JP5414143B2 - Method for producing sulfide solid electrolyte - Google Patents

Description

  The present invention relates to a method for producing a sulfide-based solid electrolyte. More specifically, the present invention relates to a production method for efficiently producing a particulate sulfide-based solid electrolyte powder.

  In the current lithium ion secondary battery, an organic electrolyte is used as an electrolyte. Although organic electrolytes have high ionic conductivity and excellent performance as secondary batteries, the electrolyte is liquid and flammable, so there are concerns over intrinsic safety such as leakage and ignition when used as batteries. ing.

  As an electrolyte for the next-generation lithium secondary battery, development of a safer solid electrolyte is desired. As a method for producing a solid electrolyte for a lithium secondary battery, a production method by mechanical grinding such as a mechanical milling method is known.

Patent Document 1 discloses a lithium ion conductive sulfide crystal for firing a sulfide glass having a composition of Li ₂ S: 68 to 74 mol% and P ₂ S ₅ : 26 to 32 mol% at a specific temperature. A method for producing a vitrified glass is disclosed.
This Patent Document 1 discloses that a mechanical milling process is disclosed as a method of using a mixture of starting materials as a sulfide-based glass, and it is preferable to use a ball mill from the viewpoint of obtaining large mechanical energy in the mechanical milling process. Has been. Furthermore, it is described that it is preferable to use a planetary ball mill because it can generate very high impact energy efficiently. In the examples, a planetary ball mill is used to obtain sulfide glass which is a white yellow powder.

However, when a sulfide-based solid electrolyte is produced by the method disclosed in Patent Document 1, the reactant may adhere to the wall surface or ball surface of a container used for mechanical milling, making it difficult to take out the product. For this reason, when it was going to manufacture a sulfide type solid electrolyte industrially with a mechanical milling method, there existed concern that the manufacture yield of a target object may worsen or it may become a cause of the contamination at the time of the next manufacture. Furthermore, in order to increase the production yield of the target product, re-grinding is necessary, which is an obstacle to efficiently manufacturing the target product.
Patent Document 1 does not describe the particle size of the obtained powder.
JP 2005-228570 A

  An object of the present invention is to provide a method for producing a sulfide-based solid electrolyte with a high yield and an efficient one-step reaction.

As a result of intensive studies, the inventors have found that the amount of product adhering to the reaction vessel or the ball can be significantly reduced by adding specific mechanical energy and reacting, and have completed the present invention.
According to the present invention, the following method for producing a sulfide-based solid electrolyte is provided.
1. A production method for obtaining a sulfide-based solid electrolyte in one step by mechanical pulverization using a ball mill, wherein 0.02 to 1 kJ per second of energy is applied to 1 kg of raw material at the time of mechanical pulverization, and the particle size is 2000 μm or less. A method for producing a sulfide-based solid electrolyte in which 80% by mass or more of the powder is obtained.
2. 2. The production method according to 1, wherein the sulfide-based solid electrolyte further contains sulfur and two or more elements selected from lithium, phosphorus, silicon, and germanium.
3. 3. The manufacturing method according to 1 or 2, wherein the portion in contact with the sulfide-based solid electrolyte in the ball mill is made of alumina, zirconia, or alumina and zirconia.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the sulfide type solid electrolyte by a one step reaction with a high yield can be provided.

  The sulfide-based solid electrolyte production method of the present invention produces a solid electrolyte in one step by mechanical pulverization using a ball mill.

  As the ball mill used in the production method of the present invention, a rolling ball mill, a vibration ball mill, a planetary ball mill, or the like can be used.

Furthermore, in the manufacturing method of the present invention, mechanical energy of 0.02 to 1 kJ per second is applied to 1 kg of raw material (charged material) in mechanical pulverization using a ball mill. When the mechanical energy to be added is less than 0.02 kJ, the reaction rate is remarkably slow and the reaction time may be long. For this reason, manufacturing efficiency cannot be achieved. On the other hand, when the mechanical energy applied exceeds 1 kJ, the amount of contents attached to the reaction vessel or the ball increases, and it may be difficult to remove. In addition, since the content attached to the reaction vessel or the ball has a large particle size, the production efficiency may be lowered in that the particle size is not suitable for a solid electrolyte member for a battery unless pulverized again.
Preferably, mechanical energy of 0.1 to 0.5 kJ per second is applied to 1 kg.

