WO2021080134A1 - Method of producing lpscl solid electrolyte for lithium secondary battery - Google Patents

Abstract

The present invention relates to a method of producing an LPSCl solid electrolyte for a lithium secondary battery. The present invention provides a method of producing a sulfide-based solid electrolyte, the method comprising the steps of: (a) providing a first solution comprising lithium polysulfide (Li2Sx, wherein 2≤x≤8); (b) producing a second solution comprising Li3PS4+y (wherein, 0<y≤3) by mixing P2S5 in the first solution; (c) mixing and stirring the second solution and a third solution in which Li2S and LiX (X=Cl, Br, or I) are mixed; and (d) drying and heat-treating the mixed solution.

Description

Manufacturing method of LPSCL solid electrolyte for lithium secondary battery

The present invention relates to a solid electrolyte for a lithium secondary battery, and more particularly, to a method of manufacturing an LPSCl solid electrolyte.

All-Solid-State Battery refers to the replacement of a liquid electrolyte with a solid electrolyte among the above battery components. Compared to liquid electrolytes, the all-solid secondary battery has no risk of explosion or fire, simplifies the manufacturing process, and is attracting attention as a next-generation secondary battery due to its high energy density potential.

Sulfide-based electrolyte (SSE) is attracting attention as a solid electrolyte for all-solid secondary batteries. However, the production of LPSCl, which is a representative sulfide-based SSE, _{can be obtained by mixing Li 2} S and P ₂ S ₅ and performing high-energy milling for a long time and then sintering.

As an alternative for solving the problem of mechanical synthesis, efforts to manufacture SSE by liquid synthesis are being made. This method can synthesize LPS in a short time compared to mechanical synthesis, but has a disadvantage in that it exhibits low ionic conductivity due to impurities.

Meanwhile, in the conventional SSE manufacturing liquid phase process, polar solvents such as NMF have been used to increase the solubility because sulfides exhibit low solubility in THF, DMC or DME. However, NMF is not preferable as a solvent because it exhibits high toxicity.

In order to solve the problems of the prior art, an object of the present invention is to provide a method of manufacturing a sulfide-based solid electrolyte having high ionic conductivity while applying a low-energy liquid phase process.

In addition, an object of the present invention is to provide a method of preparing a sulfide-based solid electrolyte by a liquid process using a low toxicity solvent.

In order to achieve the above technical problem, the present invention comprises the steps of: (a) providing a first solution containing _{lithium polysulfide (Li 2} S _{x, where 2≦x≦8);} (b) preparing a second solution containing Li 3 PS _{4+y (here, 0<y≦3)} by mixing _{P 2} S _{5 with the first solution;} (c) mixing and stirring the second solution and a third solution in which Li ₂ S and LiX (X=Cl, Br or I) are mixed; And (d) drying and heat treating the mixed solution.

In the present invention, the step (a) may include mechanical milling a mixed solution of Li2S and excess sulfur (S) to prepare lithium polysulfide.

In the present invention, the lithium polysulfide preferably contains at least one compound selected from the group consisting of Li2S3, Li2S4, Li2S6 and Li2S8.

In addition, in the present invention, the first solution may be at least one solvent selected from the group consisting of THF, DMC and DME.

In the present invention, the LPSX may be Li ₆ PS _5+y Cl.

In the present invention, the step (d) is preferably carried out at a temperature of 500 ~ 600 ℃.

According to the present invention, it is possible to prepare a high purity sulfide-based solid electrolyte with a simple process and a low toxicity solvent based on a liquid phase process.

1 is a schematic diagram for explaining a method of manufacturing a sulfide-based solid electrolyte according to an embodiment of the present invention.

2 is a graph showing Raman analysis results of electrolyte samples prepared according to Examples and Comparative Examples of the present invention.

3 is a graph showing XRD analysis results of LPSCl samples prepared according to the method of Comparative Example of the present invention.

4 is a graph showing the XRD analysis results of LPSCl samples prepared according to an embodiment of the present invention.

5 is a graph showing the results of measuring electrical conductivity of LPSCl samples prepared according to Examples and Comparative Examples of the present invention.

6 is a graph showing a result of measuring the ionic conductivity of LPSCl subjected to heat treatment at a temperature of 550° C. according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail by describing a preferred embodiment of the present invention with reference to the drawings.

