Preparation method of composite organic solvent, electrolyte and lithium-sulfur battery

Abstract

The application provides a preparation method of a composite organic solvent, an electrolyte and a lithium-sulfur battery. An aromatic hydrocarbon ether compound A or a nitro aromatic ether compound with 1-3 halogen positions on a ring of the A is mixed with an imidazole ionic liquid B, and then is compounded with 1,4-dioxane or 1,3-cyclopentene to obtain a composite organic solvent. The composite organic solvent has a sulfur-repelling function, can effectively inhibit excessive dissolution of polysulfides, reduce the loss of sulfur active substances, and further contains a small amount of polysulfide capturing solid sulfur ionic liquid. When the composite organic solvent is used to prepare an electrolyte of a lithium-sulfur battery, the dissolution of polysulfides is effectively inhibited, the "shuttle effect" is reduced, the loss of polysulfides is reduced, the appropriate dissolution ratio of polysulfides in the electrolyte is ensured, the generation of an SEI passivation film on a negative electrode diaphragm is facilitated, the growth of lithium dendrites is prevented, and the purpose of greatly improving the cycle performance of the lithium-sulfur battery is achieved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery material technology, specifically relating to a method for preparing a composite organic solvent that can suppress the polysulfide shuttle effect, a lithium-sulfur battery electrolyte prepared using the composite organic solvent, and a lithium-sulfur battery prepared using the lithium-sulfur battery electrolyte. Background Technology

[0002] Lithium-ion batteries have been widely used in daily life; however, their energy density is still insufficient to meet the needs of many applications. Lithium-sulfur batteries, with their very high theoretical specific capacity (1672 mAh / g) and theoretical energy density (2570 Wh / kg), coupled with the low price and abundant reserves of sulfur, have become a key research focus for next-generation lithium-ion rechargeable batteries. Lithium-sulfur batteries, as a high-capacity alternative to lithium-ion batteries, have been extensively studied. The electrochemical reaction of sulfur involves several intermediates, among which lithium polysulfides (Li₂Sn, 4≤n≤8) are soluble in the electrolyte and exhibit a "shuttle effect," which directly leads to a decrease in battery cycle life. Therefore, suppressing the shuttle effect of polysulfides is particularly important.

[0003] To address the capacity decay problem in lithium-sulfur batteries, researchers have proposed numerous strategies related to the positive electrode, negative electrode, and electrolyte. For optimizing the positive electrode, the chemical adsorption of polysulfide ions by polar metal compounds (oxides, sulfides, nitrides, etc.) suppresses shuttle behavior, thereby slowing down capacity decay. Alternatively, sulfur can be composited with various conductive porous carbons, filling the high specific surface area carbon pores to ensure sufficient contact between the conductive phase and insulating sulfur, promoting charge transfer. For the negative electrode, developing novel two-dimensional and three-dimensional lithium metal negative electrodes increases the specific surface area and accelerates charge transfer. Regarding the electrolyte, adding functional additives promotes the construction of a denser and more stable SEI film on the negative electrode, preventing the loss of active material due to reactions between the electrolyte, polysulfides, and lithium metal. While these strategies can suppress the shuttle effect to some extent, improving battery cycle stability remains a challenge.

