Method for regenerating or restoring the performance of halide-based solid electrolytes

Abstract

The present invention relates to a method for restoring the performance of a halide-based solid electrolyte, and more specifically, when the halide-based solid electrolyte is exposed to air and then heat-treated, the ionic conductivity of the halide-based solid electrolyte, which has decreased due to exposure to air, is restored to the same level as before the air exposure.

Description

[Technical Field]

[0001] This invention claims priority to U.S. Provisional Application No. 63 / 518,260, filed August 8, 2023, U.S. Regular Application No. 18 / 461,166, filed September 5, 2023, and Korean Patent Application No. 10-2024-0105579, filed August 7, 2024.

[0002] The present invention relates to a halide-based solid electrolyte and a method for restoring or recovering the performance of an all-solid-state battery containing the halide-based solid electrolyte. [Background technology]

[0003] Lithium batteries have limitations in terms of capacity, stability, output, size, and miniaturization. Therefore, there is a need for battery development technology that can overcome these limitations and provide an alternative.

[0004] As alternatives to lithium secondary batteries, ongoing research is being conducted on metal-air batteries, which have a very large theoretical capacity, all-solid-state batteries, which are safe and do not pose a risk of explosion, supercapacitors, which have high output, NaS batteries or RFBs (redox flow batteries), which are large-sized, and thin film batteries, which are ultra-small.

[0005] An all-solid-state battery is a battery in which the liquid electrolyte used in conventional lithium secondary batteries is replaced with a solid. Therefore, since no flammable solvents are used in the battery, there is absolutely no risk of fire or explosion due to the decomposition reaction of conventional electrolytes, which significantly improves safety. Furthermore, all-solid-state batteries have the advantage of being able to use Li metal or Li alloys as the anode material, which dramatically improves the energy density relative to the mass and volume of the battery.

[0006] However, although the use of the solid electrolyte in an all-solid-state battery can ensure safety, it may result in a decrease in ionic conductivity, and furthermore, the use of a liquid electrolyte in combination with the solid electrolyte to ensure the ionic conductivity of the solid electrolyte results in a decrease in strength.

[0007] Generally, to ensure the safety of all-solid-state batteries while preventing a decline in battery performance and processability, the ionic conductivity and strength of the solid electrolyte must both be maintained at a certain level or above.

[0008] However, there remains a need in the industry for solid electrolytes that offer both ionic conductivity and strength.

[0009] Among solid electrolytes, halide-based solid electrolytes have high oxidation stability and are in high demand. However, halide-based solid electrolytes are more susceptible to moisture than conventional sulfide-based solid electrolytes, which can lead to problems such as reduced battery performance and processability.

[0010] Therefore, there is a need for technological development of a method for complementing the water resistance of halide-based solid electrolytes or for restoring the performance of halide-based solid electrolytes that have been exposed to moisture. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2013-219017 Summary of the Invention [Problem to be solved by the invention]

[0012] As a result of extensive research to solve the above problem, the inventors have found that when a halide-based solid electrolyte, Li3InCl5 (LIC), is exposed to air containing moisture and then heat-treated at a certain temperature, the ionic conductivity that had decreased due to the moisture exposure is restored by the heat treatment. In one aspect, the ionic conductivity is restored to the level before the moisture exposure.

[0013] Therefore, an object of the present invention is to provide a method for restoring or regenerating the performance of a halide-based solid electrolyte. [Means for solving the problem]

[0014] In order to achieve the above object, the present invention provides a method for recovering the performance of a halide-based solid electrolyte, comprising: (S1) exposing the halide-based solid electrolyte to air; and (S2) heat-treating the halide-based solid electrolyte exposed to air.

[0015] In one embodiment of the present invention, the heat treatment may be carried out at a temperature of 200° C. to 400° C. In one aspect, the heat treatment may be carried out at a temperature of 220° C. to 380° C., 250° C. to 350° C., 275° C. to 325° C., or 300° C. to 350° C.

[0016] In one embodiment of the present invention, the heat treatment may be performed in ambient air. In one aspect, the heat treatment may be performed in an inert atmosphere.

[0017] In one embodiment of the present invention, the halide-based solid electrolyte may be a lithium halide-based solid electrolyte.

[0018] In one embodiment of the present invention, the lithium halide-based solid electrolyte may contain one or more selected from the group consisting of Li3InCl6, Li2ZrCl6, and Li3YCl6.

[0019] In one embodiment of the present invention, the restored performance may be ionic conductivity.

