Preparation method of wide temperature range deep eutectic electrolyte containing cyclic sulfonium cation

Abstract

The application provides a preparation method of a wide-temperature-range deep eutectic electrolyte containing a ring sulfonium cation, and belongs to the technical field of electrolyte material preparation. The application is used to solve the problems of the existing deep eutectic electrolyte, such as insufficient stability of the cation, poor low-temperature performance and complicated synthesis process. The steps of the application comprise the following steps: S1, preparing a yellowish viscous ring sulfonium halide; S2, adding the ring sulfonium halide and a lithium salt of a target weak coordination anion into an ionic liquid solvent to generate a high-purity ring sulfonium salt; S3, preparing a composite HBD; S4, adding the composite HBD, the high-purity ring sulfonium salt and an alkali metal salt into a dry three-necked flask to perform stirring to obtain a mixed system; and S5, performing vacuum drying on the mixed system after the stirring is completed to obtain a uniform transparent functional deep eutectic electrolyte.

Description

Technical Field

[0001] This invention relates to a method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations, belonging to the field of electrolyte material preparation technology. Background Technology

[0002] Deep eutectic electrolytes (DES), as a novel type of green electrolyte material, have become an important research direction for replacing traditional flammable organic electrolytes due to their outstanding advantages such as low toxicity, high chemical stability, controllable composition, and low-cost preparation, showing broad application prospects in the field of electrochemical energy storage. However, the existing cation systems of deep eutectic electrolytes mostly rely on traditional types such as quaternary ammonium salts, imidazole salts, and quaternary phosphonium salts, which expose many insurmountable limitations in practical applications, seriously restricting their promotion in high-performance electrochemical devices: First, the cations have strong nucleophilicity and are prone to redox side reactions with positive electrode active materials under high voltage conditions, leading to electrode structure damage and electrolyte decomposition; Second, they are sensitive to Li + / Na + The system has insufficient ability to regulate the solvation effect of alkali metal ions, and there is a strong competitive migration effect between cations and alkali metal ions; thirdly, it has poor low-temperature adaptability. When the temperature drops, the viscosity of the system increases sharply, and the ion diffusion resistance increases significantly, which cannot meet the requirements for use in extreme low-temperature environments.

[0003] Thionium salts (containing S) + Sulfur cations, as a novel type of ionic liquid cation precursor, possess unique electronic structural advantages: the electronegativity of sulfur is lower than that of nitrogen and phosphorus, making the antioxidant capacity of sulfonium cations significantly stronger than that of traditional ammonium and phosphonium salt cations, theoretically suitable for electrode systems with higher voltages; simultaneously, their lower lattice energy helps reduce the viscosity of the electrolyte system and improve ion conductivity. However, the application of sulfonium salts in deep eutectic electrolytes remains unexplored, as existing sulfonium salt materials themselves have structural defects: firstly, most existing sulfonium salts adopt chain molecular structures (such as trimethylsulfonium), lacking cyclic structure designs, resulting in insufficient cation rigidity and limited thermal stability, making it difficult to meet the high-temperature operation requirements of batteries; secondly, the molecular structure has not been optimized for deep eutectic formation, resulting in weak interaction with hydrogen bond donors (HBD), making it impossible to form a stable and homogeneous deep eutectic system, and prone to phase separation; finally, the competitive migration problem between sulfonium cations and alkali metal ions has not been solved through molecular modification, limiting their practical application in battery devices.

[0004] Therefore, there is an urgent need in this field to develop a functionalized deep eutectic electrolyte material based on cyclic thioonium salt cations and its synthesis method. This material needs to precisely overcome the shortcomings of existing technologies: on the one hand, by strengthening the rigidity and thermal stability of the cations through cyclic structure design, and improving their antioxidant capacity to adapt to high-voltage electrode systems; on the other hand, by optimizing the interaction efficiency between the thioonium salt and the hydrogen bond donor (HBD), ensuring the formation of a stable and homogeneous deep eutectic system; simultaneously, by controlling the molecular structure to weaken the interaction between the thioonium cation and alkali metal ions (Li₂O₃). + / Na + The competitive migration effect of alkali metal ions increases the migration number of alkali metal ions while taking into account the conductivity over a wide temperature range, thereby providing a high-safety and high-stability electrolyte solution for alkali metal battery electrochemical devices, and promoting the performance upgrade and industrial application of related electrochemical devices. Summary of the Invention

