KR102314201B1 - Manufacturing Methods of LPSCl Solid Electrolyte For Li Based Secondary Batteries - Google Patents

Abstract

The present invention relates to a method for manufacturing an LPCl solid electrolyte for a lithium secondary battery. The present invention provides a method comprising the steps of: (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) drying and heat-treating the mixed solution.

Description

Manufacturing method of LPSCl solid electrolyte for lithium secondary battery {Manufacturing Methods of LPSCl Solid Electrolyte For Li Based Secondary Batteries}

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

All-Solid-State Battery refers to the replacement of liquid electrolyte with solid electrolyte among the above battery components. Compared to liquid electrolytes, all-solid-state secondary batteries are attracting attention as next-generation secondary batteries because they do not have the risk of battery explosion or fire, simplify the manufacturing process, and increase energy density.

A sulfide-based electrolyte (SSE) is attracting attention as a solid electrolyte for all-solid-state secondary batteries. However, LPSCl, which is a representative sulfide-based SSE, _{can be obtained by mixing Li 2} S and P ₂ S ₅ and sintering the mixture after long-term high-energy milling.

As an alternative to solving the mechanical synthesis problem, efforts are being made to manufacture SSE by a liquid phase synthesis method. Although this method can synthesize LPS in a shorter time than mechanical synthesis, it has a disadvantage in that it exhibits low ionic conductivity due to impurities.

On the other hand, in the conventional liquid phase process for preparing SSE, a polar solvent such as NMF has been used to increase solubility because sulfide exhibits low solubility in THF, DMC or DME. However, NMF is not preferred as a solvent because it exhibits high toxicity.

Laidong Zhou et al, ACS Energy Lett. 2019, 4, 265-270

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

Another object of the present invention is to provide a method for preparing a sulfide-based solid electrolyte in a liquid phase process using a low-toxic solvent.

In order to achieve the above technical object, the present invention, (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) drying and heat-treating the mixed solution.

In the present invention, step (a) may include manufacturing lithium polysulfide by mechanically milling a mixed solution of _{Li 2 S and excess sulfur (S).}

In the present invention, the lithium polysulfide preferably includes at least one compound selected from the group consisting _{of Li 2} S ₃ , Li ₂ S ₄ , Li ₂ S ₆ and Li ₂ S _{8 .}

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

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

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

In the present invention, the particle size of the LPSX compound powder is less than 1 μm, preferably distributed within 20 nm to 1 μm. At this time, the particle size was observed with SEM (Scanning Electron Microscope), and ZEISS GEMINI500 was used. At this time, the accelerating voltage was scanned at 2 kV and analyzed under the condition of non-open air. The size of an individual particle refers to the maximum length of the particle on the SEM image.

In addition, in the present invention, the LPSX compound preferably has an NMR full width at half maximum (δx) of 4<δx<5. At this time, the NMR can be measured by a 400MHz Solid stat NMR spectrometer of AVANCE III HD (Bruker), larmor frequency: 162.02MHz, spinning rate, 25kHz, pulse width: 1.5us (75° deg), Repetition time: Analyzed under 30 sec conditions.

It is also preferred that the LPSX compound contains a bridging sulfur peak in the element S region in XPS analysis. At this time, XPS analysis may be measured by ESCALAB250 of VGScientific. When measuring XPS, for qualitative analysis, a narrow scan is performed on the corresponding component after the survey wide scan. At this time, the pass energy is 50.0eV (wide scan) and 20eV (narrow scan), respectively, and the step size is 1eV (wide scan) and 0.1, respectively. eV (narrow scan).

According to the present invention, it is possible to prepare a sulfide-based solid electrolyte of high purity using a simple process and a low-toxic 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.
FIG. 2A is an electron microscope photograph of the solid electrolyte sample powder prepared in Example 1, and FIG. 2B is an electron microscope photograph of the commercial solid electrolyte sample powder.
3 is a graph showing the Raman analysis results of the SSE samples prepared by Example 1 and Comparative Example 1.
4 is a graph showing XRD patterns taken after heat treatment of SSE samples prepared according to Comparative Examples at different temperatures.
5 is a graph showing an XRD pattern taken after heat treatment of the SSE sample prepared according to Example 1 of the present invention.
6 is a graph showing the ion conductivity analysis results of Examples and Comparative Examples.
7 is a graph showing the ionic conductivity of the LPSCl sample of an embodiment of the present invention.
8 is a graph showing the results of NMR analysis of Examples and Comparative Examples.
9A and 9B are graphs showing voltage capacity curves of Examples and Comparative Examples, respectively.
10 is a graph showing the cycle characteristics measurement results of LPSCl electrolytes of Examples and Comparative Examples.
11 is a graph showing XPS analysis results of the solid electrolyte sample prepared in Example 1. FIG.
12 is a graph showing XPS analysis results of Comparative Examples.
13 is a graph showing the XPS analysis result of another comparative example.

