Synthesis method of mannitol carbonate sulfate

Abstract

The invention discloses a synthesis method of mannitol carbonate sulfate, and belongs to the technical field of organic synthesis. The synthesis method provided by the invention comprises the following steps: reacting 1, 3, 4, 6-tetrachloro-2, 5-hexanediol with chlorosulfonic acid in the presence of an acid-binding agent to obtain an intermediate solution as shown in a formula (II); formula (II); and mixing the intermediate solution as shown in the formula (II) with anhydrous carbonate, heating to a first set temperature for reaction, and then heating to a second set temperature for reaction in the presence of a phase transfer catalyst to obtain the mannitol carbonic sulfate. The whole process route is short, the yield is high, and the total yield of two steps reaches 88% or above; meanwhile, few by-products are generated, the purification difficulty is low, the reaction time is short, few hazardous wastes are generated, operation is easy and convenient, and industrial large-scale production is facilitated.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a method for synthesizing mannitol sulfate carbonate. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Lithium-ion batteries, with their significant advantages such as no memory effect, long cycle life, and high energy density, have become the preferred energy storage solution for electric vehicles and other fields. As a key component of lithium-ion batteries, the performance of the electrolyte directly affects the battery's capacity, cycle stability, rate capability, and safety. The introduction of functional additives is currently one of the important ways to efficiently improve the overall performance of batteries. Among many organic sulfonate additives, cyclic sulfonates, due to the strong electronegativity of the central sulfur atom, are more easily reduced at the negative electrode interface to form a stable SEI film compared to cyclic carbonates. This effectively reduces charge transfer impedance, improves cycle performance, and inhibits battery gas buildup and the increase in DC internal resistance (DCR) during high-temperature cycling.

[0004] Mannitol sulfate carbonate, as a promising class of cyclic sulfonate additives, contains both sulfate and carbonate functional groups in its molecular structure. Specifically, the sulfur atom in the sulfate group is bonded to a highly electronegative oxygen atom, giving the sulfate oxygen a significant negative electrostatic potential. This allows it to attract Li through electrostatic attraction. + They combine with or form coordination bonds with polysulfides; the carbonyl oxygen and ester oxygen of the carbonate group also exhibit a negative electrostatic potential and can participate in Li + Solvation or SEI film formation. This unique structure allows it to form a composite SEI layer rich in inorganic salts (such as Li2SO4, Li2CO3) and organic sulfate esters after reduction and decomposition at the negative electrode interface. This helps to enhance the interfacial mechanical stability and ionic conductivity, inhibit the continuous decomposition of the electrolyte, and thus optimize battery performance.

[0005] However, the currently reported methods for preparing mannitol carbonate sulfate compounds still have significant shortcomings. Existing synthetic processes generally require multiple steps such as hydroxyl protection, carbonate esterification, and sulfation, resulting in a long overall process route. Furthermore, the synthesis process easily generates numerous byproducts, leading not only to low yields of the target product but also increasing the difficulty of subsequent purification. These problems, to some extent, limit the large-scale application of such additives and have become a technical challenge that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a method for synthesizing mannitol carbonate sulfate. The preparation method of the present invention is simple and easy to operate, with high yield and high product purity, and can be used to improve the rate performance, high-temperature storage and high-temperature cycling performance of lithium-ion batteries.

[0007] This invention provides a method for synthesizing mannitol sulfate carbonate, comprising the following steps: S1. 1,3,4,6-Tetrachloro-2,5-hexanediol was reacted with chlorosulfonic acid in the presence of an acid-binding agent to obtain an intermediate solution as shown in formula (II). Equation (II); S2. The intermediate solution shown in formula (II) is mixed with anhydrous carbonate and heated to a first set temperature for reaction. Then, in the presence of a phase transfer catalyst, the temperature is raised to a second set temperature for reaction to obtain mannitol carbonate sulfate.

[0008] In this invention, the structural formula of 1,3,4,6-tetrachloro-2,5-hexanediol is shown in formula (I): Formula (I).

