
Li ₃ PO ₄ particles were obtained in the same manner as in Example 1 from the resulting mixture D ^x1 .

[Comparative Example 2]
According to the conditions shown in Tables 1 and 2, 0.59 kg of Li ₂ CO ₃ and 0.82 kg of sulfuric acid were added to 10 L of solution X ¹ (pH at 25° C.=7.2, temperature of 20° C.) to form a mixed solution. The same operation as in Example 1 was performed except that A ^x2 (content of sulfuric acid per 1 mol of Li ions in mixed solution A ^x2 = 0.50 mol, pH at 25 ° C. = 5.8, temperature 30 ° C.) was prepared. to obtain Li ₃ PO ₄ particles.

[Comparative Example 3]
Li ₃ PO ₄ particles were obtained in the same manner as in Example 1 except that the conditions shown in Tables 1 and 2 were followed and the mixture A ¹ was not subjected to nitrogen bubbling.

[Comparative Example 4]
According to the conditions shown in Tables 1 and 2, 5 L of water and 1.65 kg of phosphoric acid were mixed, and then stirred and mixed while dropping 2.74 kg of NaOH solution, and then stirred for 10 minutes to obtain a mixed solution C ^x4 ( Li ₃ PO ₄ particles were obtained in the same manner as in Example 1 except that the content of NaOH to 1 mol of phosphoric acid=2.6 mol, pH at 25° C.=11, and temperature of 60° C.).

[Comparative Example 5]
According to the conditions shown in Tables 1 and 2, 5 L of water and 1.35 kg of phosphoric acid were mixed, and then ^1.98 kg of NaOH solution was added dropwise while stirring and mixing, and then stirred for another 10 minutes. Li ₃ PO ₄ particles were obtained in the same manner as in Example 1 except that the content of NaOH to 1 mol of phosphoric acid=2.3 mol, pH at 25° C.=11, and temperature of 50° C.).

<< _{Filterability} evaluation of _Li3PO4 particles>>
Measurement of Filtration Time 10 L of the mixture D obtained in each step was sampled, and the time required for solid-liquid separation into cake and filtrate by suction filtration was measured. The obtained filtrate was removed.

- Measurement of amount of washing water After 500 ml of water was added to the cake obtained when measuring the filtration time, suction filtration was performed to obtain a filtrate. The conductivity of the resulting filtrate was then measured. After measuring the electrical conductivity, the filtrate was removed and the whole amount of the filtrate was stored in another container.
The above operation was repeated until the electrical conductivity became 8 mS/cm or less, and the amount of washing water used until the conductivity became 8 mS/cm or less was measured and used as the washing water amount.

Amount of phosphorus eluted during washing The amount of P in the filtrate collected in another container was quantified using an ICP emission spectrometer (ULTIMA2, manufactured by Horiba, Ltd.). It should be noted that the smaller the amount, the better the cleaning efficiency.

<<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, including the physical properties of each Li ₃ PO ₄ particle and the conditions of the filtration treatment applied to obtain such particles.

Claims (8)

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 30000 mg/L and a sulfuric acid content of 0.52 mol to 1.00 mol per 1 mol of lithium ions (II) Add an inert gas to the obtained mixed solution A (III) A mixed solution C containing a phosphoric acid compound and an alkaline compound is added dropwise to the obtained mixed solution B, and the content of lithium per 1 mol of phosphorus step of obtaining a mixture D in which the content is 2.7 mol to 3.3 mol and the content of the alkaline compound is 1.6 mol to 2.2 mol per 1 mol of sulfuric acid (IV) the obtained mixture A method for producing Li _{3 PO 4 particles for obtaining an olivine-type lithium phosphate-based positive electrode material, comprising the step of subjecting liquid D to solid-liquid separation to obtain Li 3 PO 4 particles .} The production of Li ₃ PO ₄ particles according to claim 1, wherein the dropping speed of the mixed liquid C in the step (III) is 10 minutes to 100 minutes in terms of the time required to drop the whole amount of the mixed liquid C into the mixed liquid B. Method. _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 solid-liquid separation of step (IV) is carried out using a filter press, a centrifugal filter, or a vacuum filter, and the Li ₃ PO ₄ particles obtained have an average aspect ratio of 3-6. A method for producing Li ₃ PO ₄ particles according to any one of claims 1 to 3. 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 4. Claims 1 to 3, wherein the mixed solution C used in step (III) has a phosphorus content of 10000 ppm to 60000 ppm and an alkali compound content of 2.7 mol to 3.6 mol per 1 mol of phosphoric acid. 6. The method for producing Li ₃ PO ₄ particles according to any one of 5. _{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 6, 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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