A method for simultaneously determining fluoride ions, chloride ions, sulfate ions and main content in a bisfluorosulfonylimide acid

Abstract

The application provides a method for simultaneously determining fluorine ions, chlorine ions, sulfate ions and main content of bisfluorosulfonylimide acid, and is characterized in that the method comprises the following steps: (1) preparing standard solutions of fluorine ions, chlorine ions and sulfate ions, and establishing a standard curve according to the peak area and corresponding concentration of each anion; (2) adding a pH regulator to the bisfluorosulfonylimide acid sample to adjust the pH to a certain range; (3) feeding the treated sample into an ion chromatograph for testing; and (4) calculating the concentration of each anion in the sample to be tested according to the standard curve and the testing result of the sample, and simultaneously calculating the content of bisfluorosulfonylimide acid by using the area normalization method.

Description

Technical Field

[0001] This invention belongs to the field of detection technology, and more specifically, relates to a method for simultaneously determining the content of fluoride ions, chloride ions, sulfate ions and main components in difluorosulfonylimide acid. Background Technology

[0002] Lithium-ion electrolytes are the lifeblood of lithium-ion batteries, an indispensable core component. Lithium-ion batteries have stringent requirements for electrolyte performance, especially the content of various impurity anions. Lithium bisfluorosulfonylimide (LiFSI) is an important component of lithium-ion electrolytes, and its impurity content mainly comes from its main synthetic raw material, bisfluorosulfonylimide acid (HFSI). Common impurity anions in lithium salts in electrolytes include fluoride, chloride, and sulfate ions. Therefore, accurate detection of the content of various anions in HFSI is crucial for the performance of lithium-ion battery electrolytes. However, HFSI is a strong acid and cannot be directly tested using general anion detection methods, as this would cause irreversible damage to the ion chromatography equipment, resulting in inaccurate test results. Neutralization of HFSI is necessary, but it is easily decomposed, making it difficult to guarantee the accuracy of the test.

[0003] Patent CN108387674B discloses a method for determining the purity of lithium bis(fluorosulfonyl)imide, and patent CN114924019A discloses a method for testing chloride in bis(fluorosulfonyl)imide. Both patents can only detect the content of one substance. Currently, there are no reported industrial methods that can simultaneously and accurately determine the main content of bis(fluorosulfonyl)imide acid and the detection of fluoride, chloride, and sulfate ions. Therefore, there is a need to design a simple, accurate, and effective method for simultaneously determining the main content of bis(fluorosulfonyl)imide acid and various impurity anions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for simultaneously determining the contents of chloride ions, fluoride ions, sulfate ions, and the main content of difluorosulfonylimide in difluorosulfonylimide, thereby overcoming the limitation of existing technologies in detecting difluorosulfonylimide by simultaneously determining the main content and multiple anions.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for simultaneously determining the fluoride, chloride, sulfate, and main content in difluorosulfonylimide acid, characterized by comprising the following steps:

[0007] (1) Prepare standard solutions of fluoride ion, chloride ion and sulfate ion, and inject the prepared standard solutions of each anion into the ion chromatograph. Establish a standard curve based on the peak area and corresponding concentration of each anion.

[0008] (2) Add pH adjuster to the sample of difluorosulfonylimine to adjust the pH to a certain range;

[0009] (3) Inject the pH-adjusted sample into the ion chromatograph for testing;

[0010] (4) Calculate the concentration of each anion in the sample to be tested based on the standard curve and the sample test results, and at the same time calculate the content of difluorosulfonyl imide in the sample to be tested using the area normalization method.

[0011] The mobile phase used in the ion chromatograph is a mixture of sodium carbonate, sodium bicarbonate, organic solvent and water, wherein the molar ratio of sodium carbonate to sodium bicarbonate is (1-3):(2-5), and the volume of organic solvent accounts for 10-50% of the volume of the mobile phase.