Hereinafter, the present invention will be described in detail by describing preferred embodiments 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 instead of lithium sulfide (Li _{2 S) (S120).} In the present invention, lithium polysulfide _{may be expressed as Li 2} S _x , where x may be any real number from 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 _{may be synthesized by mechanical milling after dissolving lithium sulfide (Li 2} S) and sulfur (S) in a solvent such as THF, DMC or DME in an appropriate ratio (S110). At this time, the sulfur is preferably solid sulfur (S ₈ ) may be used. For example, a reaction formula for the production _{of Li 2} S ₃ as lithium polysulfide is as follows.

(Formula 1)

Li ₂ S + 2S → Li ₂ S ₃

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

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

Lithium polysulfide and P ₂ S ₅ react with stirring to form a solution having a composition of Li ₃ PS _4+y (here, 0<y≤3). Preferably, y has a value of 2 or more. For example, the _{reaction for generating Li 3} PS _{4+y from Li 2} S _x (eg, x=3) may be expressed by the following equation, where y=3.

(Formula 2)

3Li ₂ S ₃ + P ₂ S ₅ → 2Li ₃ PS _4+y

Referring back to FIG. 1 , separately 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, and 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, stirring was performed at 300-500 rpm using a hot plate and a magnetic bar; The mixing ratio may be appropriately selected. For example, _{the molar ratio for the preparation of Li 6} PS _5+y Cl may be calculated according to the following reaction equation.

(Formula 3)

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

Next, the stirred solution is dried at a temperature of about 70 to 150 ° C for 10 to 40 hours (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) a compound can be prepared (S150).

_{The particle size of the Li 6} PS _5+y X (where X=Cl, Br or I) powder prepared in the present invention is preferably distributed within 1 nm to 1 μm. _{Preferably, the Li 6} PS _5+y X (where X=Cl, Br or I) powder prepared in the present invention is less than 1 μm. More preferably, in the present invention, the _{particle size (particle size) of the Li 6} PS _5+y X (where X=Cl, Br or I) powder is 20 nm or more, and preferably less than 1 μm. In the present invention, the particle size of the powder is preferably distributed in the range of 20 nm to 500 nm.

Hereinafter, preferred embodiments of the present invention will be described.

<Example 1>

_{According to the composition of Li 2} S ₃ 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. Then, the solution composition was _{weighed to fit 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 Li 2} S and LiCl in a ratio of 1:1 using THF as a solvent.

Then, 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 stirred solution was stirred at a temperature of 80° C. for 24 hours and 140 After drying for 12 hours at a temperature of ℃, heat treatment was performed at a temperature of 200 ~ 700 ℃. At this time, the temperature was raised by 5 degrees per minute, and after reaching the target temperature, the temperature was maintained for 3 hours.

<Comparative Example 1>

For comparison, the manufacturing process of lithium polysulfide was omitted, and a solution in which _{lithium sulfide (Li 2} S) and P ₂ S ₅ were mixed according to the composition of _{Li 3} PS _{4 was prepared and mixed with a Li 2} S+LiCl solution. It was tested under the same conditions except that lithium polysulfide was not used. _{P 2} S ₅ precipitation was confirmed in the lithium sulfide and P ₂ S ₅ mixed solution, and eventually it was confirmed that it was not completely dissolved in the THF solvent.

The properties of the prepared LiPSCl compound were evaluated.

<Comparative Example 2>

Li ₂ S : P ₂ S ₅ : LiCl was mixed in a ratio of 42.8:41.4:15.8, put in a ball mill jar together with zirconia balls, and high energy milling was performed at 600 rpm in a ball milling equipment for 10 hours to synthesize LPSCl. .

FIG. 2A is an electron microscope photograph of the solid electrolyte sample powder prepared in Example 1, and FIG. 2B is an electron microscope photograph of a commercial solid electrolyte sample powder. Here, as a commercial solid electrolyte, Argyrodite, a product of CIS, was used.

