JP2022135548A - Production method for olivine-type lithium phosphate-based positive electrode active material - Google Patents

Abstract

To provide a production method for olivine-type lithium phosphate-based positive electrode active material which can express excellent battery characteristics while materializing sufficient improvement of the efficiency of a production process by using a low-temperature synthesis reaction by microwave irradiation.SOLUTION: A production method for an olivine-type lithium phosphate-based positive electrode active material represented by LiaMnbFecMxPO4 comprises a step (I) of adding alkaline compound solution to mixed solution of a phosphoric acid compound (a), one or more acid compounds (b) selected from sulfuric acid, hydrochloric acid and nitric acid, a lithium compound (c) and water (d1), thereby obtaining slurry I, then performing solid-liquid separation on the slurry I thereby obtaining trilithium phosphate particles A having a BET specific surface area of 10 m2/g to 200 m2/g, and a step (II) of mixing the obtained trilithium phosphate particles A, and water (d2) thereby obtaining slurry II1, then adding a metal compound (e) including a manganese compound and/or an iron compound to the slurry II1 thereby obtaining slurry II2, then irradiating the slurry II2 with microwaves at 80°C to 120°C thereby obtaining a positive electrode active material precursor.SELECTED DRAWING: None

Description

The present invention relates to a method for producing an olivine-type lithium phosphate-based positive electrode active 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. So-called olivine-type lithium phosphate-based positive electrode active materials, such as lithium manganese phosphate and lithium iron phosphate having an olivine-type structure, are known as one of the positive electrode materials that constitute such batteries, and many of them have a withstand voltage. It is manufactured by a hydrothermal synthesis reaction that requires steam blowing and heating along with the use of a vessel.

Under these circumstances, in order to improve the efficiency of the manufacturing process of the olivine-type lithium phosphate-based positive electrode active material, a manufacturing method using a synthesis reaction by microwave irradiation instead of the hydrothermal synthesis reaction has been developed. For example, Patent Document 1 describes a solid mixture containing a transition metal-containing compound, a phosphoric acid-containing compound, and a lithium-containing compound having a Li:Fe:P molar ratio of approximately 1:1:1. A method of making lithium transition metal phosphates by microwave irradiation is disclosed. Further, in Patent Document 2, liquid-phase high-speed synthesis of an olivine-type compound is performed by subjecting a liquid raw material consisting of a Li source raw material, a P source raw material, a metal source raw material, and a solvent to a low-temperature short-time reaction treatment in a reaction zone irradiated with microwaves. A method is disclosed.

JP 2016-52996 A JP 2013-163618 A

However, even with the technique described in the above patent document, the temperature cannot be sufficiently lowered when irradiating microwaves, and nucleation and grain growth proceed simultaneously, making it difficult to control the grain size of the positive electrode active material. Since this tends to be difficult, there is still room for improvement in producing a positive electrode active material capable of sufficiently improving battery characteristics while improving the efficiency of the production process.

Therefore, an object of the present invention is to provide an olivine-type lithium phosphate-based positive electrode that can exhibit excellent battery characteristics while sufficiently improving the efficiency of the manufacturing process by using a low-temperature synthesis reaction by microwave irradiation. An object of the present invention is to provide a method for producing an active material.

Therefore, as a result of intensive studies to solve the above problems, the present inventors have found that by applying microwave irradiation using trilithium phosphate (Li ₃ PO ₄ ) particles, compared to general hydrothermal synthesis reactions found that it is possible to stably produce an olivine-type lithium phosphate-based positive electrode active material that can sufficiently improve battery characteristics while enabling treatment at low temperatures.

That is, the present invention provides the following formula (X):
_{LiaMnbFecMxPO4 ( X ) _}
(In formula (X), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd a, b, c, and x satisfy 0<a≦1.2, 0≦b≦1.2, 0≦c≦1.2, 0≦x≦0.3, and b+c≠0; In addition, a number that satisfies a + (valence of Mn) x b + (valence of Fe) x c + (valence of M) x = 3.)
A method for producing an olivine-type lithium phosphate-based positive electrode active material represented by the following steps (I) to (II):
(I) A mixture obtained by mixing a phosphoric acid compound (a), one or more acid compounds (b) selected from sulfuric acid, hydrochloric acid and nitric acid, a lithium compound (c), and water (d1) After adding an alkaline compound solution to liquid i to obtain slurry I, the obtained slurry I is subjected to solid-liquid separation to obtain trilithium phosphate particles A having a BET specific surface area of 10 m ² /g to 200 m ² /g. (II) The obtained trilithium phosphate particles A and water (d2) are mixed to prepare slurry II ¹ , and then slurry II ¹ contains a metal compound (e ) to obtain a slurry II ² , and then irradiate microwaves at a temperature of 80° C. to 120° C. to obtain a positive electrode active material precursor. It provides

According to the production method of the present invention, the production process can be made more efficient by irradiating microwaves in a sufficiently low temperature range while controlling the physical properties of the trilithium phosphate particles to be used. is obtained, and it is also possible to easily control the particle diameter of the olivine-type lithium phosphate-based positive electrode active material obtained from this, and an olivine-type lithium phosphate-based positive electrode that can effectively improve battery characteristics. An active material can be stably produced.

