JP7402619B2 - Solid electrolyte manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a solid electrolyte used in an all-solid-state battery.

As a method for producing a solid electrolyte used in an all-solid-state battery, there is a liquid phase method in which a solid electrolyte raw material is reacted in a solvent and then precipitated to produce a solid electrolyte (Non-Patent Document 1).
In this conventional liquid phase method, all the raw materials for the solid electrolyte are dissolved in one solvent and reacted, and crystals of the solid electrolyte are precipitated therefrom.
This conventional liquid phase method has a problem in that it is difficult to produce the desired solid electrolyte when the raw materials contain components that are difficult to dissolve in the solvent.

As a method other than the above for producing a solid electrolyte, there is a solid-phase method, as shown in Patent Document 1, in which solid electrolyte raw materials are mixed in a ball mill or the like to produce a solid electrolyte.
However, in the solid phase method, the components are evenly mixed using a ball mill or the like, so there is a limit to the capacity of the production container, so there is a problem that the amount of solid electrolyte that can be produced at one time is small.

Japanese Patent Application Publication No. 2002-109955

Journal of the American Chemical Society 2013, 135, 975-978 Journal of the American Chemical Society 2013, 135, 975-978

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for efficiently producing a solid electrolyte even when some of the raw materials are difficult to dissolve in a solvent.

That is, the method for producing a solid electrolyte according to the present invention includes a step of dissolving a part of the raw material in a first solvent and then depositing a first precursor, and dissolving the precursor and the remainder of the raw material in a second solvent. and dissolving the second precursor in a solvent and precipitating the second precursor.

According to the solid electrolyte manufacturing method configured in this way, the raw material can be dissolved in two steps using at least two types of solvents, the first solvent and the second solvent. As a result, solid electrolytes with compositions that could not be produced using conventional liquid phase methods can be efficiently produced using liquid phase methods.

As long as the first solvent and the second solvent are different from each other, any material that dissolves in at least one of the first solvent and the second solvent can be used as a raw material. As a result, the composition range of the solid electrolyte can be further expanded.

The effects of the present invention are particularly pronounced when the raw materials contain lithium, phosphorus, sulfur, and germanium. The reason is as follows.
Germanium is difficult to dissolve in solvents in which other elements such as lithium, phosphorus, and sulfur are easily soluble. Therefore, it has not been possible to produce a solid electrolyte containing germanium as a raw material using the conventional liquid phase method. On the other hand, according to the present invention, a solvent that easily dissolves germanium can be used as the first solvent or the second solvent. As a result, a solid electrolyte containing lithium, phosphorus, sulfur, and germanium, which could not be produced by conventional liquid phase methods, can be efficiently produced by liquid phase methods.

As a specific embodiment of the present invention, the raw material contains germanium, and the first solvent or the second solvent is ethanol.

According to the method for manufacturing a solid electrolyte according to the present invention, it is possible to provide a method for easily and efficiently manufacturing a solid electrolyte even if some of the raw materials are difficult to dissolve in a solvent.
Therefore, solid electrolytes with compositions that were previously considered difficult to produce using liquid phase methods can be produced in large quantities at low cost.

FIG. 2 is a flow diagram representing a method for manufacturing a solid electrolyte according to an embodiment of the present invention. An X-ray powder diffraction pattern of a solid electrolyte according to an example of the present invention. 3 is an X-ray powder diffraction pattern of a solid electrolyte according to an example of the present invention. 3 is an X-ray powder diffraction pattern of a solid electrolyte according to an example of the present invention. 3 is an X-ray powder diffraction pattern of a solid electrolyte according to an example of the present invention.

An embodiment of the present invention will be described in detail below with reference to the drawings.

<1. Method for manufacturing solid electrolyte according to this embodiment>
The manufacturing process of the solid electrolyte according to this embodiment will be explained using FIG. 1.

First, a portion of the raw material is added to the first solvent (S1 in FIG. 1). A part of the raw material is, for example, a mixture of a powder containing an arbitrary element M and a Li ₂ S powder, and the amount of each powder is adjusted to the amount of element M contained in the solid electrolyte that is ultimately desired to be produced. It is formulated as follows.