[0005] To address the problems of insufficient cation stability, poor low-temperature performance, and cumbersome synthesis process in existing deep eutectic electrolytes, this invention proposes a method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows: The present invention includes the following steps:

[0007] Step 1: Using thioether derivatives and haloalcohols as raw materials, a cyclization reaction is carried out to obtain a pale yellow viscous cyclothionium halide. Step 2: Add the cyclothionium halide and the lithium salt of the target weakly coordinated anion to the ionic liquid solvent and stir to react. After the reaction is completed, filter to remove the generated lithium halide precipitate, and vacuum dry the filtrate to obtain high-purity cyclothionium salt. Step 3: Mix the main HBD and auxiliary HBD at a preset mass ratio to obtain a composite HBD; Step 4: Add the composite HBD, high-purity cyclothionium salt and alkali metal salt to a dry three-necked flask according to the preset molar ratio and stir to obtain a mixed system; Step 5: After stirring, the mixture is vacuum dried to obtain a uniform and transparent functionalized deep eutectic electrolyte.

[0008] Furthermore, the thioether derivative in step 1 is one of 2-hydroxyethyl ethyl thioether, 2-aminoethyl methyl thioether, and 3-methoxypropyl methyl thioether; the haloalcohol is one of 2-chloroethanol, 3-chloropropanol, and 3-bromopropanol. The cyclization reaction is carried out under either microwave-assisted or ultrasound-assisted conditions. Under microwave-assisted conditions, the power was set to 300-500 W, the reaction temperature to 80-100℃, and the cyclization reaction time to 2-4 h. Under ultrasound-assisted conditions, set the power to 200-300W, the temperature to 80-100℃, and the time to 3-5h. After the cyclization reaction was completed, unreacted raw materials were removed by vacuum distillation to obtain a pale yellow, viscous cyclothionium halide.

[0009] Furthermore, the cation of the cyclothionium salt is one of a five-membered structure containing an O heteroatom, a six-membered structure containing an O heteroatom, a five-membered structure containing an NH heteroatom, or a six-membered structure containing an NH heteroatom, and at least one cyclic substituent is hydroxyethyl; the anion is TFSI. - FSI - and BETI - One of them.

[0010] Furthermore, the general structural formula of the cation of cyclothionium salts is: five-membered ring: [S(R1)(R2)-CH2-CH2-X] + And a six-membered ring: [S(R1)(R2)-CH2-CH2-CH2-X] + One of them, wherein X = O and NH, R1 and R2 are both C1-C4 alkyl and hydroxyethyl, and at least one of R1 and R2 is hydroxyethyl.

[0011] Furthermore, in step 2, the molar ratio of the cyclothionium halide to the lithium salt of the target weakly coordinating anion is 1:1.05-1:1.1; The ionic liquid solvent is one of [EMIM]TFSI and [BMIM]FSI, and the mass of the ionic liquid solvent is 3-5 times the total mass of the reactants.

[0012] Furthermore, in step 2, the temperature of the stirring reaction is 80℃ and the stirring time is 2h, so that the halide ions and weakly coordinated anions can be fully exchanged through stirring. After stirring and reacting, the generated lithium halide precipitate was removed by filtration. The filtrate was then vacuum dried at 100°C for 12 hours to remove residual solvent, thus obtaining high-purity cyclothionium salt.

[0013] Furthermore, in step 3, the main HBD is a fluorinated polyol, which is one of 2,2,3,3-tetrafluoro-1,4-butanediol, 2,2-difluoro-1,3-propanediol, and 2,2,3,3,4,4-hexafluoro-1,5-pentanediol. The auxiliary HBD is a sulfone compound, which is one of methanesulfonylmethane, dimethyl sulfoxide, and sulfolane. The mass ratio of main HBD to auxiliary HBD is 3:1-5:1; the mixing temperature is 40℃ and the reaction time is 30min.