[0012] In difluorosulfonylimide acid, difluorosulfonylimide acid is the main component, while chloride ions, fluoride ions, and sulfate ions are impurities. The concentration difference between the main component and impurities is very large, with the main component accounting for more than 95%, while the impurity element content is generally below 100 ppm. It is impossible to simultaneously determine the content of all components using the standard curve method, and the main component decomposes and interferes with the detection of impurity elements. Therefore, existing technologies generally detect the content of each component separately. The main innovations of this invention are: first, adjusting the pH value of the sample to stabilize difluorosulfonylimide acid through a pretreatment method to prevent the decomposition of the main component from interfering with the impurity anions; second, using the standard curve method to determine the content of low-concentration impurity anions separately, while simultaneously using the area normalization method to determine the high-concentration content of the main component; and third, selecting a mobile phase with specific components and contents to achieve complete separation of different anions, improving the accuracy of the area normalization method. Thus, the goal of simultaneous determination can be achieved.

[0013] In a specific embodiment of this application, the volume of the organic solvent accounts for 25-30% of the volume of the mobile phase.

[0014] In a specific embodiment of this application, the pH is adjusted to 4.0 to 7.0 in step (2), preferably 6.0 to 7.0.

[0015] In a specific embodiment of this application, the pH adjuster in step (2) is selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia water. Preferably, the pH adjuster is an aqueous solution of sodium hydroxide with a concentration of 4-10 wt%.

[0016] In specific embodiments of this application, the organic solvent is selected from at least one of acetonitrile, methanol, and isopropanol.

[0017] In a specific embodiment of this application, step (1) specifically includes:

[0018] Prepare standard solutions of fluoride, chloride, and sulfate ions with different concentration gradients. Inject the prepared standard solutions into the ion chromatograph in descending order of concentration. Establish a standard curve based on the peak area and corresponding concentration of each anion, with a correlation coefficient of not less than 0.999.

[0019] In a specific embodiment of this application, the regenerator solution in the ion chromatograph is prepared as follows: concentrated acid is slowly added to ultrapure water, dissolved, and then ultrapure water is added until the concentrated acid concentration reaches 10-100 ppm. Finally, the solution is filtered using an aqueous filter membrane. The aqueous filter membrane has a pore size of 0.22 μm. The concentrated acid is selected from concentrated sulfuric acid, concentrated nitric acid, or concentrated phosphoric acid. Preferably, the concentrated acid is electronic grade.

[0020] In a specific embodiment of this application, the operating conditions of the ion chromatograph include: selecting a C18 type chromatographic column and equipping it with a dynamic regeneration suppressor; setting the conductivity cell temperature to 20–40°C; column temperature to 15–45°C; injection volume to 10–100 μL; and mobile phase speed to 0.1–10 mL / min.

[0021] In a specific embodiment of this application, step (2) specifically includes:

[0022] The difluorosulfonylimide sample was added to a PFA bottle containing a base liquid at room temperature, and a pH adjuster was slowly added dropwise to a certain range. The sample was then immediately tested. The base liquid was ultrapure water.

[0023] In a specific embodiment of this application, the mobile phase is prepared as follows: a certain amount of sodium carbonate and sodium bicarbonate are weighed, wherein the molar ratio of sodium carbonate to sodium bicarbonate is (1-3):(2-5), preferably 2:3. After being dissolved in ultrapure water, the mobile phase is transferred to a volumetric flask, a certain amount of organic solvent is added, and then ultrapure water is added to make up to the volume, so that the volume of the organic solvent accounts for 10-50% of the volume of the mobile phase. After ultrasonic cleaning, the mobile phase is obtained.

[0024] Difluorosulfonylimide acid is a strong acid, unstable, and easily decomposes. Pretreatment to adjust the sample pH can prevent its decomposition. A mixed solution of sodium carbonate and sodium bicarbonate acts as a buffer solvent, stabilizing the solution pH, ensuring system stability, and inhibiting the decomposition of difluorosulfonylimide acid. The addition of acetonitrile effectively and completely separates the anionic components without mutual interference. Acetonitrile is nonpolar and can adjust the polarity of the mobile phase.

[0025] The present invention provides a method for simultaneously testing the content of anions such as fluoride, chloride, and sulfate ions, as well as the main content of difluorosulfonylimide acid, in the above-described steps. This invention only requires the addition of inorganic reagents to complete the sample pretreatment, making it rapid, safe, and environmentally friendly. Furthermore, combined with ion chromatography, it offers advantages such as low detection limits, high sensitivity, good repeatability, and high accuracy, making it suitable for the determination of common trace anion contents. The detection method provided by this invention is fast, simple to operate, accurate, and has good repeatability, and can be widely applied in the manufacturing field of lithium-ion batteries.

