Method for simultaneously determining fluorine ions, chloride ions, sulfate ions and main contents in bis (fluorosulfonyl) imide acid

Abstract

The invention provides a method for simultaneously measuring fluorine ions, chloride ions, sulfate ions and main contents in bis (fluorosulfonyl) imide acid, which is characterized by comprising the following steps: (1) preparing standard solutions of fluorine ions, chloride 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 into the bis (fluorosulfonyl) imide acid sample, and regulating the pH to a certain range; (3) feeding the treated sample to an ion chromatograph for testing; and (4) calculating the concentration of each anion in the sample to be detected according to the standard curve and a sample test result, and calculating the content of the bis (fluorosulfonyl) imide acid by adopting an area normalization method.

Description

Technical Field

[0001] The invention belongs to the field of detection technology, and more specifically, relates to a method for simultaneously determining fluoride ions, chloride ions, sulfate ions and main contents in bis(fluorosulfonyl)imidic acid. Background Art

[0002] Lithium-ion electrolyte is the blood of lithium-ion batteries and an indispensable core component of lithium-ion batteries. Lithium-ion batteries have strict requirements on the performance of electrolytes, especially the content of various impurity anions in the electrolyte. Lithium bis(fluorosulfonyl)imide (LiFSI) is an important component of lithium-ion electrolytes. Its impurity content mainly comes from its main synthetic raw material, bis(fluorosulfonyl)imide acid (HFSI). Common impurity anions in electrolyte lithium salts are mainly fluoride ions, chloride ions, and sulfate ions. Therefore, accurate detection of the content of various anions in HFSI is of great significance for the performance of lithium-ion battery electrolytes. However, HFSI is a strong acid and cannot be directly tested by ion chromatography using general anion detection methods. Otherwise, it will cause irreversible damage to the ion chromatography equipment, making it impossible to accurately test the results. HFSI needs to be neutralized, but it is easy to decompose and the accuracy of the test is difficult to guarantee.

[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. At present, there is no relevant literature reporting an industrial method for accurately determining the main content of bis(fluorosulfonyl)imide acid and the fluoride ions, chloride ions, and sulfate ions therein at the same time. Therefore, it is necessary to design a method that can simply, accurately, and effectively determine the main content of bis(fluorosulfonyl)imide acid and various impurity anions therein at the same time. Summary of the invention

[0004] In view of the defects of the prior art, the object of the present invention is to provide a method for simultaneously determining the chloride ion, fluoride ion, sulfate content and the main content of bisfluorosulfonyl imide acid in bisfluorosulfonyl imide acid, so as to solve the deficiency that the prior art cannot simultaneously determine the main content and multiple anions of bisfluorosulfonyl imide acid.

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

[0006] A method for simultaneously determining the content of fluoride ions, chloride ions, sulfate ions and main ions in bis(fluorosulfonyl)imidic acid, characterized in that it comprises the following steps:

[0007] (1) preparing standard solutions of fluoride ion, chloride ion and sulfate ion, respectively injecting the prepared standard solutions of each anion into an ion chromatograph, and establishing a standard curve according to the peak area and corresponding concentration of each anion;

[0008] (2) adding a pH adjuster to the bis(fluorosulfonyl)imidic acid sample to be tested to adjust the pH to a certain range;

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

[0010] (4) Calculating the concentration of each anion in the sample to be tested according to the standard curve and the sample test results, and calculating the content of bis(fluorosulfonyl)imidic acid in the sample to be tested by using the area normalization method;

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

[0012] In bisfluorosulfonyl imide acid, bisfluorosulfonyl imide acid is the main component, and chloride ions, fluoride ions, and sulfate ions are impurities. The concentration difference between the main component and the impurities is very large, and the main component content accounts for more than 95%. Then the content of impurity elements is generally below 100ppm. It is impossible to use the standard curve method to simultaneously determine the content of all components, and the main component will decompose and interfere with the detection of impurity elements, so the prior art generally detects the content of each component separately. The main innovation of the present invention is: first, the pH value of the sample to be tested is adjusted by a pretreatment method to stabilize the bisfluorosulfonyl imide acid to prevent the decomposition of the main component from interfering with the impurity anions; second, the standard curve method is used to determine the low concentration of impurity anion content, and the area normalization method is used to synchronously determine the high concentration content of the main component; third, a mobile phase with a specific composition and content is selected so that different anions can achieve a complete separation effect and improve the accuracy of the area normalization method. Thus, the purpose of simultaneous determination can be achieved.

