Method for decolorizing and purifying bis (fluorosulfonyl) imide salt

Abstract

The invention provides a method for decolorizing and purifying bis (fluorosulfonyl) imide salt, which comprises the following steps: reacting a decolorizing agent, an accelerant and bis (fluorosulfonyl) imide salt to be decolorized and purified to obtain purified bis (fluorosulfonyl) imide salt, the decolorizing agent is prepared from one or more of H2O2, O3, M1 (ClO) n1 and MIL-101 (Fe); wherein M1 is selected from one of Li, Na, K, Ca, Mg, Zn and Al; n1 is selected from 1, 2 or 3; the accelerant comprises carbonate, bicarbonate and hydroxide. The decolorizing and purifying method of the bis (fluorosulfonyl) imide salt provided by the invention is simple in process operation, high in efficiency, low in cost and remarkable in decolorizing and purifying effect, the used decolorizing agent and accelerant are trace and easy to remove, the chromaticity and purity of the product are improved, and the loss rate of the product is low.

Description

Technical Field

[0001] The invention belongs to the technical field of purification of bisfluorosulfonyl imide salts, and particularly relates to a decolorization and purification method of bisfluorosulfonyl imide salts. Background Art

[0002] Bis(fluorosulfonyl)imide salts (such as LiFSI, NaFSI, KFSI, Zn(FSI)2, and Al(FSI)3) are widely used in new energy battery electrolytes due to their high ionic conductivity, excellent thermal stability, and electrochemical performance. However, during the synthesis process, side reactions or the presence of trace organic impurities often result in the product having a pale yellow or brown color, affecting its purity and performance. Currently, there is limited literature on the decolorization of bis(fluorosulfonyl)imide salt electrolytes, and most decolorization methods rely on traditional methods such as activated carbon adsorption and recrystallization.

[0003] For example, the existing Chinese patent CN116462165A discloses a method for synthesizing and preparing high-purity lithium bis(fluorosulfonyl)imide. In this method, recrystallization is used to purify the synthesized lithium bis(fluorosulfonyl)imide salt. While the operation is relatively complicated, it increases production costs and easily causes solvent residues in the lithium bis(fluorosulfonyl)imide, making it difficult to meet the purity requirements for practical applications. CN117246982A discloses a method for purifying lithium bis(fluorosulfonyl)imide. An organic ammonium salt is added to a mixture of lithium bis(fluorosulfonyl)imide, and an intermediate mixture is obtained by reaction. After the intermediate mixture is subjected to adsorption by a decolorizing agent to remove colored impurities, the purified intermediate mixture is reacted with lithium ions under alkaline conditions to obtain lithium bis(fluorosulfonyl)imide. The decolorizing agent used for decolorization is activated carbon particles, activated carbon fiber, zeolite or diatomaceous earth. This method uses a large amount of physical decolorizing agents such as activated carbon, which has high raw material prices and generates a large amount of solid waste, resulting in a significant increase in production and processing costs.

[0004] CN117361452A discloses a method for preparing high-purity potassium bisfluorosulfonyl imide salt. The method comprises reacting sulfuryl fluoride, ammonia, and triethylamine, followed by post-treatment to obtain triethylamine bisfluorosulfonyl imide salt. The resulting triethylamine bisfluorosulfonyl imide salt is reacted with an aqueous potassium hydroxide solution to obtain a second reaction solution, which is then purified by recrystallization to obtain pure potassium bisfluorosulfonyl imide salt. This method utilizes recrystallization to purify the synthesized potassium bisfluorosulfonyl imide. A large amount of organic solvents, both good and poor solvents, are used during the purification process, increasing production steps and production costs.

[0005] The method of decolorizing and purifying bis(fluorosulfonyl)imide salt by activated carbon adsorption or recrystallization has the problems of low efficiency, high cost and large product loss. Summary of the Invention

[0006] In view of the problems of low efficiency, high cost and large product loss in the existing method of decolorizing and purifying bisfluorosulfonyl imide salt by activated carbon adsorption or recrystallization, the present application provides a method for decolorizing and purifying bisfluorosulfonyl imide salt.

[0007] The technical solutions adopted by the present invention to solve the above technical problems are as follows: In one aspect, the present invention provides a method for decolorizing and purifying a bisfluorosulfonyl imide salt, comprising the following steps: reacting a decolorizing agent and a accelerator with the bisfluorosulfonyl imide salt to be decolorized and purified to obtain a purified bisfluorosulfonyl imide salt; The decolorizing agent includes H2O2, O3, M1(ClO) n1 、MIL-101 (Fe) one or more; Wherein, M1 is selected from one of Li, Na, K, Ca, Mg, Zn, and Al; n1 is selected from 1, 2, or 3; The promoter includes one or more of carbonates, bicarbonates, and hydroxides.

[0008] Preferably, the decolorizing agent comprises H2O2; The accelerator includes (M2) n2 CO3, M3(HCO3) n3 、M4(OH) n4 One or more of; Among them, M2, M3, and M4 are each independently selected from one of Li, Na, K, Ca, Mg, Zn, and Al; n2 is selected from 1 or 2; n3 is selected from 1 or 2; and n4 is selected from 1 or 2.

[0009] Preferably, reacting the decolorizing agent, the accelerator and the bis(fluorosulfonyl)imide salt to be decolorized and purified comprises the following steps: The solvent and the bis(fluorosulfonyl)imide salt to be decolorized and purified are mixed evenly to obtain a first mixed solution. reacting the first mixed solution, the decolorizing agent and the accelerator; The solvent includes one or more of water, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, diisopropyl carbonate, propylene carbonate, diphenyl carbonate, cyclopropane diacid diester, succinic acid diester, ethyl acetate, dichloromethane, chloroform, ethanol, ether, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, and N-methylpyrrolidone.

