Polyionic liquid artificial solid-state electrolyte interface and preparation method and application thereof

Abstract

The application relates to a polyionic liquid type artificial solid electrolyte interface and a preparation method and application thereof. The polyionic liquid type artificial solid electrolyte interface is a lithium-sulfur battery solid electrolyte interface for isolating polysulfides; the polyionic liquid type artificial solid electrolyte interface is obtained by polymerizing a mixture of uniformly mixed ionic liquid monomers, an initiator and a lithium salt; in the polyionic liquid type artificial solid electrolyte interface SEI, the ionic liquid monomers are polymerized to form a polyionic liquid, the main chain is a carbon-carbon chain, and the side chain is an ionic liquid group A with a benzene ring; the ionic liquid monomer is a cationic ionic liquid monomer containing one or more active groups and benzene ring groups.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a polyionic liquid-type artificial solid electrolyte interface, its preparation method, and its application. Background Technology

[0002] Lithium-sulfur batteries offer advantages such as low cost, environmental friendliness, and high theoretical specific energy and capacity. In the Third Industrial Revolution, new energy vehicles are considered a revolutionary technology impacting energy, the environment, transportation, and daily life. Currently, the main obstacle to the development of electric vehicles is their short driving range, which is directly related to the energy density of the power battery. The energy density of conventional power batteries for electric vehicles is currently around 250 Wh / kg, with a watt-hour cost of about 1 yuan / Wh after assembly, resulting in a driving range of 500 kilometers. Some models achieve a range of 700 kilometers, but the battery component occupies a significant amount of weight and has a high cost, making it difficult to meet market demands. Lithium-sulfur batteries have a theoretical energy density far exceeding that of traditional lithium-ion batteries. In recent years, they have seen rapid development in both theoretical research and engineering, demonstrating enormous potential. Furthermore, lithium-sulfur does not contain precious metals, and sulfur is abundant on Earth, giving them a significant cost advantage.

[0003] During the charging and discharging process of lithium-sulfur batteries, the polysulfide intermediates generated at the positive electrode dissolve in the electrolyte, pass through the separator, diffuse towards the negative electrode, and react directly with the metallic lithium at the negative electrode. This ultimately leads to irreversible loss of active materials, capacity decay, and low coulombic efficiency. Therefore, lithium-sulfur batteries have the disadvantage of poor long-cycle performance.

[0004] Polyionic liquids possess excellent thermal stability, non-flammability, and a wide electrochemical stability window, as well as excellent processability and flexibility, making them a very promising material. However, conventional polyionic liquids swell or even dissolve in ether electrolytes, failing to inhibit the migration of polysulfides.

[0005] To address the polysulfide shuttle problem in lithium-sulfur batteries, the article *Nature Communications*, 2021, 12(1):3031, describes a method using a polymeric solid electrolyte interface (SEI) formed by adding 1,3,5-benzenetrithiol as an additive to block polysulfide transport. However, due to its low degree of polymerization, the lithium-sulfur battery still suffers from capacity decay. The article *Journal of Energy Chemistry*, 2021, 52:310-317, describes the preparation of a gel-based artificial solid electrolyte interface (SEI) via electrospinning, which can improve the long-cycle performance of lithium-sulfur batteries. However, its preparation method is relatively cumbersome, and the prepared lithium-sulfur battery exhibits significant capacity decay in the first few charge-discharge cycles. Summary of the Invention

[0006] This invention provides a polyionic liquid-type artificial solid electrolyte interface, its preparation method, and its application. Starting from a polymer electrolyte that is insoluble in ether-based electrolytes, an artificial SEI is formed. It is insoluble in electrolytes, and the active groups make polymerization easier. Furthermore, the formed material does not swell and has excellent ability to isolate polysulfides, thereby improving the long-cycle performance of lithium-sulfur batteries.