[0004] If the composition of the electrolyte solvent can be modified to mitigate the dissolution of polysulfides, reduce lithium metal corrosion, and significantly improve the cycle stability and coulombic efficiency of lithium-sulfur batteries, it would be a simple, economical, and effective method. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing a composite organic solvent, an electrolyte, and a lithium-sulfur battery. The prepared composite organic solvent contains both "sulfur-repellent" functionalized aromatic hydrocarbon ethers that repel polysulfides, effectively inhibiting excessive dissolution of polysulfides and reducing the loss of sulfur active materials, and a sulfur-fixing ionic liquid that captures a small amount of polysulfides, promoting the formation of the SEI passivation film on the negative electrode of the lithium-sulfur battery. When this composite organic solvent is used to prepare the electrolyte for the lithium-sulfur battery, it effectively inhibits the dissolution of polysulfides, reduces the "shuttle effect," and minimizes the loss of polysulfides, while ensuring an appropriate dissolution ratio of polysulfide compounds in the electrolyte. During the preparation of the lithium-sulfur battery, this facilitates the formation of the SEI passivation film on the negative electrode separator, prevents the growth of lithium dendrites, and significantly improves the cycle performance of the lithium-sulfur battery.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing a multifunctional composite organic solvent, the method comprising the following steps: Step 1: Preparation of aromatic hydrocarbon ether compound A (11) Benzyloxy alkyl halide and sodium sulfonate, sodium bis(trifluorosulfonate) sulfonate, etc. are heated in an organic solvent to carry out ion exchange reaction to prepare benzyloxy compound A1 with sulfonic acid group substitution in the side chain; (12) The prepared benzyloxy compound A1 was mixed with lithium-sulfur battery electrolyte solvents such as 1,4-dioxane and 1,3-epoxypentane at a mass ratio of 1:3-1:10 to prepare aromatic hydrocarbon ether compound A; In particular, aromatic hydrocarbon ether compound A is not limited to the benzyloxy compound A1 with sulfonic acid group substitution in the side chain prepared above. Aromatic hydrocarbon compounds including those with nitro group in the side chain with strong electron-withdrawing group can also be used to prepare aromatic hydrocarbon ether compound A by directly mixing such aromatic hydrocarbon compounds with 1,4-dioxane or 1,3-epoxypentane solvent. The benzyloxyhaloalkane is one or a mixture of several benzyl halides such as 2-benzyloxybromoethane, 2-bromo-5-methoxybenzyl bromide, 3-benzyloxybromopropane, benzyl 6-bromohexane, and 2-bromo-5-methoxybenzyl bromide; The sulfonate is one or a mixture of several of the sulfonates with strong electron-withdrawing properties, such as lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonylimide), sodium 2-bromoethylsulfonate, sodium vinylsulfonate, and sodium allylsulfonate. The organic solvent for the ion exchange reaction is one or a mixture of several of the following: acetonitrile, tetrahydrofuran, dichloromethane, carbon disulfide, ethyl acetate, methanol, and ethanol. The heating reaction temperature is 25-100℃, and the reaction time is 6-24 hours; The aromatic hydrocarbon compound with a side chain containing a strongly electron-withdrawing nitro group that is directly mixed with 1,4-dioxane and 1,3-epoxypentane is a 2-nitrophenyl alkyl ether (the number of alkane carbon atoms is 1-8), such as 2-nitroanisole, 2-nitrophenethyl ether, and 2-nitrophenyloctyl ether. The aromatic hydrocarbon ether compound A can also be a nitro aromatic ether compound in which hydrogen at 1-3 positions on the aromatic ring is replaced by halogen, such as 2-fluoro-5-nitrobenzene, 2-iodo-4-nitrobenzene, 2,6-difluoro-4-nitrobenzene, and 2-nitro-3,4,5-trifluoroanisole. Step 2: Preparation of imidazole ionic liquid B (21) First, amino-type imidazoles and bromoalkanes are reacted in an organic solvent under a nitrogen atmosphere in the dark. The reaction temperature is room temperature 25-100℃. The reaction synthesizes an intermediate imidazole halide salt with a halogen group on the side chain. (22) Then, in an organic solvent with a mass percentage of 20% to 60%, the intermediate imidazole halide salt is replaced with sodium thiocyanate to form an imidazole ionic liquid B containing amino and thiol groups. The number of amino substituents on the amino-type imidazole ring is n=1-3, such as one or more of 2-aminoimidazolium, 1,4-diaminoimidazolium, 2,4-diaminoimidazolium, 4,5-diaminoimidazolium, and 2,4,5-triaminoimidazolium. The bromoalkanes are aliphatic monohaloalkanes with 2-10 carbon atoms; The organic solvent mentioned in steps (21) and (22) is one or a mixture of several of the following: acetonitrile, tetrahydrofuran, dichloromethane, carbon disulfide, ethyl acetate, methanol, and ethanol. Step 3: Preparation of multifunctional organic composite solvent C Aromatic hydrocarbon ether compound A and imidazole ionic liquid B are mixed in a mass ratio of 1:1 to 1:5, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B as active substances accounts for 10-80% of the mass ratio of the composite organic solvent, preferably 20-50%.

