JP7165048B2 - METHOD FOR MANUFACTURING LISICON-TYPE CRYSTAL PARTICLES FOR SOLID ELECTROLYTE FOR LITHIUM-ION SECONDARY BATTERY - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing LISICON-type crystal particles for solid electrolytes for use in secondary batteries such as all-solid lithium ion secondary batteries.

Lithium-ion secondary batteries currently in practical use use flammable organic solvents in the electrolyte, so it is necessary to take sufficient safety measures against leaks and fires. It is also highly difficult to convert. However, an all-solid-state lithium-ion secondary battery with an oxide-based or sulfide-based solid electrolyte has a high energy density and can be manufactured without using combustibles, so safety measures must be taken. The burden is reduced, and manufacturing costs and productivity can be easily increased. For these reasons, various developments are being actively carried out on solid electrolyte materials, which are expected to be highly useful.

In particular, Li ₄ SiO ₄ --Li ₃ PO ₄ having a LISICON type crystal structure with a framework structure formed by γ-Li ₃ PO ₄ (high temperature phase) type SiO ₄ and PO ₄ tetrahedra and LiO ₆ octahedra. In addition to being a solid electrolyte with a high lithium ion concentration due to its crystal structure, the solid solution has an excellent characteristic of exhibiting a lithium ion conductivity as high as 10 ^-4 S/cm at room temperature. It is one of the promising solid electrolyte materials.

In order to put these _LISICON -type crystal particles into practical use, it is important to achieve high purity and fine particles. A method for obtaining a lithium ion conducting solid electrolyte represented by _0.5 P _0.5 O ₄ is disclosed.

D. Wang et al./Solid State Ionics 283 (2015) 109-114

However, the LISICON-type crystal particles obtained by the production method described in the above non-patent document induce defects in the crystal structure of the LISICON-type crystal due to the pulverization treatment that must be performed in order to achieve miniaturization. There is a risk of causing a decrease in lithium ion conductivity.

Therefore, an object of the present invention is to moderately and effectively refine the LISICON type crystal represented by _{Li4 - xSi1} - _xPxO4 , so that excellent lithium ion conductivity can be expressed. An object of the present invention is to provide a method for producing LISICON-type crystal particles useful as a solid electrolyte for secondary batteries.

Accordingly, the present inventors conducted various studies and found that LISICON-type crystal particles with a high degree of crystallinity can be obtained while appropriately miniaturizing the grains by preparing a specific mixed solution and undergoing specific steps. , have completed the present invention.

That is, the present invention provides the following steps (I) to (III):
(I) A step of mixing a lithium compound, a silicate compound, a phosphoric acid compound, and water to prepare a mixed solution having a pH of 9 to 14 at 25°C. After subjecting to the hydrothermal reaction, the hydrothermal reaction product is washed and then dried to obtain a precursor mixture; , the following formula (1):
Li4 _{- xSi1 - xPxO4} (1)
(In formula (1), x represents a number satisfying 0<x<1.)
The present invention provides a method for producing LISICON-type crystal particles for a solid electrolyte of a lithium ion secondary battery represented by:

According to the method of the present invention, fine and highly crystalline LISICON type crystal particles can be produced simply by preparing a predetermined mixed solution, hydrothermally reacting it, and then calcining it. Since it is not necessary to perform a pulverization treatment for achieving the high crystallinity, it can be used as a solid electrolyte, thereby realizing a secondary battery with excellent charge-discharge characteristics.

1 is an SEM image showing LISICON-type crystal particles obtained in Example 1. FIG. 1 is an X-ray diffraction pattern of LISICON-type crystal particles obtained in Example 1. FIG. 4 is an SEM image showing LISICON-type crystal particles obtained in Comparative Example 1. FIG. 1 is an X-ray diffraction pattern of LISICON-type crystal particles obtained in Comparative Example 1. FIG.

