JP5956246B2 - Solid electrolyte and method for producing the same - Google Patents

Description

  The present invention relates to a solid electrolyte and a manufacturing method thereof, and more particularly to a solid electrolyte that can be used for a lithium ion battery used in an electric vehicle, a hybrid vehicle, an electronic device, and the like, and a manufacturing method thereof.

  In recent years, for the purpose of reducing environmental load, research and development of an electric vehicle driven by a motor, a hybrid vehicle driven by combining a motor and an engine, and the like have been actively conducted. Such automobiles are required not only to reduce the weight of the vehicle body, but also to increase the output and size of the motor and to improve the battery. In particular, in order to improve the battery, not only the energy density but also the safety is important. This applies not only to automobiles but also to electronic devices such as mobile phones, digital cameras, and personal computers.

  For example, at present, lithium ion batteries are becoming mainstream. In this lithium ion battery, a non-aqueous electrolyte solution is contained together with a separator between a positive electrode and a negative electrode, and this non-aqueous electrolyte solution has heat resistance. It is low and decomposes at around several hundred degrees Celsius. For this reason, there is a concern that the battery generates heat and ignites.

  Therefore, research and development of a solid electrolyte having high heat resistance and ionic conductivity, which replaces the non-aqueous electrolyte solution as described above, is also in progress.

As such a solid electrolyte, Patent Document 1 discloses amorphous Li ₂ S—P ₂ S ₅ , glass ceramics, and LiAlTiPO _x .

Patent Document ₂ discloses Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ and Li ₂ SAl _{2 in} addition to Li ₂ S—P ₂ S ₅ as solid electrolyte materials having excellent Li ion conductivity. S ₃ or the like have been disclosed. Furthermore, it is disclosed that Mo ₆ S ₈ which is a chevrel phase compound having a stable crystal structure is used as a positive electrode active material.

Further, Non-Patent Document 1, including the oxonium ions _{(H 3 O) 2 Mo 6} Cl 14 · 6H 2 O is disclosed.

JP 2011-40282 A JP 2010-282815 A

FWKoknat, 3 others, “CONVENIENT SYNTHESIS OF THE HEXANUCLEAR MOLYBDENUM (II) HALIDES Mo6Cl12 AND Mo6Br12 ・ 2H2O” (UK), INORG.NUCL.CHEM.LETTERS, Pergamon Press Ltd., 1980, Vol. 16, p. . 307-310

The material having a molybdenum chloride cluster skeleton described in Non-Patent Document 1 is known to allow protons and Li ions to pass between the layers because the crystal structure is a layered structure. For this reason, it can be expected as a material for obtaining a good solid electrolyte having high ionic conductivity. Further, the chevrel phase compound used as the positive electrode active material described in Patent Document 2 has a layered structure having a basic structure of the octahedral structure of Mo ₆ and has high ionic conductivity as described above. For this reason, it is considered that the chevrel phase compound can be used as an excellent solid electrolyte.

  However, in order to be an excellent solid electrolyte, in addition to having ionic conductivity, it is necessary that the passage of electrons in the solid electrolyte can be suppressed, that is, the electron conductivity is small.

Although the above document does not describe electronic conductivity, it is known that chevrel phase compounds such as Mo ₆ S ₈ have high electron conductivity due to Mo—S bonds between units. For this reason, chevrel phase compounds such as Mo ₆ S ₈ are difficult to use as solid electrolytes despite having high ionic conductivity.

  This invention is made | formed in view of said problem, The objective is to obtain the favorable solid electrolyte with small electronic conductivity.

  In order to achieve the above object, the present invention is configured such that the solid electrolyte includes a coordination compound in which pyridine is coordinated to a chevrel phase compound.

Specifically, the solid electrolyte according to the present invention is made of a material having an amorphous structure, in which lithium ions are introduced into a coordination compound in which pyridine is coordinated to a chevrel phase compound containing molybdenum and sulfur. seen including, electronic conductivity of the material, in a vacuum or an argon atmosphere, characterized in that at 20 ° C. is not more than 3.7 × ¹⁰ -7 S / cm.

  According to the experiment and research of the present inventor, it is possible to reduce the electron conductivity by coordinating pyridine to the chevrel phase compound. Furthermore, by introducing lithium ions into such a coordination compound, a solid electrolyte having lithium ion conductivity and low electronic conductivity can be obtained. Such a solid electrolyte can be used for, for example, a lithium ion battery. In that case, unlike the case of using a non-aqueous liquid electrolyte, it is not necessary to provide a separator. Furthermore, since it has higher heat resistance than the non-aqueous liquid electrolyte, heat generation and ignition can be prevented.

