Preparation method of lithium bis(fluorosulfonyl)imide

Abstract

The invention provides a method for preparing lithium bisfluorosulfonyl imide, which uses tritylamine as a nitrogen source, wherein a large trityl electron-donating group increases the reactivity of the amine, and an organic solvent neutralizes a fluorosulfonyl compound and reacts in a strongly alkaline environment, and then undergoes extraction, dehydration, and decolorization treatment, and concentrated crystallization to obtain a trityl bisfluorosulfonamide intermediate with a high yield. The intermediate is dissolved in an organic solvent, and catalytic hydrogenation is performed to obtain bisfluorosulfonyl imide acid. The intermediate is reacted with a lithium source to obtain lithium bisfluorosulfonyl imide. The lithium bisfluorosulfonyl imide is obtained by recrystallization and purification to obtain battery-grade lithium bisfluorosulfonyl imide. The invention uses tritylamine as a nitrogen source to react and prepare bisfluorosulfonyl imide, and has high reactivity, a mild route, simple separation and purification, and is conducive to industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium battery electrolytes, and particularly relates to a method for preparing lithium bis(fluorosulfonyl)imide. Background Art

[0002] As demand for lithium batteries grows, demand for lithium hexafluorophosphate (LFP), the raw material for its electrolyte, has surged, and its price has continued to rise. Compared to LFP, lithium bis(fluorosulfonyl)imide (LiSFM) offers higher conductivity and thermal stability, and exhibits virtually no side reactions. However, its synthesis and purification processes are complex, resulting in high costs. In today's market, lithium bis(fluorosulfonyl)imide (LiSFM), which originally lacks a price advantage but offers superior performance, is gradually replacing LFP as an electrolyte additive and becoming the primary electrolyte component, improving battery performance.

[0003] The existing synthesis of lithium bis(fluorosulfonyl)imide is mostly done by first synthesizing bis(fluorosulfonyl)imide acid from suitable nitrogen, sulfur and fluorine sources, and then reacting it with a lithium source to form a salt for purification. CN104495767A discloses a method for preparing a lithium salt of bisfluorosulfonyl imide, which mainly comprises the following steps: A) reacting sulfuryl chloride and ammonia in the presence of an organic base to obtain an organic alkali salt of bisfluorosulfonyl imide; B) mixing the organic alkali salt of bisfluorosulfonyl imide obtained in step A) with HF, and performing a fluorination reaction to obtain an organic alkali salt of bisfluorosulfonyl imide; C) mixing the organic alkali salt of bisfluorosulfonyl imide obtained in step B) with an alkaline substance, and performing a neutralization reaction to obtain a crude bisfluorosulfonyl imide alkali metal salt; D) purifying the crude bisfluorosulfonyl imide alkali metal salt obtained in step C) to obtain an alkali metal salt of bisfluorosulfonyl imide; and E) mixing the alkali metal salt of bisfluorosulfonyl imide obtained in step D) with a lithiating agent, and performing a displacement reaction to obtain lithium bisfluorosulfonyl imide. CN114014280A discloses a method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps: reacting urea, lithium fluoride and sulfur trioxide in anhydrous hydrogen fluoride liquid.

[0004] The existing synthesis technology of lithium bis(fluorosulfonyl)imide mainly uses aminosulfonic acid, ammonia, urea and other nitrogen sources. The use of aminosulfonic acid and urea often produces acidic gas, which, combined with strong acidic materials, severely corrodes the equipment. The participation of ammonia in the reaction is difficult to control, and low-temperature and pressure-resistant equipment is required. These reasons have a negative impact on the industrialization process of lithium bis(fluorosulfonyl)imide. Summary of the Invention

[0005] The invention provides a method for preparing lithium bis(fluorosulfonyl)imide, which has simple process, high safety and high purity of the obtained product.

[0006] The technical solution of the present invention is a method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps:

[0007] S1, dissolving triphenylamine in a first solvent, adding an acid binding agent, and then dropwise adding fluorosulfonic acid or chlorofluorosulfonyl to react. After the reaction is completed, washing, dehydration, decolorization, and reduced pressure concentration are performed, and then a first poor solvent is added to obtain tritylbisfluorosulfonamide intermediate crystals;

[0008] S2, dissolving trityl bisfluorosulfonamide in a second solvent, then introducing hydrogen, and performing hydrogenation reduction under the action of a catalyst. After the reaction is completed, the catalyst is removed, and the mixture is cooled to room temperature after dehydration, and then heated and distilled under reduced pressure to collect the fraction to obtain bisfluorosulfonyl imide acid;

[0009] S3. Under a protective atmosphere, bis(fluorosulfonyl)imide acid is added to a third solvent, and a lithium source is added to react. After the reaction, the mixture is filtered and concentrated, and a second poor solvent is added to concentrate and replace the mixture, thereby precipitating crude lithium bis(fluorosulfonyl)imide crystals; and finally, the mixture is recrystallized to obtain battery-grade lithium bis(fluorosulfonyl)imide.