The present invention will be described in detail below.
The method of the present invention comprises the following steps (I)-(III):
(I) A step of mixing a lithium compound, a silicate compound, a phosphoric acid compound, and water to prepare a mixed solution having a pH of 9 to 14 at 25°C. After subjecting to the hydrothermal reaction, the hydrothermal reaction product is washed and then dried to obtain a precursor mixture; , the following formula (1):
Li4 _{- xSi1 - xPxO4} (1)
(In formula (1), x represents a number satisfying 0<x<1.)
A method for producing LISICON-type crystal particles for a solid electrolyte of a lithium ion secondary battery represented by

The step (I) is a step of preparing a mixture (A) having a pH of 9 to 14 at 25° C. by mixing all raw material compounds of a lithium compound, a silicate compound and a phosphate compound with water. be. Thus, by using the raw material compound for obtaining the LISICON-type crystal particles and water, and obtaining the mixed solution (A) in which the pH is controlled within the above range, the hydrothermal reaction in the step (II) described later can be performed. In the hydrothermal reaction product obtained by addition, the homogeneity of the chemical composition can be improved, and the LISICON type crystal grains can be made finer and highly crystallized.

Lithium compounds that can be used as one of the raw material compounds include one or more selected from hydroxides, chlorides, carbonates, sulfates, and organic acid salts. More specifically, for example, lithium hydroxide or its hydrate, lithium peroxide, lithium chloride, lithium carbonate, lithium sulfate, lithium acetate, lithium oxalate and the like can be preferably used.

The silicate compound that can be used as one of the raw material compounds together with the lithium compound is not particularly limited as long as it is a reactive silica compound, and includes silicon dioxide, amorphous silica, Na ₄ SiO ₄ (e.g., Na ₄ SiO ₄ ·H ₂ O) and the like.

In addition, the silicic acid compound efficiently causes the hydrothermal reaction in step (II) to obtain a hydrothermal reaction product having a homogeneous chemical composition and a high degree of crystallinity, and having a sufficiently small diameter. From the point of view, fine particles are preferable, and the average particle diameter is preferably 100 nm or less, more preferably 75 nm or less.

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, it is preferable to use phosphoric acid from the viewpoint that it can also act as a pH adjuster for controlling the pH of the resulting mixed solution (A), and it is preferable to use it as an aqueous solution with a concentration of 70% by mass to 90% by mass. preferable.

The raw material compound consists of three compounds, a lithium compound, a silicate compound and a phosphoric acid compound. In step (I), all of these raw material compounds are collectively used.

Specifically, in step (I), a mixed solution (a-1) containing a lithium compound, a silicate compound and water and a mixed solution (a-2) containing a phosphoric acid compound and water are each prepared. After that, these two mixed liquids are mixed to prepare a mixed liquid (A). As a result, all of the raw material compounds and water are present in the resulting mixture (A), and a reaction product having a highly homogeneous chemical composition and a sufficiently small diameter, that is, trilithium phosphate Then, the mixture of the silicic acid compound added as the raw material compound is contained, and the miniaturization of the LISICON type crystal grains can be effectively achieved.

Mixed solution (a-1) is prepared by mixing a lithium compound and a silicate compound with water. The total content of the lithium compound and the silicate compound in the mixed solution (a-1) is determined from the viewpoint of increasing the homogeneity of the chemical composition of the reaction product produced by mixing with the mixed solution (a-2). It is preferably 1 part by mass to 50 parts by mass, more preferably 5 parts by mass to 30 parts by mass, and still more preferably 5 parts by mass to 20 parts by mass with respect to 100 parts by mass of water in (a-1). be.

Further, in preparing the mixed solution (a-1), the mixing ratio of the lithium compound and the silicate compound is preferably 3.1:0.1 to 4:1 in molar ratio (Li:Si), More preferably 3.1:0.1 to 3.9:0.9, still more preferably 3.2:0.2 to 3.8:0.8.

The liquid mixture (a-1) may be stirred in advance before being mixed with the liquid mixture (a-2) from the viewpoint of dispersing each component more uniformly. The time for stirring the mixed solution (a-1) is preferably 5 minutes to 3 hours, more preferably 10 minutes to 2 hours, still more preferably 15 minutes to 90 minutes. The stirring speed is preferably 10 cm/sec to 200 cm/sec, more preferably 15 cm/sec to 150 cm/sec, and still more preferably 20 cm/sec to 100 cm/sec.

Mixed solution (a-2) is prepared by mixing a phosphoric acid compound and water. The content of the phosphoric acid compound in the mixed solution (a-2) is preferably 3 parts by mass to 20 parts by mass, more preferably 5 parts by mass, relative to 100 parts by mass of water in the mixed solution (a-2). parts to 15 parts by mass, more preferably 7 to 15 parts by mass.