[0007] In a first aspect, embodiments of the present invention provide a polyionic liquid-type artificial solid electrolyte interface, wherein the polyionic liquid-type artificial solid electrolyte interface is a lithium-sulfur battery solid electrolyte interface used to isolate polysulfides; the polyionic liquid-type artificial solid electrolyte interface is obtained by polymerizing a uniformly mixed mixture of ionic liquid monomers, initiators and lithium salts;

[0008] In the polyionic liquid-type artificial solid electrolyte interface (SEI), the ionic liquid monomers are polymerized to form a polyionic liquid with the following general structural formula: The main chain is a carbon-carbon chain, and the side chains are ionic liquid groups A with benzene rings; n is the degree of polymerization, and n is 1000-10000;

[0009] The ionic liquid monomer is a cationic ionic liquid monomer containing one or more active groups and benzene ring groups.

[0010] Preferably, the cationic ionic liquid monomer specifically includes: imidazole, pyrrole, pyridine, piperidine, and quaternary ammonium salt cationic ionic liquids;

[0011] The active group includes a vinyl group.

[0012] Preferably, the lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(oxalateborate).

[0013] The lithium salt in the mixture accounts for 5 wt% to 40 wt% of the ionic liquid monomer content.

[0014] Preferably, the initiator includes a thermal initiator or a photoinitiator;

[0015] The thermal initiator includes one or more of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dialkyl peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide;

[0016] The photoinitiator includes one or more of the following: 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide;

[0017] The initiator in the mixture accounts for 0.1 wt% to 5 wt% of the ionic liquid monomer content.

[0018] Preferably, the polymerization conditions are: a temperature of 40℃-80℃ and a polymerization time of 6-12 hours; or, 365nm ultraviolet light irradiation for 2-10 minutes.

[0019] Secondly, embodiments of the present invention provide a method for preparing the polyionic liquid-type artificial solid electrolyte interface described in the first aspect, the method comprising:

[0020] The ionic liquid monomer, initiator and lithium salt are mixed uniformly in a certain proportion to form a mixture;

[0021] The mixture is polymerized to obtain the polyionic liquid-type artificial solid electrolyte interface;

[0022] The polymerization conditions are as follows: a temperature of 40℃-80℃ and a polymerization time of 6-12 hours; or, 365nm ultraviolet light irradiation for 2-10 minutes.

[0023] Preferably, before uniformly mixing the ionic liquid monomer, initiator, and lithium salt in a specific ratio to form a mixture, the method further includes: preparing the ionic liquid monomer.

[0024] More preferably, the preparation of the ionic liquid monomer specifically includes:

[0025] Benzyl chloride containing an active group was dissolved in ethyl acetate and reacted with a quaternizable heterocyclic compound. After the reaction was completed, the mixture was distilled under reduced pressure. After distillation, impurities were washed away with n-hexane, and then the product was obtained by distillation under reduced pressure.

[0026] The product was dissolved in chloroform, and the lithium salt was dissolved in deionized water. The mixture was slowly added dropwise and stirred for 12-36 hours. After stirring, the mixture was washed with water until no chloride ions remained, and then distilled under reduced pressure to obtain an ionic liquid monomer containing one or more active groups and benzene ring groups.

[0027] The vacuum distillation is carried out at a temperature of 50℃-70℃, a time of 30min-60min, and a pressure of 10mPa-20mPa.

[0028] Thirdly, embodiments of the present invention provide a negative electrode for a lithium-sulfur battery, wherein the negative electrode has the polyionic liquid-type artificial solid electrolyte interface described in the first aspect above.

[0029] Fourthly, embodiments of the present invention provide a lithium-sulfur battery, wherein the lithium-sulfur battery includes the negative electrode described in the third aspect above.

[0030] The polyionic liquid artificial solid electrolyte interface, its preparation method, and its application provided in this invention start from polymer electrolytes that are insoluble in ether electrolytes to form an artificial SEI. It is insoluble in electrolytes, and the active groups make polymerization easier. The formed material does not swell and has excellent ability to isolate polysulfides, thereby improving the long-cycle performance of lithium-sulfur batteries. Attached Figure Description

[0031] The technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0032] Figure 1 This is a flowchart of the preparation method according to an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram illustrating the preparation principles of the ionic liquid monomer and artificial SEI in Examples 1-12 of this invention.