[0010] Furthermore, the first solvent includes but is not limited to one or more of acetone, dichloromethane, tetrahydrofuran, ethyl acetate or acetonitrile; the acid binding agent includes but is not limited to sodium hydroxide, potassium hydroxide, sodium hydride, potassium hydride, sodium tert-butyl oxide or potassium tert-butyl oxide; the first poor solvent includes but is not limited to one or more of petroleum ether, heptane or toluene.

[0011] Furthermore, the molar ratio of triphenylmethane to fluorosulfonic acid or chlorofluorosulfonyl in S1 is 1:2.05-2.1.

[0012] Furthermore, the reaction temperature in S1 is lower than -10°C.

[0013] Furthermore, the second solvent in S2 is a water-containing organic solvent with a water content of 0.03-0.3 wt %, and the organic solvent includes but is not limited to a mixture of one or more of alcohols, ethers, and organic acids; and the catalyst is palladium, nickel, rhodium, rubidium, or platinum supported on activated carbon.

[0014] Furthermore, the reaction temperature in S2 is 45° C., and the reaction time is 3 to 8 hours.

[0015] Furthermore, the third solvent in S3 is at least one of dimethyl carbonate, ethyl acetate, acetonitrile, and acetone; the second poor solvent is at least one of dichloromethane, chloroform, tetrachloromethane, benzene, toluene, xylene, trimethylbenzene, petroleum ether, n-hexane, cyclohexane, and n-heptane.

[0016] Furthermore, the lithium source in S3 includes but is not limited to at least one of metallic lithium, lithium hydride, lithium carbonate, lithium carboxylate, lithium borate, lithium phosphate, lithium perchlorate, lithium halide, lithium hydroxide, amide lithium, and alkyl lithium; the molar ratio of the lithium source to the bis(fluorosulfonyl)imide acid is 0.26 to 1.05:1.

[0017] Furthermore, during recrystallization in S3, the crude lithium bis(fluorosulfonyl)imide is dissolved in a third solvent, then concentrated and crystallized, a second poor solvent is added, concentrated, filtered, and vacuum-dried to obtain battery-grade lithium bis(fluorosulfonyl)imide.

[0018] The synthetic route of the present invention is specifically:

[0019]

[0020] The present invention has the following beneficial effects:

[0021] 1. In the existing conventional methods, the source of nitrogen is mainly ammonia, such as ammonia gas, liquid ammonia, ammonium salts, etc. The use of ammonia gas or liquid ammonia to participate in the reaction will result in a violent exotherm, and the reactants will easily gasify, requiring low-temperature and pressure-resistant equipment. The reaction is difficult to control, causing huge safety hazards. Other nitrogen sources, such as aminosulfonic acid, will generate a large amount of acidic gas, and high temperature is required to promote gas escape to complete the reaction, which will cause serious corrosion to the equipment. The side reactions associated with high temperature will also increase the difficulty of purification. The present invention uses triphenylmethylamine as the nitrogen source, which has a higher boiling point, a mild exothermic reaction, and is easy to control; moreover, the reaction is carried out in a strongly alkaline environment, is not easy to generate acidic gas, and the reaction temperature is not high, which will basically not cause corrosion to the equipment.

[0022] 2. As a large electron-donating group, the trityl group greatly activates the nitrogen-hydrogen bond, making the disubstituted fluorosulfonyl group easy to carry out in a strong alkaline environment, with high reaction activity and mild reaction conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is lithium bis(fluorosulfonyl)imide 19 F-NMR spectrum;

[0024] Figure 2 It is lithium bis(fluorosulfonyl)imide 19 F-NMR trifluoromethylbenzene internal standard nuclear magnetic spectrum;

[0025] Figure 3 This is the IC anion test spectrum of lithium bis(fluorosulfonyl)imide;

[0026] Figure 4 This is a photo of lithium bis(fluorosulfonyl)imide. DETAILED DESCRIPTION

[0027] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0028] Example 1

[0029] A method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps:

[0030] 1) Under nitrogen, add 260g of tritylamine solid to a 2L three-necked flask, add 1700g of dichloromethane, and stir until dissolved. Cool to -20°C and slowly add 88g of sodium hydroxide solid, controlling the temperature not to exceed -10°C. After addition, stir until dissolved. In a glove box, transfer 200g of fluorosulfonic acid to a constant pressure dropping funnel and slowly add dropwise to the tritylamine solution, controlling the temperature not to exceed -10°C, over 1.5 hours. After the addition is complete, time the reaction for 5 hours and terminate.