The present invention will be described in detail below.
The method for producing the olivine-type lithium phosphate-based positive electrode active material of the present invention comprises the following formula (X):
_{LiaMnbFecMxPO4 ( X ) _}
(In formula (X), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd a, b, c, and x satisfy 0<a≦1.2, 0≦b≦1.2, 0≦c≦1.2, 0≦x≦0.3, and b+c≠0; In addition, a number that satisfies a + (valence of Mn) x b + (valence of Fe) x c + (valence of M) x = 3.)
A method for producing an olivine-type lithium phosphate-based positive electrode active material represented by the following steps (I) to (II):
(I) A mixture obtained by mixing a phosphoric acid compound (a), one or more acid compounds (b) selected from sulfuric acid, hydrochloric acid and nitric acid, a lithium compound (c), and water (d1) After adding an alkaline compound solution to liquid i to obtain slurry I, the obtained slurry I is subjected to solid-liquid separation to obtain trilithium phosphate particles A having a BET specific surface area of 10 m ² /g to 200 m ² /g. (II) The obtained trilithium phosphate particles A and water (d2) are mixed to prepare slurry II ¹ , and then slurry II ¹ contains a metal compound (e ) to obtain a slurry II ² , and then irradiate microwaves at a temperature of 80° C. to 120° C. to obtain a positive electrode active material precursor.

The olivine-type lithium phosphate-based positive electrode active material obtained by the production method of the present invention has the following formula (X):
_{LiaMnbFecMxPO4 ( X ) _}
(In formula (X), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd a, b, c, and x satisfy 0<a≦1.2, 0≦b≦1.2, 0≦c≦1.2, 0≦x≦0.3, and b+c≠0; In addition, a number that satisfies a + (valence of Mn) x b + (valence of Fe) x c + (valence of M) x = 3.)
is represented by
That is, in the present invention, by using the trilithium phosphate (Li ₃ PO ₄ ) particles A having a BET specific surface area within a limited range obtained in the step (I), the reaction proceeds with the particles A as nuclei. Therefore, grain growth can be moderately moderated. Then, in the subsequent step (II), if a positive electrode active material precursor obtained by irradiating microwaves at a sufficiently low temperature is used, excessive grain growth can be suppressed, resulting in excellent battery characteristics. It is possible to obtain an olivine-type lithium phosphate-based positive electrode active material. In this way, it is possible to stably produce a highly useful olivine-type lithium phosphate-based positive electrode active material while making it possible to improve the efficiency of the production process.

The olivine-type lithium phosphate-based positive electrode active material represented by the formula (X) is an olivine-type lithium phosphate-based positive electrode active material containing at least manganese (Mn) or iron (Fe) (hereinafter, “particles (X)” (also called secondary particles), which are secondary particles formed by agglomeration of primary particles. In formula (X), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. , preferably Mg or Zr. a is 0<a≤1.2, preferably 0.6≤a≤1.2, more preferably 0.65≤a≤1.15, still more preferably 0.7≤ a≤1.1. b is 0≤b≤1.2, preferably 0.25≤b≤0.8, more preferably 0.35≤b≤0.8. c is 0≤c≤1.2, preferably 0.2≤c≤0.75, more preferably 0.2≤c≤0.65. These b and c satisfy b+c≠0. x is 0≤x≤0.3, preferably 0≤x≤0.15, more preferably 0≤x≤0.1. These a, b, c, and x are numbers satisfying a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3.
More specifically, the olivine-type lithium phosphate-based positive electrode active material represented by the formula ₍ X ₎ includes, for example, _LiMnPO4 , _LiFePO4 , _{LiMn0.8Fe0.2PO4} , _{LiMn0.1Fe0.9PO4 ,} and _{LiMn0.8 . Fe0.1Mg0.1PO4 , LiMn0.8Fe0.1Zr0.05PO4 , and the like} .

The step (I) provided in the production method of the present invention includes a phosphoric acid compound (a) and one or more acid compounds (b) selected from sulfuric acid, hydrochloric acid and nitric acid (hereinafter referred to as "acid compound (b)"). Also abbreviated), a lithium compound (c), and water (d1) are mixed to obtain a mixed liquid i, an alkaline compound solution is added to obtain a slurry I, and then the obtained slurry I is subjected to solid-liquid separation. to obtain trilithium phosphate particles A having a BET specific surface area of 10 m ² /g to 200 m ² /g.

Usable phosphoric acid compounds (a) 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, it is preferable to use phosphoric acid, and it is more preferable to use it as an aqueous solution having a concentration of 70 to 90% by mass.

The acid compound (b) that can be used is one or more selected from sulfuric acid, hydrochloric acid and nitric acid, and has the effect of improving the pH environment of the mixed liquid I and increasing the solubility of the lithium compound (c). . Among them, from the viewpoint of increasing the solubility of the lithium compound (c), it is preferable to use sulfuric acid, and it is more preferable to use concentrated sulfuric acid having a concentration of 95% by mass or more.

