A method for improving air stability of a sulfide solid-state electrolyte

Abstract

The application belongs to the field of new energy battery materials, and discloses a method for improving air stability of a sulfide solid electrolyte. The method comprises the following steps: adding the sulfide solid electrolyte, boric acid and 1-ethyl-3-methyl imidazole bis-trifluoromethyl sulfonimide salt into a ball milling tank, and performing ball milling treatment to obtain a mixture; placing the mixture for 12-36 hours, and then placing the mixture in a muffle furnace at 180-260 DEG C for 1-4 hours to complete the improvement of the air stability of the sulfide solid electrolyte. Through the synergistic effect of boric acid and 1-ethyl-3-methyl imidazole bis-trifluoromethyl sulfonimide salt, a composite coating layer with rigid barrier and hydrophobic filling effects is formed on the surface of the sulfide solid electrolyte, so that the air stability of the sulfide solid electrolyte is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of new energy battery materials technology, and in particular to a method for improving the air stability of sulfide solid electrolytes. Background Technology

[0002] Sulfide solid electrolytes (LPSCs) are core materials for all-solid-state batteries. They offer high room-temperature ionic conductivity and good machinability, making them suitable for replacing liquid electrolytes and separators in traditional lithium-ion batteries. However, LPSCs are inorganic solid electrolytes, primarily composed of sulfides, phosphides, and oxides. They contain numerous phosphorus-sulfur bonds, which react with oxygen and moisture in the air, leading to poor air stability. In air, they readily react with oxygen and water, resulting in irreversible ionic conductivity decay and the generation of large amounts of toxic gases such as H2S, posing safety hazards.

[0003] Current methods for improving the air stability of sulfide electrolytes include coating with inorganic oxides. However, uneven coating can lead to localized exposure, poor hydrophobicity, and easy hydrolysis under high humidity. Organic hydrophobic polymer coatings, on the other hand, have insufficient density, are prone to detachment, and exhibit poor thermal stability. For example, patent CN114464876B discloses a sulfide / polymer composite solid electrolyte and its preparation method. Boric acid is added to modify the sulfide solid electrolyte. The boric acid melts during calcination and uniformly coats the surface of the sulfide solid electrolyte, effectively improving the structural stability of the sulfide. However, this method is complex. The polyethylene oxide polymer is hydrophilic, and hydrogen bonds and coordination interactions exist between the boric acid and the polyethylene oxide polymer, restricting polymer chain movement and reducing ion conductivity. Furthermore, the boric acid occupies passivation sites on the boric acid surface, enhancing the hydrophilicity of the system, resulting in poor composite effects and a tendency to trigger side reactions.

[0004] Therefore, existing technologies still need improvement and development. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for improving the air stability of sulfide solid electrolytes, aiming to solve the problem of poor composite modification effect of existing sulfide solid electrolytes.

[0006] The technical solution of the present invention is as follows: A first aspect of the present invention provides a method for improving the air stability of a sulfide solid electrolyte, comprising the following steps: The sulfide solid electrolyte, boric acid, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt were added to a ball mill jar and ball milled to obtain a mixture. The mixture is allowed to stand for 12 to 36 hours, and then placed in a muffle furnace and kept at 180 to 260°C for 1 to 4 hours to improve the air stability of the sulfide solid electrolyte.

[0007] Optionally, the sulfide solid electrolyte is Li 7-n PS 6-n X is one of Cl, Br, and I, where 0 < n ≤ 2.

[0008] Optionally, the mass ratio of the sulfide solid electrolyte, boric acid, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is 10:(0.3~0.8):(0.12~0.32).

[0009] Optionally, the ball milling process is performed at a speed of 150-300 rpm for 3-8 hours, with a ball-to-material ratio of (1-3):1.

[0010] Optionally, the ball milling process is an intermittent ball milling process, which includes continuous ball milling in a cycle and shutdown cooling. The continuous ball milling time is 20-40 minutes, and the shutdown cooling time is 5-15 minutes.

[0011] Optionally, the ball milling media in the ball milling process include zirconium oxide with a diameter of 3 mm and zirconium oxide with a diameter of 5 mm, wherein the mass ratio of the zirconium oxide with a diameter of 3 mm to the zirconium oxide with a diameter of 5 mm is 1:1.

[0012] Optionally, the settling process is carried out in an inert gas with a water content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm.

