JP2012193051A - Method of manufacturing inorganic solid electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an inorganic solid electrolyte high in ion conductivity, high in thermal and electrochemical stability, which is expected to be applied to a battery material such as a lithium ion secondary cell etc., an electric storage material such as an electrolysis condenser, an electric double layer capacitor etc. and an electrochemical device such as an indicating element etc.SOLUTION: This method of manufacturing an inorganic solid electrolyte is a method of manufacturing an inorganic solid electrolyte obtainable from an inorganic raw material containing lithium sulfide and other sulfides as essential components, and this method includes a mechanical treating process in which the inorganic raw material is mixed and pulverized and a heat treatment process, and the processes are alternatively repeated more than once.

Description

  The present invention relates to a method for producing an inorganic solid electrolyte. More specifically, a method for producing an inorganic solid electrolyte expected to be applied to battery materials such as lithium ion secondary batteries and lithium primary batteries, electric storage materials such as electrolytic capacitors and electric double layer capacitors, and electrochemical devices such as display elements About.

In recent years, against the backdrop of growing interest in environmental issues, the shift from fossil fuels such as oil and coal to renewable energy such as wind and solar has been promoted. Is attracting attention. Among them, secondary batteries that can be repeatedly charged and discharged are used not only in electronic devices such as mobile phones and laptop computers, but also in various fields such as automobiles and airplanes. Research and development aimed at improving performance of materials used in batteries are being conducted. In particular, a lithium-ion battery having a large capacity and a light weight is a secondary battery that is expected to expand further in the future, and is a battery that is most actively researched and developed.
However, most of the lithium ion secondary batteries currently in use use lithium that is chemically or electrochemically highly reactive inside the battery, and in addition, flammable and flammable organic solvents are used. Used for electrolyte. Therefore, in actual use, there is a problem in reliability at high temperatures or in an overcharge / overdischarge state, and there is a danger that a situation such as ignition or burst explosion may occur when it is severe. As a result, at the present time, increasing the safety is a very important issue.
In response to these technical demands, research on lithium ion conductive solid electrolyte materials using inorganic materials and research and development on all-solid lithium secondary batteries using the materials have become active. Lithium ion conductive solid electrolytes are not flammable and flammable, and are being researched for their high heat resistance and electrochemical stability, and today they are inorganic materials that have ionic conductivity comparable to organic electrolytes. Solid electrolytes are also being obtained. In particular, as an inorganic solid electrolyte, researches on sulfide-based lithium ion conductive solid electrolytes containing sulfur atoms in their constituent materials and all-solid lithium secondary batteries using the same have been active. It is known that this sulfide-based inorganic solid electrolyte includes an amorphous system, a crystalline system, and a mixture thereof. Furthermore, systems containing atoms such as silicon, germanium or phosphorus are known for these materials.
Known methods for synthesizing such inorganic solid electrolytes include a melt quenching method and a mechanical milling method. In the melt quenching method, the mixed material powder is mixed into a glassy carbon crucible, melted at 950 ° C in an argon stream, reacted, and then quenched into liquid nitrogen for rapid vitrification. This is a method for obtaining an inorganic solid electrolyte. Alternatively, it is a method of vacuum-sealing in a glass tube and heating and melting it, followed by quenching with ice water or the like (Patent Documents 1 and 2). In addition, the mechanical milling method is a method of producing an inorganic solid electrolyte by producing lithium ion conductivity by mixing starting materials for synthesis at high speed for a long time with a planetary ball mill under normal temperature and normal pressure (Patent Literature). 2, 3, 4). Furthermore, a method for producing a lithium ion conductive solid electrolyte in a relatively short time when a lithium sulfide-based raw material is reacted at a temperature of 150 ° C. or higher and 300 ° C. or lower, particularly at a high temperature, using a ball mill is disclosed (Patent Document 5). ).