[0009] Preferably, the molar ratio of 1,3,4,6-tetrachloro-2,5-hexanediol, the acid-binding agent, and chlorosulfonic acid is 1 : (1.9~2.2) : (1.9~2.2).

[0010] Preferably, the acid-binding agent is selected from one or more of triethylamine, pyridine, dimethylamine, and aniline.

[0011] Preferably, the reaction in step S1 is carried out in anhydrous N,N-dimethylformamide; the reaction temperature in step S1 is -10~5℃, and the reaction time is 20~80min.

[0012] Preferably, in step S2, the ratio of the theoretical molar amount of the intermediate shown in formula (II) to the added molar amount of anhydrous carbonate is 1: (3.5~5.5); the carbonate includes one or more of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, lithium carbonate and lithium bicarbonate.

[0013] Preferably, in step S2, the first set temperature is 60~80℃, and the reaction time to the first set temperature is 0.5~5h.

[0014] Preferably, the phase transfer catalyst comprises one or more of tetrabutylammonium bromide, triethylbenzylammonium chloride, tetrahexylammonium chloride, tetrabutylammonium chloride, tetrahexylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium hydrogen sulfate, and trioctylmethylammonium chloride.

[0015] Preferably, the molar amount of the phase transfer catalyst added is 0.5 to 10 mol of the theoretical molar amount of the intermediate shown in formula (II).

[0016] Preferably, the second set temperature is 120~140℃, and the reaction time to reach the second set temperature is 0.5~5h.

[0017] Preferably, after step S2, a purification step is also included, specifically as follows: the reaction product of step S2 is poured into cold water to precipitate the product, and after filtration, washing with hot water and recrystallization with an alcohol solvent, purified mannitol sulfate carbonate is obtained.

[0018] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The method for synthesizing mannitol carbonate sulfate provided by the present invention uses 1,3,4,6-tetrachloro-2,5-hexanediol as the starting material. By simplifying the cumbersome steps such as hydroxyl protection in the traditional process, the overall process route is shortened, and the yield of the target product is significantly improved. The total yield of the two steps is over 88%. At the same time, the generation of by-products is reduced, the difficulty of subsequent purification is reduced, and the problems of low yield and many by-products in the existing process are solved. Moreover, the reaction time is short, the amount of hazardous waste generated is small, the operation is simple, and it is conducive to industrial scale-up production.

[0019] (2) The mannitol carbonate ester compound synthesized in this invention can form a stable composite SEI layer at the negative electrode interface due to the synergistic effect of the sulfate and carbonate functional groups in the molecular structure. This effectively inhibits the continuous decomposition of the electrolyte, significantly improves the high-temperature cycle stability, rate performance and high-temperature storage performance of lithium-ion batteries, and enhances the overall performance of the battery. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1 This is the infrared spectrum of mannitol sulfate carbonate prepared in Example 1 of this invention. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] This invention provides a method for synthesizing mannitol sulfate carbonate, comprising the following steps: S1. 1,3,4,6-Tetrachloro-2,5-hexanediol was reacted with chlorosulfonic acid in the presence of an acid-binding agent to obtain an intermediate solution as shown in formula (II). Equation (II); S2. The intermediate solution shown in formula (II) is mixed with anhydrous carbonate and heated to a first set temperature for reaction. Then, in the presence of a phase transfer catalyst, the temperature is raised to a second set temperature for reaction to obtain mannitol carbonate sulfate.

[0024] The reaction route of the above technical solution of the present invention is as follows: ; .

[0025] In step S1 of this invention, 1,3,4,6-tetrachloro-2,5-hexanediol is used as the starting material, and the hydroxyl group (-OH) in its molecule is the reactive site: the lone pair electrons of the oxygen atom of the hydroxyl group can combine with the sulfur atom in chlorosulfonic acid (ClSO3H) through nucleophilic attack, resulting in a nucleophilic substitution reaction. Due to the steric hindrance difference in the chemical environment of the hydroxyl group within the molecule, chlorosulfonic acid preferentially reacts with the hydroxyl group with less steric hindrance; at the same time, the acid-binding agent neutralizes the hydrogen chloride (HCl) generated by the reaction, preventing the accumulation of acidic substances from interfering with the reaction equilibrium, making the conversion of the hydroxyl group to the sulfate ester group (-OSO3H) irreversible, and finally generating the intermediate shown in formula (II).