[0013] Optionally, the heating rate of the muffle furnace is 5~10℃ / min when firing the mixture.

[0014] Optionally, after heat treatment of the mixture, the following step is further included: sieving through a 120-mesh sieve.

[0015] Beneficial Effects: This invention provides a method for improving the air stability of sulfide solid electrolytes. Compared with existing technologies, the advantages of this invention are: This invention adopts a composite interface design concept of "rigid coating + flexible filling coating," forming a composite coating layer on the surface of the sulfide solid electrolyte through the synergistic effect of boric acid and ionic liquid. Specifically, boric acid dehydrates and melts during heat treatment to form a rigid BOB framework, while the ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt) is chemically anchored within the framework. Therefore, a composite protective layer with both physical barrier and hydrophobic protection functions is constructed on the surface of the sulfide solid electrolyte, improving its air stability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a process for improving the air stability of sulfide solid electrolytes according to the present invention. Detailed Implementation

[0017] This invention provides a method for improving the air stability of sulfide solid electrolytes. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] like Figure 1 As shown, this embodiment of the invention provides a method for improving the air stability of sulfide solid electrolytes, comprising the following steps: The sulfide solid electrolyte, boric acid, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt were added to a ball mill jar and ball milled to obtain a mixture. The mixture is allowed to stand for 12 to 36 hours, and then placed in a muffle furnace and kept at 180 to 260°C for 1 to 4 hours to improve the air stability of the sulfide solid electrolyte.

[0019] This embodiment employs a composite interface design approach of "rigid coating + flexible filling coating," forming a composite coating layer on the surface of the sulfide solid electrolyte through the synergistic effect of boric acid and ionic liquid. Specifically, boric acid undergoes dehydration and melting during heat treatment to form a rigid BOB framework, while the ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt) is chemically anchored within the framework. Therefore, a composite protective layer with both physical barrier and hydrophobic protection functions is constructed on the surface of the sulfide solid electrolyte, improving its air stability.

[0020] Specifically, this embodiment has at least the following functions: First, ball milling is used to thoroughly mix the sulfide solid electrolyte, boric acid, and ionic liquid, ensuring a more uniform distribution of boric acid and ionic liquid on the surface of the sulfide solid electrolyte particles. The use of grinding balls of different sizes in the mixed ball milling process provides both impact dispersion and refining grinding effects, which helps to break up powder agglomerates and promotes the uniform distribution of boric acid and ionic liquid on the surface of the sulfide solid electrolyte.

[0021] Second, by allowing the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt to come into full contact with boric acid through a static treatment, it can be further evenly distributed and pre-anchored, which is beneficial for forming a more continuous composite coating layer during subsequent heat treatment.

[0022] Third, boric acid undergoes dehydration and condensation through low-temperature heat treatment (180~260℃) to form a boron-oxygen coating layer containing a BOB structure. This boron-oxygen coating layer can act as a rigid framework, providing a physical barrier to the surface of the sulfide solid electrolyte, reducing direct contact between moisture and oxygen in the air and the surface of the sulfide solid electrolyte.

[0023] Therefore, this embodiment forms a stable composite coating layer on the surface of the sulfide solid electrolyte. In this composite coating layer, the rigid BOB provides a high-strength framework and a physical barrier to improve air stability, while the flexible ionic liquid fills the gaps in the framework, providing hydrophobicity and contributing to the overall improvement in air stability. This effectively slows down the hydrolysis reaction and ionic conductivity decay of the sulfide solid electrolyte during air exposure, significantly improving its air stability.

[0024] In some embodiments, the sulfide solid electrolyte is Li 7-n PS 6-n X is one of Cl, Br, and I, where 0 < n ≤ 2.

[0025] In some embodiments, the mass ratio of the sulfide solid electrolyte, boric acid, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is 10:(0.3~0.8):(0.12~0.32).

[0026] In this embodiment, the mass ratio of the sulfide solid electrolyte, boric acid, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt can be 10:0.3:0.12, 10:0.5:0.20, 10:0.8:0.32, or any value within the above range. When the mass ratio of the sulfide solid electrolyte, boric acid, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is within the above range, the boron-oxygen coating layer formed by the boric acid can be matched with the hydrophobic filling effect provided by the ionic liquid, thereby forming a composite coating layer with good continuity and stability on the surface of the sulfide solid electrolyte. If the amount of boric acid and ionic liquid added is too low, it can easily lead to surface passivation and insufficient coating protection; if the amount added is too high, it can easily cause the modified components to agglomerate or accumulate on the surface of the sulfide solid electrolyte, affecting ion conduction.