2a and 2b, it can be seen that the commercial powder has a large size of 4 to 8 μm, whereas the particles of the solid electrolyte sample powder prepared in the present invention have a relatively very small size of about 20 nm to 1 μm. have.

3 is a graph showing the Raman analysis results of the SSE samples prepared by Example 1 and Comparative Example 1.

Referring to Figure 3, in the case of the LPSCl solution (No added sulfr) to which the 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, when _{a solution of lithium polysulfide and P 2} S ₅ mixed (added sulfur LP3S) is analyzed, both Li ₂ S and P ₂ S ₅ are dissolved to form PS ₄ ^3- It can be confirmed that a peak is formed, and it can be confirmed that the peak disappears due to the complete reaction of _{P 2} S _{5 which} was dissolved in the LPSCl solution (added sulfur LPSCl) in which the synthesis is completed.

4 is a graph showing an XRD pattern taken after heat treatment of the SSE sample prepared according to Comparative Example 1 at different temperatures.

Referring to FIG. 4 , the 2θ=27° peak is a peak representing _{Li 2 S.} This peak appears clearly when heat treatment is carried out at 300° C. or less, and from _{this, it can be confirmed that Li 2} S is ionized and _{does not react with P 2} S ₅ and most of it is precipitated as it is. On the other hand, LiCl peaks at 2θ = 35° and 50° can be confirmed as other impurities. _{In addition, it is estimated that the decrease of the Li 2} S peak in the 550°C heat-treated sample is due to the solid-phase reaction.

5 is a graph showing an XRD pattern taken after heat treatment of the SSE sample prepared according to Example 1 of the present invention.

As shown, 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.

On the other hand, it can be seen that, unlike FIG. 5, Li 2 S 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.

6 is a graph showing the ionic conductivity analysis results of the SSE sample of Example (Added sulfur) and the SSE sample of Comparative Example 1 (No sulfur). Ion conductivity was measured with a VMP3 device from Biologic. The measurement conditions are as follows.

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

Referring to FIG. 6 , it can be seen that the SSE sample of Example 1 exhibits high ionic conductivity. In addition, it can be seen that the SSE sample of Example 1 exhibits the highest ionic conductivity value at a temperature of 500 to 600°C.

7 is a graph showing the ionic conductivity of the LPSCl sample of Example 1 heat-treated at 550 ℃.

8 is a graph showing the results of NMR analysis of the SSE sample of Example 1 and the SSE sample of Comparative Example 2;

Referring to FIG. 8 , the sample of Example 1 has an NMR full width at half maximum of about 4.42 ppm (82.27 to 86.69 ppm). In contrast, the half width of the sample of Comparative Example 2 is about 5.42 ppm (81.5 to 87.08 ppm). That is, it can be seen that the half-width of the sample of Example 1 has a value smaller than the half-width of 2 for comparison. In the present invention, the preferred NMR half width (δx) is preferably 3<δx<5.4. More preferably, 4<δx<5, even more preferably 4.4<x<5.

When the relaxation time is short, solid, or high in viscosity, or when the spin quantum number is greater than 1/2, the NMR half width increases and vice versa, the NMR half width decreases. it is judged to do

<Experimental example>

A battery cell was prepared using the LPSCl prepared in Example 1 as an electrolyte. The cell is composed of a stacked structure of positive electrode (NCM622:SE:SPB)/LPSCl/Li-In powder and is manufactured as a compression cell. The electrochemical properties of the fabricated cells were evaluated. For the characteristics, the battery characteristics were evaluated for each C-rate (0.1C, 0.2C, 0.5C, 1C, 2C) under the conditions of 55℃, and the graph evaluating the coulombic efficiency (CE) was conducted at the conditions of 0.5C and 55℃. became

For comparison, a battery cell was manufactured using LPSCl prepared in Comparative Example 1 as an electrolyte, and electrochemical properties were evaluated.

9A and 9B are graphs showing the voltage capacity curves of the LPSCl electrolyte of Example 1 and the LPSCl electrolyte of Comparative Example 1, respectively, and FIG. 10 is a graph showing the cycle characteristics measurement results of the LPSCl electrolyte of Example 1 and Comparative Example 1. am.

