Solvent for manufacturing sulfide-based solid electrolyte membrane

Abstract

The present invention relates to a solvent for manufacturing a sulfide-based solid electrolyte membrane, comprising hexyl isobutyrate and a non-polar organic solvent containing an ester group. When a solid electrolyte membrane is manufactured using the solvent, excellent properties thereof and high ionic conductivity are ensured.

Description

Solvent for manufacturing sulfide-based solid electrolyte membranes

[0001] The present invention relates to a solvent for manufacturing a solid electrolyte membrane, and more specifically, to a solvent for manufacturing a sulfide-based solid electrolyte membrane.

[0002] The present invention claims priority based on Korean Patent Application No. 10-2024-0190803 filed on December 19, 2024, the entire contents of said application incorporated herein by reference.

[0003] With research focusing on the safety issues and energy density of high-capacity batteries, all-solid-state batteries are gaining prominence as next-generation batteries. These batteries significantly improve safety by replacing flammable liquid electrolytes, which are prone to explosions, with solid electrolytes. Solid electrolytes used in all-solid-state batteries include oxide-based, sulfide-based, and polymer-based types; among these, active research is being conducted on sulfide-based solid electrolytes, which exhibit the highest ionic conductivity.

[0004] For the commercialization of sulfide-based all-solid-state batteries, ease of fabricating large-area cells must be ensured. To achieve this, technology that produces a solid electrolyte in the form of a separator, similar to conventional lithium-ion batteries, is essential. To manufacture large-area solid electrolyte membranes, a method is used in which a solid electrolyte membrane composition is cast onto a substrate to produce the solid electrolyte membrane.

[0005] These solid electrolyte membrane compositions are used by dissolving the solid electrolyte and binder, etc., in a non-polar organic solvent. However, conventional non-polar organic solvents, such as xylene, toluene, and hexane, have problems such as non-uniform viscosity when forming the solid electrolyte membrane composition or clogging the nozzle of equipment for large-area sheets due to their low boiling point and high vapor pressure.

[0006] The objective of the present invention is to provide a solvent for manufacturing a sulfide-based solid electrolyte membrane that secures excellent ionic conductivity while solving the aforementioned problems.

[0007] A solvent for manufacturing a sulfide-based solid electrolyte membrane according to one embodiment of the present invention comprises hexyl isobutyrate.

[0008] In one embodiment, the solvent may further include a nonpolar organic solvent.

[0009] In one embodiment, the content of the non-polar organic solvent may be 60 wt% or less with respect to 100 wt% of the solvent.

[0010] In one embodiment, the nonpolar organic solvent may include an ester group.

[0011] In one embodiment, the nonpolar organic solvent may comprise one or more selected from isobutyl isobutyrate, n-butyl butyrate, hexyl butyrate, 2-ethyl hexyl acetate, ethyl hexanoate, di-isobutyl ketone, n-heptyl acetate, hexyl acetate, d-limonene, trimethylbenzene, and isopropyl benzene.

[0012] In one embodiment, the solvent may have a boiling point of 150 to 200°C.

[0013] In one embodiment, the solvent may have a vapor pressure of 0.2 to 4.5 mmHg at 25°C.

[0014] In one embodiment, the solvent may have a flash point of 50°C or higher.

[0015] A solvent for manufacturing a sulfide-based solid electrolyte membrane according to one embodiment of the present invention includes hexyl isobutyrate, thereby enabling excellent characteristics and high ionic conductivity when manufacturing a solid electrolyte membrane.

[0016] Figure 1 is a graph showing the cyclic voltammetry of a battery including Example 1.

[0017] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0018] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0019] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0020] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0021] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0022]

[0023] Solvent for manufacturing sulfide-based solid electrolyte membranes

[0024] A solvent for manufacturing a sulfide-based solid electrolyte membrane according to one embodiment of the present invention includes hexyl isobutyrate, thereby enabling excellent characteristics and high ionic conductivity when manufacturing a solid electrolyte membrane.

[0025] In one embodiment, the solvent for manufacturing a sulfide-based solid electrolyte membrane may include hexyl isobutyrate. That is, the solvent for manufacturing a sulfide-based solid electrolyte membrane may include only hexyl isobutyrate. Because hexyl isobutyrate has appropriate vapor pressure and boiling point, it can provide viscosity stability and uniformity when forming a solid electrolyte membrane composition compared to conventional non-polar organic solvents, and can also secure high ionic conductivity.