The element M is an element that is easily dissolved in a different type of solvent from other elements contained in the sulfide-based solid electrolyte, such as lithium, phosphorus, and sulfur. Specific examples of this element M include Group 14 elements such as germanium, tin, and silicon.

After adding and dissolving a portion of the raw materials in the first solvent, the mixture is stirred until the reaction is completed (S2 in FIG. 1).

The first solvent is not particularly limited as long as it can dissolve the powder. Specific examples of the first solvent include organic solvents such as ethanol and N-methylformamide having an acceptor number (AN), which indicates the polarity of the solvent, of 10 or more.

After the powder is completely dissolved in the first solvent, the first solvent is removed using an evaporator or the like to precipitate the first precursor of the solid electrolyte (S3 in FIG. 1).

Next, the remainder of the raw material is added to the first precursor so as to have the final composition of the solid electrolyte, and the second solvent is added thereto (S4 in FIG. 1). The first precursor and the remainder of the raw material are dissolved in a second solvent, and stirred until the reaction between the first precursor and the remainder of the raw material is completed (S5 in FIG. 1).

The remainder of the raw material may include, for example, powder containing lithium, phosphorus, sulfur, and the like. In this embodiment, Li ₂ S powder and P ₂ S ₅ powder are used.

The second solvent is not particularly limited as long as it can dissolve the first precursor and the remainder of the raw material. Specific examples of the second solvent include organic solvents such as tetrahydrofuran having a donor number (DN), which indicates the polarity of the solvent, of 15 or less.

After the reaction is completely completed, the second solvent is removed using an evaporator to precipitate the second precursor (S6 in FIG. 1).

The second precursor precipitated in this manner is pressed to produce pellets. The pellet is vacuum sealed in a quartz glass tube or the like, heat treated (S7 in FIG. 1), and cooled to room temperature to obtain a solid electrolyte (S8 in FIG. 1).

<Properties and usage of the produced solid electrolyte>
The solid electrolyte obtained in this way may be used as a solid electrolyte layer of an all-solid-state secondary battery in pellet form, or it may be crushed into a powder and then used as a positive electrode layer or a negative electrode layer of an all-solid-state secondary battery. , may be used as a component of a solid electrolyte layer.

The solid electrolyte manufactured by the manufacturing method described above has high ionic conductivity at 25° C., for example, 10 ⁻⁴ S/cm or more, more preferably 10 ⁻³ S/cm or more. be.

According to the method for producing a solid electrolyte as explained above, the raw materials are dissolved twice in the first solvent and in the second solvent, which is different from the conventional liquid phase method that uses only one type of solvent. In comparison, the variety of raw materials that can be used can be significantly increased.

That is, even when using elements M such as germanium, tin, and silicon, which are difficult to dissolve in organic solvents that dissolve elements such as lithium, phosphorus, and sulfur constituting the sulfide-based solid electrolyte, the first By making the solvent and the second solvent have different components, and using a solvent in which the element M such as germanium, tin, silicon, etc. is easily dissolved in either the first solvent or the second solvent, a liquid phase can be formed. can be used.

If the liquid phase method is used, solid electrolytes can be manufactured on a much larger scale than the solid phase method, which creates solid electrolytes by mixing powders in a ball mill or the like. Therefore, it is possible to greatly improve the productivity of solid electrolytes having compositions that could not be manufactured by conventional liquid phase methods and could only be manufactured by solid phase methods.

Since the solid electrolyte is a sulfide-based solid electrolyte containing elements such as lithium, phosphorus, and sulfur, the ionic conductivity of the solid electrolyte can be improved. Moreover, since this Lucas solid electrolyte further contains Group 14 elements such as germanium, tin, and silicon, it is possible to further improve the ionic conductivity.