JP-A-5-310418 JP 2008-103096 A JP 2005-228570 A JP 2008-4334 A JP 9-303971 A

However, in the melt quenching method, the inorganic raw material is melted at a high temperature of 800 ° C. or higher and then rapidly cooled. Therefore, special equipment is required for industrial production. On the other hand, in the mechanical milling method, in order to increase ion conductivity, it is necessary to perform milling for a long time, and the synthesized sample adheres firmly to the pot container and the balls to be used by the milling process, and only the sample is taken out. This requires a considerable amount of time, which is disadvantageous for industrial production. In the reaction using a ball mill at a temperature of 150 ° C. or higher and 300 ° C. or lower, a solid electrolyte was obtained in a short time, but its ionic conductivity was low. In addition, a special apparatus was required for the mixing reaction at a high temperature.
This invention is made | formed in view of the said present condition, and it aims at providing the industrial manufacturing method of the inorganic solid electrolyte with high ion conductivity and thermal and electrochemical stability high.

The present invention
(1) In a method for producing an inorganic solid electrolyte obtained from an inorganic material raw material containing lithium sulfide and other sulfides as essential components, each step includes a mechanical treatment step and a heat treatment step of mixing and grinding the inorganic material raw material. The method for producing an inorganic solid electrolyte is characterized by alternately repeating a plurality of times.
(2) The method for producing an inorganic solid electrolyte according to (1), wherein the heat treatment temperature in the heat treatment step is 100 to 700 ° C., and the respective steps are alternately repeated four times or more.
(3) The method for producing an inorganic solid electrolyte according to (1) or (2), wherein the molar ratio of lithium sulfide, which is an essential component of the inorganic material raw material, is 45 to 90% of the total raw material.
About.

  ADVANTAGE OF THE INVENTION According to this invention, the method of manufacturing an inorganic solid electrolyte with high lithium ion conductivity can be provided in a short time.

XRD measurement of the inorganic solid electrolyte produced in Example 1

  The method for producing an inorganic solid electrolyte of the present invention includes a mechanical treatment step and a heat treatment step for mixing and crushing inorganic material raw materials, and each step is alternately repeated a plurality of times. The order of the mechanical treatment step and the heat treatment step may be any, but it is preferable to perform the mechanical treatment step first because the conversion of the raw material hardly occurs only by the heat treatment step. Note that these steps are preferably performed in an inert dry gas atmosphere such as nitrogen or argon or in a vacuum because lithium sulfide is reactive with oxygen and water.

  By mixing and pulverizing, a shearing force is applied to an inorganic material raw material containing lithium sulfide and other sulfides as essential components, a reaction occurs between the raw material particles, and it can be converted into an inorganic solid electrolyte. The reaction can be carried out at any temperature, but preferably when the reaction is carried out at a temperature of 50 to 150 ° C. while applying a shearing force, the reaction rate increases and the reaction is promoted because of the refinement due to the shearing force. A conductive inorganic solid electrolyte is obtained. A preferred temperature is 55 to 145 ° C, more preferably 60 to 140 ° C.

Equipment that can be used in the mechanical treatment process includes ball mills such as rolling ball mills, vibration ball mills, and planetary ball mills, spiral-type, ribbon-type, screw-type, high-speed fluid-type and other container-fixed mixing and grinding machines, or cylindrical types, There are complex type mixing and grinding machines such as twin cylindrical type, horizontal cylindrical type, V type and double cone type. Of these, mixed pulverization by a ball mill is preferable. This is because conversion to an electrolyte easily proceeds by applying a strong shearing force between the raw material particles. Among them, it is more preferable to use a vibration ball mill or a planetary ball mill, and a vibration ball mill is most preferable. The reaction conditions may be appropriately adjusted depending on the equipment used.
In the ball mill, the material to be used, the material of the ball to be put in the container, the surface area, and the rotational speed are important. The difference in the surface area of the balls used with respect to the container volume is related to the contact ratio with the raw material particles, and the relationship with the volume ratio of the balls is related to the shearing force applied to the raw material particles. Therefore, the larger the surface area ratio and volume ratio, and the faster the rotation speed, the stronger the bonding interface can be formed between the raw material particles. The volume ratio of the balls to be used to the pot volume is selected from 5 to 60%, preferably 20 to 40%. The ball mill to be used is preferably equipped with a temperature adjusting means in order to keep the temperature in the container at a specific temperature, and is not particularly limited, but is equipped with a jacket or an electric heater that can circulate a temperature-controlled heating medium. Is preferred.