The pH of the mixed solution (a-2) at 25°C is preferably 12 to 14, more preferably 12.5, from the viewpoint of adjusting the pH of the resulting mixed solution (A) to 9 to 14 at 25°C. ~14, more preferably 13-14. A pH adjuster may be used to adjust the pH of the mixture (a-2) to the above range. Such a pH adjuster is not particularly limited, but from the viewpoint of easily adjusting the pH of the mixture (a-2), water such as lithium hydroxide, sodium hydroxide, potassium hydroxide or ammonium hydroxide Preference is given to using oxides.

The mixed solution (a-2) may be stirred in advance before being mixed with the mixed solution (a-1) from the viewpoint of dissolving or dispersing each component more uniformly. The time for stirring the mixed solution (a-2) is preferably 1 to 30 minutes, more preferably 2 to 20 minutes, still more preferably 2 to 10 minutes. The stirring speed is preferably 10 cm/sec to 200 cm/sec, more preferably 15 cm/sec to 150 cm/sec, and still more preferably in terms of the flow speed of the mixture (a-2) on the inner wall surface of the reaction vessel. is between 20 cm/sec and 100 cm/sec.

Next, in step (I), the mixed solution (a-1) and the mixed solution (a-2) are mixed to obtain a mixed solution (A). The method of mixing the mixed solution (a-1) and the mixed solution (a-2) is not particularly limited, but the mixed solution (a-2) is added dropwise to the mixed solution (a-1) being stirred. preferably. Thus, the mixed liquid (a-2) containing the phosphoric acid compound is added dropwise to the mixed liquid (a-1) containing the lithium compound and the silicate compound little by little, so that all of the raw material compounds and water are mixed. While containing, the homogeneity of the chemical composition of the reaction product can be further enhanced.
At this time, the rate of dropping the mixed liquid (a-2) into the mixed liquid (a-1) is preferably 0.1 part by mass/min to 0.1 part by mass/min with respect to 10 parts by mass of the mixed liquid (a-1). It is 4 parts/minute, more preferably 0.15 parts/minute to 0.4 parts/minute, still more preferably 0.2 parts/minute to 0.35 parts/minute. The stirring speed of the mixed solution (a-1) when the mixed solution (a-2) is added dropwise is preferably 10 cm/sec or more in terms of the flow speed of the mixed solution (a-1) on the inner wall surface of the reaction vessel. 200 cm/sec, more preferably 15 cm/sec to 150 cm/sec, and even more preferably 20 cm/sec to 100 cm/sec.

In obtaining the mixed solution (A), the mass ratio ((a-1):(a-2)) of the mixed solution (a-1) and the mixed solution (a-2) to be mixed is preferably 20:1. ~1:4, more preferably 10:1 to 1:3, still more preferably 5:1 to 2:3.

The temperature of the mixture (a-1) when mixing the mixture (a-1) and the mixture (a-2) is preferably 10°C to 80°C, more preferably 15°C to 70°C. and more preferably 20°C to 60°C. The temperature of the mixture (a-2) is preferably 10°C to 80°C, more preferably 15°C to 70°C, still more preferably 20°C to 60°C.

The time for mixing the mixture (a-1) and the mixture (a-2) is preferably 10 minutes to 24 hours, more preferably 15 minutes to 18 hours, still more preferably 30 minutes to 12 hours. is. Further, at this time, stirring may be performed from the viewpoint of dissolving or dispersing each component more uniformly and improving the homogeneity of the chemical composition of the reaction product. The stirring speed is preferably 10 cm/sec to 200 cm/sec, more preferably 15 cm/sec to 150 cm/sec, still more preferably 20 cm/sec in terms of the flow speed of the mixture (A) on the inner wall surface of the reaction vessel. sec to 100 cm/sec.

By mixing the mixed solution (a-1) and the mixed solution (a-2), all the raw material compounds are mixed at once, and the lithium phosphate and the silicic acid compound added as the raw material compound are contained. A mixture (A) is obtained. These trilithium phosphate and silicate compound are fine particles having an average particle size of 100 nm or less, and are converted into a precursor mixture (B ) well. The total content of the lithium phosphate and the silicate compound in the mixture (A) is preferably 0.5% by mass to 40% by mass, more preferably 1% by mass. to 35% by mass, more preferably 1.5% to 30% by mass. The pH of the mixture (A) at 25° C. is 9-14, preferably 10-14, more preferably 10.5-14. In adjusting the pH of the mixed liquid (A) so that it falls within this range, the above pH adjuster may be used as necessary.
It can be confirmed by X-ray diffraction that lithium phosphate is produced and contained as a mixture in the liquid mixture (A).

