Structural analysis method for solid electrolyte membranes

Abstract

A method for analyzing the structure of a solid electrolyte membrane, comprising dissolving a solid electrolyte in a polar solvent that selectively dissolves only the solid electrolyte from a solid electrolyte membrane including the solid electrolyte and a binder, is provided. The method for analyzing the structure of a solid electrolyte membrane according to one embodiment of the present invention can efficiently remove only the solid electrolyte while maintaining the structure of the solid electrolyte membrane including the solid electrolyte and the binder, and analyze the structure of the solid electrolyte membrane.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0024417, filed February 23, 2023, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for analyzing the structure of a solid electrolyte membrane. [Background technology]

[0003] Currently, various batteries that can overcome the limitations of lithium secondary batteries are being researched from the viewpoints of battery capacity, safety, output, size increase, miniaturization, etc.

[0004] Academia and industry are continuously researching metal-air batteries, which have a much larger theoretical capacity than lithium secondary batteries, solid-state batteries, which are safe and do not pose a risk of explosion, supercapacitors, NaS batteries or RFBs (redox flow batteries), which are large-scale batteries, and thin film batteries, which are ultra-miniaturized batteries.

[0005] Among these, solid-state batteries refer to batteries in which part or all of the liquid electrolyte used in conventional lithium secondary batteries is replaced with a solid, and they can significantly improve safety by not using flammable solvents inside the battery and completely eliminating the risk of fire or explosion caused by the decomposition reaction of conventional electrolytes.In addition, they have the advantage of being able to use Li metal or Li alloy as the anode material, which can dramatically improve the energy density relative to the mass and volume of the battery.

[0006] In particular, inorganic solid electrolytes for solid-state batteries can be divided into sulfide-based and oxide-based solid electrolytes. Currently, the solid electrolyte that has seen the most technological development is the sulfide-based solid electrolyte, and materials have been developed that have ionic conductivity close to that of organic electrolyte solutions.

[0007] In recent years, research has been progressing on techniques to analyze the internal structure of solid electrolytes in order to improve their ionic conductivity. However, conventional solid electrolytes have a low binder content, making structural analysis difficult. Even when structural analysis of solid electrolytes is attempted, the cross-sections observed in scanning electron microscope (SEM) images are 2D, making three-dimensional structural analysis difficult.

[0008] A method for analyzing sulfide-based solid electrolytes using computer simulation has been developed (see Patent Document 1). However, the computer simulation indirectly generates the three-dimensional structure of the sulfide-based solid electrolyte based on the conduction properties of lithium ions, and therefore has the problem that it only predicts the structure of the sulfide-based solid electrolyte, resulting in a slight decrease in accuracy in structural analysis of the binder and pores inside the solid electrolyte membrane.

[0009] The present inventors have completed the present invention as a result of studying a method for analyzing a solid electrolyte membrane, which allows for efficient removal of only the solid electrolyte from the structure of the solid electrolyte membrane while maintaining the structure of the solid electrolyte membrane, and allows for accurate analysis of the structure of the solid electrolyte membrane including the frame made of a binder. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Korean Patent Publication No. 2019-0123002 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention provides a method for analyzing the structure of a solid electrolyte membrane, which can efficiently remove only the solid electrolyte from the structure of the solid electrolyte membrane while maintaining the structure of the membrane, and can analyze the structure of the solid electrolyte membrane, specifically the structure of the binder. [Means for solving the problem]

[0012] According to a first aspect of the present invention, The present invention provides a method for analyzing the structure of a solid electrolyte membrane, which includes dissolving a solid electrolyte membrane containing a solid electrolyte and a binder in a polar solvent.

[0013] In one embodiment of the present invention, the polar solvent comprises one or more selected from the group consisting of water and alcohols.

[0014] In one embodiment of the present invention, the alcohol comprises an alcohol having 4 or less carbon atoms.

[0015] In one embodiment of the present invention, the solid electrolyte may include one or more selected from the group consisting of sulfide-based electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes.