[0020] In one embodiment of the present invention, the ionic conductivity of the halide-based solid electrolyte after the heat treatment may be restored to a level of 90% to 100% of the ionic conductivity before exposure to air (for example, compared to a pristine halide-based solid electrolyte). [Effects of the Invention]

[0021] According to the present invention, the performance of a halide-based solid electrolyte can be restored by heat treatment. For example, by heat treating a halide-based solid electrolyte that has been exposed to air containing moisture, the performance (e.g., ionic conductivity) of the halide-based solid electrolyte can be restored to a level equal to or higher than that before the halide-based solid electrolyte was exposed to air and / or moisture. As shown in FIG. 1, the halide-based solid electrolyte can be recovered. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a graph showing the results of ionic conductivity measurements and XRD (X-ray diffraction) analysis for halide-based solid electrolytes that were exposed to air and then heat-treated in Examples 1, 6, and 7. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will now be described in more detail to aid in its understanding.

[0024] As used herein, the term "halide-based solid electrolyte" includes inorganic solid electrolytes containing halides, and the halides may include, for example, fluorides, chlorides, bromides, or iodides. In one aspect, the solid electrolyte does not include an oxide-based solid electrolyte or a sulfide-based solid electrolyte. In one embodiment of the present invention, the sulfide-based solid electrolyte may include one or more selected from the group consisting of LiPSX (X = Cl, Br, or I), LiGePS, and LiPS. For example, the halide-based solid electrolyte may include one or more selected from the group consisting of Li3YBr6, Li3YCl6, and Li3YBr2Cl4.

[0025] In some embodiments, the sulfide-based solid electrolyte comprises Li6PS5Cl.

[0026] However, the sulfide-based solid electrolyte is not limited thereto, and any sulfide-based solid electrolyte commonly used in the art may be widely used.

[0027] For example, in some embodiments, the halide-based solid electrolyte comprises a compound represented by Formula 1 below or a mixture thereof: [Chemical formula 1] Li a M b A c X d

[0028] In the formula 1, M is selected from P, Sn, Sb, As, and Ge; A is selected from S, Se and Te; X is selected from Cl, Br and I; 5≦a<7.5, 0.5 <b<1.5、4<c<6および0.5<d<2である。

[0029] In some embodiments, the halide-based solid electrolyte can be represented by Formula 2: [Chemical formula 2] Li 6-3aM a Br b Clc

[0030] In Chemical Formula 2, M is a metal other than Li, 0 < a < 2, 0 < b < 6, 0 < c < 6, and b + c = 6. Preferably, M is selected from Sc, Y, B, Al, Ga, and In, where 0 < a < 2, 0 < b < 6, 0 < c < 6, and b + c = 6.

[0031] As used herein, the term "air" means an environment containing moisture and is not limited by the amount of moisture or other factors such as temperature and pressure.

[0032] As used herein, the term "pristine" may mean the state of a halide-based solid electrolyte before exposure to air.

[0033] Method for restoring performance of halide-based solid electrolyte The present invention relates to a method for recovering the performance of a halide-based solid electrolyte. In one aspect, the performance may include the ionic conductivity of the halide-based solid electrolyte.

[0034] The method for recovering the performance of a halide-based solid electrolyte according to the present invention includes: (S1) exposing the halide-based solid electrolyte to air or providing a halide-based solid electrolyte exposed to air; and (S2) heat-treating the halide-based solid electrolyte exposed to air. The performance of the halide-based solid electrolyte decreases after being exposed to air. After the heat treatment, the performance of the halide-based solid electrolyte improves. For example, in one aspect, the performance includes the ionic conductivity of the halide-based solid electrolyte.

[0035] Generally, halide-based solid electrolytes exhibit weak resistance to moisture. Therefore, when exposed to humid air, the halide element undergoes hydration or oxidation, resulting in changes to its internal structure, which can lead to a decrease in performance, including ionic conductivity. When the halide-based solid electrolyte exposed to air is heat-treated, the halide-based solid electrolyte that existed before exposure to air is re-formed, and performance, including ionic conductivity, can be restored. From one perspective, as shown in Table 1 below, halide-based solid electrolytes that form hydrates without oxides are easier to recover.

[0036] For example, as shown in Table 1 below, LIC (Li3InCl6) forms HO hydrate when exposed to moisture or air, but returns to the original LIC as the hydrate is removed during heat treatment. This restores ionic conductivity. However, rather than simply forming a hydrate, in the case of LZC (Li2ZrCl6) or LYC (Li3InCl6), other by-products are formed and the original substance does not change even after heat treatment.

[0037] [Table 1]

[0038] In one embodiment of the present invention, the heat treatment may be carried out at a temperature of 200°C to 400°C.

[0039] Specifically, the heat treatment temperature may be 200° C. or higher, 220° C. or higher, or 240° C. or higher, or 400° C. or lower, 350° C. or lower, or 300° C. or lower. In one aspect, the lower limit may be 200° C. or higher, 210° C. or higher, 220° C. or higher, 230° C. or higher, 240° C. or higher, 250° C. or higher, 260° C. or higher, 270° C. or higher, 280° C. or higher, 290° C. or higher, 300° C. or higher, 310° C. or higher, 320° C. or higher, 330° C. or higher, 340° C. or higher, or 350° C. or higher. In one aspect, the lower limit may be 400° C. or lower, 390° C. or lower, 380° C. or lower, 370° C. or lower, 360° C. or lower, 350° C. or lower, 340° C. or lower, or 325° C. or lower.