In step (II), after subjecting the mixture (A) obtained in step (I) to a hydrothermal reaction at 100° C. or higher, the hydrothermal reaction product is washed and then dried to obtain a precursor mixture ( B) is obtained. The hydrothermal reaction in step (II) is carried out under pressure in a reaction vessel filled with the mixture (A) containing all of the starting compounds and water in a pressure vessel or the like.

When the mixed solution (A) obtained in step (I) is stirred before proceeding to step (II), such stirring may be performed in a reaction vessel, and then the reaction vessel is placed in a pressure vessel or the like. It should be stored. From the viewpoint of efficiently producing a precursor mixture of LISICON-type crystal particles, such stirring is preferably continued until the hydrothermal reaction in step (II) is completed in a reaction vessel such as a pressure vessel. At this time, the stirring speed of the mixed solution (A) is preferably 15 cm/sec or more, more preferably 15 cm/sec to 80 cm/sec in terms of the flow speed of the mixed solution (A) on the inner wall surface of the reaction vessel. and more preferably 15 cm/sec to 70 cm/sec. The stirring method is not particularly limited as long as this stirring speed is achievable. For example, a method using a stirring blade or a pump described in JP-A-2014-118328 is used to stir the slurry in the synthesis vessel. methods and the like can be suitably used.
Furthermore, when using the above-mentioned stirring method, from the viewpoint of uniformly causing a hydrothermal reaction in the entire mixed liquid (A), a baffle plate is installed in the reaction vessel, the rotation direction of the stirring blade, or the liquid feeding direction of the pump. It is effective to disturb the flow of the mixture (A) by intermittently reversing the flow of the liquid mixture (A).

The temperature (reaction temperature) of the mixed solution (A) during the hydrothermal reaction may be 100°C or higher, preferably 130°C to 250°C, more preferably 140°C to 230°C. At this time, the pressure and reaction time are preferably 0.3 MPa or more and 10 minutes or more when the reaction temperature is 100 ° C. or higher, and 0.3 MPa to 2 MPa and 10 minutes to 24 minutes when the reaction is performed at 130 ° C. to 250 ° C. When the reaction is carried out at 140° C. to 230° C., the pressure is preferably 0.4 MPa to 1.8 MPa for 10 minutes to 16 hours.

Moreover, the atmosphere in the reaction vessel in the hydrothermal reaction is not limited, but from the viewpoint of easiness of adjusting the atmosphere, it is preferably under air or under water vapor.

After subjecting the liquid mixture (A) to the above hydrothermal reaction, the hydrothermal reaction product is washed and then dried. Such a hydrothermal reaction product can be obtained by solid-liquid separation of the mixed liquid (A) after the hydrothermal reaction, and the obtained hydrothermal reaction product is a mixture of lithium phosphate and lithium silicate, that is, a LISICON type crystal It comprises a particle precursor mixture (B). Apparatuses used for solid-liquid separation include, for example, a filter press and a centrifugal filter. Among them, it is preferable to use a filter press from the viewpoint of obtaining a hydrothermal reaction product efficiently.

Next, the recovered hydrothermal reaction product is washed from the viewpoint of effectively removing water-soluble impurities such as anionic components derived from the raw materials. Water may be used for such washing, and the amount of water is preferably 5 parts by mass to 50 parts by mass, more preferably 7 parts by mass to 50 parts by mass, relative to 1 part by mass of the dry mass of the hydrothermal reaction product. parts by mass, more preferably 9 to 50 parts by mass. The temperature of such water is preferably 5° C. to 70° C., more preferably 20° C. to 70° C., from the viewpoint of effectively removing water-soluble impurities.

The washed hydrothermal reaction product is then dried. Drying means include spray drying, box drying, fluidized bed drying, external heat drying, freeze drying, vacuum drying, etc. Among them, LISICON obtained by firing in step (III) described later Spray drying is preferable from the viewpoint of effectively controlling the growth of the mold crystal grains more than necessary and sufficiently miniaturizing the grains.

