Process for the preparation of low water high purity electrolyte imine lithium salts

Abstract

The application relates to the technical field of electrolyte imine lithium salt material preparation, in particular to a preparation method of low-water high-purity electrolyte imine lithium salt, which comprises the following steps: (1) ammonium fluoride and acetonitrile are added into a reactor, the reactor is sealed and cooled at a temperature of 0-5 DEG C, vacuum is drawn to a negative pressure, then sulfuryl fluoride gas is introduced to normal pressure, a secondary amine with a boiling point of not more than 100 DEG C is added, sulfuryl fluoride gas is continuously introduced to continuously react, the reaction is ended when the reaction pressure in the sealed system does not change any more, and the reaction liquid is subjected to reduced pressure distillation to obtain an intermediate product; (2) under a protective atmosphere, an organic solution containing a secondary amine lithium salt compound is added dropwise into the obtained intermediate product, and a lithiation reaction is carried out while stirring, the reaction is ended after concentration, and the final product lithium bisfluorosulfonylimide is obtained through crystallization under anhydrous conditions, filtration and drying. The lithium bisfluorosulfonylimide obtained by the method has high purity, and the water content is less than 20 ppm.

Description

Technical Field

[0001] This invention relates to the field of electrolyte imine lithium salt material preparation technology, specifically to a method for preparing low-water, high-purity electrolyte imine lithium salt. Background Technology

[0002] Key materials for lithium-ion batteries include the positive electrode, negative electrode, separator, and electrolyte. The electrolyte plays a crucial role in transferring charge between the positive and negative electrodes, and its quality directly affects the battery's cycle life, safety performance, and energy density. The key component influencing electrolyte performance is the solute lithium salt, whose physicochemical properties significantly impact electrolyte performance. Based on the central atom of the anion in the lithium salt, common lithium salts can be mainly classified as: ① phosphorus-based lithium salts with phosphorus (P) as the central atom, such as lithium hexafluorophosphate (LiPF6); ② boron-based lithium salts with boron (B) as the central atom, such as lithium tetrafluoroborate (LiBF4); ③ imine lithium salts with nitrogen (N) as the central atom, such as lithium bis(fluorosulfonyl)imide (LiFSI).

[0003] Currently, the most widely used commercially available lithium solute is LiPF6, which boasts high conductivity but also suffers from poor thermal stability, demanding preparation processes, and suboptimal high and low temperature performance. Compared to the traditional lithium salt LiPF6, the lithium solute LiFSI offers the following advantages: ① LiFSI has a larger anionic radius, making it easier to dissociate into lithium ions, thus improving the conductivity of lithium-ion batteries; ② LiFSI does not decompose at temperatures above 200℃ and remains stable, exhibiting good thermal stability and enhancing the safety performance of lithium-ion batteries; ③ Electrolytes containing LiFSI maintain good compatibility with both positive and negative electrode materials, significantly improving the high and low temperature performance of lithium-ion batteries. Therefore, LiFSI is the electrolyte with the most promising future in lithium-ion batteries.

[0004] The prior art CN111620315A discloses a method for preparing lithium bis(fluorosulfonyl)imide. In this method, ammonium fluoride and sulfonyl fluoride are reacted with a tertiary amine (such as triethylamine or tetramethylpropylenediamine) in an organic solvent such as acetonitrile to obtain a tertiary amine salt intermediate of bis(fluorosulfonyl)imide. This intermediate is then reacted with lithium oxide powder in an organic solvent at room temperature, followed by filtration, solvent removal, crystallization, and drying to obtain lithium bis(fluorosulfonyl)imide. The product purity is greater than 99.9%, and the product yield is between 89-95%. Although this patented method uses anhydrous and chlorine-free raw materials, in the actual reaction process, lithium hydroxide, a byproduct of the reaction between lithium oxide and the tertiary amine salt intermediate of bis(fluorosulfonyl)imide, also reacts with the intermediate to generate water. At low or room temperatures, the reaction rate between lithium oxide and water is very slow. Lithium oxide cannot remove the generated water, and a certain amount of water remains in the reaction system. During the post-processing distillation and concentration, lithium bis(fluorosulfonyl)imide will undergo partial hydrolysis, resulting in the prepared lithium bis(fluorosulfonyl)imide product having a water content greater than 0.01%, a sulfate ion content greater than 0.03%, and a fluoride ion content greater than 0.02%. The product quality is difficult to meet the requirements of the lithium battery industry for electrolyte salts.