[0026] Step S2 first involves mixing the intermediate solution of formula (II) obtained in step S1 with a solid anhydrous carbonate and reacting it at a first set temperature. At this point, the solid carbonate provides an alkaline environment at its surface and the solution interface, promoting the deprotonation of the sulfate ester group (-OSO3H) in the intermediate molecule, forming a sulfate anion (-OSO3H) with significantly enhanced nucleophilicity. - This negative ion, acting as a highly efficient intramolecular nucleophile, attacks a neighboring carbon center activated by a chlorine atom within the same molecule, initiating intramolecular nucleophilic substitution; the chloride ion (Cl...) - The molecule is removed as a leaving group, and completes the first ring closure by forming a new covalent bond, constructing the intermediate of formula (III) containing a sulfate ester ring. This step is carried out under anhydrous or slightly aqueous conditions, which suppresses possible hydrolytic side reactions of the sulfate ester bond and ensures the high efficiency and purity of the ring-closing reaction.

[0027] Formula (III).

[0028] Subsequently, in the presence of a phase-transfer catalyst, the reaction system is heated to a higher, second set temperature. During this stage, the phase-transfer catalyst reacts with carbonate ions (CO3-) on the surface of the solid carbonate. 2- The activated carbonate ion forms ion pairs soluble in the organic phase, thereby "transporting" the carbonate ion into the homogeneous reaction system, greatly increasing its effective reaction concentration and migration rate. The activated carbonate ion acts as a strong nucleophile, attacking the remaining carbon atom bonded to the chlorine atom in the intermediate of formula (III), resulting in an intermolecular nucleophilic substitution reaction. After the chlorine ion leaves, the adjacent hydroxyl oxygen atom of the newly formed carbonate group immediately launches an intramolecular nucleophilic attack on the carbonyl carbon, completing the second ring closure and ultimately constructing the mannitol carbonate sulfate target molecule containing both a sulfate ring and a carbonate ring. This high-temperature reaction under anhydrous conditions also minimizes the risk of carbonate bond hydrolysis, ensuring the structure and purity of the final product.

[0029] In this invention, the structural formula of 1,3,4,6-tetrachloro-2,5-hexanediol is shown in formula (I): Formula (I); its CAS number is 36120-61-3.

[0030] In an optional embodiment of the present invention, the molar ratio of 1,3,4,6-tetrachloro-2,5-hexanediol, the acid-binding agent, and chlorosulfonic acid is 1 : (1.9~2.2) : (1.9~2.2), more preferably 1 : (2.0~2.1) : (2.0~2.1), to ensure sufficient reaction.

[0031] In an optional embodiment of the present invention, the acid-binding agent is selected from one or more of triethylamine, pyridine, dimethylamine, and aniline; it is an organic base that can rapidly combine with the hydrogen chloride generated in the reaction to form a salt, and the generated salt has low solubility in organic solvents, which facilitates subsequent separation. At the same time, it has moderate alkalinity and will not undergo side reactions with raw materials or intermediates, thus maintaining the stability of the reaction system.

[0032] In an optional embodiment of the present invention, the reaction in step S1 is carried out in anhydrous N,N-dimethylformamide. Since chlorosulfonic acid is easily decomposed in water, an anhydrous environment can prevent its degradation. Anhydrous N,N-dimethylformamide can dissolve organic raw materials and chlorosulfonic acid, and has good compatibility with both low-temperature and high-temperature reactions, providing a suitable medium for the reaction. The present invention does not impose any special restrictions on the amount of anhydrous N,N-dimethylformamide used. Preferably, the mass ratio of 1,3,4,6-tetrachloro-2,5-hexanediol to anhydrous N,N-dimethylformamide is 1:(2~10), more preferably 1:(2~5).