  By performing such a mechanical treatment process, a solid electrolyte layer is formed at the strong bonding interface between the raw material particles, the resulting solid electrolyte layer is easily peeled off, and does not cause strong adhesion to containers and balls, etc. An inorganic solid electrolyte is formed. The rotation speed and treatment time can be appropriately adjusted according to the reaction. The faster the rotation speed and the longer the treatment time, the higher the conversion rate from the raw material. The rotation speed is 10 revolutions / minute or more, preferably 100 revolutions / minute or more, more preferably 200 revolutions / minute or more. Since the reaction temperature may not be controlled by frictional heat even if the rotational speed is too high, the upper limit is 1000 revolutions / minute or less, preferably 800 revolutions / minute or less, more preferably 600 revolutions / minute or less. One treatment time is 0.1 to 100 hours, more preferably 0.3 to 30 hours, and further preferably 0.4 to 10 hours. When the treatment is performed in a plurality of times, the total treatment time is preferably within 100 hours, preferably within 50 hours.

  The heat treatment step of the present invention may be a temperature at which the raw material and the inorganic solid electrolyte are not melted. By performing the heat treatment, the reaction at the raw material particle interface is promoted and amorphization progresses, so that it can be converted into an ion-conductive inorganic solid electrolyte, and a part or all of the amorphous solid electrolyte is partly or entirely. It can be crystallized and ion conductivity can be improved. The heat treatment may be either stirring or mixing or standing, but is preferably standing. The treatment temperature is preferably in the range of 100 to 700 ° C. By performing heat treatment at a temperature within this range, a thin layer of an inorganic solid electrolyte can be formed at the bonding interface between the raw material particles. Preferably, it is 150-600 degreeC, More preferably, it is 170-500 degreeC, More preferably, it is 1800-400 degreeC. The treatment time for one time may be adjusted appropriately depending on the treatment temperature. 0.5 to 24 hours are preferable, and 1 to 12 hours are more preferable. When the treatment is performed in a plurality of times, the total treatment time is preferably within 100 hours, preferably within 70 hours.

  As the mechanical treatment step and the heat treatment step are alternately repeated, the conversion of the raw material proceeds and the ionic conductivity is improved by the amorphization. By carrying out the mechanical treatment step after the heat treatment step, the thin layer of the inorganic solid electrolyte formed at the raw material particle interface by the heat treatment step is peeled off, and miniaturization proceeds and the conversion to an amorphous solid electrolyte is more performed. move on. Therefore, the number of times of repeating alternately may be appropriately determined by plural times or more, but is 4 times or more, preferably 5 times or more, more preferably 6 times or more, and further preferably 8 times or more. Here, the number of repetitions means that the set of the mechanical treatment process and the heat treatment process is one. Moreover, after repeating several times, you may stop by either a mechanical treatment process or a heat treatment process.

  The inorganic solid electrolyte that can be synthesized by the production method of the present invention contains lithium sulfide and other sulfides as essential components. The other sulfide is preferably at least one compound selected from the group consisting of phosphorus sulfide, silicon sulfide, germanium sulfide, aluminum sulfide, boron sulfide, barium sulfide and gallium sulfide. Preferred are phosphorus sulfide, aluminum sulfide, silicon sulfide, germanium sulfide, and boron sulfide.