[0026] The detection method provided by this invention has better operability and practicality, is accurate and fast, and effectively overcomes the characteristics of difluorosulfonylimide acid being easy to decompose and having poor stability, which is of great significance for the quality control of lithium battery products.

[0027] This invention provides a method for simultaneously determining the content of impurities such as fluoride ions, chloride ions, and sulfate ions in difluorosulfonylimide acid, which has the following beneficial effects:

[0028] (1) The method provided by the present invention can quickly and effectively separate the main component of difluorosulfonylimide acid and the fluoride ions, chloride ions and sulfate ions therein by adjusting the solution composition of the elution mobile phase. Furthermore, the peaks of various anions do not interfere with each other, the baseline is stable, and the accuracy of the detection results is guaranteed.

[0029] (2) The method provided by the present invention can simultaneously and effectively test the content of impurity ions and main components, ensuring the accuracy and reliability of the test results.

[0030] (3) The method provided by the present invention pretreatment the difluorosulfonylimide sample and adjust the sample pH so that the difluorosulfonylimide can exist stably in the solution without decomposition, thus ensuring the validity of the final detection results. Attached Figure Description

[0031] Figure 1 The figure shows the anionic impurity peaks and main component content peaks separated by ion chromatography of difluorosulfonylimide acid solution. As can be seen from the figure, the method of this patent can completely separate anionic impurities and main components. The extremely strong main content peak will not affect the weaker impurity content peaks, and the content of each component at different concentrations can be accurately determined.

[0032] Figure 2 The image shows magnified views of the anionic impurity peaks separated by ion chromatography of difluorosulfonylimide acid solution. As can be seen from the image, the method of this patent can completely separate the anionic impurities, and the content peaks of each anion are completely independent without superposition, so that the content of impurity anions can be accurately measured. Detailed Implementation

[0033] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] In the description of this invention, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0036] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0037] There are no particular restrictions on the purity of any raw materials used in this invention. However, it is preferred to use analytical grade or conventional purity used in the detection field.

[0038] To further illustrate the present invention, the following detailed description of a method for simultaneous determination of fluoride ions, chloride ions, sulfate ions, and main contents in difluorosulfonylimide acid, provided by the present invention, is provided in conjunction with embodiments. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are given only to further illustrate the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0039] Example 1

[0040] 1) Prepare standard solutions of fluoride, chloride and sulfate ions with different concentration gradients in the range of 0 to 10 ppm.

[0041] 2) Preparation of ion chromatograph:

[0042] Preparation of mobile phase eluent: Weigh 0.8480g sodium carbonate and 1.0080g sodium bicarbonate, dissolve them and transfer them to a 2L volumetric flask. Add 560mL acetonitrile and then add ultrapure water to make up to volume. Use after sonication to dissolve the eluent.

[0043] Preparation of regenerated solution: Slowly add 6 mL of electronic grade concentrated sulfuric acid to 3 L of ultrapure water, dissolve it, and continue to add ultrapure water to 4 L. Filter the solution using a 0.22 μm aqueous filter membrane before use.

[0044] Ion chromatograph equipment parameter settings: C18 column with regeneration suppressor; conductivity cell temperature set to 35℃; column temperature: 30℃; injection volume: 25μL; mobile phase rate: 1.0mL / min.

[0045] 3) Weigh 80g of room temperature ultrapure water into a 150mL PFA bottle, accurately weigh 1g of difluorosulfonyl imide sample into it and mix thoroughly. Then slowly add 4% NaOH solution to adjust the pH of the solution to 6.0. After the solution is fully mixed and stabilized at room temperature, make up to volume to obtain the test solution B. Weigh 5 equal portions of the same sample and perform parallel tests, namely A1, A2, A3, A4 and A5.

[0046] 4) Inject the prepared standard solutions into the ion chromatograph in descending order of concentration. Establish a standard curve based on the peak area and corresponding concentration of each anion, with a correlation coefficient of not less than 0.999.