The precursor mixture (B) obtained after drying is a mixture of lithium phosphate and lithium silicate. The average particle diameter of the precursor mixture (B) is preferably 5 nm to 250 nm, more preferably 10 nm to 200 nm, in terms of D ₅₀ value in particle size distribution based on laser diffraction/scattering method. Here, the _D50 value in particle size distribution measurement is a value obtained from a volume-based particle size distribution based on a laser diffraction/scattering method, and the _D50 value means the particle size (median diameter) at 50% cumulative. do. Therefore, when spray drying is employed as the drying means, the particle size of the precursor mixture (B) may be adjusted by appropriately optimizing the operating conditions of the spray dryer used.

Step (III) is a step of firing the precursor mixture (B) obtained in step (II) at 400°C to 1000°C. Through such step (III), it is possible to obtain LISICON-type crystal particles that are fine particles with extremely high crystallinity and high purity, and are very useful as a solid electrolyte for lithium ion secondary batteries.

The firing temperature in step (III) is 400° C. to 1000° C., preferably 500° C. to 900° C., from the viewpoint of effectively miniaturizing the LISICON-type crystal particles while enhancing the crystallinity of the resulting LISICON type crystal particles. More preferably, it is 600°C to 800°C. From the same viewpoint, the firing time is preferably 0.5 hours to 30 hours, more preferably 1 hour to 24 hours, and still more preferably 1 hour to 18 hours.

The atmosphere in the firing is not particularly limited, and may be an air atmosphere, an inert gas atmosphere, or a reducing condition, but the air atmosphere is preferable from the viewpoint of convenience. The apparatus used for such baking is not particularly limited as long as it is capable of adjusting the temperature, and any of batch type, continuous type, and heating type (indirect or direct) can be used. , an externally heated kiln or a roller hearth.

The average particle size of the LISICON-type crystal particles produced by the method of the present invention is preferably 70 nm to 300 nm, more preferably 70 nm to 250 nm, still more preferably 70 nm to 200 nm.
Here, the average particle size of the LISICON-type crystal particles means the average value of the measured values of the particle size (long axis length) of several tens of particles in observation using an SEM or TEM electron microscope. .

In addition, the BET specific surface area of the obtained LISICON-type crystal particles is preferably 3 m ² /g or more, more preferably 5 m ² /g or more, from the viewpoint of obtaining a lithium ion secondary battery with excellent charge-discharge characteristics. , more preferably 7 m ² /g or more.

The LISICON-type crystal particles produced by the method of the present invention are particles containing an extremely small amount of water-soluble impurities such as SO ₃ . For example, when a sulfate is used as a raw material compound, the content of water-soluble impurities (SO ₃ content) in the resulting LISICON-type crystal particles is preferably 500 ppm or less, more preferably 300 ppm or less.

The LISICON-type crystal particles produced by the method of the present invention are oxides having a LISICON-type crystal structure, and are specifically represented by the following formula (1).
Li4 _{- xSi1 - xPxO4} (1)
(In formula (1), x represents a number satisfying 0<x<1.)
_{More specific examples include Li3.5Si0.5P0.5O4 , Li3.9Si0.9P0.1O4 and Li3.1Si0.1P0.9O4 . _ _}

Thus, according to the method of the present invention, it is possible to produce LISICON-type crystal particles having a high degree of crystallinity and effectively miniaturized particle sizes. Therefore, it is possible to easily obtain a solid electrolyte for an all-solid lithium ion secondary battery that can exhibit excellent charge-discharge characteristics.

A lithium-ion secondary battery to which the LISICON-type crystal particles produced by the method of the present invention can be appropriately applied as a solid electrolyte has a positive electrode, a negative electrode, and a solid electrolyte as essential components, including a positive electrode active material layer, a solid There is no particular limitation as long as a laminate in which the electrolyte layer and the negative electrode active material layer are laminated in this order is formed.

Here, regarding the positive electrode active material layer, as long as it can release lithium ions during charging and absorb lithium ions during discharging, the material configuration is not particularly limited, and a known material configuration can be used. . For example, a positive electrode active material layer made of various polyanion-type positive electrode active materials obtained by hydrothermally reacting raw material compounds can be preferably used.

In addition, the negative electrode active material layer is not particularly limited in its material composition as long as it can occlude lithium ions during charging and can release lithium ions during discharging, and known material compositions can be used. For example, a negative electrode active material layer made of titanium niobium oxide or sodium lithium titanate composite oxide obtained by hydrothermally reacting raw materials can be preferably used.