The particle size of the powder pulverized by the ball mill is 80% by mass or more when the particle size is 2000 μm or less. If it is less than 80% by mass, it may cause clogging during transfer. Moreover, it is not preferable to use a solid electrolyte having a thickness exceeding 2000 μm as a solid electrolyte because the interface resistance between the solid electrolyte layer and the electrode increases. For this reason, particles having a particle size larger than 2000 μm need to be further pulverized to have a small particle size. In this case, since it is necessary to use smaller balls, it is necessary to transfer the powder.
The product adhering to the reaction vessel or ball after ball milling exceeds 2000 μm in particle size.

  Further, there is a concern that a part of the reaction product may be denatured due to heat accumulation in the reaction system during pulverization by the ball mill. In this case, the temperature in the reaction system is preferably controlled by a cooling jacket or the like. More preferably, the temperature in the reaction system is preferably maintained at 300 ° C. or lower. When the temperature in the reaction system exceeds 300 ° C., a by-product containing a crystal having low ionic conductivity may be generated.

In the ball mill, the portion in contact with the sulfide-based solid electrolyte is preferably made of alumina, zirconia, or alumina and zirconia. Specifically, a container for storing raw materials, a ball stirred in the container, and the like. These members / parts may be made of alumina, zirconia or the like, or may be coated on the surface with these substances.
By using such a ball mill, it is possible to further reduce the amount of the product adhering to the portion in contact with the sulfide-based solid electrolyte.

The sulfide solid electrolyte produced by the production method of the present invention can use a lithium ion conductive solid material such as an organic compound, an inorganic compound, or a material comprising both organic and inorganic compounds, and is well known in the lithium ion battery field. Can be used.
However, the sulfide-based solid electrolyte preferably contains two or more elements selected from lithium, phosphorus, silicon, and germanium in addition to sulfur in terms of ease of application to batteries.
More preferably, it contains sulfur and lithium, and one or more elements selected from phosphorus, silicon, and germanium in that a high ion conductive solid electrolyte member is obtained.

Examples of the raw material for the sulfide-based solid electrolyte that can be used in the present invention include lithium sulfide, diphosphorus pentasulfide, simple phosphorus, simple sulfur, simple silicon, simple germanium, silicon sulfide, germanium sulfide, and the like.
The sulfide-based solid electrolyte is preferably produced using lithium sulfide and diphosphorus pentasulfide and / or simple phosphorus and simple sulfur as raw materials. Hereinafter, these preferable raw materials will be described.

As lithium sulfide (Li ₂ S), those commercially available without particular limitation can be used, but those having high purity are preferable as described below.
Lithium sulfide has a total content of lithium salts of sulfur oxides as impurities of 0.15% by mass or less, preferably 0.1% by mass or less. Furthermore, the content of lithium N-methylaminobutyrate that may be mixed during the production process is 0.15% by mass or less, 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 obtained electrolyte is a glassy electrolyte (fully amorphous). That is, when the total content of the lithium salt of sulfur oxide exceeds 0.15% by mass, the obtained electrolyte is a crystallized product from the beginning, and the ionic conductivity of this crystallized product is low.
Furthermore, even if this crystallized product is subjected to a heat treatment, the crystallized product is not changed, and a solid electrolyte having high ionic conductivity cannot be obtained.

Further, 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 battery.
Therefore, in order to obtain a high ion conductive electrolyte, it is necessary to use lithium sulfide with reduced impurities.

The method for producing lithium sulfide is not particularly limited as long as it can reduce at least the above impurities.
For example, it can also be obtained by purifying lithium sulfide produced by the following method. Among these production methods, the method a or b is particularly preferable.
a. A method in which lithium hydroxide and hydrogen sulfide are reacted at 0 to 150 ° C. in an aprotic organic solvent to produce lithium hydrosulfide, and this reaction solution is then desulfurized at 150 to 200 ° C. -330312).
b. A method of directly producing lithium sulfide by reacting lithium hydroxide and hydrogen sulfide at 150 to 200 ° C. in an aprotic organic solvent (Japanese Patent Laid-Open No. 7-330312).
c. A method of reacting lithium hydroxide and a gaseous sulfur source at a temperature of 130 to 445 ° C. (Japanese Patent Laid-Open No. 9-283156).

There is no restriction | limiting in particular as a purification method of the lithium sulfide obtained as mentioned above. Preferable purification methods include, for example, International Publication No. WO2005 / 40039.
Specifically, the lithium sulfide obtained as described above is washed at a temperature of 100 ° C. or higher using an organic solvent.
The organic solvent used for washing is preferably an aprotic polar solvent, and more preferably, the aprotic organic solvent used for lithium sulfide production and the aprotic polar organic solvent used for washing are the same. .
Examples of the aprotic polar organic solvent preferably used for washing include aprotic polar organic compounds such as amide compounds, lactam compounds, urea compounds, organic sulfur compounds, cyclic organophosphorus compounds, Or it can use suitably as a mixed solvent. In particular, N-methyl-2-pyrrolidone (NMP) is selected as a good solvent.