[0010] Preferably, in the first mixed solution, the molar concentration of the bisfluorosulfonyl imide salt to be decolorized and purified is 0.01-45.0 mol / L.

[0011] Preferably, the mass ratio of the decolorizing agent to the first mixed solution is (0.0001~0.2):1.

[0012] Preferably, the mass ratio of the accelerator to the first mixed solution is (0.0001-0.8):1.

[0013] Preferably, the mass ratio of the accelerator to the first mixed solution is (0.01-0.1):1.

[0014] Preferably, the bis(fluorosulfonyl)imide salt to be decolorized and purified includes one or more of LiFSI, NaFSI, KFSI, CaH3FSI, Mg(FSI)2, Zn(FSI)2, and Al(FSI)3.

[0015] Preferably, the reaction temperature is 0-100° C., and the reaction time is 1 min-8 h.

[0016] Preferably, the reaction temperature is 20-80° C., and the reaction time is 1 h-6 h.

[0017] The present application provides a method for decolorizing and purifying a bisfluorosulfonyl imide salt, which has the following effects: 1) The decolorizer used has an oxidative decolorization function or has a substance that can capture oxygen in the air and convert it into oxygen free radicals, and has extremely high selectivity for pigment molecules or other colored impurities in the bisfluorosulfonyl imide salt. The decolorizer can react with the pigment molecules or other colored impurities, and the added alkaline promoter can react with the decolorizer in the system to further promote the decolorizer to generate oxygen free radicals, hydroxyl free radicals and other substances. The product generated by the reaction of the decolorizer and the promoter can further undergo oxidative decolorization with the pigment molecules or other colored impurities, thereby achieving complete decolorization. At the same time, the products of the oxidation of pigment molecules, the products of the oxidation of other colored impurities, and the salts formed after the decolorizer is reduced all have very low solubility in the system. Therefore, they can be removed through simple filtration and phase separation, thereby improving the purity and whiteness of the bisfluorosulfonyl imide salt in the organic phase, effectively reducing the impurity content of the bisfluorosulfonyl imide salt, and meeting the high requirements of lithium-ion batteries for electrolyte materials. 2) During the reaction between the decolorizer, the promoter, and the bisfluorosulfonyl imide salt to be decolorized and purified, the promoter, while decolorizing and purifying the bisfluorosulfonyl imide salt to be decolorized and purified, can also remove trace amounts of residual HF in the system or HF generated by the slight decomposition of the bisfluorosulfonyl imide salt due to its alkalinity, further improving the purity of the bisfluorosulfonyl imide salt and meeting the high requirements of lithium-ion batteries for electrolyte materials. 3) The decolorization and purification method of bisfluorosulfonyl imide salt provided by the present invention has simple process operation, high efficiency, low cost, easy operation, significant decolorization and purification effect, and the decolorizer and accelerator used are trace and easy to remove. It can greatly improve the removal rate of colored impurities in bisfluorosulfonyl imide salt, thereby improving the color and purity of the product, with a low product loss rate, and is suitable for large-scale industrial production. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] The present invention provides a method for decolorizing and purifying a bisfluorosulfonyl imide salt, comprising the following steps: reacting a decolorizing agent and a accelerator with the bisfluorosulfonyl imide salt to be decolorized and purified to obtain a purified bisfluorosulfonyl imide salt; The decolorizing agent includes H2O2, O3, M1(ClO) n1 , MIL-101 (Fe) or more; wherein M1 is selected from one of Li, Na, K, Ca, Mg, Zn, and Al; n1 is selected from 1, 2, or 3; The accelerators include carbonates, bicarbonates, and hydroxides.

[0020] The present application provides a method for decolorizing and purifying a bisfluorosulfonyl imide salt, which has the following effects: 1) The decolorizer used has an oxidative decolorization function or has a substance that can capture oxygen in the air and convert it into oxygen free radicals, and has extremely high selectivity for pigment molecules or other colored impurities in the bisfluorosulfonyl imide salt. The decolorizer can react with the pigment molecules or other colored impurities, and the added alkaline promoter can react with the decolorizer in the system to further promote the decolorizer to generate oxygen free radicals, hydroxyl free radicals and other substances. The product generated by the reaction of the decolorizer and the promoter can further undergo oxidative decolorization with the pigment molecules or other colored impurities, thereby achieving complete decolorization. At the same time, the products of the oxidation of pigment molecules, the products of the oxidation of other colored impurities, and the salts formed after the decolorizer is reduced all have very low solubility in the system. Therefore, they can be removed through simple filtration and phase separation, thereby improving the purity and whiteness of the bisfluorosulfonyl imide salt in the organic phase, effectively reducing the impurity content of the bisfluorosulfonyl imide salt, and meeting the high requirements of lithium-ion batteries for electrolyte materials. 2) During the reaction between the decolorizer, the promoter, and the bisfluorosulfonyl imide salt to be decolorized and purified, the promoter, while decolorizing and purifying the bisfluorosulfonyl imide salt to be decolorized and purified, can also remove trace amounts of residual HF in the system or HF generated by the slight decomposition of the bisfluorosulfonyl imide salt due to its alkalinity, further improving the purity of the bisfluorosulfonyl imide salt and meeting the high requirements of lithium-ion batteries for electrolyte materials. 3) The decolorization and purification method of bisfluorosulfonyl imide salt provided by the present invention has simple process operation, high efficiency, low cost, easy operation, significant decolorization and purification effect, and the decolorizing agent used is trace and easy to remove. It can greatly improve the removal rate of colored impurities in bisfluorosulfonyl imide salt, thereby improving the color and purity of the product, with a low product loss rate, and is suitable for large-scale industrial production.

[0021] In some embodiments, the decolorizing agent comprises H2O2; The accelerator includes (M2) n2 CO3, M3(HCO3) n3 、M4(OH) n4 One or more of; Among them, M2, M3, and M4 are each independently selected from one of Li, Na, K, Ca, Mg, Zn, and Al; n2 is selected from 1 or 2; n3 is selected from 1 or 2; and n4 is selected from 1 or 2.