Lithium compounds (c) that can be used include lithium hydroxide (eg, LiOH.H ₂ O), lithium carbonate (eg, Li ₂ CO ₃ ), lithium sulfate, lithium acetate, and hydrates thereof. Among them, lithium carbonate is preferable from the viewpoint of controlling the BET specific surface area of the trilithium phosphate particles A within a desired range, and from the viewpoint of improving the efficiency of the manufacturing process and reducing the manufacturing cost.

The amount of water (d1) to be mixed is determined based on the phosphorus contained in the phosphate compound (a) from the viewpoint of ensuring the solubility or dispersibility of each component, and from the viewpoint of increasing the production efficiency of the trilithium phosphate particles A. The amount is preferably 6 to 25 mol, more preferably 8 to 18 mol, per 1 mol.

After the phosphate compound (a), acid compound (b), lithium compound (c), and water (d1) are mixed in advance to obtain a mixture i, the mixture i is treated with an alkali as described later. Slurry I may be obtained by adding a compound solution.
In the resulting mixed solution i, the ratio of the molar amount of lithium contained in the lithium compound (c) to the molar amount of phosphorus contained in the phosphoric acid compound (a) (lithium:phosphorus) is preferably 2.5: 1 to 3.2:1, more preferably 2.6:1 to 3.1:1, still more preferably 2.8:1 to 3.05:1.
The phosphoric acid compound (a), the acid compound (b), the lithium compound (c), and water (d1) are mixed in amounts that provide such a quantitative relationship to prepare a mixed solution i. Then, as will be described later, an alkaline compound solution is added to the mixed liquid i to obtain a slurry I.

The order of mixing the phosphoric acid compound (a), the acid compound (b), the lithium compound (c), and the water (d1) is not particularly limited, but from the viewpoint of ensuring the solubility or dispersibility of each component. Therefore, it is preferable to mix the phosphoric acid compound (a), the acid compound (b), and the water (d1), and then add and mix the lithium compound (c) to the resulting mixture.

Next, an alkaline compound solution is added to the obtained mixed liquid i. Thereby, the BET specific surface area of the trilithium phosphate particles A can be controlled. The alkali compound solution that can be used includes an aqueous solution containing sodium hydroxide or an aqueous solution containing potassium hydroxide.

When adding the alkaline compound solution, it is preferable to drop the alkaline compound solution into the mixed liquid i. At this time, the dropping rate of the alkaline compound solution is preferably 0.03 mol/min to 4 mol/min, and more preferably, based on the molar amount of the alkaline compound contained in the alkaline compound solution dropped into the mixture i. is 0.04 mol/min to 3 mol/min.

The pH of the obtained slurry I at 25° C. is preferably from −1 to 3, more preferably -1 to 2.5, even more preferably -1 to 2.0.

Next, the resulting slurry I is subjected to solid-liquid separation and precipitated and collected to obtain trilithium phosphate particles A in high yield. Apparatuses used for solid-liquid separation include, for example, a Buchner funnel, a filter press, a centrifugal filter, a vacuum filter and the like. Among them, it is preferable to use a Buchner funnel or a filter press from the viewpoint of obtaining Li ₃ PO ₄ particles efficiently.

It is preferable to isolate trilithium phosphate particles A by filtering the resulting precipitate after further washing with water to obtain a cake. The amount of water used in washing is preferably 50 to 2000 parts by mass, more preferably 100 to 1500 parts by mass, per 1 part by mass of the trilithium phosphate particles A. In addition, you may dry after that. Such drying means include vacuum drying, spray drying, box drying, fluidized bed drying, external heat drying, and freeze drying. Among them, box type drying is preferable.

The BET specific surface area of the obtained trilithium phosphate particles A is 10 m ² /g to 200 m ² /g, preferably 13 m ² from the viewpoint of achieving excellent battery characteristics while improving the efficiency of the production process. /g to 180 m ² /g, more preferably 15 m ² /g to 150 m ² /g. The BET specific surface area of the trilithium phosphate particles A means a value obtained from an adsorption isotherm by a nitrogen adsorption method.

The average particle diameter (D ₅₀ ) of the trilithium phosphate particles A is preferably 1.0 μm to 12 μm, more preferably 1.5 μm to 12.0 μm, still more preferably 2.0 μm to 12.0 μm. 0 μm. The "average particle size" in the trilithium phosphate particles A means the _D50 value (particle size (median diameter) at 50% cumulative) obtained from a volume-based particle size distribution based on a laser diffraction/scattering method. do.

In (II) provided in the production method of the present invention, the trilithium phosphate particles A obtained in step (I) and water (d2) are mixed to prepare a slurry II ¹ , and then a manganese compound is added to the slurry II ¹ and/or a metal compound (e) containing an iron compound is added to obtain a slurry II ² , and then microwaves are irradiated at a temperature of 80° C. to 120° C. to obtain a positive electrode active material precursor.

In preparing slurry II ¹ , the amount of water (d2) to be mixed is determined from the viewpoint of ensuring the solubility or dispersibility of each component, and from the viewpoint of increasing the production efficiency of the olivine-type lithium phosphate-based positive electrode active material. , preferably 1.5 to 8 parts by mass, more preferably 2 to 5 parts by mass, per 1 part by mass of the trilithium phosphate particles A.