[0040] From one perspective, if the heat treatment temperature is less than 200°C, the components hydrated or oxidized by exposure to air may not be converted back into the original halide-based solid electrolyte, and ionic conductivity may not be restored. If the heat treatment temperature exceeds 400°C, the process cost for restoring ionic conductivity in air may be high, and the components of the halide-based solid electrolyte that have been deformed by exposure may induce other side reactions, or the solid electrolyte itself may be thermally decomposed, preventing ionic conductivity from being restored.

[0041] In one embodiment of the present invention, the heat treatment may be carried out in air. The air is not particularly limited as long as it contains moisture.

[0042] In one embodiment of the present invention, the halide-based solid electrolyte may be a lithium halide-based solid electrolyte. In one aspect, the halide may include, for example, fluoride, chloride, bromide, or iodide.

[0043] From one perspective, the method for recovering the performance of a halide-based solid electrolyte by heat treatment may be more suitable for a lithium halide-based solid electrolyte among halide-based solid electrolytes. The lithium halide-based solid electrolyte may be more likely to be exposed to air and have chemical reaction products on the surface thereof form the original lithium halide-based solid electrolyte by heat treatment, which may be more advantageous for recovering performance such as ionic conductivity.

[0044] In one embodiment of the present invention, the lithium halide-based solid electrolyte may contain one or more selected from the group consisting of Li3InCl6, Li2ZrCl6, and Li3YCl6.

[0045] In one embodiment of the present invention, the performance may be ionic conductivity.

[0046] A method for restoring the performance of a halide-based solid electrolyte according to one embodiment of the present invention is based on the principle that a structural change of a halide-based solid electrolyte due to exposure to air is restored to a state close to its original structure by heat treatment, and may be advantageous for restoring ionic conductivity, which is closely related to the structure of a halide-based solid electrolyte.

[0047] Furthermore, as can be seen from the XRD results shown in Figure 1, the original substance has been restored.

[0048] In one embodiment of the present invention, the ionic conductivity of the halide-based solid electrolyte after the heat treatment can be recovered to a level of 90% to 100% compared to before exposure to air, specifically, 90% or more, 93% or more, 95% or more, or 98% or more. The degree of recovery of the ionic conductivity may be proportional to the degree of recovery of the internal structure of the halide-based solid electrolyte.

[0049] Preferred examples will be described below to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. Naturally, such changes and modifications also fall within the scope of the appended claims.

[0050] The following examples and comparative examples were carried out using the halide-based solid electrolyte, air exposure process and heat treatment process shown in Table 2 below.

[0051] [Table 2]

[0052] Example 1 The halide-based solid electrolyte Li3InCl6 was exposed to air with a humidity of 45% for 1 minute and allowed to react for 24 hours.

[0053] The Li3InCl6 exposed to and reacted in air was heat treated at 260°C for 8 hours.

[0054] Example 2 The same procedure as in Example 1 was carried out except that the heat treatment temperature was 150°C.

[0055] Example 3 The same method as in Example 1 was carried out except that the heat treatment temperature was 450°C.

[0056] Example 4 The same procedure as in Example 1 was carried out, except that the reaction time after exposure to air was 12 hours.

[0057] Example 5 The same procedure as in Example 1 was carried out, except that the reaction time after exposure to air was 6 hours.

[0058] Example 6 The same procedure as in Example 1 was carried out except that Li2ZrCl6 was used as the halide-based solid electrolyte and the heat treatment temperature was set to 350°C.

[0059] Example 7 The same procedure as in Example 1 was carried out except that Li3YCl6 was used as the halide-based solid electrolyte and the heat treatment temperature was set to 550°C.

[0060] Comparative Example 1 The same procedure as in Example 1 was carried out, except that Li6PS5Cl was used as a sulfide-based solid electrolyte instead of a halide-based solid electrolyte. In the present invention, the term "halide-based" means that the halide includes Sc, Y, B, Al, Ga, and / or In. For example, Formula 1 is an example of a halide-based solid electrolyte.

[0061] Experimental Example 1: Measurement of performance recovery of solid electrolyte membrane To confirm the degree of performance recovery of the halide-based solid electrolyte exposed to air, the ionic conductivity of the halide-based solid electrolyte was measured before exposure to air (Pristine), after exposure to air (Air-Exp), and after heat treatment (Air-HT), and X-ray diffraction (XRD) analysis was performed to analyze the internal components of the halide-based solid electrolyte at each step. The ionic conductivity and XRD analysis methods are as follows:

[0062] Ionic conductivity measurement To measure the ionic conductivity of the solid electrolyte membrane, the solid electrolyte membrane was placed in a polyether ether ketone (PEEK) holder with a diameter of 10 mm, and the ionic conductivity was measured using a titanium rod as a blocking electrode.

