JP2015076284A - Method for manufacturing solid electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solid electrolyte capable of shortening manufacturing time largely.SOLUTION: There is provided a method for manufacturing a solid electrolyte containing a Li element, S element and P element including a step of contacting lithium sulfide with at least one kind of raw material containing sulphur and phosphorus selected from phosphorus sulfide, element sulphur and element phosphorus in an ether solvent under a condition of following formula. A:B=74±0.5:26±0.5, where A is the amount (mole) of the lithium sulfide used in the step, and B is the amount (mole) of the phosphorus sulfide, the element sulphur and the element phosphorus used in the step in terms of PS.

Description

  The present invention relates to a method for producing a sulfide-based solid electrolyte.

In recent years, there has been an increasing demand for lithium ion secondary batteries used in personal digital assistants, portable electronic devices, small household power storage devices, motorcycles powered by motors, electric vehicles, hybrid electric vehicles, and the like.
As a method for ensuring the safety of a lithium ion secondary battery, an all-solid secondary battery using an inorganic solid electrolyte instead of an organic electrolyte has been studied.

  As a solid electrolyte of an all-solid secondary battery, for example, a sulfide-based solid electrolyte using sulfide as a raw material has been studied. It is known that a sulfide-based solid electrolyte is produced by reacting lithium sulfide and diphosphorus pentasulfide in a solvent (for example, Patent Documents 1 and 2 and Non-Patent Document 1).

International Publication No. 2004/093099 International Publication No. 2009/047977

J. et al. Am. Chem. Soc. 2013, 135, 975-978 “Anomalous High Ionic Conductivity of Nanoporous β-Li3PS4”

  An object of this invention is to provide the manufacturing method of the solid electrolyte which can shorten manufacturing time.

According to the present invention, the following method for producing a solid electrolyte is provided.
1. Lithium sulfide,
At least one raw material containing sulfur and phosphorus selected from phosphorus sulfide, elemental sulfur and elemental phosphorus,
Including a step of contacting in an ether solvent under the conditions of the following formula:
A method for producing a solid electrolyte containing Li element, S element and P element.
A: B = 74 ± 0.5: 26 ± 0.5
(In the formula, A is the amount (mole) of the lithium sulfide used in the step. B is the phosphorus sulfide, the single sulfur and the single phosphorus used in the step converted into P ₂ S ₅ . (The amount (moles) of the phosphorus sulfide, the elemental sulfur, and the elemental phosphorus when it is used.)
2. 2. The method for producing a solid electrolyte according to 1, wherein the solvent has a boiling point of 65 to 200 ° C.
3. The method for producing a solid electrolyte according to 1 or 2, wherein the ether solvent is a cyclic ether.
4). 4. The method for producing a solid electrolyte according to any one of 1 to 3, wherein the ether solvent is tetrahydrofuran.
5. The manufacturing method of the solid electrolyte in any one of 1-4 whose average particle diameter of the said lithium sulfide is 100 micrometers or less.
6). At least one feedstock diphosphorus pentasulfide (P 2 _{S 5)} The method of any of the solid electrolyte prepared according to 1-5 are comprising the sulfur and phosphorus.
7). The manufacturing method of the solid electrolyte in any one of 1-6 whose temperature of the said contact is 20-200 degreeC.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the solid electrolyte which can shorten manufacturing time can be provided.

Is a graph showing the relationship between the reaction time and the unreacted Li ₂ S in Comparative Examples 1-3 and Examples 1-3.

The method for producing a solid electrolyte of the present invention includes a step of bringing the following raw materials (A) and (B) into contact in an ether solvent under the conditions of the following formula.
(A) Lithium sulfide (B) Raw material containing sulfur and phosphorus selected from phosphorus sulfide, elemental sulfur and elemental phosphorus A: B = 74 ± 0.5: 26 ± 0.5
(In the formula, A is the amount (mol) of lithium sulfide used in the above step. B is the phosphorus sulfide, simple sulfur and simple phosphorus used in the above step when converted to P ₂ S ₅ . (The amounts (moles) of phosphorus sulfide, elemental sulfur and elemental phosphorus.)