LPSCl of Examples In the case of using a solid electrolyte, the cell test showed good performance with a discharge capacity of 175 mAh/g at 0.5C and also maintained a coulombic efficiency of 99.8% during 50 cycles. In addition, it was confirmed that it has a discharge capacity of 100 mAh/g even under the condition of 2C. On the other hand, when the LPSCl solid electrolyte of Comparative Example was used, a discharge capacity of 165 mAh/g was exhibited, and it can be seen that a discharge capacity of 50 mAh/g, a rather low discharge capacity, was exhibited under the condition of 2C.

11 is a graph showing XPS analysis results of the solid electrolyte sample prepared in Example 1, wherein (a) is an element S region, (b) is an element P region analysis results.

Referring to FIG. 11 , in LPSCl of Example 1, a bridging sulfur peak can be confirmed in the S zone. By additives and polysulfide is produced made weaker the binding of the P ₂ S ₅ sikyeotgo further promote the reaction of Li ₂ S Therefore, the Li ₂ S and P ₂ S ₅ was possible to completely soluble in the solvent THF. At this time, bonds such as S-Cl, SP, and Li-S linked to S are formed. Such a reaction can be confirmed at the peak having a binding energy of 163.63. Meanwhile, in the S region, the peak corresponding to bridging sulfur is 163.63 eV, the peak corresponding to the P ₂ S ₅ region is 162.31 eV, and the peak corresponding to LPSCl is 160.9 EeV.

Meanwhile, in the element P region, _{the peak corresponding to P-Cl, P 2} S _5, PO, etc. bonding to P is 133.41 eV, the peak corresponding to P ₂ S ₅ is 132.32 eV, and the peak corresponding to LPSCl is 131.42 eV.

12 and 13 are graphs showing XPS analysis results of solid electrolyte samples prepared in Comparative Examples 1 and 2, respectively.

12, in the XPS analysis element S region of the solid electrolyte of Comparative Example 1, _{the peak corresponding to the region of P 2} S ₅ is 162.32eV, and the peak corresponding to LPSCl is 161.1EeV. In the element P region, _{the peak corresponding to P-Cl, P 2} S _5, PO, etc. bonding to P is 133.57 eV, the peak corresponding to P ₂ S ₅ is 132.20 eV, and the peak corresponding to LPSCl is 131.37 eV. In Comparative Example 1, _{it can be seen that P-Cl, P 2} S _5, PO, and the like are formed.

12 and 13, since the solid electrolyte synthesized by the wet synthesis method dissolves in a solvent to form LPSCl after weakening the bond, it shows various bonds of P with the conventional dry LPSCl, and in particular, the solid prepared in Example 1 In the case of an electrolyte, it shows a somewhat unordered structure, such as showing various bonds with S, and thus can exhibit high ionic conductivity.

Referring to FIG. 13 , it can be seen that, when synthesizing the solid electrolyte LPSCl prepared in Comparative Example 2, _{bonds such as P-Cl, P 2} S _{5 and PO are not formed.} In addition, in the XPS analysis element S _{region, the peak corresponding to the region of P 2} S ₅ is 162.12eV, the peak corresponding to LPSCl is 160.90EeV, and the peak corresponding to P2S5 in the element P region is 132.15eV, the peak corresponding to LPSCl is 131.28 eV.

Claims (9)

(a) providing a first solution comprising lithium polysulfide (Li ₂ S _x , wherein 2<x<4);
(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 to prepare an LPSX compound,
The first to third solutions are solutions containing the same solvent selected from the group consisting of THF, DMC and DME,
The step (a) is a method for producing a sulfide-based solid electrolyte, characterized in that it comprises the step of manufacturing lithium polysulfide by mechanical milling a mixed solution _{of Li 2 S and excess sulfur (S).}
delete delete delete According to claim 1,
The LPSX is Li ₆ PS _5+y Cl (0<y≤3) Method for producing a sulfide-based solid electrolyte, characterized in that. 6. The method of claim 5,
The heat treatment of step (d) is a method for producing a sulfide-based solid electrolyte, characterized in that performed at a temperature of 500 ~ 600 ℃. According to claim 1,
The method for producing a sulfide-based solid electrolyte, characterized in that the particle size of the LPSX compound powder is less than 1 μm. According to claim 1,
The LPSX compound has an NMR half width (δx) of 4<δx<5. According to claim 1,
The method for producing a sulfide-based solid electrolyte, characterized in that the LPSX compound contains a bridging sulfur peak in the element S region on XPS analysis.

Images