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

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

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

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

[0017] In a specific implementation of the present application, the step (1) is specifically:

[0018] Standard solutions of fluoride ion, chloride ion and sulfate ion with different concentration gradients were prepared, and the prepared standard solutions were injected into the ion chromatograph in order from high to low concentration. A standard curve was established based on the peak area and corresponding concentration of each anion, and the correlation coefficient was not less than 0.999.

[0019] In a specific embodiment of the present application, the regeneration liquid in the ion chromatograph is prepared by slowly adding concentrated acid to ultrapure water, adding ultrapure water to a certain concentrated acid concentration of 10 to 100 ppm after dissolution, and finally filtering with a water filter membrane. The pore size of the water filter membrane is 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 the present application, the operating conditions of the ion chromatograph include: selecting a C18 chromatographic column and equipping it with a dynamic regeneration suppressor; setting the conductivity cell temperature to 20-40°C; column temperature: 15-45°C; injection volume: 10-100 μL; mobile phase speed: 0.1-10 mL / min.

[0021] In a specific implementation of the present application, step (2) is specifically as follows:

[0022] Add the bis(fluorosulfonyl)imidic acid sample into a PFA bottle containing a base liquid at room temperature, slowly add a pH adjuster to a certain range, and then immediately test it on a machine; wherein the base liquid is ultrapure water.

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

[0024] Bis(fluorosulfonyl)imidic acid is a strong acidic substance, unstable and easy to decompose. Pretreatment to adjust the pH value of the sample can prevent its decomposition. The mixed solution of sodium carbonate and sodium bicarbonate as a buffer solvent can stabilize the pH of the solution, ensure the stability of the system, and inhibit the decomposition of bis(fluorosulfonyl)imidic acid. The addition of acetonitrile can effectively and completely separate the anionic components without mutual interference. Among them, acetonitrile is non-polar and can adjust the polarity of the mobile phase.

[0025] The above steps of the present invention provide a method for simultaneously testing the anions such as fluoride ions, chloride ions, sulfate ions and the main content of bisfluorosulfonyl imide acid in bisfluorosulfonyl imide acid. The present invention only needs to add inorganic reagents to complete the pretreatment of the sample to be tested, which is fast, safe and environmentally friendly, and combined with ion chromatography, it has the advantages of low detection limit, high sensitivity, good repeatability, high accuracy, etc., and is suitable for the determination of common trace anion content. The detection method provided by the present invention is fast and simple to operate, the results are accurate, and the repeatability is good, and it can be widely used in the manufacturing field of lithium ion batteries.

[0026] The detection method provided by the present invention has better operability and practicability, is accurate and rapid, and effectively overcomes the characteristics of bis(fluorosulfonyl)imidic acid being easy to decompose and having poor stability, and is of great significance for the quality control of lithium battery products.

[0027] The present invention provides a method for simultaneously determining the impurities and main contents of fluoride ions, chloride ions, sulfate ions, etc. in bis(fluorosulfonyl)imidic 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 bis(fluorosulfonyl)imidic acid and the fluoride ions, chloride ions and sulfate ions therein by adjusting the solution components of the elution mobile phase, and the various anion peaks do not interfere with each other, and the baseline is stable, thereby ensuring the accuracy of the detection results.