(A) Lithium sulfide Lithium sulfide can be used without particular limitation, but high purity is preferred. Lithium sulfide can be produced, for example, by the methods described in JP-A-7-330312, JP-A-9-283156, JP-A 2010-163356, JP-A 2011-084438, and JP-A 2011-136899.

Specifically, lithium hydroxide and hydrogen sulfide are reacted at 70 ° C. to 300 ° C. in a hydrocarbon-based organic solvent to produce lithium hydrosulfide, and then the reaction solution is dehydrosulfurized to form lithium sulfide. Can be synthesized (Japanese Patent Laid-Open No. 2010-163356).
In addition, lithium hydroxide and hydrogen sulfide are reacted at 10 ° C. to 100 ° C. in an aqueous solvent to produce lithium hydrosulfide, and then the reaction liquid is dehydrosulfurized to synthesize lithium sulfide (special feature). Open 2011-084438).

  The lithium sulfide preferably has a total lithium oxide lithium salt content of 0.15% by mass or less, more preferably 0.1% by mass or less, and a lithium N-methylaminobutyrate content. The content is preferably 0.15% by mass or less, more preferably 0.1% by mass or less. When the total content of the lithium salt of sulfur oxide is 0.15% by mass or less, the solid electrolyte obtained by the melt quenching method or the mechanical milling method becomes a glassy electrolyte (fully amorphous). On the other hand, when the total content of the lithium salt of sulfur oxide exceeds 0.15% by mass, the obtained electrolyte may become a crystallized product from the beginning.

  In addition, when the content of lithium N-methylaminobutyrate is 0.15% by mass or less, a deteriorated product of lithium N-methylaminobutyrate does not deteriorate the cycle performance of the lithium ion battery. When lithium sulfide with reduced impurities is used, a high ion conductive electrolyte can be obtained.

When lithium sulfide is produced based on the above-mentioned JP-A-7-330312 and JP-A-9-283156, it is preferable to purify the lithium sulfide because it contains a lithium salt of a sulfur oxide.
On the other hand, lithium sulfide produced by the method for producing lithium sulfide described in JP-A-2010-163356 may be used without purification because it contains a very small amount of sulfur oxide lithium salt or the like.
As a preferable purification method, for example, a purification method described in International Publication No. WO2005 / 40039 and the like can be mentioned. Specifically, the lithium sulfide obtained as described above is washed at a temperature of 100 ° C. or higher using an organic solvent.
From the viewpoint of further increasing the reaction rate, it is preferable to use lithium sulfide described in JP2011-136899A. By modifying lithium sulfide using a solvent containing a polar solvent, lithium sulfide having a large specific surface area can be prepared.

  However, the present invention allows the reaction to proceed easily without the above modification by reacting in a specific solvent. Therefore, from the viewpoint of reducing the production process, the above modification is performed. It is preferable not to do so. This is particularly useful when there is a greater merit in manufacturing cost when the manufacturing process is reduced than when the reaction rate is further increased.

Further, the average particle diameter of the lithium sulfide particles used as a raw material is preferably 100 μm or less, more preferably 80 μm or less, and further preferably 50 μm or less.
The particle size of the lithium sulfide particles is measured by a LASER diffraction method using a Mastersizer 2000 of MALVERN and calculated from the volume-based average particle size. The measurement is desirably performed directly in the slurry state without passing through the dry state. This is because once drying is performed, particles are aggregated at the time of drying, and the apparent particle size may be increased. The lithium sulfide particles preferably have a pore volume of 0.01 ml / g or more. When the pore volume is 0.01 ml / g or more, it is easy to react with raw materials other than lithium sulfide particles, and the lithium sulfide particles are easily crushed and more easily reacted.

(B) Raw material to be a sulfur source and a phosphorus source As the raw material (B), at least one selected from phosphorus sulfide, elemental sulfur and elemental phosphorus is used.
The raw material is selected to include sulfur and phosphorus. For example, phosphorus sulfide, phosphorus sulfide and elemental sulfur, phosphorus sulfide and elemental phosphorus, elemental sulfur and elemental phosphorus are used.
Preferably, phosphorus sulfide or a combination of elemental sulfur and elemental phosphorus is used. More preferred is phosphorus sulfide.