The method for producing a solid electrolyte according to the present invention includes a solid containing a material having an amorphous structure, in which lithium ions are introduced into a coordination compound in which pyridine is coordinated to a chevrel phase compound containing molybdenum and sulfur. a manufacturing method of the electrolyte, by immersing the coordination compound to the butyl lithium / hexane mixture, characterized that you have provided the step of introducing the lithium ion to the coordination compound. Moreover, you may provide the process of introduce | transducing a lithium ion into a coordination compound by immersing a coordination compound in a naphthalene / lithium / tetrahydrofuran liquid mixture instead of the process.

  According to the solid electrolyte and the manufacturing method thereof according to the present invention, it is possible to obtain a good solid electrolyte with low electron conductivity.

It is a figure which shows the crystal lattice of the coordination compound by which the pyridine coordinated to the chevrel phase compound. It is a figure which shows the analysis result by the X ray diffraction method of the compound which concerns on Example 1 and Example 2 of this invention. (A) is a figure which shows the analysis result by the infrared spectroscopy of the compound which concerns on Example 1 of this invention, (b) shows the analysis result by the infrared spectroscopy of the compound which concerns on Example 2 of this invention. FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its method of application, or its application.

  The solid electrolyte according to the present invention is a material in which lithium (Li) ions are introduced into a coordination compound in which pyridine (py) is coordinated to a chevrel phase compound containing molybdenum (Mo) and sulfur (S). It is characterized by including.

In the present specification, the chevrel phase compound refers to a compound represented by M _x Mo ₆ S ₈ (M is a metal element and x ≧ 0). That, _Mo 6 _{S 8} also called Chevrel phase compounds, _Li x _Mo 6 _{S 8,} for example Li ions _Mo 6 _{S 8} has been introduced that Chevrel phase compounds. In this specification, a compound in which py is coordinated as a ligand to these chevrel phase compounds is referred to as a coordination compound.

The chevrel phase compound has an octahedron composed of Mo ₆ as a basic structure, and these structures are regularly bonded to each other to show a stable crystal structure. Since ion conduction paths are formed between such regularly bonded basic structures, and Li ions are introduced in the present invention, a solid electrolyte having particularly high Li ion conductivity can be obtained. it can.

  Furthermore, in the solid electrolyte according to the present invention, pyridine is coordinated to the chevrel phase compound, whereby the electron conductivity can be reduced by reducing the Mo-S bond of the chevrel phase compound resulting from the electron conductivity. . For this reason, the electron conductivity can be further reduced by increasing the coordination number of pyridine.

  Specifically, as shown in FIG. 1, six Mo atoms per molecule of chevrel phase compound, and pyridine is coordinated to all of them to reduce the electronic conductivity to a value very close to zero. can do. At this time, the stable crystal structure of the chevrel phase compound collapses to an amorphous structure.

  The method for producing a solid electrolyte according to the present invention is not particularly limited as long as it can synthesize a coordination compound in which pyridine (py) is coordinated and lithium is introduced as described above.

For example, a chevrel phase compound represented by Mo ₆ S ₈ can be synthesized by reacting a compound containing Mo such as MoCl ₁₂ with a compound containing S such as NaSH. In addition, when a chevrel phase compound is synthesized using the above-described compound, or after the synthesis, pyridine is coordinated to the chevrel phase compound by a conventional method. Thereby, Mo ₆ S ₈ (py) _y (0 <y ≦ 6) is generated, but other molecules may be included depending on the material used for the synthesis, for example, (Na ₂ S) _x Mo ₆ S ₈ (py) _y (x ≧ 0, 0 <y ≦ 6) may be synthesized. If it does in this way, it will be thought that electronic conductivity can be reduced by eliminating the coupling | bonding between the units of a chevrel phase compound, and forming a clearance structure. The number of molecules of py coordinated to Mo ₆ S ₈ is not particularly limited, but as the number increases, the electron conductivity of the solid electrolyte can be reduced.

Thereafter, Li ions are introduced to generate (Na ₂ S) _x Li _z Mo ₆ S ₈ (py) _y (x ≧ 0, 0 <y ≦ 6, z> 0). The method for introducing Li ions is not particularly limited. For example, lithium ions can be introduced into a compound by immersing the compound synthesized as described above in a solution containing lithium such as a butyl lithium solution.

  The solid electrolyte according to the present invention can be manufactured using the material thus obtained.

Below, the Example for demonstrating in detail about the solid electrolyte which concerns on this invention, and its manufacturing method is shown. In this example, (Na ₂ S) _x Li _Z Mo ₆ S ₈ (py) _y was produced as a material constituting the solid electrolyte, and the relationship between the coordination number of pyridine and the electron conductivity in the material was examined. First, the production method of (Na ₂ S) _x Li _Z Mo ₆ S ₈ (py) _y of two types (low py number and high py number) having different py coordination numbers is described in Example 1 and Example 2, respectively. Will be described. Note that x, y, and z in the chemical formulas shown in this example are x ≧ 0, y> 0, and z> 0 unless otherwise specified.