The amount of the organic solvent used for washing is not particularly limited, and the number of times of washing is not particularly limited, but is preferably 2 or more. Cleaning is preferably performed under an inert gas such as nitrogen or argon.
Further, preferably, the washed lithium sulfide is used at a temperature equal to or higher than the boiling point of the organic solvent used for washing at a normal gas pressure or a reduced pressure for 5 minutes or more under an inert gas stream such as nitrogen, preferably about 2 to 2 minutes. Dry for 3 hours or more.

As long as diphosphorus pentasulfide (P ₂ S ₅ ) is industrially manufactured and sold, it can be used without particular limitation. In place of P ₂ S ₅ , elemental phosphorus (P) and elemental sulfur (S) in a corresponding molar ratio can also be used. Simple phosphorus (P) and simple sulfur (S) can be used without particular limitation as long as they are industrially produced and sold.

The mixing molar ratio of the above lithium sulfide, diphosphorus pentasulfide or simple phosphorus and simple sulfur is usually 50:50 to 80:20, preferably 60:40 to 75:25, from the viewpoint of improving ion conductivity.
Particularly preferably, it is about Li ₂ S: P ₂ S ₅ = 70: 30 (molar ratio).

When the sulfide solid electrolyte obtained by the production method of the present invention is heat-treated at a predetermined temperature, a crystallized solid electrolyte can be generated. The heat treatment temperature is preferably 190 ° C to 340 ° C, more preferably 195 ° C to 335 ° C, and particularly preferably 200 ° C to 330 ° C.
When the solid electrolyte produced by the above preferred mixing molar ratio is crystallized, in X-ray diffraction (CuKα: λ = 1.5418Å), 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, Diffraction peaks at 19.8 ± 0.3 deg, 21.8 ± 0.3 deg, 23.8 ± 0.3 deg, 25.9 ± 0.3 deg, 29.5 ± 0.3 deg, 30.0 ± 0.3 deg A lithium ion conductive solid electrolyte having the following can be obtained. A solid electrolyte having such a crystal structure has extremely high lithium ion conductivity.

Production Example (1) Production of Lithium Sulfide (Li ₂ S) Lithium sulfide was produced according to the method of the first aspect (two-step method) of JP-A-7-330312. Specifically, N-methyl-2-pyrrolidone (NMP) 3326.4 g (33.6 mol) and lithium hydroxide 287.4 g (12 mol) were charged into a 10 liter autoclave equipped with a stirring blade, and 300 rpm, 130 The temperature was raised to ° C. After the temperature rise, hydrogen sulfide was blown into the liquid at a supply rate of 3 liters / minute for 2 hours. Subsequently, this reaction solution was heated in a nitrogen stream (200 cc / min) to dehydrosulfide a part of the reacted hydrogen sulfide. As the temperature increased, water produced as a by-product due to the reaction between the hydrogen sulfide and lithium hydroxide started to evaporate, but this water was condensed by the condenser and extracted out of the system. While water was distilled out of the system, the temperature of the reaction solution rose, but when the temperature reached 180 ° C., the temperature increase was stopped and the temperature was kept constant. After the dehydrosulfurization reaction was completed (about 80 minutes), the reaction was completed to obtain lithium sulfide.

(2) Purification of lithium sulfide After decanting NMP in the 500 mL slurry reaction solution (NMP-lithium sulfide slurry) obtained in (1) above, 100 mL of dehydrated NMP was added and stirred at 105 ° C. for about 1 hour. . NMP was decanted at that temperature. Further, 100 mL of NMP was added, stirred at 105 ° C. for about 1 hour, NMP was decanted at that temperature, and the same operation was repeated a total of 4 times. After completion of the decantation, lithium sulfide was dried at 230 ° C. (temperature higher than the boiling point of NMP) under a nitrogen stream for 3 hours under normal pressure. The impurity content in the obtained lithium sulfide was measured. Incidentally, lithium sulfite _(Li 2 _SO 3), the content of each sulfur oxide lithium sulfate _(Li 2 SO ₄₎ and lithium thiosulfate _{(Li 2 S 2 O 3)} , and N- methylamino acid lithium (LMAB) Was quantified by ion chromatography. As a result, the total content of sulfur oxides was 0.13% by mass, and LMAB was 0.07% by mass.
Li ₂ S thus purified was used in the following examples and comparative examples.