Moreover, the method for producing a lithium ion secondary battery using the LISICON type crystal particles produced by the method of the present invention is not particularly limited, and known methods can be used. For example, as described in JP-A-2017-10816, the LISICON-type crystal particles of the present invention are used as the solid electrolyte particles contained in the positive electrode active material layer and the negative electrode active material layer, and the solid electrolyte layer includes: A solid electrolyte other than such solid electrolyte particles 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. In addition, unless otherwise indicated in the table, the content of each component indicates % by mass.

[Production Example 1] (Production of LiCoPO ₄ positive electrode active material particles)
12.72 g of LiOH.H ₂ O and 40 mL of water were mixed to obtain a slurry (c-1). 11.53 g of 85% by mass H ₃ PO ₄ was added dropwise to the obtained slurry (c-1) at 35 mL/min while stirring for 3 minutes while maintaining the temperature at 25° C., and the stirring rate was 400 rpm for 1 hour. A Li ₃ PO ₄ slurry (c-2) was obtained by stirring. Next, 21.08 g of CoSO ₄ .7H ₂ O was added to the total amount of Li ₃ PO ₄ slurry (c-2) thus obtained to obtain slurry (c-3), which was put into an autoclave. , and 170° C. for 1 hour. The pressure inside the autoclave was 0.8 MPa. The produced hydrothermal reactant was filtered and then washed with 12 parts by mass of water per 1 part by mass of the hydrothermal reactant. The washed hydrothermal reaction product was freeze-dried at −50° C. for 12 hours to obtain LiCoPO ₄ positive electrode active material particles (particle size: 100 nm).

[Example 1]
4.5 g of LiOH.H ₂ O and 0.9 g of SiO ₂ were mixed with 40 mL of water to obtain a mixture (a-1) ¹ . The pH of the mixture (a-1) ¹ at 25° C. was 13.5. Next, the obtained mixed solution (a-1) ¹ was stirred at a stirring speed of 200 rpm for 10 minutes while maintaining the temperature of 25° C., and then added to the mixed solution (a-1) ¹ which was continuously stirred. After 1.73 g of 85% H ₃ PO ₄ was added dropwise at a rate of 50 mL/min and mixed, the mixture was further stirred at a stirring speed of 200 rpm for 30 minutes to obtain a mixed liquid (A) ¹ . The mixed solution (A) ¹ had a pH of 12 at 25° C. and a total content of Li ₃ PO ₄ and SiO ₂ produced was 6 mass %.

The mixed liquid (A) ¹ thus obtained was put into an autoclave and subjected to a hydrothermal reaction at 170° C. and 1.0 MPa for 6 hours. The resulting solid content was filtered by suction, and then washed with 5 parts by mass of water per ¹ part by mass of the solid content. got Qualitative analysis by X-ray diffraction revealed that the mass ratio of the mixture Li ₃ PO ₄ and Li ₄ SiO ₄ in the resulting precursor mixture (B) ¹ was 1:1.04. The obtained precursor mixture (B) ¹ was calcined at 700° C. for 4 hours in an air atmosphere to obtain LISICON type crystal particles X ¹ .
The obtained LISICON-type crystal particles X ¹ had a Li _3.5 Si _0.5 P _0.5 O ₄ single phase, an average particle diameter of 80 nm, and a BET specific surface area of 25 m ² /g. A SEM photograph of the obtained LISICON-type crystal particles X ¹ is shown in FIG. 1, and an X-ray diffraction pattern is shown in FIG.

[Example 2]
LISICON-type oxidation was carried out in the same manner as in Example 1, except that the amount of LiOH·H ₂ O added was 5.01 g, the amount of SiO ₂ was 1.62 g, and the amount of 85% H ₃ PO ₄ was 0.35 g. A substance particle X ² was obtained.
The obtained LISICON-type oxide particles X ² had a Li _3.9 Si _0.9 P _0.1 O ₄ single phase, an average particle diameter of 80 nm, and a BET specific surface area of 25 m ² /g.

[Example 3]
LISICON-type oxidation was carried out in the same manner as in Example 1 except that the amount of LiOH.H ₂ O added was 8.10 g, the amount of SiO ₂ was 0.18 g, and the amount of 85% H ₃ PO ₄ was 3.11 g. A substance particle X ³ was obtained.
The obtained LISICON-type oxide particles X ³ had a Li _3.1 Si _0.1 P _0.9 O ₄ single phase, an average particle diameter of 80 nm, and a BET specific surface area of 25 m ² /g.