[0022] When the decolorizing agent is selected from H2O2, it has strong oxidizing properties and is highly selective to the pigment molecules or other colored impurities in the bisfluorosulfonyl imide salt, and can directly react with the pigment molecules or other colored impurities to achieve the purpose of decolorization.

[0023] The promoter is selected from the above types, and the promoter can react with the decolorizing agent to further promote the decolorizing agent to generate substances such as oxygen free radicals and hydroxyl free radicals. The product generated by the reaction of the decolorizing agent and the promoter can further undergo oxidative decolorization with pigment molecules or other colored impurities, further remove the pigment molecules or other pigment impurities in the bisfluorosulfonyl imide salt, and further decolorize the bisfluorosulfonyl imide salt to be decolorized.

[0024] In some embodiments, the MIL-101 (Fe) is a compound represented by structural formula 1. Structural formula 1.

[0025] Specifically, MIL-101 (Fe) is a metal organic framework with the molecular formula C 24 H 12 ClFeO 13 , CAS number: 1189182-67-9, the coordination metal is Fe, and the ligand is terephthalic acid.

[0026] The transition metal Fe in MIL-101 (Fe) has photocatalytic activity. Therefore, under ultraviolet-visible light irradiation, it will catalyze oxygen in the air into oxygen free radicals. The free radicals are chemically active and will quickly undergo redox reactions with pigment impurities to generate substances insoluble in the system. Therefore, the colored impurities can be removed through post-processing operations such as filtration.

[0027] In some embodiments, reacting a decolorizing agent, a accelerator, and a bis(fluorosulfonyl)imide salt to be decolorized and purified comprises the following steps: The solvent and the bis(fluorosulfonyl)imide salt to be decolorized and purified are mixed evenly to obtain a first mixed solution. The first mixed solution, the decolorizing agent and the accelerator are reacted.

[0028] Specifically, in the step of uniformly mixing the solvent and the bisfluorosulfonyl imide salt to be decolorized and purified to obtain the first mixed solution, the solvent serves to dissolve the bisfluorosulfonyl imide salt to be decolorized and purified.

[0029] In the step of reacting the first mixed solution, the decolorizing agent and the accelerator, there is no requirement for the order of adding the decolorizing agent and the accelerator, and the effect can be produced as long as the decolorizing agent and the accelerator are added. The steps include directly adding the decolorizing agent and the accelerator to the first mixed solution, stirring and mixing, and reacting at the reaction temperature; first adding the decolorizing agent to the first mixed solution, stirring and mixing, and then adding the accelerator, and then reacting; and first adding the accelerator only to the first mixed solution, stirring and mixing, and then adding the decolorizing agent, and then reacting.

[0030] The decolorizing agent reacts with the pigment molecules or other colored impurities in the bis(fluorosulfonyl)imide salt to be decolorized and purified, achieving decolorization. The accelerator reacts with the decolorizing agent, further promoting the decolorizing agent to generate substances such as oxygen free radicals and hydroxyl free radicals. The products generated by the reaction between the decolorizing agent and the accelerator can further oxidize and decolorize the pigment molecules or other colored impurities, thereby achieving complete decolorization and further improving the purity and whiteness of the bis(fluorosulfonyl)imide salt.

[0031] In some embodiments, the solvent includes one or more of water, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, diisopropyl carbonate, propylene carbonate, diphenyl carbonate, cyclopropane diacid diester, succinic acid diester, ethyl acetate, dichloromethane, chloroform, ethanol, diethyl ether, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, and N-methylpyrrolidone.

[0032] Specifically, when the solvent is selected from the aforementioned organic solvents, while being able to dissolve the bisfluorosulfonyl imide salt to be decolorized and purified, the salt formed by the reaction of the decolorizer with the pigment impurities or pigment molecules has low solubility in the organic phase, facilitating removal of the salt formed by the reaction of the decolorizer with the pigment impurities or pigment molecules through simple filtration and phase separation. It should be noted that during the filtration and phase separation steps, if the accelerator is an aqueous solution, additional water is not required for phase separation. However, if the accelerator is not an aqueous solution, water must be added for filtration and phase separation.

[0033] When the solvent is selected from the above-mentioned water, an organic solvent needs to be added for phase separation during filtration and phase separation. The bisfluorosulfonyl imide salt will enter the organic phase, while the salt generated by the reaction of the decolorizer and pigment impurities or pigment molecules will dissolve in the water, thereby achieving separation. In some embodiments, the bisfluorosulfonyl imide salt to be decolorized and purified includes one or more of LiFSI, NaFSI, KFSI, CaH3FSI, Mg(FSI)2, Zn(FSI)2, and Al(FSI)3.

[0034] In some embodiments, the reaction temperature is 0-100° C., and the reaction time is 1 min-8 h.

[0035] Specifically, the decolorizing agent itself has an oxidizing function or has a substance that can capture oxygen in the air and convert it into oxygen free radicals through photocatalytic oxidation. The reaction temperature is controlled within the range of 0-100°C and the reaction time is within the range of 10 minutes to 8 hours. This helps to undergo a redox reaction with the pigment molecules or other colored impurities in the bisfluorosulfonyl imide salt, thereby removing the pigment molecules or other colored impurities in the bisfluorosulfonyl imide salt, thereby achieving the purpose of decolorizing the bisfluorosulfonyl imide salt. Under the conditions of 0-100°C, the promoter and the decolorizing agent react, further promoting the decolorizing agent to release more oxygen free radicals, hydroxyl free radicals and other substances to react with pigment impurity molecules, further promoting decolorization. At the same time, the alkaline promoter also reacts with HF to remove trace residual HF in the system or HF generated by the slight decomposition of the bisfluorosulfonyl imide salt, generating an aqueous solution of fluoride. After removing it through phase separation, the purity of the bisfluorosulfonyl imide salt in the organic phase can be improved.