Before adding the metal compound (e) containing a manganese compound and/or an iron compound to the slurry II- ¹ , it is preferable to previously stir the slurry II- ¹ . The stirring time at this time is preferably 1 minute to 180 minutes, more preferably 5 minutes to 120 minutes.

Next, a metal compound (e) containing a manganese compound and/or an iron compound is added to slurry II- ¹ to obtain slurry II- ² .

As the metal compound (e), manganese compounds, iron compounds, and metals other than manganese compounds and iron compounds (M: M is the formula A compound having the same definition as M in (X) may be used. These metal compounds (e) may contain at least a manganese compound or an iron compound, and may contain one or more metal (M) compounds other than the manganese compound and the iron compound.

Examples of the metal compound (e) include metal halides such as fluorides, chlorides and iodides, metal sulfates, metal salts of organic acids, and hydrates thereof. Among these, organic acids having 1 to 20 carbon atoms, more preferably organic acids having 2 to 12 carbon atoms, are preferable as the organic acid constituting the organic acid metal salt. More preferred are dicarboxylic acids such as oxalic acid and fumaric acid, hydroxycarboxylic acids such as lactic acid, and fatty acids such as acetic acid.

The ratio (Li ₃ PO ₄ : (Mn+Fe)) of the molar amount of trilithium phosphate particles A in the slurry II ¹ to the molar amount of manganese and iron in the metal compound (e) to be added is the olivine-type phosphoric acid From the viewpoint of increasing the production efficiency of the lithium-based positive electrode active material, the ratio is preferably 0.95:1 to 1.05:1, more preferably 0.96:1 to 1.04:1, and still more preferably 0 .97:1 to 1.03:1.

Incidentally, when adding the metal compound (e) to the slurry II1, ^an antioxidant may be added as 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 per 1 mol of the metal compound (e) from the viewpoint of preventing inhibition of the production of the olivine-type lithium phosphate-based positive electrode active material due to excessive addition. 0.01 to 1 mol, more preferably 0.03 to 0.5 mol.

The solid content concentration of the obtained slurry II ² is preferably 10% by mass to 80% by mass, more preferably 15% by mass to 75% by mass, and still more preferably 20% by mass, from the viewpoint of improving the efficiency of the production process. % to 75% by mass.
The slurry II ² is preferably stirred after adding the metal compound (e) containing a manganese compound and/or an iron compound. The stirring time at this time is preferably 1 minute to 60 minutes, more preferably 3 minutes to 45 minutes.

The pH of the obtained slurry II ² at 25° C. is preferably 4.8 to 7.0, more preferably 5.0 to 6.0, from the viewpoint of increasing the production efficiency of the olivine-type lithium phosphate-based positive electrode active material. 8, more preferably 5.5 to 6.5.

Next, the obtained slurry II ² is irradiated with microwaves at a temperature of 80°C to 120°C. As a result, it is possible to obtain a positive electrode active material precursor for producing a highly useful olivine-type lithium phosphate-based positive electrode active material while making possible a synthesis reaction at a low temperature and sufficiently improving the efficiency of the manufacturing process. can.

The temperature during microwave irradiation is 80°C to 120°C.
In irradiating with microwaves, the slurry II ² is stored in a closed container, and the above temperature means the temperature measured by a radiation thermometer attached to the inner surface of the microwave generator. Moreover, when the slurry II ² is stored in a sealed container, it is not necessary to pressurize it, so a simple and efficient synthesis reaction can be made possible.
The slurry II ² stored in the closed container is preferably stirred. Such agitation is preferably carried out by a planetary system centered on the center of the microwave generator.

Moreover, the frequency of the microwaves to be irradiated is preferably 2 GHz to 30 GHz, more preferably 2.45 GHz to 30 GHz.
The microwave irradiation time is preferably 1 minute to 60 minutes, more preferably 1 minute to 60 minutes, from the viewpoint of sufficiently improving the efficiency of the manufacturing process while producing a highly useful olivine-type lithium phosphate-based positive electrode active material. is 3 to 60 minutes, more preferably 5 to 60 minutes.

The slurry after the microwave irradiation is subjected to solid-liquid separation in the same manner as the trilithium phosphate particles A, and the resulting precipitate is washed with water to obtain a cake, which is then filtered and then dried. Thus, a positive electrode active material precursor can be obtained.

The positive electrode active material precursor obtained in step (II) is further subjected to the following step (III):
(III) Through a step of mixing the positive electrode active material precursor obtained in step (II), the carbon source (f) and water, and then drying and firing the obtained powder, olivine-type lithium phosphate It is preferable to obtain a system positive electrode active material. As a result, it can be used as a positive electrode material that constitutes a lithium-ion secondary battery that can effectively improve battery characteristics.

The cellulose nanofibers that can be used have a fiber diameter of 1 nm to 1000 nm, and the cellulose molecular chains constituting them form a periodic structure of carbon. Therefore, by carbonizing the cellulose nanofibers and supporting them on the olivine-type lithium phosphate-based positive electrode active material, it is possible to effectively suppress the deterioration of the electronic conduction path and effectively improve the battery characteristics.