[0014] Furthermore, in step 4, the alkali metal salt is one of LiTFSI, LiFSI, NaFSI, NaTFSI, KPF6, and KTFSI; The molar ratio of composite HBD, high-purity cyclothionium salt, and alkali metal salt is 1:(2-4):(0.1-0.3); During the stirring process in a dry three-necked flask, the protective environment is an inert gas, which is either argon or nitrogen. The stirring temperature is 40-60℃, and the stirring time is 1-2 hours.

[0015] Furthermore, in step 5, the vacuum drying temperature is 60°C until the moisture content in the mixed system drops below 50 ppm, resulting in a uniform and transparent functionalized deep eutectic electrolyte.

[0016] The beneficial effects of this invention are: 1. The cyclic structure of thionium cations improves electrolyte stability, far exceeding that of traditional chain thionium salts; the synergistic effect of thionium cations and fluorine-sulfonium composite HBDs broadens the electrochemical window, making them suitable for high-voltage cathode materials such as LiCoO2 and NCM811.

[0017] 2. This invention solves the key problem of poor low-temperature performance by synergistic regulation of low-viscosity composite HBD and hydroxyethyl modification.

[0018] 3. The interaction between cyclothionium cations and alkali metal anodes and high-voltage cathodes is mild, which can induce the formation of stable solid electrolyte interface (SEI) and cathode electrolyte interface (CEI).

[0019] 4. Microwave-assisted synthesis shortens reaction time, ion exchange using ionic liquid media avoids the use of organic solvents, the entire process generates no harmful waste, and the product has high purity, making it suitable for large-scale industrial production.

[0020] 5. This invention adjusts the type of alkali metal salt (Li + / Na + / K + It can be adapted to various electrochemical devices such as lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries, and has a wide range of applications.

[0021] 6. This invention establishes a three-in-one system of "cyclothionium cation structure modification - composite HBD synergy - green process optimization": 1) The cyclic structure of the cyclothionium cation and the modification with heteroatoms / hydroxyethyl groups not only enhance thermal stability and hydrogen bonding, but also achieve efficient alkali metal ion conduction through weak coordination regulation; 2) The low viscosity of the fluorinated polyol and the high stability of the sulfone compounds in the composite HBD system form a synergy, and the multiple interactions between the two and the cyclothionium cation ensure the stability of the system over a wide temperature range; 3) The combination of microwave-assisted synthesis and ion exchange in ionic liquid media achieves green and efficient process. Attached Figure Description

[0022] Figure 1 This is a schematic flowchart of a method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations; Figure 2 This is a comparison chart of the performance test results of the deep eutectic electrolyte and the traditional imidazole salt deep eutectic electrolyte in Example 1; Figure 3 This is a comparison chart of the performance test results of the deep eutectic electrolyte and the traditional imidazole salt deep eutectic electrolyte in Example 2; Figure 4 The graph shows a comparison of the performance test results of the deep eutectic electrolyte and the traditional imidazole salt deep eutectic electrolyte in Example 3. Detailed Implementation In this embodiment, HBD is a complex hydrogen bond donor. For example... Figure 1 As shown, the steps of the method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations according to this embodiment include: S1: Preparation of pale yellow, viscous cyclothionium halide; Using thioether derivatives and haloalcohols as raw materials, a cyclization reaction was carried out under either microwave-assisted or ultrasonic-assisted conditions. After the cyclization reaction was completed, unreacted raw materials were removed by vacuum distillation to obtain a pale yellow viscous cyclothionium halide.

[0023] Under microwave-assisted conditions, the power was set to 300-500 W, the reaction temperature to 80-100℃, and the cyclization reaction time to 2-4 h. Under ultrasound-assisted conditions, set the power to 200-300W, the temperature to 80-100℃, and the time to 3-5h. The thioether derivative is one of 2-hydroxyethyl ethyl thioether, 2-aminoethyl methyl thioether, or 3-methoxypropyl methyl thioether; the haloalcohol is one of 2-chloroethanol, 3-chloropropanol, or 3-bromopropanol.