Example 1
<Synthesis Method of Mo ₆ Cl ₁₂ >
Using an agate mortar, 1.093 g (4 mmol) of Mo ₆ Cl ₅ (manufactured by Sigma Aldrich) and 1.727 g (18 mmol) of metal Mo powder (manufactured by Rare Metallic) in a dry box in an argon atmosphere. Mixed. To this, 0.195 g (3.3 mmol) of NaCl (manufactured by Manac), which had been pulverized, was further added and mixed, and the mixture was vacuum-sealed in a quartz tube (φ = 15 mm). This was put in an electric furnace, heated to 720 ° C. over 6 to 8 hours, and baked for 12 hours. Thereafter, the fired product in the quartz tube was taken out and ground in the atmosphere using an agate mortar. This was dissolved in 10 ml of ethanol (Nacalai Tesque) and stirred vigorously for 20 hours. After stirring, the solution was filtered through a Teflon (registered trademark, the same applies hereinafter) filter, and 15 ml of 36% concentrated hydrochloric acid (manufactured by Nacalai Tesque) was added to the filtrate. This resulted in a white precipitate in the solution that was removed by filtration using a Buchner funnel. Subsequently, the obtained filtrate was heated and concentrated with a heater (hot plate) while stirring. After about 5 ml of precipitate was formed in the filtrate, the filtrate was cooled with water and allowed to stand to obtain yellow needle crystals. The crystals were washed with concentrated hydrochloric acid and then dried in the air to obtain (H ₃ O) ₂ [Mo ₆ Cl ₁₄ ] 6H ₂ O. The obtained (H ₃ O) ₂ [Mo ₆ Cl ₁₄ ] 6H ₂ O was placed in a Pyrex (registered trademark) tube and heated at 300 ° C. for 2 hours using a vacuum line to obtain Mo ₆ Cl ₁₂ .

<Method of synthesizing NaSH>
Next, NaSH (H ₂ O) _x (manufactured by Sigma-Aldrich) was vacuum dried at 120 ° C. for 3 hours to obtain NaSH.

_{<(Na 2 S) x Li} Z Mo 6 S 8 (py) y ( Low py stars. Which hereinafter referred to as Y～2) process for producing>
Next, 1.0 g (1 mmol) of Mo ₆ Cl ₁₂ and 0.67 g (12 mmol) of NaSH obtained as described above were placed in a 50 ml eggplant flask in a dry box under an argon atmosphere. Furthermore, 0.41 g (6 mmol) of NaOEt (manufactured by Tokyo Chemical Industry Co., Ltd.) was put therein. After further adding 15 ml of ethanol and 4 ml of pyridine (manufactured by Katayama Chemical Co., Ltd.), a cooling tube was attached to the eggplant flask. The eggplant flask and the cooling tube were sealed in an argon atmosphere, taken out into the atmosphere, and refluxed for 2 days. The mixed solution in the eggplant flask after refluxing was filtered using a Teflon filter, and the resulting solid was placed in an Erlenmeyer flask. To this, 30 ml of methanol (manufactured by Nacalai Tesque) was added and stirred for 2 days. Then, the solution was filtered, and the resulting product was vacuum-dried to obtain about 1.0 g of (Na ₂ S). to obtain a _{x Mo 6 S 8 (py)} y (y~2).

Next, 2 ml of a butyllithium / hexane solution (manufactured by Kanto Chemical Co., Inc.) was added to 60 mg of (Na ₂ S) _x Mo ₆ S ₈ (py) _y ( _y- 2), and this was left for 1 day. After that, the solution is filtered using a Teflon filter _to give _{(Na 2 S) x Li Z} Mo 6 S 8 (py) y (y~2).

(Example 2)
_{<(Na 2 S) x Li} Z Mo 6 S 8 (py) y ( High py stars. Which hereinafter referred to as Y～4) process for producing>
150 mg of (Na ₂ S) _x Mo ₆ S ₈ (py) _y ( _{y- 2} ) synthesized in Example 1 above was placed in a 50 ml eggplant flask in a dry box under an argon atmosphere, and 5 ml of Pyridine was added. Thereafter, a cooling tube was attached to the eggplant flask, and the eggplant flask and the cooling tube were taken out in the atmosphere while being sealed in an argon atmosphere, and refluxed for 10 hours. Then, it cooled to room temperature and stirred for about half a day. By filtering the thus obtained mixture _to obtain _{(Na 2 S) x Mo 6} S 8 (py) y (y~4).

Then, in the same manner as in Example 1, by reaction with butyl lithium / hexane solution _to give _{(Na 2 S) x Li Z} Mo 6 S 8 (py) y (y~4).