[0034] Figure 3 This is a schematic diagram illustrating the preparation principle of the ionic liquid monomer and artificial SEI in Example 13 of the present invention;

[0035] Figure 4 The cycling spectrum of a lithium-sulfur battery prepared using an artificial SEI anode with the method described in Example 1 of this invention;

[0036] Figure 5 The lithium-sulfur battery cycle diagram provided in Comparative Example 1 of this invention. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any way, that is, not intended to limit the scope of protection of the present invention.

[0038] This invention proposes a polyionic liquid-type artificial solid electrolyte interface (SEI) for lithium-sulfur batteries, which has the advantages of high temperature resistance, non-flammability, non-swelling, and strong ability to isolate polysulfides.

[0039] The polyionic liquid-type artificial SEI of the present invention is obtained by polymerizing a uniformly mixed mixture of ionic liquid monomer, initiator and lithium salt;

[0040] In polyionic liquid-type artificial SEIs, ionic liquid monomers are polymerized to form polyionic liquids, with the general structural formula being: The main chain is a carbon-carbon chain, and the side chains are ionic liquid groups A with benzene rings; n is the degree of polymerization, and n is 1000-10000;

[0041] Ionic liquid monomers are cationic ionic liquid monomers containing one or more active groups and benzene ring groups.

[0042] The aforementioned cationic ionic liquid monomers specifically include: imidazole, pyrrole, pyridine, piperidine, and quaternary ammonium salt cationic ionic liquids;

[0043] The active groups include, but are not limited to, vinyl groups.

[0044] Lithium salts include one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(oxalato)borate; the lithium salts in the mixture account for 5 wt% to 40 wt% of the ionic liquid monomer content.

[0045] The initiator includes a thermal initiator or a photoinitiator; the thermal initiator includes one or more of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dialkyl peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide; the photoinitiator includes one or more of the following: 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; the initiator accounts for 0.1 wt% to 5 wt% of the ionic liquid monomer content in the mixture.

[0046] The polyionic liquid-type artificial SEI of the present invention can be prepared by the following method. Figure 1 This is a flowchart of the preparation method according to an embodiment of the present invention. Figure 1 As shown:

[0047] Step 110: Mix the ionic liquid monomer, initiator and lithium salt in a uniform ratio to form a mixture;

[0048] The ionic liquid monomer can be prepared by the following method:

[0049] Step 1: Benzyl chloride containing an active group and a quaternizable heterocyclic compound are dissolved in ethyl acetate and reacted. After the reaction is complete, the mixture is distilled under reduced pressure. After distillation, impurities are washed away with n-hexane, and then the product is obtained by distillation under reduced pressure.

[0050] Step 2: Dissolve the product from Step 1 in chloroform, dissolve the lithium salt in deionized water, add it slowly dropwise, and stir for 12-36 hours. After stirring, wash with water until no chloride ions remain, and then distill under reduced pressure to obtain an ionic liquid monomer containing one or more active groups and benzene ring groups.

[0051] The vacuum distillation process involves a temperature of 50℃-70℃, a time of 30min-60min, and a pressure of 10mPa-20mPa.

[0052] To determine if there is any chloride ion residue after rinsing with water until no chloride ion residue remains, you can test the rinse water with AgNO3 solution to detect whether AgCl is generated, which will indicate the presence of chloride ion residue.

[0053] The lithium salts include one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(oxalatoborate). The lithium salt constitutes 5 wt% to 40 wt% of the ionic liquid monomer content in the mixture.

[0054] The initiator includes thermal initiators or photoinitiators; thermal initiators include one or more of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dialkyl peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide; photoinitiators include one or more of the following: 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. The initiator in the mixture accounts for 0.1 wt% to 5 wt% of the ionic liquid monomer content.

[0055] Step 120: Polymerize the mixture to obtain a polyionic liquid-type artificial solid electrolyte interface;

[0056] The polymerization conditions are: a temperature of 40℃-80℃ and a polymerization time of 6-12 hours; or, irradiation with 365nm ultraviolet light for 2-10 minutes.