The present invention is not limited to the above embodiments.
For example, in the embodiment described above, element M, which has a different type of solvent in which it is easily soluble than lithium, phosphorus, sulfur, etc., is dissolved in the first solvent as part of the raw material, but element M is dissolved in the first solvent as a part of the raw material. It may be dissolved in the second solvent.
The first solvent and the second solvent are not limited to those described above, and various types can be used depending on the element to be dissolved.
Further, the remainder of the raw material does not have to be the entire remainder of the raw material. More specifically, in addition to using the first and second solvents depending on the desired composition, for example, third and fourth solvents may be used to obtain the third and fourth precursors. Alternatively, a multi-stage liquid phase method may be used.

Since the ionic conductivity at room temperature is higher than other solid electrolytes, the solid electrolyte is preferably a sulfide-based solid electrolyte containing Group 14 elements, but is not limited to sulfide-based solid electrolytes. Can be used for various types of solid electrolytes. The composition is not limited to the one described above, and can be changed to various other compositions.

The first solvent and the second solvent are not limited to those described above, and any solvent may be used as long as it can dissolve the element that becomes the raw material of the solid electrolyte, and various kinds of solvents can be used in combination. The first solvent and the second solvent do not necessarily have to have different components, and may use the same components. This is because it is thought that even if the solvent is the same, dissolving the raw materials in several batches makes it easier to dissolve them.
In addition, various modifications can be made without departing from the spirit of the present invention.

Next, an example of this embodiment will be described. Of course, the present invention is not limited only to the following examples.

(Example 1)
<Production of solid electrolyte>
In a glove box whose interior was replaced with argon (Ar), Li ₂ S (purity 99.9%, Mitsuwa) and GeS ₂ (purity 99.9%, Wako Pure Chemical Industries) were used to obtain a 2Li ₂ S/GeS ₂ composition. 1.5g of powder was mixed in. The prepared powder was added and dissolved in 40 ml of ethanol as the first solvent placed in a 50 ml beaker, and stirred overnight. After the reaction was completed, ethanol was distilled off at 80° C. under reduced pressure using a rotary evaporator to obtain a first precursor. The first precursor obtained was then treated with Li ₂ S (99.9% purity, Mitsuwa) and P2S5 (99% purity, Aldrich) so that the final composition was Li ₁₀ GeP ₂ S ₁₂ ), 40 ml of tetrahydrofuran (THF) as a second solvent was further added and stirred under an Ar atmosphere. After the reaction was completed, tetrahydrofuran was completely removed using a rotary evaporator at 80° C. under reduced pressure to obtain a second precursor. Pellets were prepared by pressing 150 mg of the obtained second precursor at 380 MPa, and the pellets were vacuum-sealed in a quartz glass tube and heat-treated. The conditions for this heat treatment were 550°C for 4 hours. A solid electrolyte was obtained by cooling the heat-treated pellets to room temperature.

<Evaluation of solid electrolyte>
The ionic conductivity of the obtained solid electrolyte was measured.
The ionic conductivity was measured by pressing indium foil onto both sides of the pellet-shaped solid electrolyte obtained by the above method. In addition, the ionic conductivity was measured while changing the measurement temperature from 17°C to 140°C, and the activation energy was determined using the Arrhenius equation. Furthermore, the crystal material of the obtained powder was evaluated using a powder X-ray diffractometer.
The X-ray diffraction pattern of the solid electrolyte prepared in Example 1 is shown in FIG. When this X-ray diffraction pattern was compared with the X-ray diffraction pattern of the standard material Li ₁₀ GeP ₂ S ₁₂ ICSD#248307, it was confirmed that the desired Li ₁₀ GeP ₂ S ₁₂ crystal was formed. It was done. More specifically, in X-ray diffraction measurement using Cu Kα rays, 2θ=12.3±0.5°, 14.3±0.5°, 17.3±0.5°, 20.1±0.5°, 20.4±0.5°, 23.9±0.5°, 26.8 Positions of ±0.5°, 29.4±0.5°, 36.6±0.5°, 37.6±0.5°, 40.9±0.5°, 41.4±0.5°, 42.2±0.5°, 47.3±0.5°, 51.6±0.5°, 52.6±0.5° We were able to obtain a crystalline Li ₁₀ GeP ₂ S ₁₂ solid electrolyte with a peak of . Furthermore, the ionic conductivity of the solid electrolyte obtained in Example 1 was 4.5×10 ⁻⁴ S/cm at 25° C., and the activation energy was 27 kJ/mol.