[0005] Existing technology CN114506829A discloses a method for preparing lithium bis(fluorosulfonyl)imide, which involves reacting triethylamine salt of bis(fluorosulfonyl)imide with alkaline lithium (lithium hydroxide) in a lithiation reaction. Water and triethylamine generated during the reaction are removed by simultaneous reaction and distillation. The purity of the reaction product is greater than 99.9%, and the yield reaches 96-98%. Although the product yield is improved compared to the previous method, this process involves the presence of a larger amount of water during the reaction and distillation concentration processes, resulting in more severe hydrolysis of the lithium bis(fluorosulfonyl)imide. The prepared lithium bis(fluorosulfonyl)imide still has a water content greater than 0.01%, a sulfate ion content greater than 0.05%, and a fluoride ion content greater than 0.03%. The product prepared by this method also fails to meet the quality requirements of electrolyte salts for lithium batteries.

[0006] To address the issue that water generated during existing processes affects the physicochemical properties of the final bis(fluorosulfonyl)imide lithium, this invention develops a method for preparing low-water, high-purity electrolyte imide lithium salt. Summary of the Invention

[0007] To address the aforementioned technical problems, a method for preparing low-water, high-purity electrolyte lithium imide salt is provided. The lithium bis(fluorosulfonyl)imide obtained by this method has a purity of up to 99.99%, with a water content of less than 20 ppm, fluoride and sulfate ion contents of less than 5 ppm each, and a chloride ion content of less than 2 ppm.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0009] A method for preparing low-water, high-purity electrolyte lithium imine salt includes the following steps:

[0010] (1) Add ammonium fluoride and acetonitrile to the reactor, seal it and cool it at 0-5℃. After evacuating to negative pressure, introduce sulfuryl fluoride gas to normal pressure. After mixing evenly, add secondary amine with a boiling point not exceeding 100℃. At the same time, continuously introduce the sulfuryl fluoride gas to carry out the reaction. Stop the reaction when the reaction pressure in the sealed system no longer changes. Distill the reaction solution under reduced pressure to obtain the intermediate product.

[0011] (2) Under a protective atmosphere, an organic solution containing a secondary amine lithium salt compound is added dropwise to the obtained intermediate product while stirring to carry out the lithiation reaction. After the reaction is completed, the product is concentrated, crystallized under anhydrous conditions, filtered, and dried to obtain the final product, lithium difluorosulfonylimide, which is a low-water, high-purity electrolyte lithium salt.

[0012] Further, the secondary amine is one or more of diethylamine and diisopropylamine; the secondary amine lithium salt compound is one of lithium dimethylamino, lithium diethylamino, and lithium diisopropylamino. Since the final product, lithium difluorosulfonylimide, is easily decomposed by heat, especially in the presence of trace amounts of water, secondary amines with excessively high boiling points are unsuitable, and boiling points exceeding 100°C are detrimental to removal after the lithiation reaction.

[0013] Preferably, the secondary amino groups in the secondary amine, excluding the active hydrogen, are the same as the organic groups in the secondary amine lithium salt compound, excluding the lithium ion. For example, when the secondary amine used is diethylamine, the secondary amine lithium salt compound is preferably diethylaminolithium, which facilitates the regeneration of diethylamine after the diethylaminolithium reacts with the intermediate via lithiation, allowing it to be reused in step (1).

[0014] More preferably, the secondary amine is diisopropylamine, and the secondary amine lithium salt compound is diisopropylaminolithium. The secondary amine acts as a catalyst and acid-binding agent in step (1). The acid-binding agent used in conventional prior art is a tertiary amine such as triethylamine, while the present invention uses diisopropylamine with greater steric hindrance, which is more conducive to the dissociation of ammonium fluoride and the activation of thioyl fluoride, so that the condensation reaction in step (1) proceeds faster and more effectively. The subsequent use of a lithium salt with the same secondary amine group can regenerate the secondary amine after the lithiation reaction, thereby realizing the recycling and reuse in the previous step.