[0031] Weigh 470g of potassium dihydrogen phosphate, add 1000ml of deionized water, stir to dissolve, transfer to a 3L separatory funnel, pour in the tritylbis(fluorosulfonamide) reaction solution, shake vigorously, degas, and let stand for 10 minutes to separate the aqueous and organic phases. Transfer the aqueous phase to a 2L separatory funnel, add 300g of dichloromethane, shake vigorously, separate, and collect the organic phase. Combine the two organic phases, add 300g of anhydrous magnesium sulfate, and stir to dehydrate for 1 hour. Filter, add 80g of activated carbon to the filtrate, and stir to decolorize for 1 hour. Filter, transfer the filtrate to a 2L single-necked flask, rotary evaporation to remove the dichloromethane, concentrate until crystals begin to form, and transfer to a 1L three-necked flask. Gradually cool to -10°C, and add 150g of n-heptane dropwise over 1 hour. After the addition is complete, incubate at -10°C to grow the crystals overnight. Filter to obtain the tritylbis(fluorosulfonamide) intermediate, with a yield of 95.2% based on tritylamine.

[0032] 2) In a 1L hydrogenation reactor, 211.7g of tritylbisfluorosulfonamide was dissolved in 200g of ethanol. 80g of a 0.3%-0.5% palladium-on-carbon catalyst was added. The reaction was heated to 45°C and hydrogen was introduced at 20-25 psi. The reaction was allowed to proceed for 5 hours. The hydrogen was then discontinued, the atmosphere replaced with nitrogen, and the reaction was filtered in a glove box. The filtrate was dehydrated overnight by adding 50g of molecular sieves. After filtration, the filtrate was distilled under reduced pressure to a pressure of <-0.1 MPa. The colorless, transparent liquid at a distillation temperature of 35-40°C was collected to obtain bisfluorosulfonyl imide acid. The yield, based on tritylbisfluorosulfonamide, was 92.8%.

[0033] 3) Under nitrogen, add 3.9g of lithium carbonate and 50g of dimethyl carbonate to a 100ml three-necked flask. Cool to 10-15°C and slowly add bis(fluorosulfonyl)imide acid dropwise, controlling the temperature not to exceed 35°C. After completion of the addition, react for 1.5-3h, monitoring the pH at 5-6, and terminate the reaction. Filter and concentrate under reduced pressure. After concentration, add 50g of dichloromethane and continue concentrating and replacing the solution three times to obtain crude lithium bis(fluorosulfonyl)imide crystals, with a yield of 92.7% based on bis(fluorosulfonyl)imide acid.

[0034] 4) In a glove box, take 18.7g of lithium bis(fluorosulfonyl)imide and place it in a 100ml single-necked bottle. Add 50g of dimethyl carbonate, filter to remove insoluble matter, and concentrate under reduced pressure. After concentration, add 20g of dichloromethane, concentrate and replace, filter, and vacuum dry at 60°C to obtain battery-grade lithium bis(fluorosulfonyl)imide. See the photo of the product. Figure 4The purity meets the relevant provisions of the People's Republic of China Nonferrous Metals Industry Standard YS / T 1302-2019. The recovery rate based on the crude lithium bis(fluorosulfonyl)imide is 91.5%.

[0035] The test results of the obtained battery-grade lithium bis(fluorosulfonyl)imide product in accordance with the Chinese Nonferrous Metals Industry Standard YS / T 1302-2019 are shown in Table 1 below.

[0036] Table 1

[0037]

[0038]

[0039] The obtained battery-grade lithium bis(fluorosulfonyl)imide product 19 F-NMR spectrum Figure 1 As shown in the figure, it can be seen that the fluorine spectrum of lithium bis(fluorosulfonyl)imide in deuterated methanol has a peak position of 50.15ppm. 19 F-NMR trifluoromethylbenzene internal standard nuclear magnetic spectrum see Figure 2 .