[0057] The polyionic liquid-type artificial solid electrolyte interface of the present invention is formed in situ on the negative electrode of a lithium-sulfur battery. The lithium-sulfur battery assembled using this electrode has easier polymerization due to the active groups in the artificial SEI. The benzene ring groups in the polymer liquid give the artificial SEI the advantages of being non-flammable, non-swelling, and having a strong ability to isolate polysulfides, which helps to improve the long cycle performance of the lithium-sulfur battery.

[0058] To better understand the technical solution provided by the present invention, the following uses several specific examples to illustrate the specific process of preparing polyionic liquid-type artificial SEI using the method provided in the above embodiments of the present invention.

[0059] Example 1

[0060] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0061] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separation), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0062] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0063] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups and lithium bis(trifluoromethanesulfonyl)imide (30 wt% of the ionic liquid monomer content) were mixed evenly. Then, a thermal initiator, azobisisobutyronitrile (1 wt% of the ionic liquid monomer content), was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and heated at 60°C for 9 hours to obtain an artificial SEI.

[0064] Example 2

[0065] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0066] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 0 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separately), and then distilled under reduced pressure at 50 °C for 60 min to obtain 14.2 g of the product.

[0067] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 30min, and after distillation, it was freeze-dried to obtain 17.3g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0068] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups and lithium bis(trifluoromethanesulfonyl)imide (5 wt% of the ionic liquid monomer content) were mixed evenly. Then, a thermal initiator, azobisisobutyronitrile (0.1 wt% of the ionic liquid monomer content), was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and heated at 40°C for 6 hours to obtain an artificial SEI.

[0069] Example 3

[0070] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0071] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separation), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0072] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0073] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups and lithium bis(trifluoromethanesulfonyl)imide (40 wt% of the ionic liquid monomer content) were mixed evenly. Then, a thermal initiator, azobisisobutyronitrile (5 wt% of the ionic liquid monomer content), was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and heated at 80°C for 12 hours to obtain artificial SE I.

[0074] Example 4

[0075] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0076] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separately), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0077] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0078] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups and lithium bis(trifluoromethanesulfonyl)imide (30 wt% of the ionic liquid monomer content) were mixed evenly. Then, a thermal initiator, benzoyl peroxide (1 wt% of the ionic liquid monomer content), was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and heated at 60°C for 9 hours to obtain an artificial SEI.

[0079] Example 5

[0080] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0081] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separately), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0082] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0083] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups and lithium bis(trifluoromethanesulfonyl)imide (5 wt% of the ionic liquid monomer content) were mixed evenly. Then, a thermal initiator, benzoyl peroxide (0.1 wt% of the ionic liquid monomer content), was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and heated at 40°C for 6 hours to obtain an artificial SEI.

[0084] Example 6

[0085] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0086] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separately), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0087] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0088] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups and lithium bis(trifluoromethanesulfonylimide) comprising 40 wt% of the ionic liquid monomer content were mixed evenly. Then, a thermal initiator, benzoyl peroxide comprising 5 wt% of the ionic liquid monomer content, was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode sheet and heated at 80°C for 12 hours to obtain an artificial SEI.

[0089] Example 7

[0090] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0091] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separately), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0092] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0093] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups and lithium bis(trifluoromethanesulfonylimide) comprising 30 wt% of the ionic liquid monomer were mixed evenly. Then, a thermal initiator, 2-hydroxy-methylphenylpropane-1-one comprising 1 wt% of the ionic liquid monomer, was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and irradiated with a 365 nm ultraviolet lamp for 5 minutes to obtain an artificial SEI.

[0094] Example 8

[0095] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0096] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separately), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0097] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0098] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups was mixed with lithium bis(trifluoromethanesulfonylimide) at 5 wt% of the ionic liquid monomer content. Then, a thermal initiator, 2-hydroxy-methylphenylpropane-1-one at 0.1 wt% of the ionic liquid monomer content, was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and irradiated with a 365 nm ultraviolet lamp for 5 minutes to obtain an artificial SEI.

[0099] Example 9

[0100] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0101] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separately), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0102] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0103] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups and lithium bis(trifluoromethanesulfonylimide) comprising 40 wt% of the ionic liquid monomer were mixed uniformly. Then, a thermal initiator, 2-hydroxy-methylphenylpropane-1-one comprising 5 wt% of the ionic liquid monomer, was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was uniformly coated onto the negative electrode and irradiated with a 365 nm ultraviolet lamp for 10 minutes to obtain an artificial SEI.