[0036] The reaction temperature can be in the range of 0-20° C., 20-40° C., 40-60° C., 60-80° C., or 80-100° C. The reaction time can be in the range of 1 min-60 min, 1 h-1.5 h, 1.5 h-2.5 h, 2.5 h-4 h, 4 h-5 h, 5 h-6 h, 6 h-7 h, or 7 h-8 h.

[0037] If the temperature is lower than 0°C, the reaction between the decolorizing agent and the colored impurities is very slow and has no industrial economic value. The reaction of the promoter catalyzing the decolorizing agent is very slow, and the water phase may solidify due to the low temperature, which is not conducive to promoting the decolorization reaction. If the temperature is higher than 100°C, the promoter is concentrated, and the decolorizing agent decomposes rapidly and easily forms an explosive mixture with the organic solvent, which poses a safety risk and leads to the production of new uncontrollable by-products, thereby reducing the purity of the bisfluorosulfonyl imide salt.

[0038] In some preferred embodiments, the reaction temperature is 20-80° C., and the reaction time is 1 h-6 h.

[0039] When the reaction temperature and time are within the above ranges, the reaction rate is high, the reaction time is appropriate, the process time is shortened, and the preparation cost is reduced.

[0040] More preferably, the reaction temperature is 40-50° C., and the reaction time is 2-4 hours.

[0041] In some embodiments, in the first mixed solution, the molar concentration of the bis(fluorosulfonyl)imide salt to be decolorized and purified is 0.01-45.0 mol / L.

[0042] Specifically, in the first mixed solution, the molar concentration of the bisfluorosulfonyl imide salt to be decolorized and purified is in the range of 0.01 to 45.0 mol / L, which helps the solvent to better and quickly dissolve the bisfluorosulfonyl imide salt to be decolorized and purified, and at the same time facilitates the reaction of the decolorizer, the promoter and the pigment impurities to remove colored impurities in the bisfluorosulfonyl imide salt.

[0043] In the first mixed solution, the molar concentration of the bisfluorosulfonyl imide salt to be decolorized and purified can be in the following ranges: 0.01-1 mol / L, 1-8 mol / L, 8-10 mol / L, 10-20 mol / L, 20-30 mol / L, 30-40 mol / L or 40-45 mol / L.

[0044] In some embodiments, the mass ratio of the decolorizing agent to the first mixed solution is (0.0001-0.2):1.

[0045] Specifically, the mass ratio of the decolorizing agent to the first mixed solution is in the range of (0.0001-0.2):1, which is conducive to the reaction between the decolorizing agent and the colored impurities to remove the colored impurities in the bisfluorosulfonyl imide salt.

[0046] The mass ratio of the decolorizing agent to the first mixed solution can be in the following ranges: (0.0001-0.005):1, (0.005-0.009):1, (0.009-0.01):1, (0.01-0.02):1, (0.02-0.05):1, (0.05-0.1):1, (0.1-0.15):1 or (0.15-0.2):1.

[0047] In some preferred embodiments, the mass ratio of the decolorizing agent to the first mixed solution is (0.005-0.1):1.

[0048] Further preferably, the mass ratio of the decolorizing agent to the first mixed solution is (0.005~0.05):1.

[0049] In some preferred embodiments, the decolorizing agent includes one or more of H2O2, O3, (M1ClO)n1; M1 is selected from one of Li, Na, K, Ca, Mg, Zn, and Al; and n1 is selected from 1, 2, or 3.

[0050] Specifically, the decolorizing agent is selected from the above types, has strong oxidizing properties, and can directly react with the pigment molecules or other pigment impurities in the bisfluorosulfonyl imide salt to be decolorized, remove the pigment molecules or other pigment impurities, achieve the purpose of decolorizing the bisfluorosulfonyl imide salt, and improve the whiteness of the bisfluorosulfonyl imide salt.

[0051] In some embodiments, the mass ratio of the accelerator to the first mixed solution is (0.0001-0.8):1.

[0052] The mass ratio of the accelerator to the first mixed solution is (0.0001-0.8):1, which is conducive to the reaction between the accelerator and the decolorizer, further removing pigment molecules or other pigment impurities, and improving the purity and whiteness of the purified bisfluorosulfonyl imide salt.

[0053] The mass ratio of the accelerator to the first mixed solution can be in the following ranges: (0.0001-0.0005):1, (0.0005-0.0009):1, (0.0009-0.001):1, (0.001-0.002):1, (0.002-0.005):1, (0.005-0.01):1, (0.01-0.02):1, (0.02-0.05):1, (0.05-0.1):1, (0.1-0.2):1, (0.2-0.5):1 or (0.5-0.8):1.

[0054] In some preferred embodiments, the mass ratio of the accelerator to the first mixed solution is (0.01-0.1):1.

[0055] In some embodiments, reacting a decolorizing agent and a accelerator with the bisfluorosulfonyl imide salt to be decolorized and purified to obtain a purified bisfluorosulfonyl imide salt comprises the following steps: The solvent and the bis(fluorosulfonyl)imide salt to be decolorized and purified are mixed evenly to obtain a first mixed solution. reacting the first mixed solution, the decolorizing agent and the accelerator; After the reaction is completed, post-treatment is performed to obtain a purified bisfluorosulfonyl imide salt; The post-treatment comprises the following steps: obtaining a second mixed solution after the reaction is completed, performing phase separation on the second mixed solution to obtain an organic phase, performing solid-liquid separation to obtain a filtrate, and performing reduced pressure distillation and drying on the filtrate to obtain a purified bisfluorosulfonyl imide salt solid.