(Example 2)
A solid electrolyte was produced using the same method as in Example 1, except that the pellet heat treatment conditions were 550° C. for 14 hours. Figure 2 shows the X-ray powder diffraction pattern of the solid electrolyte finally obtained. From the results shown in FIG. 1, it was confirmed that the desired Li ₁₀ GeP ₂ S ₁₂ crystal was formed. Furthermore, the measured ionic conductivity was 3.1×10 ^-3 S/cm at 25°C, and the activation energy was 26 kJ/mol.

(Example 3)
A solid electrolyte was produced using the same method as in Example 1, except that the pellet heat treatment conditions were 550° C. for 24 hours. Figure 2 shows the X-ray powder diffraction pattern of the solid electrolyte finally obtained. From the results shown in FIG. 2, it was confirmed that the desired Li ₁₀ GeP ₂ S ₁₂ crystal was formed. Furthermore, the measured conductivity was 4.5×10 ^-3 S/cm at 25°C, and the activation energy was 26 kJ/mol.

(Example 4)
In a glove box whose interior was replaced with argon (Ar), Li ₂ S (purity 99.9%, Mitsuwa) and GeS ₂ (purity 99.9%, Wako Pure Chemical Industries) were used to obtain a 2Li ₂ S/GeS ₂ composition. 1.5g of powder was mixed in. The prepared powder was added and dissolved in 40 ml of N-methylformamide (NMF) as the first solvent placed in a 50 ml beaker and stirred overnight. After the reaction was completed, N-methylformamide was distilled off at 250° C. under reduced pressure using a rotary evaporator to obtain a first precursor. Next, to the obtained first precursor, Li ₂ S (purity 99.9%, Mitsuwa) and P ₂ S ₅ (purity 99%) were added so that the final composition was Li ₁₀ GeP ₂ S ₁₂ %, Aldrich), 40 ml of tetrahydrofuran (THF) as a second solvent was further added, and stirring was performed under an Ar atmosphere. After the reaction was completed, tetrahydrofuran was completely removed using a rotary evaporator under reduced pressure or at 80°C to obtain a second precursor. Further, 150 mg of the obtained second precursor was pressed at 380 MPa to produce pellets, and the pellets were vacuum-sealed in a quartz glass tube and heat-treated. The conditions for this heat treatment were 550°C for 4 hours. A solid electrolyte was obtained by cooling the heat-treated pellets to room temperature.

Figure 3 shows the X-ray powder diffraction pattern of the solid electrolyte finally obtained. From the results shown in FIG. 3, it was confirmed that the desired Li ₁₀ GeP ₂ S ₁₂ crystal was formed. Furthermore, the measured conductivity was 1.1×10 ^-3 S/cm at 25°C, and the activation energy was 27 kJ/mol.

(Example 5)
Li ₂ S (purity 99.9%, Mitsuwa), SiS ₂ (purity 99.9%, Wako Pure Chemical), and SnS 2 (purity 99.9%, Wako Pure Chemical) were used in a glove box whose interior was replaced with argon (Ar). Then, 0.5 g of powder was mixed to have a composition of 2.7Li ₂ S・1.08SiS ₂・0.27SnS ₂ . The prepared powder was added and dissolved in 40 ml of ethanol as the first solvent placed in a 40 ml beaker and stirred overnight. After the reaction was completed, ethanol was distilled off at 80° C. under reduced pressure using a rotary evaporator to obtain a first precursor. Next, to _the obtained first precursor, _{Li 2 S} (purity 99.9%, _Mitsuwa ) _{and P2S5} (purity After adding 99% (Aldrich), 40 ml of tetrahydrofuran (THF) as a second solvent was further added and stirring was performed under an Ar atmosphere. After the reaction was completed, tetrahydrofuran was completely removed using a rotary evaporator at 80° C. under reduced pressure to obtain a second precursor. Pellets were prepared by pressing 150 mg of the obtained second precursor at 380 MPa, and the pellets were vacuum-sealed in a quartz glass tube and heat-treated. The heat treatment conditions were 550°C for 24 hours. A solid electrolyte was obtained by cooling the heat-treated pellets to room temperature.