As phosphorus sulfide, P ₂ S ₃ (phosphorus trisulfide) _, P ₂ S ₅ (phosphorus pentasulfide), or the like can be used. P ₂ S ₅ is particularly preferable.
P ₂ S ₅ can be used without particular limitation as long as it is industrially manufactured and sold.

(C) Halogen compound A halogen compound can be further used as a raw material.
Examples of the halogen compound include LiF, LiCl, LiBr, LiI, BCl ₃ , BBr ₃ , BI ₃ , AlF ₃ , AlBr ₃ , AlI ₃ , AlCl ₃ , SiF ₄ , SiCl ₄ , SiCl ₃ , Si ₂ Cl ₆ , SiBr _{4. , SiBrCl 3, SiBr 2 Cl 2} , SiI 4, PF 3, PF 5, PCl 3, PCl 5, PBr 3, PI 3, P 2 Cl 4, P 2 I 4, SF 2, SF 4, SF 6, S ₂ F ₁₀ , SCl ₂ , S ₂ Cl ₂ , S ₂ Br ₂ , GeF ₄ , GeCl ₄ , GeBr ₄ , GeI ₄ , GeF ₂ , GeCl ₂ , GeBr ₂ , GeI ₂ , AsF ₃ , AsCl ₃ , AsBr ₃ , _{AsI 3, AsF 5, SeF 4} , SeF 6, SeCl 2, SeCl 4, Se 2 Br 2, SeBr _{, SnF 4, SnCl 4, SnBr} 4, SnI 4, SnF 2, SnCl 2, SnBr 2, SnI 2, SbF 3, SbCl 3, SbBr 3, SbI 3, SbF 5, SbCl 5, PbF 4, PbCl 4, PbF _{2, PbCl 2, PbBr 2,} PbI 2, BiF 3, BiCl 3, BiBr 3, BiI 3, TeF 4, Te 2 F 10, TeF 6, TeCl 2, TeCl 4, TeBr 2, TeBr 4, TeI 4, NaI , NaF, NaCl, NaBr and the like. A lithium or phosphorus compound is preferred. Moreover, a bromine compound is preferable. Specifically, preferably LiCl, _LiBr, LiI, is PCl _5, PCl _3, PBr ₅ and PBr _3, more preferably LiCl, LiBr, LiI and PBr _3, particularly preferably LiBr, and PBr _3.

Furthermore, you may add the compound (vitrification promoter) which reduces a glass transition temperature as a raw material (D). Examples of vitrification promoters include Li ₃ PO ₄ , Li ₄ SiO ₄ , Li ₄ GeO ₄ , Li ₃ BO ₃ , LiBO ₂ (lithium metaborate), Li ₃ AlO ₃ , Li ₃ CaO ₃ , Li ₃ InO. _3, inorganic compounds such as Na ₃ PO ₄ , Na ₄ SiO ₄ , Na ₄ GeO ₄ , Na ₃ BO ₃ , Na ₃ AlO ₃ , Na ₃ CaO ₃ , and Na ₃ InO ₃ .

In addition to the raw materials (A) to (D), silicon (Si), Na ₂ S (sodium sulfide), POCl ₃ , POBr _{3 and the} like can also be used.

About the mixture ratio of each said raw material, the molar ratio of raw material (A): raw material (B) is 74 ± 0.5 (73.5-74.5): 26 ± 0.5 (25.5-26.5). It is. Preferably (A) :( B) = 74 ± 0.4: 26 ± 0.4, more preferably (A) :( B) = 74 ± 0.3: 26 ± 0.3, Preferably (A) :( B) = 74 ± 0.2: 26 ± 0.2. In this range, the manufacturing time can be shortened.
Most preferably, component (A) is lithium sulfide and component (B) is diphosphorus pentasulfide.

  The ratio [(A) + (B) :( C)] of the molar amount of the raw material (C) to the total molar amount of the raw materials (A) and (B) is preferably 50:50 to 99: 1 (molar ratio). More preferably 55:45 to 98: 2 (molar ratio), still more preferably 60:40 to 98: 2 (molar ratio), and particularly preferably 70:30 to 98: 2. .