[0033] In an optional embodiment of the present invention, the reaction temperature in step S1 is -10 to 5°C. Because the reaction between 1,3,4,6-tetrachloro-2,5-hexanediol and chlorosulfonic acid is exothermic, a reaction temperature above 10°C easily leads to product decomposition, low selectivity, and increased byproducts; a temperature below -5°C results in excessively low reactivity, requiring an increased reaction time and significantly reducing production efficiency. The reaction time is 20 to 80 minutes, more preferably 30 to 60 minutes.

[0034] After step S1 is completed, the intermediate solution shown in formula (II) is directly filtered to remove the precipitate generated after the acid-binding agent reaction.

[0035] In an optional embodiment of the present invention, in step S2, the ratio of the theoretical molar amount of the intermediate shown in formula (II) to the added molar amount of anhydrous carbonate is 1:(3.5~5.5), more preferably 1:(3.8~4.5; the anhydrous carbonate neutralizes the excess chlorosulfonic acid in step S1 and the byproduct acid of the sulfate ester cyclization reaction in step S2, and also neutralizes the acidic hydrogen of the two sulfate ester groups, while serving as a nucleophile in the carbonate cyclization process in step S2. In an optional embodiment of the present invention, the carbonate includes one or more of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, lithium carbonate, and lithium bicarbonate.

[0036] In an optional embodiment of the present invention, in step S2, the first set temperature is 60~80℃, and the heating time to the reaction is 0.5~5h, more preferably 2~5h. Under the first set temperature and alkaline conditions, the acidic hydrogen on the sulfonic acid group of the intermediate shown in formula (II) is partially or completely deprotonated to form a sulfonate ion. This makes the oxygen atom carry a stronger negative charge, significantly enhancing nucleophilicity. While the nucleophilic oxygen atom attacks the β-carbon atom, chloride ions (Cl...)... - The carbon atom is expelled from the molecule as a leaving group and forms a new CO bond between the nucleophilic oxygen atom and the β-carbon atom. Meanwhile, the original C-C and SO bonds of the molecule remain unchanged, eventually forming a five-membered ring, generating the intermediate shown in formula (III).

[0037] In an optional embodiment of the present invention, the phase transfer catalyst comprises one or more of tetrabutylammonium bromide, triethylbenzylammonium chloride, tetrahexylammonium chloride, tetrabutylammonium chloride, tetrahexylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium bisulfate, and trioctylmethylammonium chloride. The phase transfer catalyst promotes the exchange of matter between the organic phase intermediate and the aqueous phase carbonate, transferring carbonate ions to the organic phase via ion pairs, accelerating the nucleophilic substitution reaction, and improving the reaction rate and conversion rate.

[0038] In an optional embodiment of the present invention, the molar amount of the phase transfer catalyst is 0.5 to 10 mol% of the theoretical molar amount of the intermediate shown in formula (II), more preferably 1 to 8 mol%, and even more preferably 4 to 8 mol%.

[0039] In an optional embodiment of the present invention, the second set temperature is 120~140℃, more preferably 130~140℃. The carbonate cyclization reaction requires a high activation energy, and high temperature can accelerate the intramolecular nucleophilic substitution rate. The reaction time for heating to the second set temperature is 0.5~5h, more preferably 0.5~3h.

[0040] After the reaction in step S2 is completed, the present invention also includes a purification step, which is as follows: the reaction product of step S2 is poured into cold water to precipitate the product, and after filtration, washing with hot water and recrystallization with alcohol solvent, purified mannitol carbonate sulfate is obtained.

[0041] The preparation method described above is simple and easy to operate, and the post-processing is simple, with high yield and high purity.

[0042] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not have any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used. In the following embodiments, 1,3,4,6-tetrachloro-2,5-hexanediol was purchased from Achemica.

[0043] Example 1 This embodiment provides a method for synthesizing mannitol sulfate carbonate.