Usable water-soluble carbon materials include, for example, one or more selected from sugars, polyols, polyethers, and organic acids. More specifically, for example, monosaccharides such as glucose, fructose, galactose and mannose; disaccharides such as maltose, sucrose and cellobiose; polysaccharides such as starch and dextrin; ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol and butane. polyols and polyethers such as diols, polyvinyl alcohol and glycerin; and organic acids such as citric acid, tartaric acid and ascorbic acid. Among these, glucose, fructose, sucrose, and dextrin are preferred, and glucose is more preferred, from the viewpoint of enhancing solubility and dispersibility in a solvent and effectively functioning as a carbon material.
Similar to cellulose nanofibers, such a water-soluble carbon material is carbonized into carbon, which is carried on the olivine-type lithium phosphate-based positive electrode active material.

Among these carbon sources (f), it is preferable to use cellulose nanofibers and/or glucose, and more preferably cellulose nanofibers, from the viewpoint of improving the efficiency of the manufacturing process and effectively improving the battery characteristics. preferable.

The amount of the carbon source (f) mixed in step (III) is preferably 0.8 parts by mass in terms of carbon atoms of the carbon source (f) with respect to 100 parts by mass of the olivine-type lithium phosphate-based positive electrode active material. to 15 parts by mass, more preferably 1 to 10 parts by mass. Apparatuses used for solid-liquid separation include, for example, stirrers, stirring mixers, rotary powder mixers, stirring powder mixers, planetary mills, ball mills, bead mills, and attritor mills. Among them, mixed pulverization by a planetary mill, ball mill, bead mill, or attritor mill is preferable.
Further, the calcination in step (III) is performed at 400° C. or higher, preferably 400° C. to 800° C., in an inert gas atmosphere or under reducing conditions for 5 minutes to 3 hours, preferably 0.3 hours to 1.5 hours. conditions are preferred. The apparatus used for firing may be any heating furnace capable of controlling the atmosphere, and examples thereof include a box furnace and an externally heated rotary kiln.

The average particle size (D ₅₀ ) of the obtained olivine-type lithium phosphate positive electrode active material is preferably 1 μm to 12 μm, more preferably 2 μm to 12 μm. The “average particle size” in the olivine-type lithium phosphate-based positive electrode active material is, like trilithium phosphate particles A, the _D50 value (cumulative 50 means the particle size (median diameter) in %.
The BET specific surface area of the obtained olivine-type lithium phosphate-based positive electrode active material is preferably 14 m ² /g to 50 m ² /g, more preferably 14 m ² /g, from the viewpoint of expressing excellent battery characteristics. ˜30 m ² /g. The BET specific surface area of the olivine-type lithium phosphate-based positive electrode active material means a value obtained from an adsorption isotherm obtained by a nitrogen adsorption method, similarly to the BET specific surface area of the trilithium phosphate particles A.

The olivine-type lithium phosphate-based positive electrode active material of the present invention is a material used as a positive electrode active material for lithium ion secondary batteries. Specifically, for example, the olivine-type lithium phosphate-based positive electrode active material of the present invention, acetylene black, Ketjenblack, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc. are kneaded to prepare a positive electrode slurry. , the current collector is coated, and then press-molded to produce a positive electrode.
Lithium ion secondary batteries to which the positive electrode obtained using the olivine-type lithium phosphate-based positive electrode active material of the present invention can be applied include a positive electrode, a negative electrode, an electrolytic solution, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte. It is not particularly limited as long as it is.

Since the olivine-type lithium phosphate-based positive electrode active material of the present invention is a highly pure and fine particle, a highly useful positive electrode can be obtained.

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. For example, lithium metal, graphite, silicon-based (Si, SiOx), lithium titanate, carbon materials such as amorphous carbon, and the like can be used. It is preferable to use an electrode made of an intercalate material capable of electrochemically intercalating and deintercalating lithium ions, particularly a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination, for example, a combination of graphite and silicon can be used.

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 electrolyte of a lithium ion secondary battery, and examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, 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.

The solid electrolyte electrically insulates the positive and negative electrodes and exhibits high lithium ion conductivity. _{For example , La0.51Li0.34TiO2.94 , Li1.3Al0.3Ti1.7 ( PO4 ) 3 , Li7La3Zr2O12 , 50Li4SiO4.50Li3BO3 , Li2.9PO3.3N0.46 , Li3.6Si _ _ 0.6P0.4O4 , Li1.07Al0.69Ti1.46 ( PO4 ) 3 , Li1.5Al0.5Ge1.5 ( PO4 ) 3 , Li10GeP2S12 , Li3.25Ge0.25P0.75S4 , 30Li2S . _ 26B2S3.44LiI , 63Li2S.36SiS2.1Li3PO4 , 57Li2S.38SiS2.5Li4SiO4 , 70Li2S.30P2S5 , 50Li2S.50GeS2 , Li7P _ _ _ _ _ 3} S ₁₁ and Li _3.25 P _0.95 S ₄ may be used.

The shape of the lithium-ion secondary battery having the above configuration is not particularly limited, and may be various shapes such as a coin shape, a cylindrical shape, a square shape, or an irregular shape enclosed in a laminated outer package. .

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

Li ₃ PO ₄ particles were produced according to each production example.
Table 1 shows the BET specific surface area and average particle diameter (D ₅₀ ) of each Li ₃ PO ₄ particle obtained.