[0007] This invention provides a lithium-sulfur battery electrolyte, which is prepared by mixing the composite organic solvent prepared above with conventional lithium salts for lithium-sulfur batteries.

[0008] The present invention provides a lithium-sulfur battery comprising the lithium-sulfur battery electrolyte.

[0009] Furthermore, the lithium-sulfur battery is a lithium-sulfur coin cell containing the electrolyte.

[0010] Furthermore, the lithium-sulfur coin cell battery is composed of a positive electrode, a negative electrode, a separator, and a liquid electrolyte, wherein the liquid electrolyte is a lithium-sulfur battery electrolyte prepared by the composite organic solvent.

[0011] The beneficial effects of this invention are as follows: 1. This invention provides a functionalized aromatic hydrocarbon ether compound A. Due to the principle of like charge repulsion of sulfonates in polysulfides and the steric hindrance of the aromatic ring, the anionic sulfonic acid utilizes the electron-withdrawing group to repel the charged sulfonates in polysulfides and the steric hindrance of the aromatic skeleton structure to inhibit the dissolution of polysulfides in the electrolyte, reduce the loss of active sulfides, and ensure the full utilization of the capacity of lithium-sulfur batteries. 2. This invention provides an imidazole ionic liquid B with amino and thiol groups in the side chain. It has a lower viscosity than traditional ionic liquids, which is beneficial for ion transport in the electrolyte. The amino group in the side chain can interact with the sulfide anions in the polysulfide in a "hydrogen bond"-like manner. The strong chemical bond between the amino group and the sulfide group plays a "sulfur fixation" role, reducing the precipitation of polysulfides at the negative electrode. This ensures that there is an appropriate proportion of polysulfides dissolved in the electrolyte, which is beneficial for the growth of the SEI passivation film on the negative electrode.

[0012] 3. This invention combines sulfur-repellent aromatic hydrocarbon ether compound A with sulfur-fixing ionic liquid B, and mixes them in a certain proportion in 1,4-dioxane or 1,3-epoxypentane solvent to form a multifunctional organic composite solvent C. This ensures the dissolution balance of polysulfides in the electrolyte. This composite solvent is used to prepare lithium-sulfur battery electrolytes, which effectively inhibits the dissolution of polysulfides, reduces the "shuttle effect", and reduces the loss of polysulfides. It also ensures an appropriate dissolution ratio of polysulfide compounds in the electrolyte. When preparing lithium-sulfur batteries, it is beneficial to the formation of SEI passivation film on the negative electrode separator, prevents the growth of lithium dendrites, and achieves the goal of significantly improving the cycle performance of lithium-sulfur batteries. Attached Figure Description

[0013] Figure 1 This is a flowchart illustrating the synthetic process of multifunctional aromatic hydrocarbon ether compound A in this invention.

[0014] Figure 2 This is a flowchart illustrating the synthesis process of aminoimidazolium ionic liquid B in this invention.

[0015] Figure 3 The diagram shows the cycle life of Examples 1, 8 and Comparative Example 2 in this invention. Detailed Implementation

[0016] The following embodiments are intended to further illustrate the content of the present invention, but the scope of protection of the claims of the present invention is not limited by the embodiments.

[0017] Example 1 The composite organic solvent was prepared using the following method: Step 1: Preparation of aromatic hydrocarbon ether compound A (11) 2-Benzyloxybromoethane and lithium trifluoromethylsulfonate are heated in tetrahydrofuran at a temperature of 70-90°C for 6-10 hours to carry out an ion exchange reaction to prepare benzyloxy compound A1 with sulfonic acid group substitution in the side chain. (12) The prepared benzyloxy compound A1 is mixed with 1,4-epoxyhexacyclohexane or 1,3-epoxypentane solvent at a mass ratio of 1:3 to prepare aromatic hydrocarbon ether compound A.