[0026] In one embodiment, the solvent for manufacturing a sulfide-based solid electrolyte membrane may further include a nonpolar organic solvent, in which case the content of the nonpolar organic solvent may be 60 wt% or less relative to 100 wt% of the total solvent. Specifically, the content of the nonpolar organic solvent may be 55 wt% or less, 50 wt% or less, 45 wt% or less, 40 wt% or less, 35 wt% or less, 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, or 10 wt% or less. By satisfying the aforementioned ranges for the content of the nonpolar organic solvent, the solvent for manufacturing the solid electrolyte membrane can maintain an appropriate vapor pressure and boiling point even if it contains an organic solvent in addition to hexyl isobutyrate, thereby exhibiting the aforementioned advantages. If the content of the above-mentioned nonpolar organic solvent exceeds the upper limit of the aforementioned range, the boiling point becomes excessively low or the vapor pressure becomes high, making it impossible to resolve the problems of conventional nonpolar organic solvents.

[0027] In one embodiment, the non-polar organic solvent may be an organic solvent containing an ester group, and specifically may include one or more selected from isobutyl isobutyrate, n-butyl butyrate, hexyl butyrate, 2-ethyl hexyl acetate, ethyl hexanoate, di-isobutyl ketone, n-heptyl acetate, hexyl acetate, d-limonene, trimethylbenzene, and isopropyl benzene.

[0028] In one embodiment, the solvent for manufacturing a sulfide-based solid electrolyte membrane may have a boiling point of 150 to 200°C. Specifically, it may be 155 to 200°C, 160 to 200°C, 165 to 200°C, 170 to 200°C, 175 to 200°C, or 180 to 200°C. In addition, in one embodiment, the solvent may have a vapor pressure of 0.2 to 4.5 mmHg at 25°C, specifically 0.4 to 4.5 mmHg, 0.6 to 4.5 mmHg, 0.8 to 4.5 mmHg, 1 to 4.5 mmHg, 0.2 to 4 mmHg, 0.4 to 4 mmHg, 0.6 to 4 mmHg, 0.8 to 4 mmHg, or 1 to 4 mmHg.

[0029] By satisfying the aforementioned ranges independently of each other, the solvent can have viscosity stability and uniformity when forming a solid electrolyte membrane composition compared to conventional non-polar organic solvents.

[0030] In one embodiment, the solvent may have a flash point of 50°C or higher. Specifically, the flash point may be 55°C or higher, 60°C or higher, 65°C or higher, or 70°C or higher. By satisfying the aforementioned ranges for the flash point, the solvent can secure chemical stability compared to conventional non-polar organic solvents.

[0031]

[0032] sulfide-based solid electrolyte membrane

[0033] A sulfide-based solid electrolyte membrane according to another embodiment of the present invention is manufactured using the aforementioned solvent for manufacturing sulfide-based solid electrolyte membranes, has high ionic conductivity, and can exhibit excellent characteristics during large-scale manufacturing for large area.

[0034] In one embodiment, a sulfide-based solid electrolyte membrane can be used by dissolving a sulfide-based solid electrolyte and a binder in the aforementioned solvent for manufacturing a sulfide-based solid electrolyte membrane.

[0035] The above sulfide-based solid electrolyte is, for example, Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (where p and q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In), Li3PS4, Li7P3S 11 , Li 7-x PS 6-x Cl x (where 0≤x≤2), Li 7-x PS 6-x Br x (where 0≤x≤2), and Li 7-x PS 6-x I x (However, it may be one or more selected from 0≤x≤2).

[0036] The above-mentioned sulfide-based solid electrolyte is manufactured by processing starting materials, such as Li2S or P2S5, using methods such as melt quenching or mechanical milling. Additionally, heat treatment may be performed after such processing. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. Furthermore, the solid electrolyte may include, for example, sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the sulfide-based solid electrolyte materials described above. For example, the solid electrolyte may be a material containing Li2S-P2S5.

[0037] From the perspective of a more desirable implementation of ionic conductivity, the sulfide-based solid electrolyte may have an argyrodite crystal structure.

[0038] Sulfide-based solid electrolytes with an azirodite-based crystal structure may contain, for example, Li, P, S, and halogen elements, and may additionally contain other doping elements as needed. As additional doping elements are included in the azirodite-based crystal structure, the moisture stability of the solid electrolyte may be improved, or electrochemical properties such as the capacity of the battery may be more preferably realized.

[0039] The above binder may further include a binder which is nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), styrene-butadiene-styrene copolymer, acrylic resin, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, or a combination thereof.

[0040] At this time, the content of the binder may be 1 to 5 wt% based on the total weight of the solid electrolyte. Specifically, the content of the binder may be 1 to 4 wt%, 1 to 3 wt%, 2 to 5 wt%, 2 to 4 wt%, or 2 to 3 wt%. If the content of the binder is too low, binding between the porous support and the solid electrolyte or between solid electrolyte particles does not occur well, resulting in an increase in internal voids within the sheet, which may lead to a deterioration in mechanical strength and cause a short circuit in the battery. If the content of the binder is too high, aggregation between solid electrolyte particles occurs too strongly, which may instead lead to an increase in internal voids within the sheet, resulting in a deterioration in mechanical strength and cause a short circuit in the battery. Additionally, the internal resistance may increase, causing a decrease in the ionic conductivity of the solid electrolyte membrane. In addition, when the binder content satisfies the above range, the ionic conductivity of the solid electrolyte sheet, the capacity, and the lifespan characteristics of the battery can be more preferably realized.