[Production Example 1: Production of Li ₃ PO ₄ -A particles]
124.6 g of phosphoric acid (85% purity, manufactured by Kanto Chemical Co., Ltd.), 73.6 g of sulfuric acid (96% purity, manufactured by Kanto Chemical Co., Ltd.), and 270 g of water were placed in a 2 L plastic container and stirred for 5 minutes using a stirring blade. , to prepare a mixture i-1. Next, 59.9 g of lithium carbonate (purity 99.95%, manufactured by Kanto Kagaku Co., Ltd.) was added to the resulting mixture i-1 at a rate of 20 g/min, and stirred for 15 minutes using a stirring blade to obtain carbonic acid. Lithium was completely dissolved. Thereafter, 180.09 g of sodium hydroxide aqueous solution (purity 48%, manufactured by Kanto Kagaku Co., Ltd.) was added at a rate of 30 g/min to obtain slurry I-1. The resulting slurry I-1 was subjected to solid-liquid separation using a Buchner funnel, and then the obtained solid content was washed with 1 L of water to obtain a Li ₃ PO ₄ cake, which was placed in a constant temperature bath at 100°C for 12 hours. After drying for a few hours, Li ₃ PO ₄ -A particles were obtained.

[Production Example 2: Production of Li ₃ PO ₄ -B particles]
Li ₃ PO ₄ -B particles were obtained in the same manner as in Production Example 1, except that the sodium hydroxide aqueous solution was added at a rate of 200 g/min.

[Production Example 3: Production of Li ₃ PO ₄ —C Particles]
Li ₃ PO ₄ —C particles were obtained in the same manner as in Production Example 1, except that the sodium hydroxide aqueous solution was added at a rate of 15 g/min.

[Production Example 4: Production of Li ₃ PO ₄ -D particles]
Li ₃ PO ₄ -D particles were obtained in the same manner as in Production Example 1, except that the sodium hydroxide aqueous solution was added at a rate of 5 g/min.

Using the above Li ₃ PO ₄ particles, each positive electrode active material was produced.
Table 2 shows the average particle size (D ₅₀ ) of each positive electrode active material obtained, the evaluation result of the presence or absence of a heterogeneous phase by XRD analysis, and the evaluation result of the discharge capacity in the lithium ion secondary battery, together with various conditions at the time of production. show. Table 3 shows the solid content concentration of the slurry II ² and the BET specific surface area of each positive electrode active material obtained.

The BET specific surface area of the positive electrode active material was measured using a nitrogen-helium mixed gas containing 30% nitrogen using an automatic flow specific surface area measuring device (FlowSorb III 2305, manufactured by Shimadzu Corporation).
The average particle size (D ₅₀ ) of the positive electrode active material was measured using a laser diffractometer (Microtrac MT3000II, manufactured by MicrotracBEL) for the particle size distribution. A refractive index of 1.52 was adopted, ethanol was used as a solvent, and the solvent refractive index was measured as 1.36.

[Example 1]
11.6 g of Li ₃ PO ₄ -A particles obtained in Production Example 1 and 30 g of water were mixed and stirred for 5 minutes to prepare slurry II ¹ x ₁ . 16.9 g of MnSO ₄ .5H ₂ O and 8.34 g of FeSO ₄ .7H ₂ O were added to the obtained slurry II ¹ x ₁ and stirred for 5 minutes to obtain slurry II ² x ₁ (pH at 25°C = 6 .1) was obtained.
The resulting slurry II ² x ₁ was placed in a fluororesin container and irradiated with microwaves at a temperature of 90° C. for 10 minutes using a microwave heating device (MWS-2, manufactured by Berghof, frequency 2450 MHz) to obtain slurry II ³ . x ₁ is obtained. The obtained slurry II ³ x ₁ was subjected to solid-liquid separation using a Buchner funnel, and then the obtained solid content was washed with 500 mL of water to obtain a cake, which was dried in a constant temperature bath at 100 ° C. to obtain a positive electrode. An active material precursor (e1') was obtained.
3 g of the obtained positive electrode active material precursor (e1′), 0.85 g of cellulose nanofiber (water content: 80%, carbon atom equivalent: 2.5% by mass), 5 g of water, and 80 g of zirconia balls (φ1 mm) were placed in a planetary ball mill. The mixture was placed in a container, mixed for 10 minutes at a speed of 400 rpm in a planetary ball mill (P-5, manufactured by Fritsch), and then dried in a constant temperature bath at 80° C. to obtain a powder.
Next, using a tubular electric furnace (TMF-500N, manufactured by AS ONE), the obtained powder was heated at 700° C. for 1 hour under the condition of nitrogen flow (300 mL/min) to obtain a positive electrode active material carrying carbon. A substance (e1) (formula: LiMn _0.7 Fe _0.3 PO ₄ ) was obtained.

[Example 2]
A positive electrode active material (e2) supporting carbon was obtained in the same manner as in Example 1, except that microwaves were applied for 30 minutes at a temperature of 90° C. using a microwave heating device.

[Example 3]
A positive electrode active material (e3) supporting carbon was obtained in the same manner as in Example 1, except that microwaves were applied for 10 minutes at a temperature of 80° C. using a microwave heating device.

