Method for regenerating or recovering performance of halide-based solid electrolyte

Abstract

The present invention relates to a method for recovering the performance of a halide-based solid electrolyte. More specifically, when the halide-based solid electrolyte is heat-treated after exposure to air, the ionic conductivity of the halide-based solid electrolyte reduced by the air exposure is recovered to a level similar to that before the air exposure.

Description

Method for regenerating or recovering the performance of a halide-based solid electrolyte

[0001] This application claims priority to U.S. Provisional Application No. 63 / 518,260, filed August 8, 2023, U.S. Non-Provisional 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 regenerating or recovering the performance of an all-solid-state battery comprising the halide-based solid electrolyte.

[0003] Lithium batteries have limitations in terms of capacity, stability, output, and their ability to be scaled up and miniaturized. Therefore, battery development technology that overcomes these limitations and can replace them is needed.

[0004] As an alternative to lithium secondary batteries, ongoing research is being conducted on metal-air batteries with very large theoretical capacities, all-solid-state batteries with no risk of explosion in terms of safety, supercapacitors for output, NaS batteries or RFBs (redox flow batteries) for large-scale applications, and thin film batteries for miniaturization.

[0005] All-solid-state batteries replace the liquid electrolytes used in conventional lithium secondary batteries with solid electrolytes. Consequently, they eliminate the use of flammable solvents, significantly improving safety by eliminating the risk of fire or explosion caused by decomposition reactions of conventional electrolytes. Furthermore, all-solid-state batteries can utilize lithium metal or lithium alloys as anode materials, dramatically improving energy density relative to the battery's mass and volume.

[0006] However, while solid-state batteries can ensure safety by using the solid electrolyte, their ionic conductivity may be reduced. Furthermore, using a liquid electrolyte as a means to secure the ionic conductivity of the solid electrolyte also poses the problem of reduced strength.

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

[0008] However, there is still a demand in the industry for solid electrolytes that have both ionic conductivity and strength properties.

[0009] Meanwhile, among solid electrolytes, halide-based solid electrolytes are experiencing increasing demand due to their high oxidation stability. However, compared to conventional sulfide-based solid electrolytes, halide-based solid electrolytes are more vulnerable to moisture, which can degrade battery performance and processability.

[0010] Accordingly, there is a need for technological development for a method to supplement the water resistance of a halide-based solid electrolyte and / or restore the performance of a halide-based solid electrolyte exposed to moisture.

[0011] [Prior Art Literature]

[0012] [Patent Document]

[0013] (Patent Document 1) Japanese Patent Publication No. 2013-219017

[0014] To address the above issues, the inventors conducted comprehensive research and discovered that when Li3InCl5 (LIC), a halide-based solid electrolyte, is exposed to moisture-containing air and then heat-treated at a constant temperature, the ionic conductivity reduced by moisture exposure is restored by the heat treatment. In one aspect, the ionic conductivity is restored to the level prior to moisture exposure.

[0015] Accordingly, the purpose of the present invention is to provide a method for recovering or regenerating the performance of a halide-based solid electrolyte.

[0016] To achieve the above object, the present invention provides a method for recovering the performance of a halide-based solid electrolyte, comprising: (S1) a step of exposing a halide-based solid electrolyte to air; and (S2) a step of heat-treating the halide-based solid electrolyte exposed to the air.

[0017] In one embodiment of the present invention, the heat treatment may be performed at a temperature of 200°C to 400°C. In one aspect, the heat treatment may be performed 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.

[0018] 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 under an inert atmosphere.

[0019] In one embodiment of the present invention, the halide-based solid electrolyte may be a lithium halide-based solid electrolyte.

[0020] In one embodiment of the present invention, the lithium halide-based solid electrolyte may include at least one selected from the group consisting of Li3InCl6, Li2ZrCl6, and Li3YCl6.

[0021] In one embodiment of the present invention, the recovered performance may be ionic conductivity.

[0022] 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).

[0023] 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 exposed to air containing moisture, the performance (e.g., ionic conductivity) of the halide-based solid electrolyte can be restored to a level equivalent to or higher than that prior to exposure to air and / or moisture. As illustrated in Fig. 1, the halide-based solid electrolyte can be recovered.

[0024] Figure 1 is a graph showing the results of ionic conductivity measurements and XRD (X-ray diffraction) analysis for halide-based solid electrolytes that were heat-treated after exposure to air in Examples 1, 6, and 7.