[0047] 5) Inject the pretreated sample B solution from step 3) directly into the ion chromatograph for testing. Calculate the concentration of each anion in the sample based on the standard curve, sample test results, and dilution factor. The main content of difluorosulfonylimide acid was calculated using the area normalization method.

[0048] 6) Ion chromatography was used for testing, and the test results are shown in Table 1.

[0049] Table 1:

[0050]

[0051]

[0052] Example 2

[0053] The difference between this comparative example and Example 1 is that acetonitrile in the mobile phase is replaced with methanol, while the rest of the operation remains the same.

[0054] The samples were numbered B1, B2, B3, B4, and B5. The test results are shown in Table 2.

[0055] Table 2:

[0056] Sample Name <![CDATA[F - (ppm)]]> <![CDATA[Cl - (ppm)]]> <![CDATA[SO4 2- (ppm)]]> <![CDATA[FSI - (%)]]> B1 205.32 22.21 698.41 98.11 B2 220.53 25.15 731.37 96.23 B3 250.31 30.31 714.52 99.51 B4 221.14 29.38 691.19 97.72 B5 209.19 36.45 682.35 98.05 average value 221.30 28.70 703.57 97.92 Standard deviation 17.63 5.428 19.512 1.170

[0057] Comparative Example 1

[0058] 1) Prepare standard solutions of fluoride, chloride and sulfate ions with different concentration gradients in the range of 0 to 10 ppm.

[0059] 2) Prepare the ion chromatograph according to the method in Example 1.

[0060] 3) Weigh 80g of room temperature ultrapure water into a 150mL PFA bottle, accurately weigh 1g of difluorosulfonyl imide sample into it, mix thoroughly to obtain test solution A, and weigh 5 equal portions of the same sample for parallel instrument testing, namely C1, C2, C3, C4 and C5.

[0061] 4) Inject the prepared standard solutions into the ion chromatograph in descending order of concentration. Establish a standard curve based on the peak area and corresponding concentration of each anion, with a correlation coefficient of not less than 0.999.

[0062] 5) Inject the pretreated sample A solution from step 3) directly into the ion chromatograph for testing. Calculate the concentration of each anion in the sample based on the standard curve, sample test results, and dilution factor. The main content of difluorosulfonylimide acid is calculated using the area normalization method.

[0063] 6) Ion chromatography was used for testing, and the test results are shown in Table 3.

[0064] Table 3:

[0065]

[0066]

[0067] As can be seen from Tables 1 and 2, the anions and main components in the pretreated difluorosulfonylimide solution are stable, the test results are stable, and the deviation is significantly reduced compared with the comparative results.

[0068] As shown in Table 3, the volatility of difluorosulfonylimide acid, coupled with its significant fuming and exothermic reaction upon dissolving in water, leads to poor accuracy and repeatability in the detection of impurity anions. Furthermore, the decomposition upon dissolving in water produces sulfate and fluoride ions, which are strongly acidic and have an irreversible impact on the ion chromatography column.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that the mobile phase is a mixed solution of sodium carbonate and sodium bicarbonate, without acetonitrile.

[0071] The samples were numbered D1, D2, D3, D4, and D5. The test results are shown in Table 4.

[0072] Table 4:

[0073] Sample Name <![CDATA[F - (ppm)]]> <![CDATA[Cl - (ppm)]]> <![CDATA[SO4 2- (ppm)]]> <![CDATA[FSI - (%)]]> D1 380.12 11.32 871.56 91.81 D2 780.56 59.21 5012.31 98.35 D3 1205.12 214.22 7311.55 99.01 D4 55.14 3.12 1376.26 98.56 D5 3510.14 509.18 925.93 95.35 average value 1186.22 159.41 3099.52 98.02 Standard deviation 1368.819 213.155 2917.957 1.511

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 1 is that the mobile phase is acetonitrile.

[0076] The samples were numbered E1, E2, E3, E4, and E5. The test results are shown in Table 5.