[0044] (1) Add 25.5 g of 1,3,4,6-tetrachloro-2,5-hexanediol (0.1 mol) and 20.2 g of triethylamine (0.2 mol) as an acid-binding agent to a four-necked flask, then add 100 g of N,N-dimethylformamide (DMF) and stir until the solid is completely dissolved. Cool the reaction system to 0°C, then slowly add 23.3 g (0.2 mol) of chlorosulfonic acid, controlling the dropping rate so that the temperature rise does not exceed 5°C. After the addition is complete, continue stirring the reaction at this temperature for 30 min. After the reaction is complete, filter to remove the generated triethylamine hydrochloride precipitate to obtain a DMF solution of the intermediate shown in formula (II).

[0045] (2) Transfer the intermediate solution shown in formula (II) above to a three-necked flask and add 42.4 g (0.4 mol) of anhydrous sodium carbonate. Install a reflux condenser, heat the reaction system to 65 °C, and stir and reflux for 3 h to complete the cyclization of sulfate ester.

[0046] (3) Subsequently, the reaction system was heated to 135°C and 1.72 g (0.0053 mol) of tetrabutylammonium bromide was added to it. The reaction was stirred and refluxed at this temperature for 1 h to complete the carbonate cyclization.

[0047] (4) After the reaction was completed, the reaction solution was cooled to room temperature and slowly poured into 200 mL of cold water at 4℃ with stirring to allow the product to fully separate. The product was filtered under reduced pressure through a Buchner funnel, and the resulting filter cake was washed with 60℃ hot water (50 mL × 2) to remove inorganic salts. The washed solid was dissolved in 50 mL of hot ethanol (70℃), filtered while hot, and the filtrate was allowed to stand and cool to crystallize, resulting in white crystals. The crystals were collected by filtration and dried under vacuum at 60℃ for 2 h to obtain 29.8 g (89.7 mmol) of white needle-like crystals of mannitol carbonate sulfate, with a yield of 89.7% and a purity of 99.6% (as determined by HPLC).

[0048] Figure 1 Infrared spectrum of mannitol sulfate carbonate prepared in this embodiment, 1200.70 cm⁻¹ -1 The peak is the S=O asymmetric stretching vibration peak in the sulfate ester group, at 1797.56 cm⁻¹. -1 The nearby peak represents the stretching vibration of C=O in the carbonate group.

[0049] Example 2 This embodiment provides a method for synthesizing mannitol sulfate carbonate.

[0050] (1) Add 25.5 g of 1,3,4,6-tetrachloro-2,5-hexanediol (0.1 mol) and 15.8 g of pyridine (0.2 mol) as an acid-binding agent to a four-necked flask, then add 76.5 g of N,N-dimethylformamide (DMF) and stir until the solid is completely dissolved. Cool the reaction system to 0 °C, then slowly add 23.3 g (0.2 mol) of chlorosulfonic acid, controlling the dropping rate so that the temperature rise does not exceed 5 °C. After the addition is complete, continue stirring the reaction at this temperature for 30 min. After the reaction is complete, filter to remove the generated triethylamine hydrochloride precipitate to obtain a DMF solution of the intermediate shown in formula (II).

[0051] (2) Transfer the intermediate solution shown in formula (II) above to a three-necked flask and add 42.4 g (0.4 mol) of anhydrous sodium carbonate. Install a reflux condenser, heat the reaction system to 75 °C, and stir and reflux for 3 h to complete the cyclization of sulfate ester.

[0052] (3) Subsequently, the reaction system was heated to 140°C and 2.32 g (0.0072 mol) of tetrabutylammonium bromide was added to it. The reaction was stirred and refluxed at this temperature for 1 h to complete the carbonate cyclization.

[0053] (4) After the reaction was completed, the reaction solution was cooled to room temperature and slowly poured into 200 mL of cold water at 4℃ with stirring to allow the product to fully separate. The product was filtered under reduced pressure through a Buchner funnel, and the resulting filter cake was washed with 60℃ hot water (50 mL × 2) to remove inorganic salts. The washed solid was dissolved in 50 mL of hot ethanol (70℃), filtered while hot, and the filtrate was allowed to stand and cool to crystallize, resulting in white crystals. The crystals were collected by filtration and dried under vacuum at 60℃ for 2 h to obtain 30.21 g (90.9 mmol) of white needle-like crystals of mannitol carbonate sulfate, with a yield of 90.9% and a purity of 99.61% (as determined by HPLC).