The blending amount of the raw material (D) (vitrification accelerator) is preferably 1 to 10 mol%, particularly 1 to 5 mol%, based on the total of the raw materials (A), (B) and (C). It is preferable that
The solid electrolyte glass obtained by the present invention may consist essentially of the raw materials (A) and (B) and optionally the raw materials (C) and (D), and only from these components. It may be.
“Substantially” means that the entire raw material mainly consists of the raw materials (A) and (B), and optionally the raw materials (C) and (D). It means that it is not less than wt%, or not less than 98 wt%.

  In the production method of the present invention, the raw material is contacted in an ether solvent. By using an ether solvent, the raw material is easily dissolved, and a solid electrolyte can be efficiently produced without using a mill or the like.

An ether solvent is a solvent having one or more ether bonds. The ether bond is represented as —R—O—R—, wherein each R is independently an organic group. R may be bonded to each other to form a ring.
Examples of the ether solvent include diethyl ether, diisopropyl ether, t-butyl methyl ether, phenyl methyl ether, dimethoxymethane, diethoxyethane, tetrahydrofuran (THF), dioxane, cyclopentyl methyl ether and the like.

The ether solvent is represented by —R—O—R—, and R is independently an organic group, and a solvent in which R is bonded to each other to form a ring, that is, a cyclic ether is preferable.
As the cyclic ether, it is more preferable that each R is independently a substituted or unsubstituted hydrocarbon group. More preferably, each R is independently an unsubstituted hydrocarbon group. Even more preferably, each R is independently a hydrocarbon group having 1 to 20 carbon atoms. THF is most preferred.

  In addition, the other solvent may be mixed in the solvent at the time of manufacture. Examples of other solvents include hexane (solubility parameter is 7.3), heptane, octane, decane, cyclohexane, ethylcyclohexane, methylcyclohexane, toluene (solubility parameter is 8.8), xylene (solubility parameter is 8.8). ), Ethylbenzene, ipzol 100 (manufactured by Idemitsu Kosan Co., Ltd.), ipsol 150 (manufactured by Idemitsu Kosan Co., Ltd.), IP solvent (manufactured by Idemitsu Kosan Co., Ltd.), liquid paraffin, petroleum ether, cyclopentyl methyl ether and the like.

  The solvent does not need to be dehydrated, but the amount of water is preferably 50 ppm or less, more preferably 30 ppm or less, because the amount of water may affect the amount of alkali metal hydroxide in the micronized product by-produced. .

Furthermore, the boiling point of the solvent is preferably 65 to 200 ° C. If the boiling point is low, the vapor pressure at the reaction temperature is high and a pressure vessel may be necessary. If the boiling point is high, the load for evaporating the solvent from the produced solid electrolyte may increase.
Examples of the solvent having a boiling point of 65 to 200 ° C. include diisopropyl ether, phenylmethyl ether, diethoxyethane, THF, dioxane, cyclopentylmethyl ether and the like.

Regarding the conditions for bringing the raw material into contact with the solvent, the temperature is preferably 15 to 200 ° C, particularly preferably 20 to 150 ° C.
Although depending on the reaction temperature, the time is preferably 0.5 to 25 hours, more preferably 1 to 23 hours, and particularly preferably 2 to 20 hours.
The amount of the solvent may be such that the raw material becomes a solution or slurry by the addition of the solvent. Usually, the amount of the raw material (total amount) added to 1 liter of solvent is about 0.001 to 1 kg, preferably 0.005 to 0.5 kg, and particularly preferably 0.01 to 0.3 kg. .

  The contact method is not particularly limited, and known devices such as a reaction vessel with a stirrer and various mills can be used. In the production method of the present invention, a solid electrolyte can be produced efficiently without using a special mixing and grinding device such as a bead mill, but the above device may be used as necessary.