[0027] In some preferred embodiments, the mass ratio of the sulfide solid electrolyte, boric acid, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is 10:0.5:0.20.

[0028] In some embodiments, the ball milling process is performed at a speed of 150-300 rpm for 3-8 hours, with a ball-to-material ratio of (1-3):1.

[0029] In this embodiment, the ball milling speed can be 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, or any value within the above range. The ball milling time can be 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or any value within the above range. The ball-to-material ratio in the ball milling process is 1:1, 1.5:1, 2:1, 2.5:1, 3:1, or any value within the above range.

[0030] In some embodiments, the ball milling process is an intermittent ball milling process, which includes continuous ball milling in cycles and shutdown cooling. The continuous ball milling time is 20 to 40 minutes, and the shutdown cooling time is 5 to 15 minutes.

[0031] In this embodiment, the continuous ball milling time can be 20 min, 25 min, 30 min, 35 min, 40 min, or any value within the above range. The shutdown cooling time is 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, or any value within the above range. Intermittent ball milling is used to prevent localized overheating, which can lead to various side reactions, such as the decomposition of sulfide solid electrolytes, and may also affect the coating and anchoring effects. Localized overheating can also damage the ball mill.

[0032] In some embodiments, the milling media in the ball milling process include zirconium oxide with a diameter of 3 mm and zirconium oxide with a diameter of 5 mm, wherein the mass ratio of the 3 mm zirconium oxide to the 5 mm zirconium oxide is 1:1.

[0033] In this embodiment, by using a mixture of zirconia grinding balls with diameters of 3 mm and 5 mm as the grinding media, the impact crushing effect of the larger diameter grinding balls and the grinding and dispersing effect of the smaller diameter grinding balls can be balanced. Specifically, the 5 mm diameter zirconia grinding balls are beneficial for impact crushing and dispersing the material, while the 3 mm diameter zirconia grinding balls increase the grinding contact points and promote finer dispersion, uniformly coating the boric acid and ionic liquid onto the surface of the sulfide solid electrolyte. Using them in a 1:1 mass ratio improves the mixing uniformity of the sulfide solid electrolyte, boric acid, and ionic liquid, resulting in a finer and more uniform distribution of boric acid and ionic liquid on the surface of the sulfide solid electrolyte, thus facilitating the subsequent formation of a uniform composite coating layer.

[0034] In some embodiments, the settling is carried out in an inert gas atmosphere with a water content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm. Preferably, the settling is carried out in a glove box (water and oxygen content less than 0.1 ppm).

[0035] In some embodiments, the heating rate of the muffle furnace is 5~10°C / min when firing the mixture.

[0036] In this embodiment, the heating rate of the muffle furnace is 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or any value within the above range.

[0037] In some embodiments, after heat treatment of the mixture, the following step is further included: sieving through a 120-mesh sieve.

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are intended only to illustrate the present invention and not to limit it. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1 This embodiment provides a method for improving the air stability of sulfide solid electrolytes, as detailed below: Step 1: Take a 50 mL ZrO2 ball mill jar and put in ZrO2 grinding balls (3 mm diameter and 5 mm diameter mixed in a 1:1 ratio), ball-to-material ratio (mass ratio) = 2:1.

[0040] Step 2: Add the weighed 10 g LPSC powder, 0.3 g boric acid, and 0.12 g ionic liquid to the ball mill jar, seal the ball mill jar, install it on the planetary ball mill, and set the ball mill parameters: speed 200 rpm, grinding time 5 h, and stop for 10 min every 30 min of operation.

[0041] Step 3: After ball milling, open the can in the glove box and spread the resulting paste evenly in the alumina boat for 24 hours to allow the ionic liquid to fully contact the boric acid and pre-anchor it.

[0042] Step 4: Place the alumina boat into the muffle furnace located in the glove box, heat it to 220°C at a rate of 5°C / min, and hold it at that temperature for 2 hours.

[0043] Step 5: Take out the sample, sieve it, and collect the final product.

[0044] The ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM]TFSI).