[0056] Specifically, the decolorizing agent reacts with pigment molecules or other pigment impurities to obtain product 1, the accelerator reacts with the decolorizing agent to obtain product 2, and product 2 reacts with pigment molecules or other pigment impurities to obtain product 3. Both product 1 and product 3 are insoluble in the bisfluorosulfonyl imide salt solution system, thereby obtaining a completely decolorized bisfluorosulfonyl imide salt solution in the organic phase through solid-liquid separation. The filtrate of the decolorized bisfluorosulfonyl imide salt is then subjected to reduced pressure distillation and drying to obtain a purified bisfluorosulfonyl imide salt solid.

[0057] It should be noted that the bis(fluorosulfonyl)imide salt to be decolorized and purified can be prepared by oneself or purchased from the market. Different bis(fluorosulfonyl)imide salts have different solubilities in different solvent systems.

[0058] The present invention is further described below with reference to the following examples.

[0059] Example 1 This example is used to illustrate a method for decolorizing and purifying a fluorosulfonyl imide salt disclosed in the present invention.

[0060] S1: Weigh 100 g of light yellow LiFSI solid and dissolve it in 500 mL of diisopropyl carbonate to prepare a first mixed solution containing 1.07 mol / L LiFSI. The chromaticity of the first mixed solution is measured to be 201.2 Hazen.

[0061] S2: 572.5 g of the first mixed solution obtained in step S1 was obtained. 0.5 g of a 30% hydrogen peroxide solution and 2.0 g of an 11.5% aqueous LiOH solution were weighed and added to the first mixed solution. The mixture was stirred at 40°C and 100 rpm for 3.5 hours to allow the reaction to proceed. After completion of the reaction, a second mixed solution was obtained.

[0062] S3: The second mixed solution in step S2 was phase separated to obtain an organic phase, which was then subjected to solid-liquid separation to obtain a filtrate. The filtrate was the organic phase. The colorimetry of the organic phase was measured to be 7.6 Hazen. The solvent was then removed by distillation under reduced pressure. The white solid product was vacuum dried at 65°C for 8 hours to obtain 99.5 g of the final product LiFSI. The yield was calculated, and the whiteness of the final product was tested to be 98%.

[0063] Example 2 S1: Weigh 104.0 g of dark yellow-brown NaFSI solid and dissolve it in 500 ml of ethyl methyl carbonate solution, corresponding to a concentration of about 1.0 mol / L. The chromaticity of the first mixed solution is measured to be 500.0 Hazen.

[0064] S2: Prepare 5g of ozone gas as a decolorizing agent using an ozone generator.

[0065] Obtain 644.0 g of the first mixed solution obtained in step S1, and slowly introduce the above 5 g of ozone gas into the first mixed solution through a capillary glass tube, controlling the gas flow rate to 18-20 ml / min, stirring at a speed of 200 rpm at 20°C, and conducting a first reaction for 2 hours. After the first reaction, a second mixed solution is obtained, and then 0.5 g of Na2CO3 solid is added to the second mixed solution, stirred at a speed of 200 rpm at 20°C, and a second reaction is conducted for 1.5 hours. After the second reaction, a third mixed solution is obtained.

[0066] S3: The third mixed solution in step S2 was phase separated to obtain an organic phase, which was filtered to remove the filter residue. The colorimetry of the remaining organic phase was measured to be 30.0 Hazen. The solvent was then removed by distillation under reduced pressure to obtain a white solid product. The white solid product was vacuum dried at 65° C. for 8 hours to obtain 102.8 g of the final product NaFSI. The yield was calculated, and the whiteness of the final product was tested to be 96%.

[0067] Example 3 S1: Weigh 100 g of light yellow KFSI solid and dissolve it in 200 mL of N-methylpyrrolidone to prepare a first mixed solution containing KFSI at a concentration of about 2.3 mol / L. The chromaticity of the first mixed solution is measured to be 300.8 Hazen.

[0068] S2: Weigh 0.3g of KClO solid as a decolorizing agent and 1.0g of a 50wt% K2CO3 aqueous solution as a accelerator.

[0069] 306 g of the first mixed solution obtained in step S1 was obtained, and 1.0 g of the above-mentioned 50 wt% K2CO3 aqueous solution was added to the first mixed solution, and the mixture was stirred at 400 rpm at 30°C and reacted for 1 hour. Subsequently, 0.3 g of KClO solid was added to the above system, and the mixture was stirred at 400 rpm at 30°C and reacted for 2 hours. After the reaction, a second mixed solution was obtained.

[0070] S3: The second mixed solution in step S2 was phase-separated to obtain an organic phase, which was filtered and measured to have a colorimetry of 40.0 Hazen. The solvent was then removed by distillation under reduced pressure to obtain a white solid product. The white solid product was vacuum-dried at 65° C. for 8 hours to obtain 99.2 g of the final product KFSI. The yield was calculated, and the whiteness of the final product was tested to be 98%.

[0071] Example 4 S1: Weigh 20 g of light yellow CaH3FSI solid and dissolve it in 200 mL of acetonitrile to prepare a first mixed solution containing CaH3FSI at a concentration of about 0.4 mol / L. The chromaticity of the first mixed solution is measured to be 312.5 Hazen.

[0072] S2: Weigh 0.3 g of Ca(ClO)2 solid as a decolorizing agent.

[0073] 177.2 g of the first mixed solution obtained in step S1 was obtained, and the above-mentioned 0.3 g of Ca(ClO)2 solid and 12.7 g of 0.166 wt% Ca(OH)2 aqueous solution were added to the first mixed solution at the same time. The mixture was stirred at 400 rpm at 30°C and reacted for 6 hours. After the reaction, a second mixed solution was obtained.