[0018] Step 2: Preparation of imidazole ionic liquid B (21) First, 2-aminoimidazole and bromoethane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 25~60℃ to synthesize the intermediate imidazole bromide with a side chain group. (22) Then, in an acetonitrile organic solvent of 20% by mass, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid containing amino and thiol groups, namely imidazole ionic liquid B.

[0019] Step 3: Preparation of multifunctional organic composite solvent C The aromatic hydrocarbon ether compound A obtained in the first step and the imidazole ionic liquid B obtained in the second step are mixed at a mass ratio of 1:2, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B as active substances accounts for 20% of the mass ratio of the composite organic solvent.

[0020] Example 2 The following method was used to prepare a composite organic solvent for lithium-sulfur batteries: Step 1: Preparation of aromatic hydrocarbon ether compound A (11) 2-bromo-5-methoxybenzyl bromide and lithium trifluoromethylsulfonate are heated in tetrahydrofuran at a temperature of 25-70°C for 8-12 hours to carry out an ion exchange reaction to prepare benzyloxy compound A1 with sulfonic acid group substitution in the side chain. (12) The prepared benzyloxy compound A1 is mixed with 1,4-epoxyhexacyclohexane or 1,3-epoxypentane commonly used lithium-sulfur electrolyte solvent at a mass ratio of 1:5 to prepare aromatic hydrocarbon ether compound A.

[0021] Step 2: Preparation of imidazole ionic liquid B (21) First, 2-aminoimidazolium and bromobutane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 25-80℃ to synthesize the intermediate imidazolium bromide with a side chain group. (22) Then, in an organic solvent of acetonitrile with a mass percentage of 25%, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid containing amino and thiol groups, namely imidazole ionic liquid B.

[0022] Step 3: Preparation of multifunctional organic composite solvent C The aromatic hydrocarbon ether compound A obtained in the first step and the imidazole ionic liquid B obtained in the second step are mixed at a mass ratio of 1:2, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B as active substances accounts for 25% of the mass ratio of the composite organic solvent.

[0023] Example 3 The following method was used to prepare a composite organic solvent for lithium-sulfur batteries: Step 1: Preparation of aromatic hydrocarbon ether compound A (11) 2-Bromo-5-methoxybenzyl bromide and sodium 2-bromoethylsulfonate were heated in tetrahydrofuran at a temperature of 25-80°C for 6-10 hours to carry out an ion exchange reaction to prepare benzyloxy compound A1 with sulfonic acid group substitution in the side chain. (12) The prepared benzyloxy compound A1 is mixed with 1,4-epoxyhexacyclohexane or 1,3-epoxypentane in a common lithium-sulfur electrolyte solvent at a mass ratio of 1:3 to prepare aromatic hydrocarbon ether compound A.

[0024] Step 2: Preparation of imidazole ionic liquid B (21) First, 2,4-diaminoimidazolium and bromopentane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 25-80℃ to synthesize the intermediate imidazolium bromide with a side chain group. (22) Then, in a 30% by mass tetrahydrofuran organic solvent, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid containing amino and thiol groups, namely imidazole ionic liquid B.

[0025] Step 3: Preparation of multifunctional organic composite solvent C Aromatic hydrocarbon ether compound A and imidazole ionic liquid B are mixed at a mass ratio of 1:3, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B, which are active substances, accounts for 30% of the mass of the composite organic solvent.

[0026] Example 4 The following method was used to prepare a composite organic solvent for lithium-sulfur batteries: Step 1: Preparation of aromatic hydrocarbon ether compound A (11) 3-Benzyloxybromopropane and sodium 2-bromoethylsulfonate are heated in tetrahydrofuran at a temperature of 60-90°C for 12-15 hours to carry out an ion exchange reaction to prepare benzyloxy compound A1 with sulfonic acid group substitution in the side chain. (12) The prepared benzyloxy compound A1 is mixed with 1,4-epoxyhexacyclohexane or 1,3-epoxypentane in a common lithium-sulfur electrolyte solvent at a mass ratio of 1:6 to prepare aromatic hydrocarbon ether compound A.