[0016] In one embodiment of the present invention, the binder comprises a fibrous binder or a particulate binder.

[0017] In one embodiment of the present invention, the binder comprises one or more selected from the group consisting of polytetrafluoroethylene (PTFE), ethylene-vinyl acetate (EVA), styrene-ethylene-butylene-styrene (SEBS), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), and hydrogenated nitrile butadiene rubber (HNBR).

[0018] In one embodiment of the present invention, the polar solvent in the dissolving step is supplied so that the concentration of the solid electrolyte is 10% by weight or less.

[0019] In one embodiment of the present invention, the dissolving step is carried out for 5 minutes to 1 hour. [Effects of the Invention]

[0020] A method for structural analysis of a solid electrolyte membrane according to one embodiment of the present invention involves dissolving a solid electrolyte in a solid electrolyte membrane made of a solid electrolyte and a binder using a polar solvent that selectively dissolves only the solid electrolyte, thereby effectively removing the solid electrolyte from the solid electrolyte membrane while maintaining the structure of the solid electrolyte membrane due to the remaining binder.

[0021] By removing the solid electrolyte from within the solid electrolyte membrane, the internal structure, such as the bonding state of the binder that constitutes the solid electrolyte membrane, can be easily confirmed. [Brief explanation of the drawings]

[0022] [Figure 1] 1A to 1C are schematic diagrams illustrating a structural analysis process of a solid electrolyte membrane according to an embodiment. [Figure 2]3 is a photograph showing a structural analysis process of a solid electrolyte membrane according to an example. [Figure 3a] 1 shows SEM (Scanning Electron Microscope) images of the solid electrolyte membranes obtained in Examples and Comparative Examples. [Figure 3b] 1 shows SEM images of the solid electrolyte membranes obtained in Examples and Comparative Examples. [Figure 3c] 1 shows SEM images of the solid electrolyte membranes obtained in Examples and Comparative Examples. [Figure 3d] 1 shows SEM images of the solid electrolyte membranes obtained in Examples and Comparative Examples. [Figure 3e] 1 shows SEM images of the solid electrolyte membranes obtained in Examples and Comparative Examples. [Figure 3f] 1 shows SEM images of the solid electrolyte membranes obtained in Examples and Comparative Examples. [Figure 3g] 1 shows SEM images of the solid electrolyte membranes obtained in Examples and Comparative Examples. [Figure 3h] 1 shows SEM images of the solid electrolyte membranes obtained in Examples and Comparative Examples. [Figure 3i] 1 shows SEM images of the solid electrolyte membranes obtained in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0023] The embodiments provided by the present invention can all be achieved by the following description. It should be understood that the following description describes preferred embodiments of the present invention, and that the present invention is not necessarily limited thereto.

[0024] Unless the measurement conditions and methods for the physical properties described herein are specifically described, the physical properties are measured according to the measurement conditions and methods commonly used by those of ordinary skill in the art.

[0025] As used herein, the term "structural analysis of a solid electrolyte membrane" refers to analyzing the structure of the binder, i.e., the frame formed by the binder, after removing the solid electrolyte from a solid electrolyte membrane containing a solid electrolyte and a binder, and thus may refer to structural analysis of the binder. The solid electrolyte membrane may be manufactured by a wet process or a dry process. The wet process uses a solvent, so some solvent may remain in the solid electrolyte membrane, but the amount of residue is negligible. The dry process does not use a solvent, and the solid electrolyte membrane consists only of a solid electrolyte and a binder. Therefore, the structure of the binder can be analyzed by removing the solid electrolyte from the solid electrolyte membrane.

[0026] Structural analysis method for solid electrolyte membranes FIG. 1 is a schematic diagram showing a method for structural analysis of a solid electrolyte membrane according to an embodiment.