[0074] S3: The second mixed solution in step S2 was phase-separated and filtered to obtain a filtrate. The color of the filtrate was measured to be 20.3 Hazen. The solvent was then distilled off under reduced pressure to obtain a white solid product. The white solid product was vacuum-dried at 65°C for 8 hours to obtain 19.1 g of the final product CaH3FSI. The yield was calculated and the whiteness of the final product was tested to be 97%.

[0075] Example 5 S1: Weigh 20 g of light yellow Mg(FSI)2 solid and dissolve it in 200 mL of dimethyl carbonate to prepare a first mixed solution containing 0.25 mol / L Mg(FSI)2. The chromaticity of the first mixed solution is measured to be 410.5 Hazen.

[0076] S2: Obtain 234 g of the first mixed solution obtained in step S1, add 1.0 g of 30 wt% H2O2 dropwise to the first mixed solution, and at the same time add 1.0 g of Mg2(OH)2CO3 solid to the first mixed solution, and stir at a speed of 150 rpm at 25°C to react for 5 hours. A small amount of bubbles are generated during the reaction. After the bubbles stop being generated, the reaction is completed to obtain a second mixed solution.

[0077] S3: The second mixed solution in step S2 was separated into phases to obtain an organic phase, and the colorimetry of the organic phase was measured to be 32.2 Hazen. The solvent was then removed by distillation under reduced pressure to obtain a white solid product. The white solid product was vacuum dried at 65°C for 8 hours to obtain 19.5 g of the final product Mg(FSI)2. The yield was calculated, and the whiteness of the final product was tested to be 98%.

[0078] Example 6 S1: Weigh 30 g of light yellow Zn(FSI)2 solid and dissolve it in 300 mL of ethyl acetate to prepare a first mixed solution containing 0.23 mol / L Zn(FSI)2. The chromaticity of the first mixed solution is measured to be 232.5 Hazen.

[0079] S2: Hydrogen peroxide is a decolorizing agent.

[0080] 298.2 g of the first mixed solution obtained in step S1 was obtained, 0.6 g of a 30% by mass hydrogen peroxide solution was weighed and added dropwise to the first mixed solution, and 825.0 g of a 0.004 wt% saturated aqueous zinc hydroxide solution was added to the first mixed solution. The mixture was stirred at 50° C. and 200 rpm and reacted for 6 hours and 40 minutes to obtain a second mixed solution.

[0081] S3: The second mixed solution in step S2 was separated and the organic phase was taken for colorimetry measurement, which was 8.9 Hazen. The solvent was then distilled off under reduced pressure to obtain a white solid product. The white solid product was vacuum dried at 65°C for 6 hours to obtain 29.1 g of the final product Zn(FSI)2. The yield was calculated and the whiteness of the final product was tested to be 97%.

[0082] Example 7 S1: Weigh 100 g of light yellow KFSI solid and dissolve it in 100 mL of pure water to prepare a first mixed solution containing 4.5 mol / L KFSI. The chromaticity of the first mixed solution is measured to be 300.7 Hazen.

[0083] S2: Hydrogen peroxide is a decolorizing agent.

[0084] 200 g of the first mixed solution obtained in step S1 was obtained, 0.4 g of a 30% mass fraction hydrogen peroxide solution was weighed and added dropwise to the first mixed solution. At the same time, 1.0 g of a 10.0 wt% KHCO3 aqueous solution was added to the first mixed solution. The mixture was stirred at 40°C and 150 rpm for 4 hours to obtain a second mixed solution.

[0085] S3: The second mixed solution in step S2 was subjected to phase separation to remove the accelerator aqueous phase to obtain an organic phase. The colorimetry of the organic phase was measured to be 10.3 Hazen, and the solvent was subsequently removed by distillation under reduced pressure to obtain a white solid product. The white solid product was vacuum dried at 65° C. for 8 hours to obtain 99.5 g of the final product KFSI. The calculated yield and the whiteness of the final product were tested to be 98%.

[0086] Example 8 S1: Weigh 100 g of light yellow KFSI solid and dissolve it in 150 mL of ethyl methyl carbonate to prepare a 3.0 mol / L first mixed solution containing KFSI. The chromaticity of the first mixed solution is measured to be 481.5 Hazen.

[0087] S2: Hydrogen peroxide is a decolorizing agent.

[0088] Obtain 251.5 g of the first mixed solution obtained in step S1, weigh 0.1 g of a 30 wt% H2O2 solution, and add it to the first mixed solution. At the same time, add 0.1 g of a 50 wt% K2CO3 aqueous solution to the first mixed solution. The reaction is carried out at 45°C and 150 rpm for 4 hours to obtain a second mixed solution.

[0089] S3: The second mixed solution in step S2 was phase-separated, and the colorimetry of the organic phase was measured to be 7.9 Hazen. The solvent was then removed by distillation under reduced pressure to obtain a white solid product. The white solid product was vacuum-dried at 65° C. for 8 hours to obtain 99.5 g of the final product KFSI. The yield was calculated, and the whiteness of the final product was tested to be 98%.

[0090] Example 9 S1: Weigh 100 g of light yellow LiFSI solid and dissolve it in 500 mL of dimethyl carbonate to prepare a 1.07 mol / L first mixed solution containing LiFSI. The chromaticity of the first mixed solution is measured to be 400.2 Hazen.

[0091] S2: MIL-101 (Fe) solid is a decolorizing agent.

[0092] 635 g of the first mixed solution obtained in step S1 was obtained, 0.1 g of MIL-101 (Fe) was weighed and added to the first mixed solution, and 2.0 g of an 11.5% mass fraction LiOH aqueous solution was added to the first mixed solution. A XEPU-1338LMS model 8W dual-wavelength (365 nm, 254 nm) ultraviolet lamp was used as the light source. At the same time, an approximately 500 ml air balloon was connected to the reaction flask to ensure oxygen supply. The reaction was carried out at 30°C and a rotation speed of 100 rpm under ultraviolet light irradiation for approximately 3.5 hours. After the reaction was completed, a second mixed solution was obtained.