[0027] Step 2: Preparation of imidazole ionic liquid B (21) First, 2,4-diaminoimidazolium and bromopentane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 30-70℃ to synthesize the intermediate imidazolium bromide with a side chain group. (22) Then, in a tetrahydrofuran organic solvent of 25% by mass, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid containing amino and thiol groups, namely imidazole ionic liquid B.

[0028] Step 3: Preparation of multifunctional organic composite solvent C Aromatic hydrocarbon ether compound A and imidazole ionic liquid B are mixed at a mass ratio of 1:3, and then compounded with solvent 1,4-dioxane or 1,3-epoxypentane. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B as active substances accounts for 50% of the mass ratio of the compound organic solvent.

[0029] Example 5 The following method was used to prepare a composite organic solvent for lithium-sulfur batteries: Step 1: Preparation of aromatic hydrocarbon ether compound A (11) 3-Benzyloxybromopropane and sodium vinylsulfonate are heated in tetrahydrofuran at a temperature of 60-90°C for 6-10 hours to carry out an ion exchange reaction to prepare benzyloxy compound A1 with sulfonic acid group substitution in the side chain. (12) The prepared benzyloxy compound A1 is mixed with 1,4-epoxyhexacyclohexane or 1,3-epoxypentane in a common lithium-sulfur electrolyte solvent at a mass ratio of 1:6 to prepare aromatic hydrocarbon ether compound A.

[0030] Step 2: Preparation of imidazole ionic liquid B (21) First, 2,4-diaminoimidazolium and bromohexane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 30-85℃ to synthesize the intermediate imidazolium bromide with a side chain group. (22) Then, in a tetrahydrofuran organic solvent of 40% by mass, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid containing amino and thiol groups, namely imidazole ionic liquid B.

[0031] Step 3: Preparation of multifunctional organic composite solvent C Aromatic hydrocarbon ether compound A and imidazole ionic liquid B are mixed at a mass ratio of 1:4, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B, which are active substances, accounts for 60% of the mass of the composite organic solvent.

[0032] Example 6 The following method was used to prepare a composite organic solvent for lithium-sulfur batteries: Step 1: Preparation of aromatic hydrocarbon ether compound A (11) Benzyl 6-bromohexane and sodium allyl sulfonate are heated in tetrahydrofuran at a temperature of 30-90°C for 6-10 hours to carry out an ion exchange reaction to prepare benzyloxy compound A1 with sulfonic acid group substitution in the side chain. (12) The prepared benzyloxy compound A1 is mixed with 1,4-epoxyhexacyclohexane or 1,3-epoxypentane in a common lithium-sulfur electrolyte solvent at a mass ratio of 1:7 to prepare aromatic hydrocarbon ether compound A.

[0033] Step 2: Preparation of imidazole ionic liquid B (21) First, 2,4,5-triaminoimidazolium and bromohexane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 30-80℃ to synthesize the intermediate imidazolium bromide with a side chain group. (22) Then, in a 30% by mass tetrahydrofuran organic solvent, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid containing amino and thiol groups, namely imidazole ionic liquid B.

[0034] Step 3: Preparation of multifunctional organic composite solvent C Aromatic hydrocarbon ether compound A and imidazole ionic liquid B are mixed at a mass ratio of 1:5, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B, which are active substances, accounts for 60% of the mass of the composite organic solvent.

[0035] Example 7 The following method was used to prepare a composite organic solvent for lithium-sulfur batteries: Step 1: Preparation of aromatic hydrocarbon ether compound A (11) 2-bromo-5-methoxybenzyl bromide and sodium allyl sulfonate were heated in tetrahydrofuran at a temperature of 30-70°C for 6-10 hours to carry out an ion exchange reaction to prepare benzyloxy compound A1 with sulfonic acid group substitution in the side chain. (12) The prepared benzyloxy compound A1 is mixed with 1,4-epoxyhexacyclohexane or 1,3-epoxypentane commonly used lithium-sulfur electrolyte solvent at a mass ratio of 1:8 to prepare aromatic hydrocarbon ether compound A.