[0024] S2: Add the lithium salt of the cyclothionium halide and the target weakly coordinating anion to an ionic liquid solvent to generate a high-purity cyclothionium salt. The cyclothionium halide and the lithium salt of the target weakly coordinating anion were added to an ionic liquid solvent at a molar ratio of 1:1.05-1:1.1. The ionic liquid solvent was either [EMIM]TFSI or [BMIM]FSI, and its mass was 3-5 times the total mass of the reactants. The reaction was carried out at 80°C for 2 hours with stirring to ensure sufficient exchange between the halide ions and the weakly coordinating anion. After stirring, the generated lithium halide precipitate was removed by filtration. The filtrate was then vacuum dried at 100°C for 12 hours to remove residual solvent, yielding high-purity cyclothionium salt.

[0025] Cyclothium salts are used as HBAs, with HBAs serving as hydrogen bond acceptors for functionalized cyclothium salts. The cations of cyclothium salts are one of the following: a five-membered structure containing an O heteroatom, a six-membered structure containing an O heteroatom, a five-membered structure containing an NH heteroatom, or a six-membered structure containing an NH heteroatom, and at least one cyclic substituent is hydroxyethyl. The anions of cyclothium salts are TFSI. - FSI - and BETI - One of them.

[0026] The general structural formula of the cation of cyclothionium salts is as follows: Five-membered ring: [S(R1)(R2)-CH2-CH2-X] + (X = O or NH, R1 and R2 are independently C1-C4 alkyl or hydroxyethyl) Hexa-membered ring: [S(R1)(R2)-CH2-CH2-CH2-X] + (X = O or NH, R1 and R2 are independently C1-C4 alkyl or hydroxyethyl) The HBA selected in this invention has the following advantages: (1) The cyclic molecular structure significantly enhances the rigidity of the cation, inhibits molecular thermal motion, and greatly improves thermal stability; (2) The heteroatoms (O / N) provide lone pairs of electrons, which can form strong hydrogen bond interactions with hydrogen bond donors, providing thermodynamic driving force for the formation of a stable deep eutectic system; (3) When R1 or R2 is hydroxyethyl (-CH2CH2OH), its hydroxyl group can form a weak coordination with alkali metal ions, which can provide a conduction site for alkali metal ions and avoid the problem of ion migration obstruction caused by strong coordination.

[0027] Anion matching: A weakly coordinating anion is selected as the balancing anion, specifically bis(trifluoromethanesulfonyl)imide (TFSI). - ), difluorosulfonyl imide (FSI) - ) or bis(perfluoroethanesulfonyl)imide (BETI -One of the following: The weakly coordinating anion can reduce the electrostatic interaction with the cyclothionium cation, thereby reducing the frictional resistance within the system and effectively lowering the electrolyte viscosity.

[0028] S3: Preparation of composite HBD; The main HBD and auxiliary HBD were mixed at a mass ratio of 3:1 to 5:1. This ratio range ensures that the composite HBD system has sufficient hydrogen bond donor sites while maintaining a low viscosity. The mixing temperature was set at 40℃ and the reaction time was 30 min to obtain the composite HBD.

[0029] The composite HBD adopts a master-auxiliary composite hydrogen bond donor design, which achieves multiple functions such as viscosity regulation, hydrogen bond enhancement and electrochemical window widening through component synergy.

[0030] Main HBD: A fluorinated polyol is selected, specifically one of 2,2,3,3-tetrafluoro-1,4-butanediol, 2,2-difluoro-1,3-propanediol, and 2,2,3,3,4,4-hexafluoro-1,5-pentanediol. In this embodiment, 2,2,3,3-tetrafluoro-1,4-butanediol is preferred. This component possesses both low viscosity and strong hydrogen bond donor capability. The fluorine atoms in its molecule can enhance compatibility with cyclothionium cations through electrostatic interactions, inhibiting phase separation. Simultaneously, the high electronegativity of the fluorinated groups can improve the system's antioxidant capacity.

[0031] Assisted HBD: A sulfone compound is selected, specifically one of methanesulfonylmethane, dimethyl sulfoxide, and sulfolane. In this embodiment, methanesulfonylmethane is preferred. The S=O group in its molecule can react with the S=O group of the cyclothionium cation. + The formation of synergistic electrostatic interactions further enhances the stability of the deep eutectic system; at the same time, the high oxidation stability of sulfone groups can effectively broaden the electrochemical window of the electrolyte.