[0040] The IC spectrum of the obtained battery-grade lithium bis(fluorosulfonyl)imide product is as follows: Figure 3 As shown in the figure, it can be seen that the normalized content of lithium bis(fluorosulfonyl)imide FSI- is 99.86%, and F - 、Cl - 、SO4 2- The normalized content was extremely low, and the anion content determined by external standards met the standards.

[0041] Example 2

[0042] The reaction steps were the same as those in Example 1, except that the starting material fluorosulfonic acid in step 1) was replaced by chlorofluorosulfonyl. The yield of the final tritylbisfluorosulfonamide intermediate in step 1) was 87.3%.

[0043] Examples 3-4

[0044] The reaction steps are basically the same as those in Example 1, except that the sodium hydroxide in step 1) is replaced by sodium hydride and sodium tert-butyl oxide, respectively. The final yields of the obtained tritylbisfluorosulfonamide intermediate are 96.8% and 95.3%, respectively.

[0045] Examples 5-6

[0046] The reaction steps are basically the same as those in Example 1, except that the dichloromethane in step 1) is replaced by tetrahydrofuran and ethyl acetate, respectively. The yields of the tritylbisfluorosulfonamide intermediate in step 1) are 92.6% and 94.1%, respectively.

[0047] Examples 7 to 10

[0048] The reaction steps are basically the same as those in Example 1, except that the palladium / carbon catalyst in step 2) is replaced by nickel, rhodium, rubidium, and platinum supported on activated carbon, respectively. The yields of tritylbisfluorosulfonamide in step 2 are 71.7%, 88.1%, 89.3%, and 97.8%, respectively.

[0049] Examples 11 to 21

[0050] The reaction steps are basically the same as those in Example 1, except that the lithium carbonate in step 3) is replaced by metallic lithium, lithium hydride, lithium carboxylate, lithium borate, lithium phosphate, lithium perchlorate, lithium halide, lithium hydroxide, lithium amide, and tert-butyl lithium, respectively. The obtained products or yields are 98.1%, 95.4%, 90.5%, 33.7%, 19.8%, 68.4%, 90.6%, 80.3%, 63.7%, and 89.3%, respectively.

[0051] The above embodiments are merely illustrative of the technical concepts and features of the present invention. The contents described are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Within the technical scope disclosed by the present invention, equivalent changes or improvements based on the technical solutions and inventive concepts of the present invention are all encompassed within the scope of protection of the present invention.

Claims

1. A method for preparing lithium bis(fluorosulfonyl)imide, characterized in that: The following steps are involved: S1, dissolving tritylamine with a first solvent of dichloromethane, tetrahydrofuran or ethyl acetate, adding an acid binding agent of sodium hydroxide, sodium hydride or tert-butyl sodium oxide, then dropping fluorosulfonic acid to react, controlling the temperature not to exceed -10°C, extracting, washing, dehydrating, decolorizing, and concentrating under reduced pressure after the reaction is completed, and then adding a first poor solvent of n-heptane to obtain a tritylbisfluorosulfonamide intermediate crystal; S2, dissolving trityl bisfluorosulfonamide with a second solvent, ethanol, and then introducing hydrogen gas, and carrying out hydrogenation reduction under the action of a catalyst of palladium / carbon or platinum / carbon, the reaction temperature is 45°C, after the reaction is completed, filtering to remove the catalyst, dehydrating and cooling to room temperature, then heating and distilling under reduced pressure, collecting the fractions to obtain bisfluorosulfonyl imide acid; S3. Under a protective atmosphere, bis(fluorosulfonyl)imide acid is added to a third solvent, and a lithium source of lithium carbonate, metallic lithium or lithium hydride is added to react, and the temperature is controlled not to exceed 35° C. After the reaction, the reaction is filtered and concentrated, and a second poor solvent of dichloromethane is added for concentration and replacement to precipitate crude bis(fluorosulfonyl)imide lithium crystals; and finally, recrystallization is performed to prepare battery-grade bis(fluorosulfonyl)imide lithium.

2. The method according to claim 1, characterized in that: The molar ratio of triphenylmethylamine to fluorosulfonic acid in S1 is 1:2.05-2.

1.

3. The method according to claim 1, characterized in that: The molar ratio of the lithium source to the bis(fluorosulfonyl)imidic acid is 0.26-1.05:

1.

4. The method according to any one of claims 1 to 3, characterized in that: During recrystallization in S3, the crude lithium bis(fluorosulfonyl)imide is dissolved in the third solvent, then concentrated and crystallized, a second poor solvent is added, concentrated, filtered, and vacuum dried to obtain battery-grade lithium bis(fluorosulfonyl)imide.

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