[0025] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0026] The term “halide-based solid electrolyte” as used herein includes an inorganic solid electrolyte containing a halide, which may include, for example, fluoride, chloride, bromide, or iodide. 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 at least one selected from the group consisting of LiPSX (X = Cl, Br, or I), LiGePS, and LiPS. For example, the halide-based solid electrolyte may include at least one selected from the group consisting of Li3YBr6, Li3YCl6, and Li3YBr2Cl4.

[0027] In some embodiments, the sulfide-based solid electrolyte comprises Li6PS5Cl.

[0028] However, the above sulfide-based solid electrolyte is not limited thereto, and sulfide-based solid electrolytes commonly used in the art can be widely used.

[0029] For example, in some embodiments, the halide-based solid electrolyte comprises a compound represented by the following chemical formula 1 or a mixture thereof:

[0030] [Chemical Formula 1]

[0031] Li a M b A c X d

[0032] In the above chemical formula 1, M is selected from P, Sn, Sb, As, and Ge;

[0033] A is selected from S, Se and Te;

[0034] X is selected from Cl, Br and I;

[0035] 5≤a<7.5, 0.5 <b<1.5, 4<c<6 및 0.5<d<2이다.

[0036] In some embodiments, the halide-based solid electrolyte may be represented by the following chemical formula 2:

[0037] <Chemical Formula 2>

[0038] Li 6-3a M a Br b Clc

[0039] In the above chemical formula 2, M is a metal other than Li, and a is 0 <a<2이고, b는 0<b<6이고, c는 0<c<6이고, b+c=6이다. 바람직하게는, M은 Sc, Y, B, Al, Ga 및 In 중에서 선택되며, 여기서 0<a<2, 0<b<6, 0<c<6 및 b+c=6이다.

[0040] The term “air” as used herein means an environment containing moisture, and is not limited by the amount of moisture or other factors such as temperature, pressure, etc.

[0041] The term "pristine" as used herein may refer to the state of a halide-based solid electrolyte before exposure to air.

[0042]

[0043] Method for recovering the performance of a halide-based solid electrolyte

[0044] The present invention relates to a method for restoring the performance of a halide-based solid electrolyte. In one aspect, the performance may include the ionic conductivity of the halide-based solid electrolyte.

[0045] A method for restoring the performance of a halide-based solid electrolyte according to the present invention comprises the steps of (S1) exposing a 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; wherein the performance of the halide-based solid electrolyte decreases after exposure to air. After the heat-treating, the performance of the halide-based solid electrolyte improves. For example, in one aspect, the performance includes ionic conductivity of the halide-based solid electrolyte.

[0046] In general, halide-based solid electrolytes are susceptible to moisture, and thus, when exposed to air containing moisture, their internal structural changes, such as hydration or oxidation of the halide element, may result in a decline in performance, including ionic conductivity. When the halide-based solid electrolyte exposed to air is heat-treated, the halide-based solid electrolyte prior to exposure to air is re-formed, thereby restoring performance, including ionic conductivity. In one aspect, as shown in Table 1 below, halide-based solid electrolytes that form hydrates without oxides are easier to recover.

[0047] For example, as shown in Table 1 below, in the case of LIC (Li3InCl6), H2O hydrate is formed when exposed to moisture or air, but when heat-treated, the hydrate is removed and returns to the original LIC. Therefore, ionic conductivity is restored. However, in the case of LZC (Li2ZrCl6) or LYC (Li3InCl6), where a simple hydrate is not formed, other by-products are formed and the original substance does not change even after heat-treatment.

[0048]

[0049] ElectrolyteExposureHeat TreatmentPristineAir ExposureHeat Treatment in AirLi2ZrCl6LiCl + ZrO2+ HClLiCl + ZrO2(350℃)Li3YCl6LiCl·H2O + YCl3·H2OLiCl + YOCl +2HCl (550℃)Li3InCl 6 Li3InCl6·H2O + a little HCl and In2O3Li3InCl6+ a little In2O3 (260℃)

[0050]

[0051] In one embodiment of the present invention, the heat treatment may be performed at a temperature of 200°C to 400°C.

[0052] Specifically, the heat treatment temperature may be 200°C or higher, 220°C or higher, or 240°C or higher, and may be 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.