[0032] S4: Add the composite HBD, high-purity cyclothionium salt and alkali metal salt to a dry three-necked flask and stir to obtain a mixed system; The appropriate alkali metal salt is selected based on the type of the target electrochemical device. In this embodiment, one of the following alkali metal salts is used: LiTFSI, LiFSI, NaFSI, NaTFSI, KPF6, and KTFSI. The amount of alkali metal salt added needs to be precisely controlled to balance the ion concentration and the system viscosity.

[0033] The molar ratio of composite HBD, high-purity cyclothionium salt and alkali metal salt is 1:(2-4):(0.1-0.3). During the stirring process in a dry three-necked flask, the protective environment is an inert gas, which is either argon or nitrogen. The stirring temperature is 40-60℃ and the stirring time is 1-2h.

[0034] S5: After stirring, the mixture is vacuum dried to obtain a uniform and transparent functionalized deep eutectic electrolyte.

[0035] After stirring, the system was placed in a vacuum drying oven and dried under vacuum at 60°C to remove residual trace amounts of moisture until the moisture content dropped to below 50 ppm, finally obtaining a uniform and transparent functionalized deep eutectic electrolyte.

[0036] In summary, this invention constructs a three-in-one system of "cyclothionium cation structure modification - composite HBD synergy - green process optimization": (1) The cyclic structure of the cyclothionium cation and the modification of heteroatoms / hydroxyethyl groups not only enhance thermal stability and hydrogen bonding, but also achieve efficient conduction of alkali metal ions through weak coordination regulation; (2) The low viscosity characteristics of fluorinated polyols and the high stability of sulfone compounds in the composite HBD system form a synergy, and the multiple interactions between the two and the cyclothionium cations ensure the stability of the system over a wide temperature range; (3) The combination of microwave-assisted synthesis and ion exchange in ionic liquid media achieves green and efficient process.

[0037] Example 1 The preparation of this embodiment uses the optimal combination, specifically selecting five-membered ring hydroxyethyl modification.

[0038] Step 1: Preparation of the five-membered ring [O-cyclothionium(CH2CH2OH)]Cl In a dry 100 mL microwave-safe reactor, 10.6 g (0.1 mol) of 2-hydroxyethyl ethyl sulfide and 8.0 g (0.1 mol) of 2-chloroethanol were added and stirred until homogeneous. The reactor was placed in a microwave reactor, and the power was set to 400 W, the temperature to 90 °C, and the reaction time to 3 h. After the reaction was completed, the product was transferred to a rotary evaporator and distilled under reduced pressure at 80 °C for 30 min to remove unreacted raw materials, yielding a pale yellow viscous liquid, which is the five-membered ring [O-cyclothionium(CH2CH2OH)]Cl.

[0039] Step 2: Preparation of the five-membered ring [O-cyclothionium(CH2CH2OH)]TFSI 14.8 g (0.08 mol) of the product from step one and 26.3 g (0.084 mol) of LiTFSI were added to 50 mL of [EMIM]TFSI solvent, and the mixture was stirred at 80 °C for 2 h. After the reaction was complete, the LiCl precipitate was removed by filtration, and the filtrate was transferred to a vacuum drying oven and dried under vacuum at 100 °C for 12 h to obtain a white solid, which is the five-membered ring [O-cyclothionium(CH2CH2OH)]TFSI.

[0040] Step 3: Preparation of deep eutectic electrolyte 1. Preparation of composite HBD: Weigh 14.4 g (0.08 mol) of 2,2,3,3-tetrafluoro-1,4-butanediol and 3.6 g (0.024 mol) of methanesulfonylmethane, stir and mix at 40℃ for 30 min to form composite HBD; 2. Mixing and compounding: 10.0 g (0.02 mol) of the product from step 2, 18.0 g (0.06 mol) of composite HBD and 1.17 g (0.004 mol) of LiTFSI were added to a 50 mL three-necked flask and stirred at 50 °C for 1.5 h under argon protection; 3. Purification treatment: Vacuum drying at 60℃ yields a homogeneous and transparent deep eutectic electrolyte.