[0027] Referring to FIG. 1, the present invention relates to a method for structural analysis of a solid electrolyte membrane, which may include immersing a solid electrolyte membrane including a solid electrolyte and a binder in a polar solvent to dissolve the solid electrolyte. After dissolving the solid electrolyte, a framework consisting of the binder can be obtained, and the structure of the solid electrolyte membrane can be analyzed based on this. While FIG. 1 illustrates a sulfide-based solid electrolyte membrane including a sulfide-based solid electrolyte and a fibrous binder, the present invention is not limited thereto.

[0028] A method for analyzing the structure of a solid electrolyte membrane according to one embodiment of the present invention includes a dissolving step of dissolving a solid electrolyte in a polar solvent, the solid electrolyte being a solid electrolyte and a binder. The dissolving step can remove large chunks of solid electrolyte that have permeated the structure of the solid electrolyte membrane. The polar solvent selectively dissolves only the solid electrolyte, but not the binder. According to one embodiment of the present invention, the polar solvent may include one or more selected from the group consisting of water and alcohol. According to one embodiment of the present invention, the alcohol has four or fewer carbon atoms. If the carbon number is too high, the polarity may decrease, potentially reducing functionality as a solvent. Considering both functionality and ease of handling, ethanol is a preferred alcohol solvent.

[0029] According to one embodiment of the present invention, in the dissolving step, the polar solvent is supplied so that the concentration of the solid electrolyte is 10 wt % or less, 5 wt % or less, 3 wt % or less, or 1 wt % or less. If the concentration of the solid electrolyte in the polar solvent is too high, the solubility of the polar solvent decreases, and the solid electrolyte may not be effectively removed or an additional removal process may be required. Because the solid electrolyte content in the solid electrolyte membrane is high, the removal process can be easily performed in one go.

[0030] In the above process, the dissolution time may be 5 minutes to 1 hour. If it is less than 5 minutes, the solid electrolyte may remain in the solid electrolyte membrane, and if it exceeds 1 hour, the processability may be reduced. Specifically, the dissolution time may be 5 minutes or more, 8 minutes or more, or 10 minutes or more, or 40 minutes or less, 50 minutes or less, or 1 hour or less. The dissolution step may be performed only once.

[0031] The solid electrolyte is not particularly limited as long as it is a solid electrolyte commonly used in the art and is soluble in the solvent according to an embodiment of the present invention. According to an embodiment of the present invention, the solid electrolyte includes an inorganic solid electrolyte, and the inorganic solid electrolyte is a sulfide-based solid electrolyte, a halide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof.

[0032] The sulfide-based solid electrolyte is an electrolyte component containing sulfur atoms, and is not particularly limited to a specific component, and may include one or more of a crystalline solid electrolyte, an amorphous solid electrolyte (glassy solid electrolyte), and a glass ceramic solid electrolyte.

[0033] The sulfide-based solid electrolyte may be represented by the following chemical formula 1:

[0034] [Chemical formula 1] L a1 M b1 P c1 S d1 A e1

[0035] In Chemical Formula 1, L is an element selected from Li, Na, and K, M is an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al, and Ge, A is I, Br, Cl, or F, a1 to e1 are composition ratios of the elements, and a1:b1:c1:d1:e1 is 1-12:0-1:1:2-12:0-5.

[0036] For example, the sulfide-based solid electrolyte may be an LPS-type sulfide containing sulfur and phosphorus, an LPSCl-type sulfide, or a Li 4-x Ge 1-x P x S4 (x is 0.1 to 2, specifically, x is 3 / 4, 2 / 3), Li 10±1 MP2X 12 (M=Ge, Si, Sn, Al, X=S, Se), Li 3.833 Sn 0.833 As 0.166 S4, Li4SnS4, Li 3.25 Ge 0.25 P0.75 Examples of the cation exchange material include, but are not limited to, LiS-S4, Li2S-P2S5, B2S3-Li2S, xLi2S-(100-x)P2S5 (x is 70 to 80), Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-LiCl-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2S-SiS2-Li3N, Li2S-SiS2-LiI, and Li2S-B2S3-LiI. For example, the LPSCl-type sulfide may be Li6PS5Cl.