[0104] Example 10

[0105] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0106] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separately), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0107] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0108] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups was mixed with lithium bis(trifluoromethanesulfonylimide) at 30 wt% of the ionic liquid monomer content. Then, a thermal initiator, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone at 1 wt% of the ionic liquid monomer content, was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and irradiated with a 365 nm ultraviolet lamp for 5 minutes to obtain an artificial SEI.

[0109] Example 11

[0110] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0111] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separation), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0112] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0113] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups was mixed with lithium bis(trifluoromethanesulfonylimide) at 5 wt% of the ionic liquid monomer content. Then, a thermal initiator, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone at 0.1 wt% of the ionic liquid monomer content, was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was uniformly coated onto the negative electrode and irradiated with a 365 nm ultraviolet lamp for 2 minutes to obtain an artificial SEI.

[0114] Example 12

[0115] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 2 As shown. The preparation process is as follows:

[0116] 10 g of 4-vinylbenzyl chloride and 6.5 g of N-methylimidazole were dissolved in 20 ml of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 ml of n-hexane (separately), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0117] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0118] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups was mixed with lithium bis(trifluoromethanesulfonylimide) at 40 wt% of the ionic liquid monomer content. Then, a thermal initiator, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone at 5 wt% of the ionic liquid monomer content, was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and irradiated with a 365 nm ultraviolet lamp for 10 minutes to obtain an artificial SEI.

[0119] Example 13

[0120] The schematic diagram of the preparation reaction principle in this embodiment is shown below. Figure 3 As shown. The preparation process is as follows:

[0121] 10 g of 4-vinylbenzyl chloride and 6.5 g of 4-methylpyridine were dissolved in 20 mL of ethyl acetate and reacted at 40 °C for 48 hours. After the reaction was completed, the mixture was rotary distilled at 60 °C for 40 min. After distillation, the mixture was washed three times with 20 mL of n-hexane (separation), and then distilled under reduced pressure at 60 °C for 40 min to obtain 14.0 g of the product.

[0122] 14g of the product obtained in the previous step was dissolved in 15ml of chloroform; 20g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 15ml of deionized water, and the solution was slowly added dropwise at 40℃, with stirring continued at 40℃ for 24 hours. After the reaction was completed, the solution was washed three times with plenty of water, and the washing water was tested with AgNO3 solution to find that it contained no chloride ions. The solution was then distilled under reduced pressure at 70℃ for 40min, and after distillation, it was freeze-dried to obtain 17.1g of a yellow transparent liquid, which is the cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups.

[0123] A cationic ionic liquid monomer containing unsaturated bonds and benzene ring groups was mixed with lithium bis(trifluoromethanesulfonylimide) at 40 wt% of the ionic liquid monomer content. Then, a thermal initiator, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone at 5 wt% of the ionic liquid monomer content, was added. After magnetic stirring for 2 hours, a homogeneous solution was obtained. The solution was then uniformly coated onto the negative electrode and irradiated with a 365 nm ultraviolet lamp for 10 minutes to obtain an artificial SEI.

[0124] Assemble the battery for testing:

[0125] A 1Ah lithium-sulfur pouch battery was assembled using a commercial electrolyte (1M LiTFSI+DME / DOL(1:1)) as the lithium-sulfur electrolyte, an artificial SEI prepared in Example 1 on a 50μm ultrathin lithium strip as the negative electrode, carbon-coated aluminum foil as the current collector, polypropylene (PP) as the separator, and a Mo6S8+S8+graphene nanosheets (GNs)+carbon nanotubes (CNTs) composite material (mass ratio 20:60:10:10) as the positive electrode material.

[0126] After the above-mentioned battery was left to stand for 12 hours, its electrochemical performance was tested on the LAND battery testing system at a rate of 0.1C and a test temperature of 25°C. The electrochemical performance test results of this Example 1 are shown below. Figure 4 It can be seen that the capacity retention rate remains at around 55% after 60 cycles.