1 is a schematic diagram for explaining a method of manufacturing a sulfide-based solid electrolyte according to an embodiment of the present invention.

The present invention is characterized in that lithium polysulfide is used in place of lithium sulfide (Li _{2 S) (S120).} In the present invention, lithium polysulfide _{may be represented by Li 2} S _x , where x may be any real number of 2 to 8.

For example, lithium polysulfide includes at least one compound selected from the group consisting _{of Li 2} S ₂ , Li ₂ S ₃ , Li ₂ S ₄ , Li ₂ S ₆ and Li ₂ S _8.

For example, in the present invention, lithium polysulfide _{can be synthesized by dissolving lithium sulfide (Li 2} S) and sulfur (S) in a solvent such as THF, DMC or DME in an appropriate ratio and then mechanically milling (S110). In this case, sulfur is preferably solid sulfur (S ₈ ) may be used. For example, the reaction formula for the generation _{of Li 2} S ₃ as lithium polysulfide is as follows.

(Formula 1)

Li2S + 2S → Li ₂ S ₃

In step S120, mechanical milling may be performed by grinding means such as grinding.

Subsequently, P ₂ S ₅ is mixed with the lithium polysulfide solution and stirred (S130). In this case, the stirring step may be performed by placing a magnetic bar in an Erlenmeyer flask and stirring at 300 to 500 rpm on a hot plate. By stirring, P ₂ S ₅ is completely dissolved in the solution and exhibits a transparent color.

By stirring, lithium polysulfide and P ₂ S ₅ react to produce a solution having a composition of _{Li 3} PS _{4+y (here, 0<y≦3).} Preferably, y has a value of 2 or more. As an example, the _{reaction for generating Li 3} PS _{4+y from Li 2} S _x (eg x=3) can be expressed by the following equation, in which case y=3.

(Formula 2)

3Li ₂ S ₃ + P ₂ S ₅ → 2Li ₃ PS _4+y

Referring back to FIG. 1, apart from the preparation of lithium polysulfide, Li ₂ S and lithium salt are mixed and stirred in an appropriate solvent such as THF (S140). Mixing and stirring may be performed at room temperature for 24 hours. In the present invention, at least one selected from the group consisting of LiCl, LiBr, or LiI may be used as the lithium salt.

Then, the solutions prepared in steps S130 and S140 are mixed and stirred (S150). At this time, the stirring was performed at 300-500 rpm using a hot plate and a magnetic bar; The mixing ratio can be appropriately selected. For example, _{the molar ratio for the preparation of Li 6} PS _5+y Cl can be calculated according to the following reaction equation.

(Chemical Formula 3)

Li ₃ PS _4+y + Li ₂ S + LiCl → Li ₆ PS _5+y Cl

Next, the stirred solution is dried for 10 to 40 hours at a temperature of about 70 to 150°C (S140), and heat-treated at a temperature of 500 to 600°C for 1 to 3 hours to Li ₆ PS _5+y X (where X = Cl, Br or I) compounds can be prepared (S150).

Hereinafter, a preferred embodiment of the present invention will be described.

<Example>

According to the Li ₂ S ₃ composition of lithium polysulfide, Li2S and sulfur (S) were weighed in a molar ratio of 1:2, dispersed in a THF solvent, and mechanically milled in a mortar for 30 minutes. Subsequently, the solution composition was _{weighed to match Li 3} PS _4+y (y=3), _{mixed with P 2} S ₅ , and then stirred on a hot plate using a magnetic bar.

Separately, a solution was prepared by mixing and stirring THF as a solvent and Li ₂ S and LiCl in a ratio of 1:1.

Subsequently, the Li ₃ PS _4+y (y=3) solution and the Li2S+LiCl mixed solution were mixed and stirred for 3 days using a magnetic bar on a hot plate. The agitated solution was stirred at 80° C. for 24 hours and 140° C. After drying for 12 hours at a temperature of ℃, it was heat-treated at a temperature of 200 ~ 700 ℃. At this time, the temperature was raised by 5 degrees per minute and maintained for 2 hours after reaching the target temperature.

<Comparative Example>

For comparison, the manufacturing process of lithium polysulfide was omitted, and a solution in which lithium sulfide (Li2S) and P2S5 were mixed according to the composition of Li3PS4 was prepared and mixed with the Li2S+LiCl solution. It was tested under the same conditions except that lithium polysulfide was not used. In the mixed solution of lithium sulfide and P2S5, precipitation of P2S5 could be confirmed, and eventually it could be confirmed that it was not completely dissolved in the THF solvent.