[0036] Step 2: Preparation of imidazole ionic liquid B (21) First, 2,4,5-triaminoimidazole and bromooctane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 50°C to synthesize the intermediate imidazole bromide with a side chain group. (22) Then, in a 40% by mass dichloromethane organic solvent, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid B containing amino and thiol groups.

[0037] Step 3: Preparation of multifunctional organic composite solvent C Aromatic hydrocarbon ether compound A and imidazole ionic liquid B are mixed at a mass ratio of 1:2, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B, which are active substances, accounts for 70% of the mass of the composite organic solvent.

[0038] Example 8 The following method was used to prepare a composite organic solvent for lithium-sulfur batteries: Step 1: Selection of Aromatic Hydrocarbon Ether Compound A 2-fluoro-5-nitroanisole, a benzene ring compound with halogenated side chains and a strong electron-withdrawing nitro group, was selected as the multifunctional aromatic hydrocarbon ether compound A. Step 2: Preparation of imidazole ionic liquid B (21) First, 2,4,5-triaminoimidazole and bromooctane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 30-80℃ to synthesize the intermediate imidazole bromide with a side chain group. (22) Then, in a 30% dichloromethane organic solvent, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid containing amino and thiol groups, namely imidazole ionic liquid B.

[0039] Step 3: Preparation of multifunctional organic composite solvent C 2-Fluoro-5-nitrobenzyl ether and imidazole ionic liquid B are mixed at a mass ratio of 1:4, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B as active substances accounts for 80% of the mass ratio of the composite organic solvent.

[0040] Example 9 The following method was used to prepare a composite organic solvent for lithium-sulfur batteries: Step 1: Selection of Aromatic Hydrocarbon Ether Compound A 2,6-difluoro-4-nitroanisole, a benzene ring compound with halogenated side chains and a strong electron-withdrawing nitro group, was selected as aromatic hydrocarbon ether compound A.

[0041] Step 2: Preparation of imidazole ionic liquid B (21) First, 2,4-diaminoimidazole and bromooctane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 30-70℃ to synthesize the intermediate imidazole bromide with a side chain group. (22) Then, in a 30% dichloromethane organic solvent, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid containing amino and thiol groups, namely imidazole ionic liquid B.

[0042] Step 3: Preparation of multifunctional organic composite solvent C 2-Fluoro-5-nitrobenzyl ether and imidazole ionic liquid B are mixed at a mass ratio of 1:5, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B as active substances accounts for 50% of the mass ratio of the composite organic solvent.

[0043] Example 10 The following method was used to prepare a composite organic solvent for lithium-sulfur batteries: Step 1: Selection of Aromatic Hydrocarbon Ether Compound A 2-Nitro-3,4,5-trifluoroanisole, a benzene ring compound with halogenated side chains and a strong electron-withdrawing nitro group, was selected as aromatic hydrocarbon ether compound A.

[0044] Step 2: Preparation of imidazole ionic liquid B (21) First, 2,4-diaminoimidazole and bromooctane were reacted in the organic solvent acetonitrile under a nitrogen atmosphere in the dark at a reaction temperature of 25-60℃ to synthesize the intermediate imidazole bromide with a side chain group. (22) Then, in a 25% by mass dichloromethane organic solvent, the intermediate imidazole bromide salt is added to replace sodium thiocyanate to form a functionalized ionic liquid B containing amino and thiol groups.

[0045] Step 3: Preparation of multifunctional organic composite solvent C 2-Fluoro-5-nitrobenzyl ether and imidazole ionic liquid B are mixed at a mass ratio of 1:3, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B as active substances accounts for 40% of the mass ratio of the composite organic solvent.

[0046] Example 11 In conclusion, Figure 1 The synthesis process for aromatic hydrocarbon ether compound A, Figure 2 The synthesis process of aminoimidazolium ionic liquid B involves mixing the composite organic solvent prepared in any of Examples 1-10 with a conventional lithium salt for lithium-sulfur batteries to prepare a lithium-sulfur battery electrolyte.

[0047] Furthermore, a lithium-sulfur battery was prepared using this lithium-sulfur battery electrolyte.