[Comparative Example 1]
11.38 g of Li ₂ CO ₃ , 2.30 g of (NH ₄ )H ₂ PO ₄ and 1.20 g of SiO ₂ were mixed with 40 mL of water and pulverized at 400 rpm for 4 hours using a planetary ball mill to obtain a precursor mixture (B ). LISICON-type crystal particles Y ¹ were obtained by firing the obtained precursor mixture (B) in an air atmosphere at 900° C. for 10 hours.
The obtained LISICON-type crystal particles Y ¹ had a Li _3.5 Si _0.5 P _0.5 O ₄ single phase, an average particle diameter of 500 nm, and a BET specific surface area of 1 m ² /g. A SEM photograph of the obtained LISICON-type crystal particles Y ¹ is shown in FIG. 3, and an X-ray diffraction pattern is shown in FIG.

"Evaluation test"
Using the LISICON type crystal particles X ¹ to X ³ and Y ¹ obtained in Examples 1 to 3 and Comparative Example 1, all-solid lithium ion secondary batteries were produced.
Specifically, the _LiCoPO4 positive electrode active material particles obtained in Production Example 1 were used for the positive electrode, and the positive electrode active material:solid electrolyte (mass ratio) was mixed at a mixing ratio of 75:25, and then put into a press jig. to form a positive electrode active material layer. Further, only the LISICON-type crystal particles obtained in Examples 1 to 3 and Comparative Example 1 were added to the layer to form a solid electrolyte layer, which was then pressed for 2 minutes at 16 MPa using a hand press. , a disk-shaped positive electrode of φ14 mm was obtained. Next, by attaching a lithium foil as a negative electrode to the solid electrolyte layer side, an all-solid lithium ion secondary battery was produced.

Using the produced all-solid-state lithium ion secondary battery, the charging condition is 16 mA / g, the constant current charging at a voltage of 5.0 V, the discharging condition is 16 mA / g, the constant current discharging at the final voltage of 3.5 V, A discharge capacity at 16 mA/g was determined. All charge/discharge tests were conducted at 45°C. Table 1 shows the results.

From the above results, it can be seen that the LISICON-type crystal particles obtained by the method of Example 1 exhibit superior discharge capacity compared to the LISICON-type crystal particles obtained by the method of Comparative Example 1. As can be seen from FIGS. 1 and 2, this is probably because the LISICON-type crystal particles obtained by the method of Example 1 are fine particles with a high degree of crystallinity.

Claims (4)

The following steps (I)-(III):
(I) While stirring the mixed solution (a-1) containing a lithium compound, a silicate compound and water, the mixed solution (a-2) containing a phosphoric acid compound and water is added to the mixed solution (a -1) After dropping the entire amount at a rate of 0.1 part by mass / min to 0.4 part by mass / min with respect to 10 parts by mass, stirring for 15 minutes to 12 hours , the pH at 25 ° C. is 10.5 ~ Step 14 of preparing a mixed solution containing trilithium phosphate (II) After subjecting the obtained mixed solution to a hydrothermal reaction at 100 ° C. or higher, the hydrothermal reaction product is washed and then dried. , a step of obtaining a precursor mixture (III) calcining the obtained precursor mixture at 400 ° C. to 1000 ° C., the following formula (1):
Li4 _{- xSi1 - xPxO4} (1)
(In formula (1), x represents a number satisfying 0.1≤x≤0.9 .)
A method for producing LISICON-type crystal particles for a solid electrolyte of a lithium ion secondary battery represented by In obtaining the mixed solution (A) in step (I), the mass ratio ((a-1):(a-2)) of the mixed solution (a-1) and the mixed solution (a-2) to be mixed is The method for producing LISICON-type crystal particles for a solid electrolyte of a lithium ion secondary battery according to claim 1, wherein the ratio is 5:1 to 2:3. The lithium according to claim 1 or 2 , wherein 5 parts by mass to 50 parts by mass of water is used with respect to 1 part by mass of the dry mass of the hydrothermal reaction product when washing the hydrothermal reaction product in step (II). A method for producing LISICON-type crystal particles for a solid electrolyte of an ion secondary battery. 4. The LISICON-type crystal particles for a solid electrolyte of a lithium ion secondary battery according to any one of claims 1 to 3, wherein the sintering in step (III) is performed under an air atmosphere, an inert gas atmosphere, or reducing conditions. how to manufacture

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