Production Example 1 [Production of lithium sulfide]
Under a nitrogen stream, 270 g of toluene as a nonpolar solvent was added to a 600 ml separable flask, 30 g of lithium hydroxide (Honjo Chemical Co., Ltd.) was added, and the mixture was maintained at 95 ° C. while stirring with a full zone stirring blade 300 rpm. The temperature was raised to 104 ° C. while blowing hydrogen sulfide into the slurry at a supply rate of 300 ml / min. From the separable flask, an azeotropic gas of water and toluene was continuously discharged. This azeotropic gas was dehydrated by condensing with a condenser outside the system. During this time, the same amount of toluene as the distilled toluene was continuously supplied to keep the reaction liquid level constant.
The amount of water in the condensate gradually decreased, and no distillation of water was observed 6 hours after the introduction of hydrogen sulfide (the total amount of water was 22 ml). During the reaction, the solid was dispersed and stirred in toluene, and there was no moisture separated from toluene. Thereafter, the hydrogen sulfide was switched to nitrogen and circulated at 300 ml / min for 1 hour. The solid content was filtered and dried to obtain white powder of lithium sulfide.

  When the obtained powder was analyzed by hydrochloric acid titration and silver nitrate titration, the purity of lithium sulfide was 99.0%. Further, X-ray diffraction measurement confirmed that no peaks other than the crystal pattern of lithium sulfide were detected. The average particle size was 450 μm (slurry solution). In addition, the particle diameter of lithium sulfide was measured using Mastersizer 2000 of MALVERN by the LASER diffraction method, and calculated from the volume standard average particle diameter.

It was 14.8 m < ² > / g when the specific surface area of the obtained lithium sulfide was measured using AUTOSORB6 (made by Sysmex Corporation) with the BET method by nitrogen gas. The pore volume was measured with the same device as the specific surface area, and it was 0.15 ml / g when determined by interpolating to 0.99 from a measurement point of relative pressure (P / P ₀ ) of 0.99 or more. .

Production Example 2 [Atomization treatment]
26 g of lithium sulfide obtained in Production Example 1 was weighed into a Schlenk bottle in a glove box. Under a nitrogen atmosphere, 500 ml of dehydrated toluene (manufactured by Wako Pure Chemical Industries) and 250 ml of dehydrated ethanol (manufactured by Wako Pure Chemical Industries) were added in this order, and the mixture was stirred with a stirrer at room temperature for 24 hours. After the reforming treatment, the bath temperature was raised to 120 ° C., and hydrogen sulfide gas was circulated at 200 ml / min for 90 minutes to carry out the treatment. After the hydrogen sulfide gas treatment, the solvent was distilled off under a nitrogen stream at room temperature, and further dried under vacuum at room temperature for 2 hours to recover atomized lithium sulfide.

The atomized lithium sulfide was evaluated in the same manner as in Production Example 1. The lithium sulfide had a purity of 97.2%, an amount of lithium hydroxide of 0.3%, an average particle size of 9.1 μm (undried slurry solution), a specific surface area of 43.2 m ² / g, and a pore volume of 0.68 ml / g. It was. Purity and lithium hydroxide content were each determined by titration. The total analysis value does not reach 100% because it contains lithium carbonate, other ionic salts, and residual solvent.

Example 1
The inside of the flask equipped with a stirrer was replaced with nitrogen, and 1.20 g of lithium sulfide of Production Example 2 (1.16 g corresponding to lithium sulfide in consideration of purity), diphosphorus pentasulfide (manufactured by Aldrich) 1.97 g, 30 ml of tetrahydrofuran (THF: Wako Pure Chemical Industries, Ltd.) with a water content of 10 ppm was charged (A / B (molar ratio) = 74.0 / 26.0), room temperature (25 ° C.) For 20 hours. After completion of the reaction, the solid component was separated by filtration. After that, THF was further added and stirred for 10 minutes, and then the solid component was filtered. This operation was repeated a total of 3 times. Then, THF was removed by drying under reduced pressure at room temperature, and further dried at 80 ° C. for 2 hours.

The ionic conductivity of the obtained solid electrolyte was 0.8 × 10 ⁻⁴ S / cm. As a result of X-ray diffraction (CuKα: λ = 1.5418Å), no peak was observed other than the halo pattern derived from amorphous, and it was confirmed that the glass was solid electrolyte glass.

Furthermore, it was vacuum-dried at 140 ° C. for 2 hours to produce a solid electrolyte. The ionic conductivity of the obtained solid electrolyte was 2.4 × 10 ⁻⁴ S / cm. As a result of X-ray diffraction (CuKα: λ = 1.5418 ＝) of this electrolyte, a peak derived from the Li ₃ PS ₄ (β) crystal could be observed.