Specific examples of phosphorus sulfide, silicon sulfide, germanium sulfide, aluminum sulfide, and boron sulfide include P ₂ S ₃ , P ₂ S ₅ , P ₄ S ₃ , P ₄ S ₅ , P ₄ S ₇ , P ₄ S ₁₀ phosphosulfurized such as silicon sulfide such SiS _2, germanium sulfide such as GeS _2, aluminum sulfide such as _Al 2 _{S 3,} include boron sulfide such as B 2 _{S 3.} Among these, phosphorus sulfide and silicon sulfide are more preferable, and phosphorus sulfide is more preferable. Among them, P ₂ S ₅ is particularly preferable. These compounds may be used alone or in combination of two or more.

  Lithium sulfide and other sulfides are essential components, but may contain other components not corresponding to any of them. The ratio of these essential components is preferably 50% by mass or more with respect to 100% by mass of the entire raw material. More preferably, it is 70% by mass or more, more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably, the raw material consists essentially of these essential components. is there.

  In the present invention, lithium sulfide and other sulfides are essential components, and the molar ratio of lithium sulfide in the essential components is preferably 45 to 90%, more preferably 60 to 80%. Here, the lithium sulfide is not particularly limited as long as it contains sulfur element and lithium element at 1: 2 (molar ratio), and lithium sulfide as a compound may be used. Lithium may be added separately so that the molar ratio is 1: 2. Similarly, for other compounds, the respective constituent elements may be added at the corresponding composition ratios.

  The above-mentioned other components are not particularly limited. For example, inorganic oxides such as aluminum oxide, phosphorus oxide, silicon oxide and titanium oxide; inorganic such as natural graphite, artificial graphite, amorphous carbon, carbon fiber and fullerene Carbons: Metals such as copper, nickel, gallium, germanium, indium, tin, organic substances such as polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide, polyethylene glycol, polyphenylene sulfide, polyethylene terephthalate, polyacetylene, polyaniline, etc. The substance chosen can be raised.

As a preferable raw material composition of the present invention, for example, when a molar ratio of lithium sulfide to phosphorus sulfide (P ₂ S ₅ ) is used at 70:30, the obtained inorganic solid electrolyte is obtained from Li ₃ PS ₄ and Li _{3 by} Raman spectroscopy. ₄ P ₂ S ₇ units coexist, and an ionic conductor in which these phases coexist at a ratio of 1: 1 is formed, and it is considered that excellent ionic conductivity is expressed.

  In the present invention, it is preferable that the raw materials are pulverized to reduce the particle size to 50 μm or less, preferably 30 μm, more preferably 10 μm or less, and to mix uniformly before the reaction. As a result, the reaction time can be shortened, the obtained sulfide lithium-based inorganic solid electrolyte can be reduced in particle size, and the fluctuation in characteristics can be reduced by increasing the contact area.

  As long as the inorganic solid electrolyte of the present invention has ionic conductivity, its crystalline state is not particularly limited, but part or all of the amorphous state is made crystalline with high lithium ion conductivity. It may be converted. The conversion from amorphous to crystalline can be achieved by further combining heat treatment at a temperature near the glass transition temperature, and may further include such a heat treatment step. Such a heat treatment temperature is 180 to 400 ° C, preferably 200 to 350 ° C.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “parts” means “parts by weight”.

In order to prevent the influence of oxygen and moisture, operations such as weighing and mixing of raw materials were performed in a glove box in which the atmosphere was controlled under an inert gas atmosphere and the dew point was controlled to -50 ° C or lower. In addition, when taking out from the glove box, it was taken out in a sealed state. The measurement was performed under the following conditions.
[Raman spectrum measurement]
It measured on condition of the following using NRS-3100 (made by JASCO Corporation).
Excitation wavelength 532 nm, exposure time 10 seconds, integration 10 times [XRD (X-ray diffraction) analysis]
The X-ray diffractometer uses a Rotorflex RU-200B rotating cathode type strong X-ray apparatus, Rigaku Denki Co., Ltd., CuKα ray (λ = 1.5418Å) generated at an acceleration voltage of 40 kV and a tube current of 200 mA, and measurement range 2θ. Measured at 10-80 ° and a step interval of 0.02 °. The obtained data was identified by performing a peak search process.
[Pellet making]
120 mg of an inorganic solid electrolyte sufficiently ground in a mortar was weighed into a mold having an inner diameter of 10 mm, uniformly filled, then applied to a press machine, and pressure molded at 3.8 t / cm ² .
[Ionic conductivity]
The prepared pellets were sandwiched between In electrodes and measured by a complex impedance method using E4980A (Agilent).