[0093] S3: The second mixed solution in step S2 was phase-separated to obtain an organic phase, and the colorimetry of the organic phase was measured to be 10.5 Hazen. The solvent was then removed by distillation under reduced pressure to obtain a white solid product. The white solid product was vacuum-dried at 65°C for 8 hours to obtain 99.5 g of the final product LiFSI. The yield was calculated, and the whiteness of the final product was tested to be 97%.

[0094] Example 10 The steps of Example 10 are similar to those of Example 1, except that the hydrogen peroxide solution added in step S2 is different from that in Example 1, the accelerator LiOH added is also different from that in Example 1, and step S3 is different.

[0095] In step S2, the decolorizing agent added in Example 10 was 500 g of a 30% by mass hydrogen peroxide solution, and the accelerator added was 200 g of 11.5 wt% LiOH. The rest was the same as in Example 1. The specific steps of Example 10 in step S3 were as follows: the second mixed solution in step S2 was phase-separated, and the colorimetry of the organic phase was measured to be 15.2 Hazen. The solvent was then removed by distillation under reduced pressure to obtain a white solid product. The white solid product was vacuum-dried at 65°C for 8 hours to obtain 93.1 g of the final product, LiFSI. The yield was low, as a large amount of the main product was oxidatively decomposed. The whiteness of the final product was 96%.

[0096] Example 11 Example 11 was identical to Example 1 in most of its steps, except that 15 g of a 30% hydrogen peroxide solution was added in step S2 of Example 11. The remainder of the steps were identical to Example 1. For the color and whiteness data for step S3 of Example 11, see Table 1.

[0097] Example 12 Example 12 was identical to Example 1 in most of its steps, except that 18 g of a 30% hydrogen peroxide solution was added in step S2. The remainder of the steps were identical to Example 1. For the color and whiteness data for step S3 in Example 12, see Table 1.

[0098] Example 13 Example 13 was identical to Example 1 in most of its steps, except that 100 g of an 11.5% aqueous LiOH solution was added in step S2 of Example 13. The remainder of the steps were identical to Example 1. The color and whiteness data for step S3 of Example 13 are shown in Table 1.

[0099] Example 14 Example 14 was identical to Example 1 in most of its steps, except that 460 g of an 11.5% aqueous LiOH solution was added in step S2 of Example 14. The remainder of the steps was identical to Example 1. The color and whiteness data for step S3 of Example 14 are shown in Table 1.

[0100] Example 15 Most of the steps in Example 15 are the same as those in Example 1, except that the decolorizing agent added in step S2 of Example 15 is 0.3 g of ozone gas, which is slowly introduced into the first mixed solution through a capillary glass tube, and the gas flow rate is controlled to be 18-20 ml / min. The rest is the same as in Example 1.

[0101] Example 16 Most of the steps in Example 16 are the same as those in Example 1, except that 0.3 g of solid KClO is added as the decolorizing agent in step S2 of Example 16. The rest of the steps are the same as those in Example 1.

[0102] Comparative Example 1 Most of the steps of Comparative Example 1 are the same as those of Example 1, except that Comparative Example 1 uses activated carbon for decolorization, and the mass of the activated carbon is 0.075 g; the decolorization method is also to add the activated carbon directly to the first mixed solution, react for 3 hours, and filter to remove the activated carbon powder, obtain the filtrate for color measurement, and the color is 82.0 Hazen. The solvent is then distilled off under reduced pressure to obtain a white solid product, and the white solid product is vacuum dried at 65°C for 8 hours to obtain 99.6 g of the final product LiFSI, and the yield is calculated. The whiteness of the final product is tested to be 86%.

[0103] Comparative Example 2 Comparative Example 2 is the same as Example 1 in most steps, except that Comparative Example 2 uses a recrystallization method for decolorization; Decolorization method: After obtaining the first mixed solution, 1000 ml of dichloroethane is added as a poor solvent to precipitate LiFSI as a solid, and the white solid is filtered to obtain a white solid. The white solid product is vacuum dried at 65° C. for 8 hours to obtain 90.2 g of the final product LiFSI, and the whiteness of the final product is 91%.

[0104] Comparative Example 3 Comparative Example 3 followed most of the same steps as Example 1, except that no LiOH aqueous solution, a accelerator, was added in Comparative Example 1, and the reaction time was 3.5 hours. The filtrate was separated and subjected to colorimetric testing. The solvent was then removed by distillation under reduced pressure to obtain a white solid product. The white solid product was vacuum-dried at 65°C for 8 hours. The final product was weighed and tested for whiteness. The test data are shown in Table 1.

[0105] The chromaticity of the first mixed solution, the chromaticity of the filtrate, the whiteness of the final product, and the product loss rate of the above embodiments and comparative examples are recorded in Table 1.

[0106] Product loss rate = (mass of the initially added bisfluorosulfonyl imide salt - mass of the final product bisfluorosulfonyl imide salt) / mass of the initially added bisfluorosulfonyl imide salt * 100%.

[0107] Table 1 By comparing Examples 1-9 and Comparative Example 3 in Table 1, in Comparative Example 3, there is no promoter, the filtrate obtained after the reaction has high chroma and low whiteness, and the HF content after decolorization is high, indicating that the decolorization and purification method of the bisfluorosulfonyl imide salt provided by the present application is effective, and the decolorizing agent includes H2O2, O3, M1(ClO) n1 , one or more of MIL-101 (Fe), M1 is selected from one of Li, Na, K, Ca, Mg, Zn, and Al; n1 is selected from 1, 2, or 3, and the promoter includes one or more of carbonate, bicarbonate, and hydroxide; a decolorizing agent and a promoter are added, the decolorizing agent can react with pigment molecules or other colored impurities, and the product generated by the reaction of the decolorizing agent and the promoter can be further oxidized and decolorized with the pigment molecules or other colored impurities, and the oxidized pigment molecules or other colored impurities, and the salts formed after the decolorizing agent is reduced have very low solubility in the system and can be precipitated from the system through simple filtration and phase separation operations, thereby improving the purity and whiteness of the bisfluorosulfonyl imide salt, effectively reducing the impurity content of the bisfluorosulfonyl imide salt, and meeting the high requirements of lithium-ion batteries for electrolyte materials.