[0037] The halide-based solid electrolyte may be represented by the following chemical formula 2:

[0038] [Chemical formula 2] Li 6-3a M a Br b Cl c

[0039] In the above chemical formula 2, M is a metal other than Li, and a is 0. <a<2であり、bは、0≦b≦6であり、cは、0≦c≦6であり、b+c=6である。

[0040] For example, the halide-based solid electrolyte may include at least one of Li3YCl6 and Li3YBr6, but is not necessarily limited thereto.

[0041] The oxide-based solid electrolyte may be represented by the following chemical formula 3:

[0042] [Chemical formula 3] Li 1+x+y Al x Ti 2-x Si y P 3-y O 12

[0043] (In the above Chemical Formula 1, x is 0≦x≦2, and y is 0≦y≦3.) For example, the oxide-based solid electrolyte may be Li 3x La 2 / 3-x LLT series with perovskite structure such as TiO3, Li 14 LISICON such as Zn(GeO4)4, Li 1.3 Al 0.3 Ti 1.7 LATP systems such as (PO4)3, (Li 1+x Ge 2-x Al x The LAGP system such as (PO4)3), phosphate system such as LiPON, etc. can be appropriately selected and used, but the present invention is not necessarily limited to these.

[0044] The method for structural analysis of a solid electrolyte membrane according to an embodiment of the present invention can be applied to any solid electrolyte membrane as long as the solid electrolyte can be dissolved in a solvent. However, in a wet-type solid electrolyte membrane manufacturing method in which the solid electrolyte membrane structure is formed by dissolving the solid electrolyte together with a conductive material and a binder in a nonpolar solvent and applying the solution, the solid electrolyte serves as a support within the solid electrolyte membrane. Therefore, when the method for structural analysis of a solid electrolyte membrane is applied, the structure of the solid electrolyte membrane may be destroyed due to dissolution of the solid electrolyte. Therefore, the method for structural analysis of a solid electrolyte membrane can be preferably applied to a solid electrolyte membrane manufactured by a dry process, in which the structure of the solid electrolyte membrane is sufficiently supported by only the binder and the solid electrolyte is introduced therein.

[0045] The binder may be a fibrous binder or a particulate binder. The fibrous binder may be contained in a solid electrolyte prepared by physically mixing the solid electrolyte and the binder during a dry process. The binder may be fiberized during the dry process to form a fibrous binder.

[0046] The binder may include at least one selected from the group consisting of polytetrafluoroethylene (PTFE), ethylene-vinyl acetate (EVA), styrene-ethylene-butylene-styrene (SEBS), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), and hydrogenated nitrile butadiene rubber (HNBR).

[0047] Preferred examples are shown below to aid in understanding the present invention. However, the following examples are provided merely to facilitate understanding of the present invention, and the present invention is not limited thereto.

[0048] [Table 1]

[0049] Example Example 1 1-1. Manufacturing of solid electrolyte membranes Styrene-ethylene-butylene-styrene (SEBS) particles (Sigma Aldrich, 200557) were dissolved in xylene at 2 wt% and then mixed with sulfide-based solid electrolyte Li6PS5Cl powder to prepare a uniform slurry. This was then coated onto a PET release film, dried, and calendered five times using a roll press to produce a solid electrolyte membrane approximately 50 μm thick. The binder content in the resulting solid electrolyte membrane was 3 wt%.

[0050] 1-2. Structural analysis of solid electrolyte membranes The solid electrolyte membrane was fixed and immersed in an aqueous solvent to a solid electrolyte concentration of 1 wt %, and then the solid electrolyte in the solid electrolyte membrane was dissolved for 10 minutes. The aqueous solvent was removed from the solid electrolyte membrane and the membrane was dried, and the structure of the resulting solid electrolyte membrane was analyzed (Figure 2).

[0051] Example 2 The same procedure as in Example 1 was carried out, except that an ethanol solvent was used instead of an aqueous solvent.

[0052] Example 3 The same procedure as in Example 1 was carried out, except that the solid electrolyte was immersed in an aqueous solvent so that the concentration was 3% by weight, and the dissolution time was 20 minutes.