Example 1
33 parts of lithium sulfide (Li ₂ S) and 67 parts of phosphorus sulfide (P ₂ S ₅ ) were weighed in a glove box, pulverized and mixed for 10 minutes in an agate mortar, and then mixed with alumina balls for pulverization and stainless steel for planetary ball mills. The pot was filled and sealed, removed from the glove box, and mixed and ground for 0.5 hour at 370 rpm using a planetary ball mill. The internal temperature at that time was 60 ° C. Next, the mixture was pulverized and mixed in an agate mortar for 10 minutes, and then heat treated at 210 ° C. for 6 hours. This operation was repeated to obtain a glassy inorganic solid electrolyte. In the middle, the ionic conductivity was measured at 25 ° C. The ionic conductivity when the mechanical treatment step and the heat treatment step were repeated five times was below the measurement limit. Table 1 shows the ionic conductivity of each step thereafter. Each step was alternately repeated 8 times, and 9.5 × 10 ⁻⁵ S / cm and further mechanical treatment showed an ionic conductivity of 1.1 × 10 ⁻⁴ S / cm. Moreover, in order to confirm the change of the crystal phase by repeating a heat treatment process and a mechanical treatment process, the result of having performed the XRD analysis about the inorganic solid electrolyte of Example 1 is shown in FIG. From FIG. 1, the crystallinity peak (2θ of 25 to 30 ° and 45 °) derived from the raw material becomes smaller as the heat treatment process and the mechanical treatment process are repeated, and after 8 times, it almost disappears and becomes amorphous. It turns out that it is.

* MM represents mechanical milling (by planetary ball mill) (Comparative Example 1)
The same operation was performed except that the heat treatment of Example 1 was not performed. The ionic conductivity of the inorganic solid electrolyte was measured by repeating the mixed pulverization for 8 hours at 370 rpm using a planetary ball mill, but the ionic conductivity was not expressed.

(Comparative Example 2)
The same operation was performed except that the planetary ball mill of Example 1 was not performed. That is, heat treatment was performed at 210 ° C. for 36 hours. Although the ionic conductivity of the obtained inorganic solid electrolyte was measured, the ionic conductivity was not expressed.

The method for producing an inorganic solid electrolyte of the present invention is capable of synthesizing an inorganic solid electrolyte with high ionic conductivity in a relatively short time, and the obtained inorganic solid electrolyte is excellent in safety and electrochemical stability. It can be applied as a battery material, and is expected to be applied to electrochemical devices such as electrolytic capacitors, electric double layer capacitors, display elements, and storage materials. In recent years, the use in various fields has expanded, and it can be suitably used as a material for lithium secondary batteries that require high safety and excellent electrical characteristics.

Claims (3)

In a method for producing an inorganic solid electrolyte obtained from an inorganic material raw material containing lithium sulfide and other sulfides as essential components, the method includes a mechanical treatment step and a heat treatment step for mixing and grinding the inorganic material raw material. A method for producing an inorganic solid electrolyte, which is repeated a plurality of times. 2. The method for producing an inorganic solid electrolyte according to claim 1, wherein the heat treatment temperature in the heat treatment step is 100 to 700 ° C., and the steps are alternately repeated four times or more. 3. The method for producing an inorganic solid electrolyte according to claim 1, wherein the molar ratio of lithium sulfide, which is an essential component of the inorganic material raw material, is 45 to 90% of the total raw material.

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