[0045] Example 2 This embodiment provides a method for improving the air stability of sulfide solid electrolytes, as detailed below: Step 1: Take a 50 mL ZrO2 ball mill jar and put in ZrO2 grinding balls (3 mm diameter and 5 mm diameter mixed in a 1:1 ratio), ball-to-material ratio (mass ratio) = 2:1.

[0046] Step 2: Add the weighed 10 g LPSC powder, 0.5 g boric acid, and 0.20 g ionic liquid to the ball mill jar, then seal the ball mill jar and install it on the planetary ball mill. Set the ball mill parameters as follows: rotation speed 200 rpm, grinding time 5 h, and stop for 10 min every 30 min of operation.

[0047] Step 3: After ball milling, open the can in the glove box and spread the resulting paste evenly in the alumina boat for 24 hours to allow the ionic liquid to fully contact the boric acid and pre-anchor it.

[0048] Step 4: Place the alumina boat into the muffle furnace located in the glove box, heat it to 220°C at a rate of 10°C / min, and hold it at that temperature for 2 hours.

[0049] Step 5: Take out the sample, sieve it, and collect the final product.

[0050] The ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM]TFSI).

[0051] Example 3 This embodiment provides a method for improving the air stability of sulfide solid electrolytes, as detailed below: Step 1: Take a 50 mL ZrO2 ball mill jar and put in ZrO2 grinding balls (3 mm diameter and 5 mm diameter mixed in a 1:1 ratio), ball-to-material ratio (mass ratio) = 2:1.

[0052] Step 2: Add the weighed 10 g LPSC powder, 0.8 g boric acid, and 0.32 g ionic liquid to the ball mill jar, seal the ball mill jar, install it on the planetary ball mill, and set the ball mill parameters: speed 200 rpm, grinding time 5 h, and stop for 10 min every 30 min of operation.

[0053] Step 3: After ball milling, open the can in the glove box and spread the resulting paste evenly in the alumina boat for 24 hours to allow the ionic liquid to fully contact the boric acid and pre-anchor it.

[0054] Step 4: Place the alumina boat into the muffle furnace located in the glove box, heat it to 220°C at a rate of 10°C / min, and hold it at that temperature for 2 hours.

[0055] Step 5: Take out the sample, sieve it, and collect the final product.

[0056] The ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM]TFSI).

[0057] Comparative Example 1 Untreated LPSC powder was used as Comparative Example 1.

[0058] Comparative Example 2 This embodiment provides a method for improving the air stability of sulfide solid electrolytes, as detailed below: Step 1: Take a 50 mL ZrO2 ball mill jar and put in ZrO2 grinding balls (3 mm diameter and 5 mm diameter mixed in a 1:1 ratio), ball-to-material ratio (mass ratio) = 2:1.

[0059] Step 2: Add the weighed 10 g LPSC powder and 0.5 g boric acid to the ball mill jar, then seal the ball mill jar and install it on the planetary ball mill. Set the ball mill parameters: speed 200 rpm, grinding time 5 h, and stop for 10 min every 30 min of operation.

[0060] Step 3: After ball milling, open the can in the glove box and spread the resulting paste evenly in the alumina boat for 24 hours to allow the ionic liquid to fully contact the boric acid and pre-anchor it.

[0061] Step 4: Place the alumina boat into the muffle furnace located in the glove box, heat it to 220°C at 8°C / min, and hold it at that temperature for 2 hours.

[0062] Step 5: Take out the sample, sieve it, and collect the final product.

[0063] Comparative Example 3 This embodiment provides a method for improving the air stability of sulfide solid electrolytes, as detailed below: Step 1: Take a 50 mL ZrO2 ball mill jar and put in ZrO2 grinding balls (3 mm diameter and 5 mm diameter mixed in a 1:1 ratio), ball-to-material ratio (mass ratio) = 2:1.

[0064] Step 2: Add the weighed 10 g LPSC powder and 0.20 g ionic liquid to the ball mill jar, then seal the ball mill jar and install it on the planetary ball mill. Set the ball mill parameters: rotation speed 200 rpm, grinding time 5 h, and stop for 10 min every 30 min of operation.

[0065] Step 3: After ball milling, open the can in the glove box and spread the resulting paste evenly in the alumina boat for 24 hours to allow the ionic liquid to fully contact the boric acid and pre-anchor it.