[0053] Example 4 The procedure was the same as in Example 1, except that the dissolution time was 30 minutes.

[0054] Example 5 The same procedure as in Example 1 was carried out, except that the binder content in the solid electrolyte membrane was 2 wt %.

[0055] Example 6 The same procedure as in Example 1 was carried out, except that EVA (ethylene-vinyl acetate, Sigma Aldrich, 340502) particles were used as the binder instead of the SEBS particles.

[0056] Example 7 The sulfide-based solid electrolyte Li6PS5Cl powder was mixed with the binder PTFE (polytetrafluoroethylene) particles (Chemours) in a mortar and the resulting mixture was calendered five times in a roll press to produce a 300μm thick solid electrolyte membrane. The binder content in the produced solid electrolyte membrane was set to 0.5wt%.

[0057] Example 8 The same procedure as in Example 3 was carried out except that the produced solid electrolyte membrane was subjected to a solvent treatment for 1 minute.

[0058] Comparative Example 1 The solid electrolyte membrane produced in Example 1 was prepared without solvent treatment.

[0059] Comparative Example 2 The solid electrolyte membrane produced in Example 7 was prepared without solvent treatment.

[0060] Experimental Example 1: Structural analysis of solid electrolyte membrane The structures of the solid electrolyte membranes obtained in the examples and comparative examples were analyzed using an SEM (Thermo Scientific, FEI Apreo SEM).

[0061] 3a to 3i are SEM images of the solid electrolyte membranes obtained in the examples and comparative examples.

[0062] 3a to 3i, in the solid electrolyte membranes of the examples, only the binder frame was clearly visible after the solid electrolyte was removed. In particular, it can be seen that the solid electrolyte contained in the solid electrolyte membrane was removed using water or ethanol, regardless of the binder structure and the manufacturing method of the solid electrolyte membrane. However, in Example 8, the dissolution time was relatively short, and it can be seen that some of the solid electrolyte remained.

[0063] On the other hand, it is difficult to confirm the binder structure of the solid electrolyte membrane of the comparative example, since the solid electrolyte dissolution step was not carried out.

[0064] Any simple modifications or variations of the present invention should fall within the scope of the present invention, and the specific scope of protection of the present invention will be apparent from the appended claims.

Claims

1. dissolving a solid electrolyte membrane containing a solid electrolyte and a binder in a polar solvent to obtain a structure containing the binder; and performing a structural analysis of the binder.

2. 2. The method for structural analysis of a solid electrolyte membrane according to claim 1, wherein the polar solvent comprises at least one selected from the group consisting of water and alcohols.

3. 3. The method for analyzing a structure of a solid electrolyte membrane according to claim 2, wherein the alcohol has four or less carbon atoms.

4. 2. The method for structural analysis of a solid electrolyte membrane according to claim 1, wherein the solid electrolyte comprises at least one selected from the group consisting of a sulfide-based electrolyte, a halide-based solid electrolyte, and an oxide-based solid electrolyte.

5. A structural analysis method for a solid electrolyte membrane as described in claim 1, wherein in the solid electrolyte membrane, the binder is a fibrous binder or a particulate binder.

6. 2. The method for analyzing a solid electrolyte membrane structure according to claim 1, wherein the binder comprises at least one selected from the group consisting of polytetrafluoroethylene (PTFE), ethylene-vinyl acetate (EVA), styrene-ethylene-butylene-styrene (SEBS), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), and hydrogenated nitrile butadiene rubber (HNBR).

7. 2. The method for analyzing a structure of a solid electrolyte membrane according to claim 1, wherein in the dissolving step, the polar solvent is supplied so that the concentration of the solid electrolyte is 10 wt % or less with respect to the total weight of the polar solvent and the solid electrolyte.

8. 8. The method for structural analysis of a solid electrolyte membrane according to claim 1, wherein the dissolving step is carried out for 5 minutes or more and 1 hour or less.

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