[0054] Example 3 The difference between this embodiment and Example 1 is that Na2CO3 was replaced with NaHCO3. The final yield was 29.11 g (87.6 mmol) of mannitol carbonate sulfate, with a yield of 87.6% and a purity of 99.65%.

[0055] Comparative Example 1 The difference between this example and Example 1 is that in step (2) of this comparative example, the reaction system was heated to 45°C. The final yield was 3.42 g (10.3 mmol) of mannitol sulfate carbonate, with a yield of 10.3% and a purity of 85.23%.

[0056] Comparative Example 2 The difference between this example and Example 1 is that in step (3) of this comparative example, the reaction system was heated to 100°C and refluxed for 1 hour. The final yield was 7.98 g (24.0 mmol) of mannitol sulfate, with a yield of 24.0% and a purity of 95.29%.

[0057] Comparative Example 3 The difference between this example and Example 1 is that in step (3) of this comparative example, the reaction system was heated to 150°C and refluxed for 1 hour. The final yield was 19.09 g (57.5 mmol) of mannitol carbonate sulfate, with a yield of 57.5% and a purity of 92.25%.

[0058] Test case 1. Preparation of electrolyte In an argon-filled glove box (moisture <10 ppm, oxygen <10 ppm), ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed uniformly at a mass ratio of 3:7. Then, 11.5% (w / w) of lithium hexafluorophosphate (LiPF6) and 2.5% (w / w) of lithium bis(fluorosulfonyl)imide (LiFSI) were slowly added to the mixed solvent, and the mixture was stirred until completely dissolved. Then, 1 wt% of vinylene carbonate (VC) and different proportions of mannitol carbonate sulfate prepared in Examples 1-3 were added to obtain the electrolyte. Ethylene sulfate was replaced with mannitol carbonate sulfate as a control.

[0059] 2. Preparation of lithium-ion batteries Lithium iron phosphate (LiFePO4), conductive carbon black Super-P, and polyvinylidene fluoride (PVDF) binder were mixed evenly in a mass ratio of 96.8:2:1.2. This mixture was then dispersed in N-methylpyrrolidone (NMP) to obtain a positive electrode slurry. The slurry was then evenly coated onto both sides of an aluminum foil, dried, and rolled to obtain a positive electrode sheet. Graphite, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed evenly in a mass ratio of 95:2:2:1. This mixture was then dispersed in deionized water to obtain a negative electrode slurry. The slurry was then evenly coated onto both sides of an aluminum foil, dried, and rolled to obtain a negative electrode sheet. The positive electrode, separator, and negative electrode are stacked in sequence, ensuring that the separator separates the positive and negative electrode and that the negative electrode completely covers the positive electrode. The stacked cells are then placed in an aluminum-plastic film packaging bag. Subsequently, the electrolyte prepared above is injected into the cells. After formation, the cells are sealed, aged, resealed, and tested for capacity to produce a 1Ah lithium iron phosphate battery.

[0060] 3. Performance Testing (1) High-temperature electrolyte acidity and color test: Prepare the electrolyte in a glove box filled with argon gas, put it into an aluminum-plastic bottle, place it in a 55℃ oven for 48 hours, and then measure the changes in the color and acidity of the electrolyte.

[0061] (2) High temperature cycle test: Under high temperature (55℃) conditions, the lithium-ion battery is charged and discharged once at 1C / 1C (battery discharge capacity is C0), with an upper limit voltage of 3.65V, and then charged and discharged for 800 cycles at 1C / 1C under normal temperature conditions (battery discharge capacity is C1). Capacity retention rate = (C1 / C0) * 100%.

[0062] The test results are shown in Table 1.