[0077] Table 5:

[0078] Sample Name <![CDATA[F - (ppm)]]> <![CDATA[Cl - (ppm)]]> <![CDATA[SO4 2- (ppm)]]> <![CDATA[FSI - (%)]]> E1 15.15 31.23 996.61 90.38 E2 912.51 501.11 2914.55 95.52 E3 51221.09 1242.53 8912.93 93.74 E4 11.32 1.51 2203.18 99.11 E5 156.44 781.98 301.96 95.92 average value 1243.30 511.67 3065.85 94.93 Standard deviation 2199.663 524.028 3423.313 3.198

[0079] Comparative Example 4

[0080] The difference between this comparative example and Example 1 is that the molar ratio of sodium carbonate to sodium bicarbonate in the mobile phase is 1:5, and the volume concentration of acetonitrile is 60%.

[0081] The samples were numbered F1, F2, F3, F4, and F5. The test results are shown in Table 6.

[0082] Table 6:

[0083] Sample Name <![CDATA[F - (ppm)]]> <![CDATA[Cl - (ppm)]]> <![CDATA[SO4 2- (ppm)]]> <![CDATA[FSI - (%)]]> F1 312.41 20.19 560.34 97.41 F2 206.11 31.43 396.15 91.38 F3 287.16 38.14 771.32 94.17 F4 321.55 19.78 416.07 89.49 F5 199.98 26.37 764.28 95.74 average value 265.44 27.18 581.63 93.64 Standard deviation 58.377 7.786 181.390 3.211

[0084] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0085] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0086] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for simultaneously determining the content of fluoride ions, chloride ions, sulfate ions, and main components in difluorosulfonylimide acid, characterized in that, Includes the following steps: (1) Prepare standard solutions of fluoride ion, chloride ion and sulfate ion, and inject the prepared standard solutions of each anion into the ion chromatograph. Establish a standard curve based on the peak area and corresponding concentration of each anion. (2) Add pH adjuster to the sample of difluorosulfonylimide to adjust the pH to 4.0~7.0; (3) Inject the pH-adjusted sample into the ion chromatograph for testing; (4) Calculate the concentration of each anion in the sample to be tested based on the standard curve and the sample test results, and at the same time calculate the content of difluorosulfonyl imide in the sample to be tested using the area normalization method; The mobile phase used in the ion chromatograph is a mixture of sodium carbonate, sodium bicarbonate, organic solvent, and water, wherein the molar ratio of sodium carbonate to sodium bicarbonate is (1~3):(2~5), and the volume of organic solvent accounts for 10~50% of the mobile phase volume. The organic solvent is selected from at least one of acetonitrile, methanol, and isopropanol; the operating conditions of the ion chromatograph include: selecting a C18 column and equipping it with a dynamic regeneration suppressor.

2. The method according to claim 1, characterized in that, In step (2), the pH adjuster is selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia water.

3. The method according to claim 1, characterized in that, The specific steps (1) are as follows: Prepare standard solutions of fluoride, chloride, and sulfate ions with different concentration gradients. Inject the prepared standard solutions into the ion chromatograph in descending order of concentration. Establish a standard curve based on the peak area and corresponding concentration of each anion, with a correlation coefficient of not less than 0.

999.

4. The method according to claim 1, characterized in that, The regenerator solution in the ion chromatograph is prepared by slowly adding concentrated acid to ultrapure water, dissolving it, and then adding more ultrapure water until the concentrated acid concentration is 10~100 ppm. Finally, it is filtered using an aqueous filter membrane.

5. The method according to claim 4, characterized in that, The concentrated acid is selected from concentrated sulfuric acid, concentrated nitric acid, or concentrated phosphoric acid.

6. The method according to claim 1, characterized in that, The operating conditions for the ion chromatograph include: conductivity cell temperature set at 20~40℃; column temperature at 15~45℃; injection volume at 10~100 μL; and mobile phase rate at 0.1~10 mL / min.

7. The method according to claim 1, characterized in that, Step (2) specifically involves: Add the difluorosulfonamide sample to a PFA bottle containing room temperature base liquid, slowly add pH adjuster to a certain range, and then immediately test on the instrument; The base liquid is ultrapure water.

8. The method according to claim 1, characterized in that, The mobile phase is prepared as follows: weigh out a certain amount of sodium carbonate and sodium bicarbonate, dissolve them in ultrapure water, transfer them to a volumetric flask, add a certain amount of organic solvent, add ultrapure water to make up to volume, and then sonicate to dissolve and clear the solution.

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