[0041] Performance Testing: The performance of the assembled Li||NCM811 battery at 1 C rate was compared with that of a traditional imidazole salt deep eutectic electrolyte. The comparison results are as follows: Figure 2 As shown, it is particularly noteworthy that the battery assembly method containing the conventional imidazole salt deep eutectic electrolyte is the same as the assembly method of the Li||NCM811 battery in all embodiments. Figure 2 It can be seen that the cyclic structure and hydroxyethyl modification in this embodiment improve the high thermal stability of the electrolyte, and the composite HBD synergistically widens the voltage window, making the Li||NCM811 battery significantly better than the traditional system in terms of cycle performance at 1C rate. Example 2 In this embodiment, a six-membered cycloalkyl group was selected for modification.

[0042] Step 1: Preparation of the six-membered ring [O-cyclothionium(CH3)(CH3)]Br 10.4 g (0.1 mol) of 3-methoxypropyl methyl sulfide and 12.3 g (0.1 mol) of 3-bromopropanol were added to a microwave-safe reactor. The reactor was set at 500 W and 100 °C for 2.5 h. The product was then distilled under reduced pressure to obtain a pale yellow liquid.

[0043] Step 2: Preparation of six-membered ring [O-cyclothionium(CH3)(CH3)]TFSI 16.5 g (0.07 mol) of the product from step one and 22.5 g (0.0735 mol) of LiTFSI were added to 40 mL of [BMIM]FSI. The mixture was stirred at 80 °C for 2 h, filtered, and dried under vacuum to obtain a white solid.

[0044] Step 3: Preparation of deep eutectic electrolyte The composite HBD is 2,2,3,3-tetrafluoro-1,4-butanediol and methylsulfonylmethane (mass ratio 3:1), and the molar ratio of each component is six-membered ring thionium salt: composite HBD: LiTFSI = 1:2:0.1. The remaining steps are the same as in Example 1.

[0045] Performance Testing: The performance of the assembled Li||NCM811 battery at 1 C rate was compared with that of a traditional imidazole salt deep eutectic electrolyte. The comparison results are as follows: Figure 3 As shown. By Figure 3 As can be seen, although this embodiment does not have hydroxyethyl modification, the cyclic design still improves rigidity, and the composite HBD further reduces viscosity. Compared with traditional imidazole salt deep eutectic electrolytes, the battery capacity retention is better. Example 3 Step 1: Preparation of the five-membered ring [NH-cyclothionium(CH2CH2OH)]Cl 10.5 g (0.1 mol) of 2-aminoethyl ethyl sulfide and 8.0 g (0.1 mol) of 2-chloroethanol were added to a microwave reactor. The reactor was heated to 300 W and reacted at 80 °C for 4 h. After vacuum distillation, a pale yellow liquid was obtained.

[0046] Step 2: Preparation of five-membered ring [NH-cyclothionium(CH2CH2OH)]FSI 14.5 g (0.078 mol) of the product from step one and 21.5 g (0.082 mol) of LiFSI were added to 50 mL of [EMIM]TFSI. The mixture was stirred at 80 °C for 2 h, filtered, and dried under vacuum to obtain a white solid.

[0047] Step 3: Preparation of deep eutectic electrolyte The composite HBD is 2,2,3,3-tetrafluoro-1,4-butanediol and methylsulfonylmethane (mass ratio 5:1), and the molar ratio of each component is cyclothionium salt:composite HBD:LiFSI = 1:4:0.3. The remaining steps are the same as in Example 1.

[0048] Performance Testing: The performance of the assembled Li||NCM811 battery at 1 C rate was compared with that of a traditional imidazole salt deep eutectic electrolyte. The comparison results are as follows: Figure 4 As shown. By Figure 4 It can be seen that the synergistic effect of the heteroatom NH and the fluorinated polyol in this embodiment reduces the activation energy of the system and helps HBD improve its high-temperature antioxidant capacity. Compared with the traditional imidazole salt deep eutectic electrolyte, the ionic conductivity is significantly improved.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations, characterized in that, include: Step 1: Using thioether derivatives and haloalcohols as raw materials, a cyclization reaction is carried out to obtain a pale yellow viscous cyclothionium halide. Step 2: Add the cyclothionium halide and the lithium salt of the target weakly coordinated anion to the ionic liquid solvent and stir to react. After the reaction is completed, filter to remove the generated lithium halide precipitate, and vacuum dry the filtrate to obtain high-purity cyclothionium salt. Step 3: Mix the main HBD and auxiliary HBD at a preset mass ratio to obtain a composite HBD; The main HBD is a fluorinated polyol, which is one of 2,2,3,3-tetrafluoro-1,4-butanediol, 2,2-difluoro-1,3-propanediol and 2,2,3,3,4,4-hexafluoro-1,5-pentanediol; The auxiliary HBD is a sulfone compound, which is one of methanesulfonylmethane, dimethyl sulfoxide, and sulfolane. Step 4: Add the composite HBD, high-purity cyclothionium salt and alkali metal salt to a dry three-necked flask according to the preset molar ratio and stir to obtain a mixed system; Step 5: After stirring, the mixture is vacuum dried to obtain a uniform and transparent functionalized deep eutectic electrolyte.