[0127] Comparative Example 1

[0128] A 1Ah lithium-sulfur pouch battery was assembled using a commercial electrolyte (1M LiTFSI+DME / DOL(1:1)) as the lithium-sulfur electrolyte, a 50μm ultrathin lithium strip as the negative electrode, carbon-coated aluminum foil as the current collector, polypropylene (PP) as the separator, and a Mo6S8+S8+graphene nanosheets (GNs)+carbon nanotubes (CNTs) (mass ratio 20:60:10:10) composite material as the positive electrode material.

[0129] After the batteries were left to stand for 12 hours, their electrochemical performance was tested on the LAND battery testing system at a rate of 0.1C and a test temperature of 25°C. The electrochemical performance test results of Comparative Example 1 are shown below. Figure 5 It can be seen that the 60-week cycle capacity retention rate is already below 40%.

[0130] The artificial SEI provided in this invention has the advantages of being non-flammable, non-swelling, and having a strong ability to isolate polysulfides. Lithium-sulfur batteries using the artificial SEI of this invention have superior long-cycle performance.

[0131] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a polyionic liquid-type artificial solid electrolyte interface, characterized in that, The method includes: The ionic liquid monomer, initiator and lithium salt are mixed uniformly in a certain proportion to form a mixture; The mixture is coated onto the negative electrode sheet and polymerized to obtain the polyionic liquid-type artificial solid electrolyte interface; The polyionic liquid-type artificial solid electrolyte interface is a lithium-sulfur battery solid electrolyte interface used to isolate polysulfides. In the polyionic liquid-type artificial solid electrolyte interface (SEI), the ionic liquid monomers are polymerized to form a polyionic liquid with the following general structural formula: A represents an ionic liquid group; n represents the degree of polymerization, where n is between 1000 and 10000. The ionic liquid monomer is a cationic ionic liquid monomer containing a vinyl group and a benzene ring group.

2. The preparation method according to claim 1, characterized in that, The cationic ionic liquid monomers specifically include: imidazole, pyrrole, pyridine, piperidine, and quaternary ammonium salt cationic ionic liquids.

3. The preparation method according to claim 1, characterized in that, The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(oxalato)borate. The lithium salt in the mixture accounts for 5 wt% to 40 wt% of the ionic liquid monomer content.

4. The preparation method according to claim 1, characterized in that, The initiator includes a thermal initiator or a photoinitiator; The thermal initiator includes one or more of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dialkyl peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide; The photoinitiator includes one or more of the following: 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; The initiator in the mixture accounts for 0.1wt%-5wt% of the ionic liquid monomer content.

5. The preparation method according to claim 1, characterized in that, The polymerization conditions are: a temperature of 40℃-80℃ and a polymerization time of 6-12 hours; or, irradiation with 365nm ultraviolet light for 2-10 minutes.

6. The preparation method according to claim 1, characterized in that, Before uniformly mixing the ionic liquid monomer, initiator, and lithium salt in a specific ratio to form a mixture, the method further includes: preparing the ionic liquid monomer.

7. The preparation method according to claim 6, characterized in that, The preparation of the ionic liquid monomer specifically includes: Benzyl chloride containing a vinyl group was dissolved in ethyl acetate and reacted with a quaternizable heterocyclic compound. After the reaction was completed, the mixture was distilled under reduced pressure. After distillation, impurities were washed away with n-hexane, and then the product was obtained by distillation under reduced pressure. The product was dissolved in chloroform, and the lithium salt was dissolved in deionized water. The mixture was slowly added dropwise and stirred for 12-36 hours. After stirring, the mixture was washed with water until no chloride ions remained, and then distilled under reduced pressure to obtain an ionic liquid monomer containing a vinyl group and a benzene ring group. The vacuum distillation is carried out at a temperature of 50℃-70℃, a time of 30min-60min, and a pressure of 10mPa-20mPa.

8. A negative electrode for a lithium-sulfur battery, characterized in that, The negative electrode has a polyionic liquid-type artificial solid electrolyte interface prepared by any of the preparation methods described in claims 1-7.

9. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery includes the negative electrode as described in claim 8.

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