[0048] Specifically, a lithium-sulfur button cell battery can be prepared, which consists of a positive electrode, a negative electrode, a separator, and a liquid electrolyte, the liquid electrolyte being the lithium-sulfur battery electrolyte.

[0049] Comparative Example 1 Compared to Example 1, the lithium-sulfur battery electrolyte did not contain the aromatic hydrocarbon ether compound A and imidazole ionic liquid B. The electrolyte in this comparative example is a lithium-sulfur battery electrolyte prepared by dissolving lithium salt in 1,3-epoxypentane.

[0050] Comparative Example 2 Compared with Example 1, the only difference is that the aromatic hydrocarbon ether compound A with the sulfur-inhibiting mechanism prepared in step one was not added to the lithium-sulfur battery electrolyte; all other steps are the same as in Example 1.

[0051] Comparative Example 3 Compared with Example 1, the only difference is that the aminoimidazolium-based ionic liquid with the sulfur fixation mechanism synthesized in step two was not added to the lithium-sulfur battery electrolyte; all other steps are the same as in Example 1.

[0052] All examples and comparative examples were prepared into CR2032 button batteries. The lithium-sulfur button batteries consist of a positive electrode, a negative electrode, a separator, and a liquid electrolyte. The electrolyte is the lithium-sulfur battery electrolyte prepared using the multifunctional composite organic solvent described in this invention. After assembly, the batteries were charged and discharged at a current density of 0.5 C, and their electrical performance data are summarized in Table 1.

[0053] Table 1. Comparison of charge-discharge coulombic efficiency and cycle performance data of the example and comparative batteries at 0.5C. like Figure 3 The figure shows a comparison of the cycle performance of lithium-sulfur batteries from Examples 1, 8, and 2 at a rate of 0.5 C.

[0054] In summary, the data shows that the electrolyte prepared by adding the multifunctional composite organic solvent described in this invention can effectively improve the capacity and cycle stability of lithium-sulfur batteries. Compared with the comparative examples, the addition of functionalized aromatic ether compounds with sulfur-inhibiting mechanisms and amino-based imidazole ionic liquids with sulfur-fixing mechanisms can effectively balance the dissolution of polysulfides and their precipitation at the negative electrode, mitigate the shuttle effect, and reduce the loss of active sulfur. For example, after 100 stable cycles, the battery in Example 8 still maintains a discharge specific capacity of 987 mAh / g, corresponding to a capacity retention rate of 94.3% for the first discharge cycle; while the capacity retention rate of electrolytes without or with only one functional compound is lower. After 100 cycles, the capacity of the battery in Comparative Example 1 decreased from 1045 mAh / g to 762 mAh / g, with a capacity retention rate of 74.9%.

Claims

1. A method for preparing a composite organic solvent, characterized in that, Includes the following steps: Aromatic hydrocarbon ether compound A or a nitro aromatic ether compound with 1-3 halogenated positions on the aromatic ring of A is mixed with imidazole ionic liquid B at a mass ratio of 1:1 to 1:10, and then mixed with solvent 1,4-dioxane or 1,3-epoxypentane to obtain a composite organic solvent. The mass fraction of aromatic hydrocarbon compound A and imidazole ionic liquid B as active substances accounts for 10-80% of the mass ratio of the composite organic solvent. The preparation of aromatic hydrocarbon ether compound A is as follows: aromatic hydrocarbon ether compound A is prepared by mixing benzyloxy compound A1 or an aromatic hydrocarbon compound with a strongly electron-withdrawing nitro group in the side chain with a solvent of 1,4-dioxane or 1,3-epoxypentane. The preparation of imidazole ionic liquid B is as follows: First, amino imidazole and bromoalkanes are reacted in an organic solvent under a nitrogen atmosphere in the dark at a temperature of 25-100°C to synthesize an intermediate imidazole halide salt with a halogen group on the side chain; then, in an organic solvent with a mass percentage of 20%-60%, the intermediate imidazole halide salt is replaced with sodium thiocyanate to form imidazole ionic liquid B containing amino and mercapto groups.