2. The method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations according to claim 1, characterized in that, The thioether derivative in step 1 is one of 2-hydroxyethyl ethyl thioether, 2-aminoethyl methyl thioether, and 3-methoxypropyl methyl thioether; the haloalcohol is one of 2-chloroethanol, 3-chloropropanol, and 3-bromopropanol. The cyclization reaction was carried out under either microwave-assisted or ultrasound-assisted conditions; Under microwave-assisted conditions, the power was set to 300-500 W, the reaction temperature to 80-100℃, and the cyclization reaction time to 2-4 h. Under ultrasound-assisted conditions, set the power to 200-300W, the temperature to 80-100℃, and the time to 3-5h. After the cyclization reaction was completed, unreacted raw materials were removed by vacuum distillation to obtain a pale yellow, viscous cyclothionium halide.

3. The method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations according to claim 1, characterized in that, The cation of the cyclothionium salt is one of a five-membered structure containing an O heteroatom, a six-membered structure containing an O heteroatom, a five-membered structure containing an NH heteroatom, and a six-membered structure containing an NH heteroatom, and at least one cyclic substituent is hydroxyethyl; the anion is TFSI. - FSI - and BETI - One of them.

4. The method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations according to claim 3, characterized in that, The general structural formula of the cation of cyclothionium salts is: five-membered ring: [S(R1)(R2)-CH2-CH2-X] + And a six-membered ring: [S(R1)(R2)-CH2-CH2-CH2-X] + One of them, wherein X = O and NH, R1 and R2 are both C1-C4 alkyl and hydroxyethyl, and at least one of R1 and R2 is hydroxyethyl.

5. The method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations according to claim 1, characterized in that, In step 2, the molar ratio of the cyclothionium halide to the lithium salt of the target weakly coordinated anion is 1:1.05-1:1.1; The ionic liquid solvent is one of [EMIM]TFSI and [BMIM]FSI, and the mass of the ionic liquid solvent is 3-5 times the total mass of the reactants.

6. The method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations according to claim 1, characterized in that, In step 2, the temperature of the stirring reaction is 80℃ and the stirring time is 2h. Stirring allows the halide ions to fully exchange with the weakly coordinated anions. After stirring and reacting, the generated lithium halide precipitate was removed by filtration. The filtrate was then vacuum dried at 100°C for 12 hours to remove residual solvent, thus obtaining high-purity cyclothionium salt.

7. The method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations according to claim 1, characterized in that, In step 3: The mass ratio of main HBD to auxiliary HBD is 3:1-5:1; the mixing temperature is 40℃ and the reaction time is 30 min.

8. The method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations according to claim 1, characterized in that, In step 4, the alkali metal salt is one of LiTFSI, LiFSI, NaFSI, NaTFSI, KPF6, and KTFSI. The molar ratio of composite HBD, high-purity cyclothionium salt, and alkali metal salt is 1:(2-4):(0.1-0.3); During the stirring process in a dry three-necked flask, the protective environment is an inert gas, which is either argon or nitrogen. The stirring temperature is 40-60℃, and the stirring time is 1-2 hours.

9. The method for preparing a wide-temperature-range deep eutectic electrolyte containing cyclic thionium cations according to claim 1, characterized in that, Step 5 involves vacuum drying at 60°C until the moisture content in the mixed system drops below 50 ppm, yielding a uniform and transparent functionalized deep eutectic electrolyte.

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