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

[0030] (3) The method provided by the present invention pre-treats the bis(fluorosulfonyl)imidic acid sample and adjusts the sample pH, so that the bis(fluorosulfonyl)imidic acid can stably exist in the solution without decomposition, thereby ensuring the validity of the final detection result. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The anion impurity peaks and main component content peaks separated by ion chromatography of bis(fluorosulfonyl)imidic acid solution. It can be seen from the figure that the patented method can completely separate the anion impurities and the main component. The extremely strong main content peak will not affect the weaker impurity content peak, and the content of each component at different concentrations can be accurately determined;

[0032] Figure 2 This is an enlarged view of each anion impurity peak separated by ion chromatography of bis(fluorosulfonyl)imidic acid solution. It can be seen from the figure that the patented method can completely separate each anion impurity, the content peaks between each anion are completely independent and non-overlapping, and the impurity anion content can be accurately measured. DETAILED DESCRIPTION

[0033] 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 used to limit the present invention.

[0034] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0035] In the description of the present invention, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0036] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0037] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure materials or materials of conventional purity used in the detection field.

[0038] In order to further illustrate the present invention, the method for simultaneously determining fluoride ions, chloride ions, sulfate ions and main contents in a bisfluorosulfonyl imide acid provided by the present invention is described in detail below in conjunction with the examples. However, it should be understood that these examples are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operating processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following examples.

[0039] Example 1

[0040] 1) Prepare standard solutions of fluoride ion, chloride ion and sulfate ion with different concentration gradients ranging from 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 respectively, dissolve and transfer to a 2L volumetric flask, add 560mL acetonitrile and then add ultrapure water to make up to volume, ultrasonically dissolve and use;

[0043] Preparation of regeneration solution: slowly add 6mL electronic grade concentrated sulfuric acid into 3L ultrapure water, continue to add ultrapure water to 4L after dissolution, and filter with 0.22μm water filter membrane before use;

[0044] The ion chromatograph equipment parameter settings were as follows: a C18 chromatographic column was used and equipped with a regeneration suppressor; the conductivity cell temperature was set to 35°C; the column temperature was 30°C; the injection volume was 25 μL; and the mobile phase speed was 1.0 mL / min.

[0045] 3) Weigh 80 g of room temperature ultrapure water in a 150 mL PFA bottle, accurately weigh 1 g of the bis(fluorosulfonyl)imidic acid sample and mix thoroughly, then slowly drop 4% NaOH solution to adjust the pH of the solution to 6.0, and after the solution is fully mixed and stabilized at room temperature, dilute to obtain a test solution B. Five equal portions of the same sample are weighed and tested in parallel, namely A1, A2, A3, A4, and A5.

[0046] 4) The prepared standard solutions were injected into the ion chromatograph in order from high to low concentrations, and a standard curve was established based on the peak area and corresponding concentration of each anion, with a correlation coefficient of not less than 0.999.

[0047] 5) The sample of solution B to be tested that has been pretreated in step 3) is directly injected into the ion chromatograph for testing. The concentration of each anion in the sample to be tested is calculated based on the standard curve, the sample test results, and the dilution multiple. The main content of bis(fluorosulfonyl)imidic acid is calculated using the area normalization method.

[0048] 6) The test was carried out using ion chromatography. 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 the acetonitrile in the mobile phase is replaced by methanol, and the other operations remain unchanged.

[0054] The sample numbers are 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[SO 4 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 ion, chloride ion and sulfate ion with different concentration gradients ranging from 0 to 10 ppm.

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

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

[0061] 4) The prepared standard solutions were injected into the ion chromatograph in order from high to low concentrations, and a standard curve was established based on the peak area and corresponding concentration of each anion, with a correlation coefficient of not less than 0.999.

[0062] 5) Directly inject the sample of solution A pretreated in step 3) into the ion chromatograph for testing. Calculate the concentration of each anion in the sample according to the standard curve, sample test results and dilution multiple. The main content of bis(fluorosulfonyl)imidic acid is calculated by area normalization method.

[0063] 6) The test was carried out using ion chromatography. The test results are shown in Table 3.