Example 1
Li ₂ S and P ₂ S ₅ (manufactured by Aldrich) produced in the above production examples were used as starting materials. About 50 g of a mixture obtained by adding 30 mol parts of P ₂ S ₅ to 70 mol parts of Li ₂ S and 175 alumina balls having a diameter of 10 mm are put into a 500 mL alumina container, and a planetary ball mill (manufactured by Fritsch: Model No. P In -5), a sulfide-based solid electrolyte was obtained as a white-yellow powder by carrying out mechanical milling treatment for 200 hours at a rotation speed of 170 rpm at room temperature (25 ° C.) in a nitrogen atmosphere. As a result of calculation from the applied power, the energy applied to the reaction system per second was 0.22 kJ / kg.

Powder X-ray diffraction measurement was performed on the obtained powder (CuKα: λ = 1.5418Å). From the obtained spectrum chart, it was confirmed that the crystal peak of Li ₂ S completely disappeared and was vitrified.
The weight adhering to the ball and the wall surface was 20% of the charged weight. As a result of measuring the particle size distribution of the obtained powder by sieving (sieving), particles having a particle size of 2000 μm or less accounted for 90% by weight of the whole particles.

Comparative Example 1
Li ₂ S and P ₂ S ₅ (manufactured by Aldrich) produced in the above production examples were used as starting materials. About 50 g of a mixture obtained by adding 30 mol parts of P ₂ S ₅ to 70 mol parts of Li ₂ S and 175 alumina balls having a diameter of 10 mm are put into a 500 mL alumina container, and a planetary ball mill (manufactured by Fritsch: Model No. P In 5), a sulfide-based glass was obtained as a white-yellow powder by mechanical milling for 20 hours at a rotation speed of 360 rpm at room temperature (25 ° C.) in a nitrogen atmosphere. As a result of calculation from the applied power, the energy added per second was 2.0 kJ / kg.
The weight adhering to the ball and the wall surface was 50% of the charged weight, and the reaction could be carried out in a short time, but there were many adhering substances, and the powder could not be recovered efficiently as compared with Example 1. As a result of measuring the particle size distribution of the powder taken out from the container in the same manner as in Example 1, the particles having a particle size of 2000 μm or less accounted for 5% by weight of the whole particles.

Comparative Example 2
Li ₂ S and P ₂ S ₅ (manufactured by Aldrich) produced in the above production examples were used as starting materials. About 50 g of a mixture obtained by adding 30 mol parts of P ₂ S ₅ to 70 mol parts of Li ₂ S and 175 alumina balls having a diameter of 10 mm are put into a 500 mL alumina container, and a planetary ball mill (manufactured by Fritsch: Model No. P In 5), mechanical milling was performed for 60 days (1440 hours) at a rotation speed of 70 rpm at room temperature (25 ° C.) under a nitrogen atmosphere. As a result of calculation from the applied power, the energy applied per second was 0.015 kJ / kg.
When the obtained powder was subjected to powder X-ray diffraction measurement (CuKα: λ = 1.5418Å), a crystal peak of Li ₂ S was observed, the progress of the reaction was insufficient, and a solid electrolyte was not obtained. It was.

The method for producing a sulfide-based solid electrolyte of the present invention is used as a method for producing a sulfide-based solid electrolyte used for a solid battery or the like.

Claims (8)

A production method for obtaining a sulfide-based solid electrolyte in one step by mechanical pulverization using a ball mill, and for 1 kg of raw material containing lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ) during mechanical pulverization A method for producing a sulfide-based solid electrolyte in which a powder having a particle size of 2000 μm or less is obtained by applying energy of 0.02 to 1 kJ per second to obtain 80% by mass or more.   The manufacturing method according to claim 1, wherein the sulfide-based solid electrolyte contains two or more elements selected from sulfur, lithium, phosphorus, silicon, and germanium. The raw material is lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P) ₂ S ₅ The manufacturing method of Claim 1 or 2 consisting of. The raw material is lithium sulfide (Li ₂ S), diphosphorus pentasulfide (P ₂ S ₅ ) And a lithium salt. Lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P) ₂ S ₅ 5) The mixing molar ratio of 50:50 to 80:20. The production method according to any one of claims 1 to 4. Lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P) ₂ S ₅ 5) The mixing molar ratio of 60:40 to 75:25. The production method according to any one of claims 1 to 4. The method according to any one of claims 1 to 6, wherein a portion of the ball mill that comes into contact with the sulfide-based solid electrolyte is made of alumina, zirconia, or alumina and zirconia. The manufacturing method according to claim 1, wherein the sulfide-based solid electrolyte is a glassy electrolyte.