The ion conductivity was measured by the following method.
The solid electrolyte was filled in a tablet molding machine, and a compact was obtained by applying a pressure of 10 MPa. Furthermore, a mixture obtained by mixing carbon and a solid electrolyte at a weight ratio of 1: 1 as an electrode is placed on both sides of the molded body, and pressure is applied again with a tablet molding machine, thereby forming a molded body for conductivity measurement (diameter of about 10 mm). , About 1 mm thick). The molded body was subjected to ionic conductivity measurement by AC impedance measurement. The conductivity value was a value at 25 ° C.

After the reaction, unreacted (residual) Li ₂ S was determined, and the progress of the reaction was examined. Residual Li ₂ S was calculated from the XRD measurement results from the area of the entire halo pattern and the area of the remaining Li ₂ S crystal peak. The results are shown in Table 1. The relationship between the reaction time and unreacted (residual) Li ₂ S is shown in FIG. In the table, G is the conductivity of glass, and GC is the conductivity of glass ceramics. In the table, the amount of residual Li ₂ S (unreacted) is calculated as a ratio of the total peak area of XRD to the peak area of residual Li ₂ S.

Example 2
A solid electrolyte was produced in the same manner as in Example 1 except that the reaction time was 12 hours in Example 1, and the conductivity and residual Li ₂ S were determined. The results are shown in Table 1 and FIG.

Example 3
A solid electrolyte was produced in the same manner as in Example 1 except that the reaction time was 5 hours in Example 1, and the conductivity and residual Li ₂ S were determined. The results are shown in Table 1 and FIG.

Example 4
In Example 1, a solid electrolyte was produced in the same manner except that the reaction temperature was changed from room temperature to 50 ° C. and the reaction time was changed to 5 hours, and conductivity and residual Li ₂ S were obtained. The results are shown in Table 1.

Comparative Example 1
A solid electrolyte was produced in the same manner as in Example 1 except that A / B (molar ratio) = 75.0: 25.0 in Example 1, and the conductivity and residual Li ₂ S were determined. The results are shown in Table 1 and FIG.

Comparative Example 2
A solid electrolyte was produced in the same manner as in Comparative Example 1 except that the reaction time was 5 hours in Comparative Example 1, and the conductivity and residual Li ₂ S were determined. The results are shown in Table 1 and FIG.

Comparative Example 3
A solid electrolyte was produced in the same manner as in Comparative Example 1 except that the reaction time was 40 hours in Comparative Example 1, and the conductivity and residual Li ₂ S were determined. The results are shown in Table 1 and FIG.

  The production method of the present invention is suitable as a method for producing a sulfide-based solid electrolyte.

Claims (7)

Lithium sulfide,
At least one raw material containing sulfur and phosphorus selected from phosphorus sulfide, elemental sulfur and elemental phosphorus,
Including a step of contacting in an ether solvent under the conditions of the following formula:
A method for producing a solid electrolyte containing Li element, S element and P element.
A: B = 74 ± 0.5: 26 ± 0.5
(In the formula, A is the amount (mole) of the lithium sulfide used in the step. B is the phosphorus sulfide, the single sulfur and the single phosphorus used in the step converted into P ₂ S ₅ . (The amount (moles) of the phosphorus sulfide, the elemental sulfur, and the elemental phosphorus when it is used.)   The method for producing a solid electrolyte according to claim 1, wherein the solvent has a boiling point of 65 to 200 ° C.   The method for producing a solid electrolyte according to claim 1, wherein the ether solvent is a cyclic ether.   The method for producing a solid electrolyte according to claim 1, wherein the ether solvent is tetrahydrofuran.   The method for producing a solid electrolyte according to claim 1, wherein the lithium sulfide has an average particle size of 100 μm or less. The method for producing a solid electrolyte according to claim 1, wherein the at least one raw material containing sulfur and phosphorus is diphosphorus pentasulfide (P ₂ S ₅ ).   The temperature of the said contact is 20-200 degreeC, The manufacturing method of the solid electrolyte in any one of Claims 1-6.

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