[0053] In one aspect, if the heat treatment temperature is less than 200°C, the components hydrated or oxidized by exposure to air may not form the original halide-based solid electrolyte, and thus ionic conductivity may not be restored. If the heat treatment temperature exceeds 400°C, the process cost for restoring ionic conductivity in air becomes expensive, and the halide-based solid electrolyte components transformed by exposure may induce other side reactions, or the solid electrolyte itself may undergo thermal decomposition, and ionic conductivity may not be restored.

[0054]

[0055] In one embodiment of the present invention, the heat treatment may be performed in air. The air is not particularly limited as long as it is an environment containing moisture.

[0056]

[0057] 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.

[0058] In one aspect, the method for recovering the performance of a halide-based solid electrolyte by the 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 prone to forming the original lithium halide-based solid electrolyte by heat treatment when exposed to air, resulting in a higher tendency for chemical reaction products on the surface to form the original lithium halide-based solid electrolyte, which may be more advantageous for recovering performance, including ionic conductivity.

[0059]

[0060] In one embodiment of the present invention, the lithium halide-based solid electrolyte may include at least one selected from the group consisting of Li3InCl6, Li2ZrCl6, and Li3YCl6.

[0061]

[0062] In one embodiment of the present invention, the performance may be ionic conductivity.

[0063] 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 of returning a structural change in a halide-based solid electrolyte due to exposure to air to a state similar to the original structure through heat treatment, and can be advantageous in restoring ionic conductivity, which is highly related to the structure of a halide-based solid electrolyte.

[0064] Additionally, as can be seen from the XRD results shown in Fig. 1, it can be seen that it has returned to its original material.

[0065]

[0066] 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% of the level before exposure to air, and specifically, can be recovered to a level of 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.

[0067] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0068]

[0069] In the following examples and comparative examples, the halide-based solid electrolyte, air exposure process, and heat treatment process were performed as described in Table 2 below.

[0070]

[0071] Halide solid electrolyte Air exposure reaction Ionic conductivity (S / cm) Heat treatment Ionic conductivity (S / cm) Humidity (%) Time (min) Time (hr) Temperature (℃) Time (hr) Example 1 LIC (Li3InCl6) 451249.7x10 -7 26082.9x10-4 Example 2 LIC (Li3InCl6)451249.7x10 -7 15081.8x10 -6 Example 3LIC (Li3InCl6)451249.7x10 -7 45082.7x10 -4 Example 4 LIC (Li3InCl6)451121.5x10 -6 26082.9x10 -4 Example 5 LIC (Li3InCl6)45161.8x10 -6 26082.9x10 -4 Example 6LZC (Li2ZrCl6)451242.2x10 -6 35081.7x10 -8 Example 7LYC (Li3YCl6)451241.5x10 -9 55082.7x10 -10 Comparative Example 1LiPSCl (Li6PS5Cl)451249.5x10 -7 26082.6x10 -4

[0072]

[0073] Example 1

[0074] Li3InCl6, a halide solid electrolyte, was exposed to air with a humidity of 45% for 1 minute and reacted for 24 hours.

[0075] Li3InCl6 exposed to air and reacted was heat treated at 260°C for 8 hours.

[0076]

[0077] Example 2

[0078] The same method as Example 1 was used except that the heat treatment temperature was set to 150°C.

[0079]

[0080] Example 3

[0081] The same method as Example 1 was used except that the heat treatment temperature was set to 450°C.

[0082]

[0083] Example 4

[0084] The same method as Example 1 was used, except that the reaction time after air exposure was set to 12 hours.

[0085]

[0086] Example 5

[0087] The same method as Example 1 was used, except that the reaction time after air exposure was set to 6 hours.

[0088]

[0089] Example 6

[0090] The same procedure as Example 1 was followed, except that Li2ZrCl6 was used as a halide-based solid electrolyte and the heat treatment temperature was set to 350°C.

[0091]

[0092] Example 7

[0093] The same procedure as Example 1 was followed, except that Li3YCl6 was used as the halide-based solid electrolyte and the heat treatment temperature was set to 550°C.

[0094]

[0095] Comparative Example 1

[0096] The same procedure as in Example 1 was followed, 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 a solid electrolyte containing Sc, Y, B, Al, Ga, and / or In as a halide. For example, Chemical Formula 1 is an example of a halide-based solid electrolyte.