[0015] Further, the organic solution containing the secondary amine lithium salt compound in step (2) is a tetrahydrofuran solution containing the secondary amine lithium salt compound;

[0016] The reaction temperature during the lithiation process shall be controlled to be no higher than 30°C;

[0017] After the organic solution containing the secondary amine lithium salt compound is added dropwise, the reaction is stirred for another 0.5-1 hour.

[0018] The non-aqueous solvent is dichloromethane.

[0019] Further, the molar ratio of the thioyl fluoride, the ammonium fluoride, and the secondary amine is (2-3.5):1:(3-5.5); the amount of the secondary amine lithium salt compound is 0.37 to 0.45 times the mass of the intermediate product.

[0020] The reaction equations for steps (1) and (2) above are as follows:

[0021]

[0022] R1R2NH represents a secondary amine.

[0023] Beneficial technical effects:

[0024] This invention uses thioyl fluoride, ammonium fluoride, and secondary amines with boiling points below 100°C as raw materials to first prepare intermediates, avoiding the problems of high equipment costs, environmental pollution, and high product impurity content caused by using highly corrosive raw materials. The intermediates of this invention are stable, and their reaction with secondary amine lithium salt compounds not only results in rapid and thorough lithiation, but also allows the reaction byproducts to be reused in the previous step if secondary amines and secondary amine lithium salt compounds with the same functional groups are selected. The entire process of this invention is anhydrous and chlorine-free, and no water is generated during the reaction. The reaction conditions of this invention are mild, and the final product, lithium electrolyte, is lithium difluorosulfonylimide, which has high quality, a purity of up to 99.99%, and a water content of less than 20 ppm, fluoride ion and sulfate ion contents of less than 5 ppm, and chloride ion content of less than 2 ppm. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specifically stated, the numerical values ​​set forth in these embodiments do not limit the scope of the invention. Techniques and methods known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques and methods should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0027] Experimental methods not specifically described in the following examples are generally determined according to national standards; if no corresponding national standard exists, they are performed according to generally accepted international standards or the standards proposed by relevant enterprises. Unless otherwise stated, all parts are parts by weight, and all percentages are weight percentages.

[0028] Example 1

[0029] The preparation method of low-water, high-purity electrolyte lithium salt includes the following steps:

[0030] (1) 100g ammonium fluoride (2.7mol) and 3000mL acetonitrile were added to a stainless steel reactor, sealed and cooled at 0℃. After being evacuated to a negative pressure of 100Pa, sulfuryl fluoride gas was introduced to atmospheric pressure. After being mixed evenly with stirring, 1093g diisopropylamine (10.8mol) was added. At the same time, the sulfuryl fluoride gas was continuously introduced to carry out the reaction. The reaction was stopped when the reaction pressure in the sealed system no longer changed (at this time, a total of 821g of sulfuryl fluoride gas was used). The reaction liquid in the reactor was distilled under high vacuum to obtain 747g of intermediate product. The distilled product was recovered.

[0031] (2) Under a nitrogen atmosphere, 1330 mL of a 2 mol / L diisopropylaminolithium tetrahydrofuran solution was slowly added dropwise to the obtained intermediate product. The lithiation reaction was carried out under stirring, while the reaction temperature was controlled not to exceed 30 °C. After the diisopropylaminolithium tetrahydrofuran solution was added, the reaction was continued for 0.5 h. After concentration under reduced pressure, crystallization was performed using dichloromethane. After filtration, the product was dried under vacuum to obtain 485.9 g of the final product, a low-water, high-purity electrolyte lithium salt—lithium difluorosulfonylimide.

[0032] In this embodiment, the yield of lithium bis(fluorosulfonyl)imide was 96.2% and the purity reached 99.99%.

[0033] Example 2

[0034] The preparation method of low-water, high-purity electrolyte lithium salt includes the following steps:

[0035] (1) 100g ammonium fluoride (2.7mol) and 3000mL acetonitrile were added to a stainless steel reactor, sealed and cooled at 5°C. After being evacuated to a negative pressure of 200Pa, sulfuryl fluoride gas was introduced to atmospheric pressure. After being mixed evenly with stirring, 1093g diisopropylamine (10.8mol) was added. At the same time, the sulfuryl fluoride gas was continuously introduced to carry out the reaction. The reaction was stopped when the reaction pressure in the sealed system no longer changed (at this time, a total of 770g of sulfuryl fluoride gas was used). The reaction liquid in the reactor was distilled under high vacuum to obtain 743.2g of intermediate product. The distilled product was recovered.