[Example 4]
A positive electrode active material (e4) supporting carbon was obtained in the same manner as in Example 1, except that microwaves were applied for 30 minutes at a temperature of 80° C. using a microwave heating device.

[Example 5]
A positive electrode active material (e5) supporting carbon was obtained in the same manner as in Example 1, except that microwaves were applied for 30 minutes at a temperature of 100° C. using a microwave heating device.

[Example 6]
A positive electrode active material (e6) supporting carbon was obtained in the same manner as in Example 1, except that microwaves were applied for 30 minutes at a temperature of 110° C. using a microwave heating device.

[Example 7]
A positive electrode active material (e7) supporting carbon was obtained in the same manner as in Example 1, except that microwaves were applied for 30 minutes at a temperature of 120° C. using a microwave heating device.

[Example 8]
A carbon-supported positive electrode active material was prepared in the same manner as in Example 1, except that only 24.14 g of MnSO ₄ .5H ₂ O was added to the slurry II ¹ x ₁ and FeSO ₄ .7H ₂ O was not added. Substance (e8) (formula: LiMnPO ₄ ) was obtained.

[Example 9]
A carbon-supported cathode active material was prepared in the same manner as in Example 1, except that only 27.80 g of FeSO ₄ .7H ₂ O was added to the slurry II ¹ x ₁ and no MnSO ₄ .5H ₂ O was added. A substance (e9) (formula: LiFePO ₄ ) was obtained.

[Example 10]
A carbon-supported positive electrode active material (e10) was prepared in the same manner as in Example 1, except that the Li ₃ PO ₄ -B particles obtained in Production Example 2 were used instead of the Li ₃ PO ₄ -A particles. got

[Example 11]
A cathode active material (e11) supporting carbon in the same manner as in Example 1, except that the Li ₃ PO ₄ -C particles obtained in Production Example 3 were used instead of the Li ₃ PO ₄ -A particles. got

[Example 12]
A carbon-supported positive electrode active material (e12) was prepared in the same manner as in Example 1, except that the Li ₃ PO ₄ -D particles obtained in Production Example 4 were used instead of the Li ₃ PO ₄ -A particles. got

[Example 13]
11.6 g of Li ₃ PO ₄ -A particles obtained in Production Example 1 and 30 g of water were mixed and stirred for 5 minutes to prepare slurry II ¹ x ₁₃ . To the resulting slurry II ¹ x ₁₃ was added 0.25 g of an aqueous sodium hydroxide solution (equivalent to 3 mol per 1 mol of Li ₃ PO ₄ particles in the slurry II ¹ x ₁₃ ) and 16.9 g of MnSO ₄ .5H ₂ O. , and 8.34 g of FeSO ₄ .7H ₂ O were added and stirred for 5 minutes to obtain slurry II ² x ₁₃ (pH=6.7 at 25° C.).
A carbon-supported cathode active material (e13) was obtained in the same manner as in Example 1, except that the obtained slurry II ² x ₁₃ was used instead of the slurry II ² x ₁ .

[Example 14]
11.6 g of the Li ₃ PO ₄ -A particles obtained in Production Example 1 and 30 g of water were mixed and stirred for 5 minutes to prepare a slurry II ¹ x ₁₄ . 0.35 g of phosphoric acid, 16.9 g of MnSO ₄ .5H ₂ O, and 8.34 g of FeSO ₄ .7H ₂ O were added to the obtained slurry II ¹ x ₁₄ and stirred for 5 minutes to obtain a slurry II ² x ₁₄ . (pH=5.0 at 25° C.).
A carbon-supported cathode active material (e14) was obtained in the same manner as in Example 1, except that the obtained slurry II ² x ₁₄ was used instead of the slurry II ² x ₁ .

[Example 15]
A positive electrode carrying carbon was prepared in the same manner as in Example 1, except that 20 g of water was used to prepare the slurry II ¹ x ₁ , and microwaves were irradiated for 30 minutes at a temperature of 90°C using a microwave heating device. An active material (e15) was obtained.

[Comparative Example 1]
A carbon-supported positive electrode active material was produced in the same manner as in Example 1, except that the slurry II ² x ₁ was placed in an autoclave and held at 160° C. for 60 minutes instead of irradiating microwaves with a microwave heating device. (c1) was obtained.

[Comparative Example 2]
A positive electrode active material (c2) supporting carbon was obtained in the same manner as in Example 1, except that microwaves were applied for 30 minutes at a temperature of 70° C. using a microwave heating device.

[Comparative Example 3]
A carbon-supported cathode active material (c3) was obtained in the same manner as in Comparative Example 1, except that the slurry II ² x ₁ was placed in an autoclave and held at 100° C. for 60 minutes.