[0063] Table 1. Electrolyte and Battery Performance Test Results

[0064] The acidity and color of the electrolytes containing mannitol carbonate sulfate synthesized using different processes in the embodiments of the present invention did not change significantly after high-temperature storage. This is because, compared to vinyl sulfate, mannitol carbonate sulfate compounds have a stable cyclic structure (high bond energy), steric hindrance, and strong thermal stability. Therefore, the acidity and color of the embodiments show less change compared to vinyl sulfate. The overall conductivity of the electrolytes prepared with mannitol carbonate sulfate in the embodiments is slightly improved. This is because the mannitol carbonate sulfate compound contains a carbonate structure, which coordinates with lithium ions in the electrolyte, potentially dissociating lithium salts and altering the solvation structure of the electrolyte, leading to a slight increase in conductivity. The high-temperature cycle performance of the batteries assembled in the embodiments is significantly better than that of batteries assembled with vinyl sulfate. This is because the sulfate groups of mannitol carbonate sulfate can accept electrons from the negative electrode surface during charging and self-reduced to form free radicals and / or ions. Simultaneously, the carbonate groups in its structure work synergistically to form Li2SO4, Li2CO3, and Li2S at the negative electrode interface. x A stable SEI film is formed. This SEI film can effectively block the direct contact between the electrolyte and the negative electrode active material, thereby inhibiting the continuous decomposition of the electrolyte solvent, reducing the generation of decomposition products, and avoiding the accumulation of by-products at the electrode interface, which leads to increased interfacial impedance or structural damage, thus improving the high-temperature cycle stability of the battery.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 synthesizing mannitol sulfate, characterized in that, Includes the following steps: S1. 1,3,4,6-Tetrachloro-2,5-hexanediol was reacted with chlorosulfonic acid in the presence of an acid-binding agent to obtain an intermediate solution as shown in formula (II). Equation (II); S2. The intermediate solution shown in formula (II) is mixed with anhydrous carbonate and heated to a first set temperature for reaction. Then, in the presence of a phase transfer catalyst, the temperature is raised to a second set temperature for reaction to obtain mannitol carbonate sulfate.

2. The synthesis method according to claim 1, characterized in that, The molar ratio of 1,3,4,6-tetrachloro-2,5-hexanediol, the acid-binding agent, and chlorosulfonic acid is 1 : (1.9~2.2) : (1.9~2.2).

3. The synthesis method as described in claim 1, characterized in that, The acid-binding agent is selected from one or more of triethylamine, pyridine, dimethylamine, and aniline.

4. The synthesis method according to claim 1, characterized in that, The reaction in step S1 is carried out in anhydrous N,N-dimethylformamide; the reaction temperature in step S1 is -10~5℃, and the reaction time is 20~80min.

5. The synthesis method according to claim 1, characterized in that, In step S2, the ratio of the theoretical molar amount of the intermediate shown in formula (II) to the added molar amount of anhydrous carbonate is 1: (3.5~5.5); the carbonate includes one or more of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, lithium carbonate and lithium bicarbonate.

6. The synthesis method according to claim 1, characterized in that, In step S2, the first set temperature is 60~80℃, and the reaction time to the first set temperature is 0.5~5h.

7. The synthesis method according to claim 1, characterized in that, The phase transfer catalyst includes one or more of tetrabutylammonium bromide, triethylbenzylammonium chloride, tetrahexylammonium chloride, tetrabutylammonium chloride, tetrahexylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium hydrogen sulfate, and trioctylmethylammonium chloride.

8. The synthesis method according to claim 1, characterized in that, The molar amount of the phase transfer catalyst added is 0.5 to 10 mol of the theoretical molar amount of the intermediate shown in formula (II).

9. The synthesis method according to claim 1, characterized in that, The second set temperature is 150~200℃, and the reaction time to reach the second set temperature is 0.5~5h.

10. The synthesis method according to claim 1, characterized in that, Following step S2, a purification step is also included, as follows: the reaction product of step S2 is poured into cold water to precipitate the product, and after filtration, washing with hot water and recrystallization with an alcohol solvent, purified mannitol sulfate carbonate is obtained.

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