[0036] (2) Under a nitrogen atmosphere, 1290 mL of a 2 mol / L tetrahydrofuran solution of lithium diisopropylaminodimethyl ...

[0037] Example 3

[0038] The preparation method of low-water, high-purity electrolyte lithium salt includes the following steps:

[0039] (1) 100g ammonium fluoride (2.7mol) and 3000mL acetonitrile were added to a stainless steel reactor, sealed and cooled at 5°C. After being evacuated to a negative pressure of 300Pa, sulfuryl fluoride gas was introduced to atmospheric pressure. After being mixed evenly with stirring, 1093g diisopropylamine (10.8mol) was added. At the same time, the sulfuryl fluoride gas was continuously introduced to carry out the reaction. The reaction was stopped when the reaction pressure in the sealed system no longer changed (at this time, a total of 773g of sulfuryl fluoride gas was used). The reaction liquid in the reactor was distilled under high vacuum to obtain 742.2g of intermediate product. The distilled product was recovered.

[0040] (2) Under a nitrogen atmosphere, 1380 mL of a 2 mol / L tetrahydrofuran solution of lithium diisopropylaminodimethyl ...

[0041] Comparative Example 1

[0042] The product of this comparative example was prepared according to the method of Example 3 in CN111620315A.

[0043] Comparative Example 2

[0044] The product of this comparative example was prepared according to the method of Example 1 in CN114506829A.

[0045] The physicochemical properties of the final products obtained in the above embodiments and comparative examples were tested, and the specific results are shown in Table 1.

[0046] Table 1. Physical and chemical properties of the final product in the examples and comparative examples.

[0047]

[0048] As shown in Table 1, the process of this invention introduces no water or chlorine, and no water is generated during the reaction. The resulting final product, lithium bisfluorosulfonylimide electrolyte, has higher quality, solving the problem in existing technologies where water is generated during the reaction process, thus affecting the quality of the final product. The process of this invention achieves a final product yield of over 95%, a product purity of 99.99%, a water content of less than 20 ppm, and chloride, fluoride, and sulfate ion contents of less than 5 ppm.

[0049] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. Process for the preparation of low water high purity electrolyte imine lithium salts, characterized in that, Includes the following steps: (1) Add ammonium fluoride and acetonitrile to the reactor, seal it and cool it at 0-5℃. After evacuating to negative pressure, introduce sulfuryl fluoride gas to normal pressure. After mixing evenly, add secondary amine with a boiling point not exceeding 100℃. At the same time, continue to introduce the sulfuryl fluoride gas to carry out the reaction. Stop the reaction when the reaction pressure in the sealed system no longer changes. Distill the reaction solution under reduced pressure to obtain the intermediate product. (2) Under a protective atmosphere, an organic solution containing a secondary amine lithium salt compound is added dropwise to the obtained intermediate product while stirring to carry out the lithiation reaction. After the reaction is completed, the product is concentrated, crystallized under anhydrous conditions, filtered, and dried to obtain the final product lithium difluorosulfonylimide, i.e., low-water high-purity electrolyte lithium salt. When the secondary amine is diethylamine, the secondary amine lithium salt compound is diethylaminolithium; When the secondary amine is diisopropylamine, the secondary amine lithium salt compound is diisopropylaminolithium.

2. The method for preparing low-water, high-purity electrolyte lithium imine salt according to claim 1, characterized in that, The organic solution containing the secondary amine lithium salt compound mentioned in step (2) is a tetrahydrofuran solution containing the secondary amine lithium salt compound; The reaction temperature during the lithiation process shall be controlled to be no higher than 30°C; After the organic solution containing the secondary amine lithium salt compound is added dropwise, the reaction is stirred for another 0.5-1 hour. Crystallization was performed using the non-aqueous solvent dichloromethane under anhydrous conditions.

3. The method for preparing low-water, high-purity electrolyte lithium imine salt according to claim 1, characterized in that, The molar ratio of the thioyl fluoride, the ammonium fluoride, and the secondary amine is (2-3.5):1:(3-5.5); the amount of the secondary amine lithium salt compound is 0.37 to 0.45 times the mass of the intermediate product.

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