[0063] Resistance was measured using an electrochemical impedance spectrometer (EIS, VM3, Bio Logic Science Instrument) at 25°C with an amplitude of 10 mV and a scan range of 1 Hz to 0.1 MHz, and the ionic conductivity of the solid electrolyte membrane was calculated using the following equation 1.

[0064]

number

[0065] In the above formula 1, σi is the ionic conductivity (mS / cm) of the solid electrolyte membrane, R is the resistance (Ω) of the solid electrolyte membrane measured by the electrochemical impedance spectrometer, L is the thickness (μm) of the solid electrolyte membrane, and A is the area (cm 2 ) means

[0066] XRD analysis 2θ (2-Theta) was measured from 5° to 40° in 0.01° increments using a Bruker APEX II XRD (voltage: 40 Kv, current: 40 mA) under Mo Ka radiation (wavelength: 0.70926 Å). The samples were sealed with boron-rich glass in an Ar-filled glove box to prevent exposure to air.

[0067] Table 1 above shows the changes in the components of the halide-based solid electrolytes that were exposed to air and then heat-treated in Examples 1, 6 and 7, expressed in chemical formulas.

[0068] Referring to Table 1, in Example 1 (LIC, Li3InCl6), in the step after exposure to air (Air-Exp), LIC was hydrated and In was oxidized to form In2O3, but in the step after heat treatment (Air-HT), the hydrated LIC returned to its original state.

[0069] In Example 6 (LZC, LiZrCl), Zr was oxidized to form ZrO and HCl in the step after exposure to air (Air-Exp), and only HCl was removed in the step after heat treatment (Air-HT), and the original LZC was not formed. Consequently, it is difficult to restore ionic conductivity.

[0070] Furthermore, in Example 7 (LYC, LiZrCl), LYC was hydrated in the step after exposure to air (Air-Exp), and in the step after heat treatment (Air-HT), Y was oxidized to form HCl, but the original LYC was not formed.

[0071] 1 is a graph showing the ionic conductivity measurement results and XRD analysis results for the halide-based solid electrolytes exposed to air and then heat-treated in Examples 1, 6, and 7. The ionic conductivity and XRD analysis were performed before exposure to air (pristine), after exposure to air (Air-Exp), and after heat treatment (Air-HT), respectively.

[0072] 1, in Example 1 (LIC), the ionic conductivity of the step after heat treatment (Air-HT) was the same as the ionic conductivity of the step before exposure to air (pristine), confirming that the degree of recovery of ionic conductivity was 100%. In addition, the XRD analysis results of the step after heat treatment (Air-HT) were also nearly the same as the ionic conductivity of the step before exposure to air (pristine), indicating that the internal structure of the LIC was restored to its original state by heat treatment.

[0073] On the other hand, in Example 6 (LZC) and Example 7 (LYC), when exposed to moisture, not only do they form hydrates like LIC, but they also form LiCl and other by-products, and it is clear that these reactions are irreversible and difficult to recover from.

[0074] Although the present invention has been described above using limited examples and drawings, the present invention is not limited thereto, and it goes without saying that various modifications and variations can be made by a person having ordinary skill in the art to which the present invention pertains within the technical spirit of the present invention and the equivalent scope of the claims set forth below.

Claims

1. (S1) exposing a halide-based solid electrolyte to air; (S2) heat-treating the halide-based solid electrolyte exposed to air; A method for restoring the performance of a halide-based solid electrolyte, comprising:

2. 2. The method for recovering the performance of a halide-based solid electrolyte according to claim 1, wherein the heat treatment is carried out at a temperature of 200° C. or higher and 400° C. or lower.

3. 2. The method for recovering performance of a halide-based solid electrolyte according to claim 1, wherein the heat treatment is carried out in air.

4. 4. The method for recovering the performance of a halide-based solid electrolyte according to claim 1, wherein the halide-based solid electrolyte is a lithium halide-based solid electrolyte.

5. The lithium halide solid electrolyte is Li ３ InCl ６ , Li ２ ZrCl ６ and Li ３ YCl ６ 5. The method for recovering performance of a halide-based solid electrolyte according to claim 4, wherein the electrolyte contains at least one selected from the group consisting of:

6. 2. The method for recovering the performance of a halide-based solid electrolyte according to claim 1, wherein the performance is ionic conductivity.

7. 2. The method for recovering the performance of a halide-based solid electrolyte according to claim 1, wherein the ionic conductivity of the halide-based solid electrolyte after the heat treatment is recovered to a level of 90% or more and 100% or less compared to that before exposure to air.

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