[0066] Step 4: Place the alumina boat into the muffle furnace located in the glove box, heat it to 220°C at a rate of 10°C / min, and hold it at that temperature for 2 hours.

[0067] Step 5: Take out the sample, sieve it, and collect the final product.

[0068] The ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM]TFSI).

[0069] Comparative Example 4 This embodiment provides a method for improving the air stability of sulfide solid electrolytes, as detailed below: Step 1: Take a 50 mL ZrO2 ball mill jar and put in ZrO2 grinding balls (3 mm diameter and 5 mm diameter mixed in a 1:1 ratio), ball-to-material ratio (mass ratio) = 2:1.

[0070] Step 2: Add the weighed 10 g LPSC powder, 0.5 g boric acid, and 0.20 g ionic liquid to the ball mill jar, then seal the ball mill jar and install it on the planetary ball mill. Set the ball mill parameters as follows: rotation speed 200 rpm, grinding time 5 h, and stop for 10 min every 30 min of operation.

[0071] Step 3: After ball milling, open the can in the glove box and spread the resulting paste evenly in the alumina boat for 24 hours to allow the ionic liquid to fully contact the boric acid and pre-anchor it.

[0072] Step 4: Place the alumina boat into the muffle furnace located in the glove box, heat it to 220°C at a rate of 10°C / min, and hold it at that temperature for 2 hours.

[0073] Step 5: Take out the sample, sieve it, and collect the final product.

[0074] The ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4).

[0075] Comparative Example 5 This embodiment provides a method for improving the air stability of sulfide solid electrolytes, as detailed below: Step 1: Take a 50 mL ZrO2 ball mill jar and put in ZrO2 grinding balls (3 mm diameter and 5 mm diameter mixed in a 1:1 ratio), ball-to-material ratio (mass ratio) = 2:1.

[0076] Step 2: Add the weighed 10 g LPSC powder, 0.5 g phosphoric acid, and 0.20 g ionic liquid to the ball mill jar, then seal the ball mill jar and install it on the planetary ball mill. Set the ball mill parameters as follows: rotation speed 200 rpm, grinding time 5 h, and stop for 10 min every 30 min of operation.

[0077] Step 3: After ball milling, open the can in the glove box and spread the resulting paste evenly in the alumina boat for 24 hours to allow the ionic liquid to fully contact the boric acid and pre-anchor it.

[0078] Step 4: Place the alumina boat into the muffle furnace located in the glove box, heat it to 220°C at a rate of 10°C / min, and hold it at that temperature for 2 hours.

[0079] Step 5: Take out the sample, sieve it, and collect the final product.

[0080] The ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM]TFSI).

[0081] Comparative Example 6 This embodiment provides a method for improving the air stability of sulfide solid electrolytes, as detailed below: Step 1: Take a 50 mL ZrO2 ball mill jar and put in ZrO2 grinding balls (3 mm diameter and 5 mm diameter mixed in a 1:1 ratio), ball-to-material ratio (mass ratio) = 2:1.

[0082] Step 2: Add the weighed 10 g LPSC powder, 0.5 g boric acid, and 0.20 g ionic liquid to the ball mill jar, then seal the ball mill jar and install it on the planetary ball mill. Set the ball mill parameters as follows: rotation speed 200 rpm, grinding time 5 h, and stop for 10 min every 30 min of operation.

[0083] Step 3: Spread the obtained paste evenly in an alumina boat. Place the alumina boat in a muffle furnace located in a glove box, heat it to 220°C at a rate of 10°C / min, and hold it at that temperature for 2 hours.

[0084] Step 4: Take out the sample, sieve it, and collect the final product.

[0085] The ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM]TFSI).

[0086] The component contents of the samples prepared in Examples 1-3 and Comparative Examples 1-6 are shown in Table 1. The conductivity of the prepared samples was tested according to the above steps. Then, the conductivity was tested again after exposure to air for 2h, 4h, 8h and 24h. The results are shown in Table 2.

[0087] Table 1. Components and content of the samples

[0088] The specific steps of the detection are as follows: 1. Sample preparation The composite electrolyte powder is cold-pressed into sheets under a pressure of 10 MPa, with a thickness of about 1 to 1.5 mm, usually 0.5 mm, and a diameter of 10 to 14 mm, usually 10 mm.

[0089] The thickness needs to be measured using a micrometer.