In Example 1 and Example 2, Li ions were introduced by the above-described method, but 10 mg of naphthalene was added to 100 mg to 200 mg of (Na ₂ S) _x Mo ₆ S ₈ (py) _y ( _y- 2). After adding a Li / THF solution and allowing it to stand for 1 day, Li ions may be introduced by filtration and washing with anhydrous hexane. A naphthalene-Li / THF solution is obtained by mixing 128 mg (1 mmol) of naphthalene, 7 mg (1 mmol) of Li metal, and 10 ml of THF. These steps are performed in a dry box in an argon atmosphere.

(Analysis of compounds)
Obtained as described above was in Example _{1 (Na 2 S) x Li} Z Mo 6 S 8 (py) y (y~2), and in Example _{2 (Na 2 S) x Li} Z Mo 6 S _In order to examine the structure of ₈ (py) _y ( _{y to} 4), X-ray diffraction (XRD) was performed on each. The result is shown in FIG.

  As shown in FIG. 2, no sharp peak was observed in the compounds of Example 1 and Example 2 in XRD. Therefore, it was confirmed that these compounds have an amorphous structure.

  Next, structural analysis was performed on the compounds of Example 1 and Example 2 using infrared spectroscopy (IR method). The result is shown in FIG.

As shown in FIG. 3 (a), in the IR spectrum of the compound of Example 1, a peak is observed in the ^{1300cm -1 ~1700cm} -1 is the absorption due to ring stretching of C = C and C = N. Further, as shown in FIG. 3 (b), a peak is observed in the compounds also ^{1300cm -1 ~1700cm} -1 Example 2. This confirmed that pyridine was coordinated to both the compounds of Example 1 and Example 2.

(Quantitative analysis of each element)
Next, the components of Example 1 and Example 2 were quantitatively analyzed for their constituent elements using X-ray photoelectron spectroscopy (XPS method). The results are shown in Table 1.

  As shown in Table 1, when Example 1 and Example 2 are compared, it can be confirmed that Example 2 has a higher proportion of nitrogen atoms (N) and that more pyridine is coordinated. It was.

(Measurement of electronic conductivity)
Next, in order to evaluate the electronic conductivity of the solid electrolyte containing the compound of Example 1 and Example 2, the electronic conductivity of the compound of Example 1 and Example 2 was measured. For this measurement, first, pellets made of the respective compounds were sandwiched between platinum plates, the platinum plates were connected to a DC power source, and a DC current was passed. At this time, the DC resistance of the compounds of Example 1 and Example 2 was measured, and the electronic conductivity of each compound was evaluated. In addition, the pellet which consists of a platinum plate and the compound of Example 1 and Example 2 was put on the conditions of 20 degreeC under vacuum or argon atmosphere, and measured. Table 2 shows the electronic conductivities of the compounds of Example 1 and Example 2 under these conditions.

As shown in Table 2, the electronic conductivity of the compound of Example 1 is 3.7 × 10 ⁻⁷ S / cm and 1.1 × 10 ⁻⁷ under the conditions of 20 ° C. in vacuum and argon atmosphere, respectively. It was shown to be good for use as a solid electrolyte, as extremely low as S / cm. Further, the electronic conductivity of the compound of Example 2 in which the coordination number of pyridine was increased was 5.0 × 10 ⁻⁹ S / cm or less of the measurement limit value in both vacuum and argon atmosphere. The value was even lower than that of the compound. That is, it was shown that the compound of Example 2 is also good for use as a solid electrolyte.

  From this result, it was shown that by coordinating pyridine to the chevrel phase compound, the electron conductivity can be reduced, and a better solid electrolyte can be obtained.

  The present invention is useful for solid electrolytes used in lithium ion batteries and the like that can be used in electric vehicles, hybrid vehicles, electronic devices, and the like.

Claims (3)

Coordination compounds pyridine Chevrel phase compounds containing molybdenum and sulfur are coordinated, lithium ions are constructed by introducing, viewed contains a material having an amorphous structure,
A solid electrolyte, wherein the material has an electron conductivity of 3.7 × 10 ⁻⁷ S / cm or less at 20 ° C. in a vacuum or an argon atmosphere . A method for producing a solid electrolyte comprising a material having an amorphous structure, wherein a lithium ion is introduced into a coordination compound in which pyridine is coordinated to a chevrel phase compound containing molybdenum and sulfur ,
A method for producing a solid electrolyte, comprising the step of introducing the lithium ions into the coordination compound by immersing the coordination compound in a butyllithium / hexane mixture. A method for producing a solid electrolyte comprising a material having an amorphous structure, wherein a lithium ion is introduced into a coordination compound in which pyridine is coordinated to a chevrel phase compound containing molybdenum and sulfur ,
A method for producing a solid electrolyte, comprising the step of introducing the lithium ions into the coordination compound by immersing the coordination compound in a naphthalene / lithium / tetrahydrofuran mixed solution.