[0108] By comparing Example 1 and Example 10, too much decolorizing agent was added in Example 10. Although the whiteness was not affected, the product loss rate was high due to the excessive addition of decolorizing agent. This is because the excessive decolorizing agent decomposes and generates a high content of oxygen free radicals. Excessive concentrations of oxygen free radicals will attack the bisfluorosulfonyl imide salt, causing its oxidative decomposition. This indicates that when the mass ratio of the decolorizing agent to the first mixed solution is within the range of (0.0001~0.2):1, while reducing costs, it is beneficial to improve the yield, purity and whiteness of the bisfluorosulfonyl imide salt, effectively reduce the impurity content of the bisfluorosulfonyl imide salt, and effectively ensure the product yield.

[0109] Comparing Example 1 with Comparative Examples 1 and 2, in Comparative Example 1, activated carbon was used to adsorb the pigment, and the obtained product had a low loss rate, a whiteness of less than 90%, and the HF impurity could not be removed. In Comparative Example 2, recrystallization was used, and although the product had a high whiteness, the HF impurity could not be removed, and the loss rate was slightly higher. However, by using the method provided in the present application, not only the whiteness of the product was higher than 90%, but the HF impurity could also be removed at the same time, the product loss rate was low, and the purity of the bisfluorosulfonyl imide salt was improved.

[0110] Comparison of Example 1 with Examples 11-12 shows that when the mass ratio of the accelerator to the first mixed solution is within the range of (0.005-0.1):1, the resulting bisfluorosulfonyl imide salt has a higher whiteness and a lower product loss rate. Comparison of Example 1 with Examples 13-14 shows that when the mass ratio of the accelerator to the first mixed solution is within the range of (0.01-0.1):1, the resulting bisfluorosulfonyl imide salt has a higher whiteness and a lower product loss rate.

[0111] Comparison of Examples 15 and 16 with Example 1 demonstrates that the use of hydrogen peroxide as a decolorizing agent results in a bisfluorosulfonyl imide salt with higher whiteness, lower product loss, and better decolorization. The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for decolorizing and purifying a bis(fluorosulfonyl)imide salt, characterized in that: The following steps are involved: reacting a decolorizing agent and a accelerator with the bisfluorosulfonyl imide salt to be decolorized and purified to obtain a purified bisfluorosulfonyl imide salt; The decolorizing agent includes H2O2, O3, M1(ClO) n1 、MIL-101 (Fe) one or more; Wherein, M1 is selected from one of Li, Na, K, Ca, Mg, Zn, and Al; n1 is selected from 1, 2, or 3; The promoter includes one or more of carbonates, bicarbonates, and hydroxides.

2. The method for decolorizing and purifying a bisfluorosulfonyl imide salt according to claim 1, wherein: The decolorizing agent includes H2O2; The accelerator includes (M2) n2 CO3, M3(HCO3) n3 、M4(OH) n4 One or more of; Among them, M2, M3, and M4 are each independently selected from one of Li, Na, K, Ca, Mg, Zn, and Al; n2 is selected from 1 or 2; n3 is selected from 1 or 2; and n4 is selected from 1 or 2.

3. The method for decolorizing and purifying a bisfluorosulfonyl imide salt according to claim 1, wherein: The decolorizing agent, the accelerator and the bis(fluorosulfonyl)imide salt to be decolorized and purified are reacted, comprising the following steps: The solvent and the bis(fluorosulfonyl)imide salt to be decolorized and purified are mixed evenly to obtain a first mixed solution. reacting the first mixed solution, the decolorizing agent and the accelerator; The solvent includes one or more of water, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, diisopropyl carbonate, propylene carbonate, diphenyl carbonate, cyclopropane diacid diester, succinic acid diester, ethyl acetate, dichloromethane, chloroform, ethanol, ether, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, and N-methylpyrrolidone.

4. The method for decolorizing and purifying a bisfluorosulfonyl imide salt according to claim 3, wherein: In the first mixed solution, the molar concentration of the bisfluorosulfonyl imide salt to be decolorized and purified is 0.01 mol / L to 45.0 mol / L.

5. The method for decolorizing and purifying bisfluorosulfonyl imide salt according to claim 3, characterized in that: The mass ratio of the decolorizing agent to the first mixed solution is (0.0001-0.2):

1.

6. The method for decolorizing and purifying bisfluorosulfonyl imide salt according to claim 3, characterized in that: The mass ratio of the accelerator to the first mixed solution is (0.0001-0.8):

1.

7. The method for decolorizing and purifying bisfluorosulfonyl imide salt according to claim 6, characterized in that: The mass ratio of the accelerator to the first mixed solution is (0.01-0.1):

1.

8. The method for decolorizing and purifying bisfluorosulfonyl imide salt according to claim 1, characterized in that: The bis(fluorosulfonyl)imide salt to be decolorized and purified includes one or more of LiFSI, NaFSI, KFSI, CaH3FSI, Mg(FSI)2, Zn(FSI)2, and Al(FSI)3.

9. The method for decolorizing and purifying bisfluorosulfonyl imide salt according to claim 1, characterized in that: The reaction temperature is 0-100° C., and the reaction time is 1 min-8 h.

10. The method for decolorizing and purifying bisfluorosulfonyl imide salt according to claim 9, characterized in that: The reaction temperature is 20-80° C., and the reaction time is 1 h-6 h.

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