2. The method for preparing the composite organic solvent as described in claim 1, characterized in that, The preparation process of the aromatic hydrocarbon ether compound A is as follows: (1) Benzyloxy alkyl halide and sulfonate are heated in an organic solvent to carry out an ion exchange reaction to prepare benzyloxy compound A1 with sulfonic acid group substitution in the side chain; the heating reaction temperature is 40-100℃ and the reaction time is 6-24 hours. (2) The prepared benzyloxy compound A1 is mixed with 1,4-dioxane or 1,3-epoxypentane solvent at a mass ratio of 1:5-1:10 to prepare aromatic hydrocarbon ether compound A.

3. The preparation method according to claim 2, characterized in that: The benzyloxyhaloalkane is one or a mixture of several of the following: 2-benzyloxybromoethane, 2-bromo-5-methoxybenzyl bromide, 3-benzyloxybromopropane, benzyl 6-bromohexane, and 2-bromo-5-methoxybenzyl bromide.

4. The preparation method according to claim 2, characterized in that: The sulfonate is one or a mixture of several of lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonylimide), sodium 2-bromoethylsulfonate, sodium vinylsulfonate, and sodium allylsulfonate.

5. The preparation method according to claim 2, characterized in that: The organic solvent for the ion exchange reaction is one or a mixture of several of the following: acetonitrile, tetrahydrofuran, dichloromethane, carbon disulfide, ethyl acetate, methanol, and ethanol.

6. The preparation method according to claim 1, characterized in that: Aromatic hydrocarbon ether compound A is prepared by mixing an aromatic hydrocarbon compound with a strongly electron-withdrawing nitro group in its side chain with a solvent of 1,4-dioxane or 1,3-epoxypentane; the aromatic ether compound with a strongly electron-withdrawing nitro group in its side chain is a 2-nitrobenzene alkyl ether, wherein the number of alkane carbon atoms is 1-8.

7. The method for preparing the composite organic solvent according to claim 1, characterized in that: The nitro aryl ether compound corresponding to A has 1-3 halogenated positions on its aromatic ring, such as 2-fluoro-5-nitrobenzene, 2-iodo-4-nitrobenzene, 2,6-difluoro-4-nitrobenzene, 2-nitro-3, or 4,5-trifluoroanisole.

8. The method for preparing the composite organic solvent according to claim 1, characterized in that: In the preparation of imidazole ionic liquid B, the number of amino substituents on the amino imidazole ring is n=1-3.

9. The method for preparing the composite organic solvent according to claim 1, characterized in that: The amino-based imidazole is one or more of 2-aminoimidazole, 1,4-diaminoimidazole, 2,4-diaminoimidazole, 4,5-diaminoimidazole, and 2,4,5-triaminoimidazole.

10. The method for preparing the composite organic solvent according to claim 1, characterized in that: In the preparation of imidazole ionic liquid B, the bromoalkane is an aliphatic monohaloalkane with 2-10 carbon atoms.

11. The preparation method according to claim 1, characterized in that: The organic solvent used in the preparation of the imidazole ionic liquid B is one or a mixture of several of the following: acetonitrile, tetrahydrofuran, dichloromethane, carbon disulfide, ethyl acetate, methanol, and ethanol.

12. The method for preparing the composite organic solvent according to claim 1, characterized in that: In the composite organic solvent, the mass fraction of the active substance accounts for 20-50% of the mass of the composite organic solvent.

13. A lithium-sulfur battery electrolyte, characterized in that, It is a lithium-sulfur battery electrolyte prepared by mixing the composite organic solvent prepared according to any one of claims 1-12 with the lithium salt of lithium-sulfur batteries.

14. A lithium-sulfur battery, characterized in that, It is a lithium-sulfur battery containing the lithium-sulfur battery electrolyte of claim 13.

15. The lithium-sulfur battery according to claim 14, characterized in that: The lithium-sulfur battery is a lithium-sulfur button cell battery, which consists of a positive electrode, a negative electrode, a separator, and a liquid electrolyte. The liquid electrolyte is a lithium-sulfur battery electrolyte prepared by the composite organic solvent obtained according to any one of claims 1-12.

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