[Comparative Example 4]
A positive electrode active material was produced without using the Li ₃ PO ₄ particles obtained in Production Example. Specifically, 2.569 g (60 mmol) of LiOH·H ₂ O, 4.4 g (110 mmol) of NaOH, and 30 mL of water were mixed to obtain a slurry. Next, while stirring the resulting slurry at a temperature of 25° C. for 10 minutes, 6.918 g of an 85% aqueous solution of phosphoric acid was added dropwise at a rate of 35 mL/min, followed by stirring for 12 hours to obtain a mixture e1. (The ratio of the molar amount of lithium to the molar amount of phosphorus (lithium:phosphorus)=1:1) was obtained.
10.1 g of MnSO ₄ .5H ₂ O and 5.00 g of FeSO ₄ .7H ₂ O were added to the total amount of the obtained mixed liquid e1 to obtain a mixed liquid e2 (pH 4.3). At this time, the molar ratio of MnSO ₄ and FeSO ₄ added was 7:3. The resulting mixture e2 was stirred at 90° C. for 12 hours under atmospheric pressure to allow the reaction to proceed, thereby obtaining a positive electrode active material precursor (c4′).
A positive electrode active material (c4) supporting carbon in the same manner as in Example 1, except that the obtained positive electrode active material precursor (c4′) was used instead of the positive electrode active material precursor (e1′). got

[Comparative Example 5]
A positive electrode active material was produced without using the Li ₃ PO ₄ particles obtained in Production Example. Specifically, _{CH3COOLi.2H2O} (Wako Pure Chemical special grade), Mn _{( CH3COO} ) _{2.4H2O (} Wako Pure _Chemical special grade), and _{NH4H2PO4 (} Wako Pure Chemical special grade) and added to 40 mL of distilled water to obtain a mixed liquid e5.
A carbon-supported cathode active material (c5) was obtained in the same manner as in Example 1, except that the obtained mixture e5 was used instead of the slurry II ² x ₁ .

《Observation of formation phase (presence or absence of heterogeneous phase)》
For the obtained positive electrode active material, the generated phase was observed by XRD (X-ray diffraction measurement device (D8-Advance, manufactured by BRUKER) analysis, and the presence or absence of a heterogeneous phase was evaluated.
Specifically, the measurement conditions are target CuKα, tube voltage 35 kV, tube current 350 mA, scanning range 10° to 80° (2θ), step width 0.02°, and scanning speed 0.13 seconds/step. Based on the chart, the crystal phases having interplanar spacing corresponding to each peak (2θ) were associated to identify the crystal phases, and the presence or absence of different phases was confirmed.

《Evaluation of Discharge Capacity》
Using the obtained positive electrode active material, first, a positive electrode for a lithium ion secondary battery was produced. Specifically, the obtained positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone was added thereto and sufficiently kneaded to obtain a positive electrode. A slurry was prepared. 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. As the separator, a known separator made of a polymeric 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).

Using the obtained lithium ion secondary battery, a charge/discharge test was performed at a constant current density. Specifically, after constant current charging with a current of 0.2 CA (34 mAh/g) and a voltage of 4.5 V, constant current discharging with a current of 3 CA and a final voltage of 2.0 V was performed. All charge/discharge tests were conducted at 30°C.

Claims (6)

The following formula (X):
_{LiaMnbFecMxPO4 ( X ) _}
(In formula (X), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd a, b, c, and x satisfy 0<a≦1.2, 0≦b≦1.2, 0≦c≦1.2, 0≦x≦0.3, and b+c≠0; In addition, a number that satisfies a + (valence of Mn) x b + (valence of Fe) x c + (valence of M) x = 3.)
A method for producing an olivine-type lithium phosphate-based positive electrode active material represented by the following steps (I) to (II):
(I) A mixture obtained by mixing a phosphoric acid compound (a), one or more acid compounds (b) selected from sulfuric acid, hydrochloric acid and nitric acid, a lithium compound (c), and water (d1) After adding an alkaline compound solution to liquid i to obtain slurry I, the obtained slurry I is subjected to solid-liquid separation to obtain trilithium phosphate particles A having a BET specific surface area of 10 m ² /g to 200 m ² /g. (II) The obtained trilithium phosphate particles A and water (d2) are mixed to prepare slurry II ¹ , and then slurry II ¹ contains a metal compound (e ) to obtain a slurry II ² , and then irradiate microwaves at a temperature of 80° C. to 120° C. to obtain a positive electrode active material precursor. . Next step (III):
(III) The olivine according to claim 1, comprising a step of mixing the positive electrode active material precursor obtained in step (II), the carbon source (f) and water, and then drying and firing the resulting powder. A method for producing a type lithium phosphate positive electrode active material. In step (II), the ratio of the molar amount of trilithium phosphate particles A in slurry II ¹ to the molar amount of manganese and iron in metal compound (e) added to slurry II ¹ (Li ₃ PO ₄ : 3. The method for producing an olivine-type lithium phosphate-based positive electrode active material according to claim 1, wherein (Mn+Fe)) is 0.95:1 to 1.05:1. The method for producing an olivine-type lithium phosphate-based positive electrode active material according to any one of claims 1 to 3, wherein the slurry II ² in step (II) has a solid content concentration of 10% by mass to 80% by mass. In the slurry I obtained in step (I), the ratio of the molar amount of lithium contained in the lithium compound (c) to the molar amount of phosphorus contained in the phosphoric acid compound (a) (lithium:phosphorus) is 2. 5:1 to 3.2:1. The method for producing an olivine-type lithium phosphate-based positive electrode active material according to any one of claims 1 to 5, wherein in step (II), the slurry II ² has a pH of 4.8 to 7.0 at 25°C. .