[0090] Electrochemical impedance spectroscopy (EIS) The sample is held in place using a blocking electrode (such as stainless steel or sputtered metal film), and an AC voltage (amplitude 10mV, frequency range 1MHz to 0.1Hz) is applied.

[0091] The bulk resistance R is obtained by fitting the semicircular intercept in the high-frequency region using EIS. bulk The low-frequency region reflects the interfacial resistance and the double-layer effect.

[0092] Geometric parameter measurement Thickness (L): The thickness of the compressed tablet is measured directly using a micrometer; Area (A): Calculate the effective contact area based on the electrode diameter; According to the formula Calculate the ionic conductivity of the corresponding material. The conductivity of the samples prepared in Examples 1-3 and Comparative Examples 1-3 was tested according to the above steps. Subsequently, the conductivity was tested again after exposure to air for 2h, 4h, 8h and 24h. The results are shown in Table 2.

[0093] Table 2. Conductivity of sulfide electrolytes

[0094] As shown in Table 2, the preparation method of the present invention, which modifies sulfides by sequentially coating them with boric acid and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt using LPSC, significantly improves the air stability of sulfides compared to the single coating modification or no modification in Comparative Examples 1-3. The sample in Example 2 exhibits the best performance. As shown in Comparative Examples 4-5, the present invention, through the compound modification of sulfide electrolytes with boric acid and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, demonstrates a more synergistic effect compared to the use of other ionic liquids or other inorganic oxyacids, effectively improving the air stability of sulfides. Regarding the air stability of the electrolyte, as shown in Comparative Example 6, the process of the present invention involves ball milling followed by settling, which, compared to ball milling without settling, further optimizes the compound modification reaction of the two modifiers, forming a more uniform and stable coating layer. Moreover, within the material ratio range of the present invention, a good coating effect can be achieved. Reducing the amount of boric acid and ionic liquid added can easily lead to insufficient surface passivation, affecting the construction of the coating layer. Excessive addition of boric acid can easily cause agglomeration on the surface of the sulfide electrolyte, and excessive addition of ionic liquid can affect the binding of boric acid and sulfide electrolyte, both of which affect the coating effect.

[0095] In summary, this invention employs a "rigid coating + flexible filling coating" method to form a coating layer on the surface of a sulfide solid electrolyte, significantly improving the air stability of the sulfide electrolyte. Specifically, the rigid BOB in the coating layer provides a high-strength framework, creating a physical barrier to enhance air stability; the flexible ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt) fills the gaps in the framework, providing hydrophobicity and contributing to the combined effect of improved air stability.

[0096] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for improving the air stability of sulfide solid electrolytes, characterized in that, Includes the following steps: The sulfide solid electrolyte, boric acid, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt were added to a ball mill jar and ball milled to obtain a mixture. The mixture is allowed to stand for 12 to 36 hours, and then placed in a muffle furnace and kept at 180 to 260°C for 1 to 4 hours to improve the air stability of the sulfide solid electrolyte.

2. The method according to claim 1, characterized in that, The sulfide solid electrolyte is Li 7-n PS 6-n X is one of Cl, Br, and I, where 0 < n ≤ 2.

3. The method according to claim 1, characterized in that, The mass ratio of the sulfide solid electrolyte, boric acid, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is 10:(0.3~0.8):(0.12~0.32).

4. The method according to claim 1, characterized in that, The ball milling process is performed at a speed of 150-300 rpm for 3-8 hours, with a ball-to-material ratio of (1-3):

1.

5. The method according to claim 4, characterized in that, The ball milling process is an intermittent ball milling process, which includes continuous ball milling in a cycle and shutdown cooling. The continuous ball milling time is 20-40 minutes, and the shutdown cooling time is 5-15 minutes.

6. The method according to claim 4, characterized in that, The ball milling media in the ball milling process include zirconium oxide with a diameter of 3 mm and zirconium oxide with a diameter of 5 mm, and the mass ratio of the zirconium oxide with a diameter of 3 mm to the zirconium oxide with a diameter of 5 mm is 1:

1.

7. The method according to claim 1, characterized in that, The settling process is carried out in an inert gas with a water content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm.

8. The method according to claim 1, characterized in that, When firing the mixture, the heating rate of the muffle furnace is 5~10℃ / min.

9. The method according to claim 1, characterized in that, After heat treatment of the mixture, the following step is also included: sieving through a 120-mesh sieve.

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