FIG. 4 shows the X-ray powder diffraction pattern of the solid electrolyte finally obtained. From the results shown in FIG. 4, it was confirmed that a Li _10.35 Sn _0.27 Si _1.08 P _1.65 S ₁₂ solid electrolyte of the desired Li ₁₀ GeP ₂ S ₁₂ crystal type was formed. Furthermore, the measured ionic conductivity was 1.1×10 ^-3 S/cm at 25°C, and the activation energy was 26 kJ/mol.

(Comparative example 1)
In a glove box whose interior was replaced with argon (Ar), Li was purified using Li ₂ S (purity 99.9%, Mitsuwa), GeS ₂ (purity 99.9%, Wako Pure Chemical Industries), and P2S5 (purity 99%, Aldrich). 1.5 g of powder was blended to have a composition of ₁₀ GeP ₂ S ₁₂ . The prepared powder was added and dissolved in 40 ml of ethanol as the first solvent placed in a 40 ml beaker, and stirred overnight. After the reaction was completed, ethanol was removed at 80° C. under reduced pressure using a rotary evaporator to obtain a first precursor. Pellets were prepared by pressing 150 mg of the obtained first precursor at 380 MPa, and the pellets were vacuum-sealed in a quartz glass tube and heat-treated. The conditions for this heat treatment were 550°C for 3 hours. A solid electrolyte was obtained by cooling the heat-treated pellets to room temperature.

FIG. 5 shows the X-ray powder diffraction pattern of the solid electrolyte finally obtained. From the results shown in FIG. 5, formation of the desired Li ₁₀ GeP ₂ S ₁₂ crystal could not be confirmed. Furthermore, the measured ionic conductivity was 10 ^-6 S/cm or less at 25°C.

To summarize the results of the above examples and comparative examples, in the comparative example in which all raw materials were dissolved and reacted in one type of solvent as in the past, it was not possible to produce the desired Li ₁₀ GeP ₂ S ₁₂ solid electrolyte. There wasn't.
On the other hand, in Examples 1 to 5, in which the raw materials were dissolved and reacted in two steps using the first solvent and the second solvent, the target Li ₁₀ GeP ₂ S ₁₂ solid electrolyte was produced. I found out that it is possible. Furthermore, it was found that all of the solid electrolytes prepared in Examples 1 to 5 had sufficiently high ionic conductivity.

Although preferred embodiments of the present invention have been described above in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person with ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea stated in the claims. It is understood that these also naturally fall within the technical scope of the present invention.

Claims (6)

A step of dissolving a portion of the raw material in a first solvent and then precipitating a first precursor;
dissolving the precursor and the remainder of the raw material in a second solvent, and then precipitating the second precursor ,
An organic solvent having an acceptor number of 10 or more is used as one of the first solvent and the second solvent, and an organic solvent having a donor number of 15 or less is used as the other of the first solvent and the second solvent. A solid electrolyte manufacturing method using a solvent . The solid electrolyte manufacturing method according to claim 1, wherein the first solvent and the second solvent are different from each other. The solid electrolyte manufacturing method according to claim 1 or 2, wherein the raw material contains lithium, phosphorus, sulfur, and Group 14 elements. 4. The solid electrolyte manufacturing method according to claim 3, wherein the Group 14 element is germanium. The solid electrolyte manufacturing method according to any one of claims 1 to 4, wherein the raw material contains germanium, and the first solvent or the second solvent is ethanol. 6. The solid electrolyte manufacturing method according to claim 1, wherein a part of the raw material contains germanium, and the first solvent is ethanol.