The properties of the prepared LiPSCl compound were evaluated.

2 is a graph showing Raman analysis results of SSE samples prepared according to Examples and Comparative Examples.

Referring to Figure 2, in the case of the LPSCl solution (No added sulfr) to which excess sulfur (S) is not added, it can be seen that no peak is formed because there is no _{Li 2} S and P ₂ S _{5 dissolved in the solution.} . On the other hand, when excess sulfur (S) is added, analysis of a mixed solution of lithium polysulfide and P2S5 (added sulfur LP3S) dissolves both _{Li 2} S and P ₂ S ₅ to form a peak of _{PS 4} ^3. It can be seen that, in the LPSCl solution (added sulfur LPSCl) that has been synthesized, the dissolved P ₂ S ₅ reacts completely, thereby confirming that the corresponding peak disappears.

3 is a graph showing an XRD pattern photographed after heat treatment of an SSE sample prepared according to a comparative example at different temperatures.

Referring to FIG. 3, a peak of 2θ = 27° is a peak representing Li2S. This peak is evident when heat-treated at 300° C. or lower, and from _{this, it can be seen that Li 2} S is ionized and _{does not react with P 2} S _5, and most of it is precipitated as it is. Meanwhile, as other impurities, a LiCl peak of 2θ = 35° and 50° can be confirmed. _{In addition, it is estimated that the decrease in the Li 2} S peak in the heat treatment sample at 550° C. is due to the solid phase reaction.

4 is a graph showing an XRD pattern photographed after heat treatment of an SSE sample prepared according to an embodiment of the present invention.

As illustrated, it can be seen that LPSCl is crystallized at a heat treatment temperature of 200° C. or higher, and it can be seen that the degree of crystallization increases as the temperature increases.

Meanwhile, unlike FIG. 3, it can be seen that Li2S and LiCl impurities are hardly observed at a temperature of 300°C or higher. On the other hand, at a heat treatment temperature of 600°C or higher, an impurity peak appears again, which is presumed to be due to thermal decomposition of LPSCl.

5 is a graph showing the results of ion conductivity analysis of the SSE sample (Added sulfur) of the Example and the SSE sample (No sulfur) of the Comparative Example. Ion conductivity was measured with a VMP3 device from Bio logic. Measurement conditions are as follows.

scan from f _i= 1.0MHz to f _i =10.0MHz, E Range -10V;10V.

Referring to FIG. 5, it can be seen that the SSE sample of the example exhibits high ionic conductivity. In addition, it can be seen that the SSE sample of the example exhibits the highest ionic conductivity value at a temperature of 500 to 600°C.

6 is a graph showing the ionic conductivity of an example LPSCl sample heat-treated at 550°C.

The present invention is applicable to a lithium secondary battery.

Claims (6)

(a) providing a first solution comprising lithium polysulfide (Li ₂ S _{x, where 2≦x≦8);} (b) preparing a second solution containing Li 3 PS _{4+y (here, 0<y≦3)} by mixing _{P 2} S _{5 with the first solution;} (c) mixing and stirring the second solution and a third solution in which Li ₂ S and LiX (X=Cl, Br or I) are mixed; And (d) a method for producing a sulfide-based solid electrolyte comprising drying and heat-treating the mixed solution. The method of claim 1, The step (a), A method for producing a sulfide-based solid electrolyte, comprising the step of mechanically milling a mixed solution of Li2S and excess sulfur (S) to produce lithium polysulfide. The method of claim 1, The lithium polysulfide method for producing a sulfide-based solid electrolyte, characterized in that it contains at least one compound selected from the group consisting of Li2S3, Li2S4, Li2S6 and Li2S8. The method of claim 1, The first solution is a method for producing a sulfide-based solid electrolyte, characterized in that at least one selected from the group consisting of THF, DMC and DME as a solvent. The method of claim 1, The LPSX is a method of manufacturing a sulfide-based solid electrolyte, characterized in that _{Li 6} PS _{5+y Cl.} The method of claim 5, The step (d) is a method of manufacturing a sulfide-based solid electrolyte, characterized in that carried out at a temperature of 500 ~ 600 ℃.

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