[0097]

[0098] Experimental Example 1: Measurement of the degree of performance recovery of a solid electrolyte membrane.

[0099] In order to determine the degree of performance recovery of a 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 XRD (X-ray diffraction) analysis was performed to analyze the internal components of the halide-based solid electrolyte at each stage. The ionic conductivity and XRD analysis methods are as follows.

[0100]

[0101] Ionic conductivity measurement

[0102] 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.

[0103] The resistance was measured at 25°C using an electrochemical impedance spectrometer (EIS, VM3, Bio Logic Science Instrument) 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 Equation 1 below.

[0104]

[0105] [Formula 1]

[0106]

[0107]

[0108] In the above equation 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 (㎛) of the solid electrolyte membrane, and A is the area (cm) of the solid electrolyte membrane. 2) means.

[0109]

[0110] XRD analysis

[0111] Using a Bruker APEX II XRD (voltage: 40 kV, current: 40 mA), 2-Theta measurements were made at 0.01˚ increments from 5˚ to 40˚ under conditions of Mo Ka radiation (wavelength: 0.70926 Å). The measurement samples were sealed with boron-rich glass in an Ar-filled glove box to prevent air exposure.

[0112]

[0113] Table 1 above shows chemical formulas of changes in the components of the halide-based solid electrolytes that were heat-treated after exposure to air in Examples 1, 6, and 7.

[0114] Referring to Table 1 above, in Example 1 (LIC, Li3InCl6), it can be seen that 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 was reverted to the original LIC.

[0115] In addition, in Example 6 (LZC, Li2ZrCl6), it can be seen that Zr was oxidized to form ZrO2 and HCl in the step (Air-Exp) after exposure to air, and that only HCl was removed in the step (Air-HT) after heat treatment, without forming the original LZC. Consequently, it is difficult to recover ionic conductivity.

[0116] In addition, in Example 7 (LYC, Li2ZrCl6), it can be seen that LYC was hydrated in the step after exposure to air (Air-Exp), and in the step after heat treatment (Air-HT), Y was oxidized and HCl was formed, but the original LYC was not formed.

[0117]

[0118] Figure 1 is a graph showing the results of ionic conductivity measurements and XRD analysis for halide-based solid electrolytes that were exposed to air and then heat-treated in Examples 1, 6, and 7. The ionic conductivity and XRD analyses were performed before exposure to air (Pristine), after exposure to air (Air-Exp), and after heat treatment (Air-HT), respectively.

[0119] Referring to Fig. 1, the ionic conductivity of the post-heat treatment stage (Air-HT) in Example 1 (LIC) was identical to the ionic conductivity of the pre-exposure stage (Pristine), confirming that the degree of ionic conductivity recovery was 100%. In addition, the XRD analysis result of the post-heat treatment stage (Air-HT) was also almost identical to the ionic conductivity of the pre-exposure stage (Pristine), indicating that the internal structure of the LIC was restored to its original material by the heat treatment.

[0120] On the other hand, in Examples 6 (LZC) and 7 (LYC), when exposed to moisture, not only simple hydrates such as LIC are formed, but also LiCl and other by-products are formed, and it can be seen that this reaction is an irreversible reaction and difficult to recover.

[0121]

[0122] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

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

2. In paragraph 1, A method for recovering the performance of a halide-based solid electrolyte, wherein the above heat treatment is performed at a temperature of 200°C to 400°C.

3. In paragraph 1, A method for recovering the performance of a halide-based solid electrolyte, wherein the above heat treatment is performed in air.

4. In paragraph 1, A method for recovering the performance of a halide-based solid electrolyte, wherein the above halide-based solid electrolyte is a lithium halide-based solid electrolyte.

5. In paragraph 4, A method for recovering the performance of a halide-based solid electrolyte, wherein the lithium halide-based solid electrolyte comprises at least one selected from the group consisting of Li3InCl6, Li2ZrCl6, and Li3YCl6.

6. In paragraph 1, A method for recovering the performance of a halide-based solid electrolyte, wherein the above performance is ionic conductivity.

7. In paragraph 1, A method for restoring the performance of a halide-based solid electrolyte, wherein the ionic conductivity of the halide-based solid electrolyte after the above heat treatment is restored to 90% to 100% of the level before exposure to air.

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