[0041]

[0042] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0043]

[0044] Example 1

[0045] A solid electrolyte membrane composition was prepared by mixing L6PS5Cl, HBNR, and hexyl isobutyrate. At this time, for 100 wt% of the solid electrolyte membrane composition, L6PS5Cl was mixed at 98 wt%, HBNR at 2 wt%, and the remainder was hexyl isobutyrate. Subsequently, the solid electrolyte membrane composition was applied and impregnated onto a glass fiber porous support using a blade coating method, and then the solid electrolyte membrane composition was dried at 50°C to remove the hexyl isobutyrate, thereby producing a solid electrolyte membrane.

[0046]

[0047] Example 2

[0048] A solid electrolyte membrane was prepared in the same manner as in Example 1, except that half of the hexyl isobutyrate was changed to isobutyl isobutyrate.

[0049]

[0050] Comparative example

[0051] A solid electrolyte membrane was prepared by carrying out the same procedure as in Example 1, except that isobutyl isobutyrate was used instead of hexyl isobutyrate.

[0052]

[0053] Experimental Example

[0054] (1) Observation of viscosity change

[0055] As an example and a comparative example, 1 L of the above solid electrolyte membrane composition was prepared and applied to equipment for large-area sheets. Comparative Example 1, which used a conventional non-polar organic solvent, evaporated rapidly, resulting in non-uniform viscosity, and problems such as clogging the equipment nozzle were not resolved. In contrast, Example 1 and Example 2 showed relatively slow changes in viscosity, and problems such as nozzle clogging were resolved.

[0056]

[0057] (2) Ionic conductivity measurement

[0058] Ionic conductivity was measured by applying a voltage of 10 mV at 30°C to a cell using SUS and a pressure of 70 MPa, using a solid electrolyte membrane prepared according to the examples and comparative examples as the working electrode, and the impedance is shown in Table 1 below.

[0059] Looking at Table 1 below, it can be seen that although the ionic conductivity of Examples 1 and 2 is about 0.1 to 0.2 mS / cm lower than that of the Comparative Example, excellent ionic conductivity of 1 mS / cm or higher was secured. Furthermore, as the aforementioned problem was resolved in the observation of the viscosity change, it can be said that high ionic conductivity was secured and excellent performance was demonstrated during film formation.

[0060]

[0061] (3) Electrochemical stability evaluation

[0062] Figure 1 is a graph showing the cyclic voltammetry of a battery including Example 1.

[0063] Figure 1 shows the results of the 1st to 10th cycles measured by scanning at 1.0 mV / s in a voltage range of 0 to 5 V, using the solid electrolyte membrane of Example 1, SUS as the working electrode, and a lithium negative electrode as the counter electrode. As shown in Figure 1, it can be seen that the waveform of the graph does not change significantly even when the cycle is repeated. In other words, it can be seen that the solid electrolyte membrane according to one embodiment of the present invention is stable even when used in a battery.

[0064] Hexyl isobutyrate (wt%) Isobutyl isobutyrate (wt%) Ionic conductivity (mS / cm) Example 1 1000 01.14 Example 2 505 01.02 Comparative Example 0100 01.21

[0065] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Containing hexyl isobutyrate, Solvent for manufacturing sulfide-based solid electrolyte membranes.

2. In Paragraph 1, The above solvent further comprises a nonpolar organic solvent, Solvent for manufacturing sulfide-based solid electrolyte membranes.

3. In Paragraph 2, The content of the above non-polar organic solvent is 60 wt% or less with respect to 100 wt% of the above solvent, Solvent for manufacturing sulfide-based solid electrolyte membranes.

4. In Paragraph 2, The above non-polar organic solvent is an organic solvent containing an ester group, Solvent for manufacturing sulfide-based solid electrolyte membranes.

5. In Paragraph 3, The above non-polar organic solvent comprises one or more selected from isobutyl isobutyrate, n-butyl butyrate, hexyl butyrate, 2-ethyl hexyl acetate, ethyl hexanoate, di-isobutyl ketone, n-heptyl acetate, hexyl acetate, d-limonene, trimethylbenzene, and isopropyl benzene. Solvent for manufacturing sulfide-based solid electrolyte membranes.

6. In Paragraph 1, The above solvent has a boiling point of 150 to 200°C, Solvent for manufacturing sulfide-based solid electrolyte membranes.

7. In Paragraph 1, The above solvent has a vapor pressure of 0.2 to 4.5 mmHg at 25°C, Solvent for manufacturing sulfide-based solid electrolyte membranes.

8. In Paragraph 1, The above solvent has a flash point of 50°C or higher, Solvent for manufacturing sulfide-based solid electrolyte membranes.

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