[0064] Table 3:

[0065]

[0066]

[0067] It can be seen from Tables 1 and 2 that the anions and main components in the bis(fluorosulfonyl)imidic acid solution after pretreatment are stable, the test result data is stable, and the deviation is significantly reduced compared with the comparative example.

[0068] As can be seen from Table 3, since bis(fluorosulfonyl)imidic acid is volatile and emits a lot of smoke and heat when dissolved in water, the impurity anion test has poor accuracy and repeatability. In addition, since it produces sulfate ions and fluoride ions after being dissolved in water and decomposes, and is strongly acidic, it has an irreversible effect 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-sodium bicarbonate without acetonitrile.

[0071] The sample numbers are 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[SO 4 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 sample numbers are 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[SO 4 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 sample numbers are 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[SO 4 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 are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to 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 further describe various possible combinations.

[0086] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for simultaneously determining the content of fluoride ions, chloride ions, sulfate ions and main ions in bis(fluorosulfonyl)imidic acid, characterized in that: The steps include: (1) preparing standard solutions of fluoride ion, chloride ion and sulfate ion, respectively injecting the prepared standard solutions of each anion into an ion chromatograph, and establishing a standard curve according to the peak area and corresponding concentration of each anion; (2) adding a pH adjuster to the bis(fluorosulfonyl)imidic acid sample to be tested to adjust the pH to a certain range; (3) injecting the pH-adjusted sample into an ion chromatograph for testing; (4) Calculating the concentration of each anion in the sample to be tested according to the standard curve and the sample test results, and calculating the content of bis(fluorosulfonyl)imidic acid in the sample to be tested by using the area normalization method; The mobile phase used in the ion chromatograph is a mixture of sodium carbonate, sodium bicarbonate, an organic solvent and water, wherein the molar ratio of sodium carbonate to sodium bicarbonate is (1-3): (2-5), and the volume of the organic solvent accounts for 10-50% of the volume of the mobile phase.

2. The method according to claim 1, characterized in that In the step (2), the pH is adjusted to 4.0-7.

0.

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

4. The method according to claim 1, characterized in that The organic solvent is selected from at least one of acetonitrile, methanol and isopropanol.

5. The method according to claim 1, characterized in that The step (1) is specifically: Standard solutions of fluoride ion, chloride ion and sulfate ion with different concentration gradients were prepared, and the prepared standard solutions were injected into the ion chromatograph in order from high to low concentration. A standard curve was established based on the peak area and corresponding concentration of each anion, and the correlation coefficient was not less than 0.

999.

6. The method according to claim 1, characterized in that The regeneration liquid in the ion chromatograph is prepared by slowly adding concentrated acid into ultrapure water, and continuing to add ultrapure water to a certain concentrated acid concentration of 10 to 100 ppm after dissolution, and finally filtering with a water filter membrane to obtain the regeneration liquid.

7. The method according to claim 6, characterized in that The concentrated acid is selected from concentrated sulfuric acid, concentrated nitric acid or concentrated phosphoric acid.

8. The method according to claim 1, characterized in that The operating conditions of the ion chromatograph include: selecting a C18 chromatographic column and equipping it with a dynamic regeneration suppressor; setting the conductivity cell temperature to 20-40°C; column temperature: 15-45°C; injection volume: 10-100 μL; mobile phase speed: 0.1-10 mL / min.

9. The method according to claim 1, characterized in that: The step (2) is specifically: Add the bis(fluorosulfonyl)imidic acid sample into a PFA bottle containing a room temperature base liquid, slowly add a pH adjuster to a certain range, and then immediately test it on the machine; Wherein, the base liquid is ultrapure water.

10. The method according to claim 1, characterized in that The mobile phase is prepared by weighing a certain amount of sodium carbonate and sodium bicarbonate respectively, dissolving them in ultrapure water and transferring them to a volumetric flask, adding a certain amount of organic solvent and then adding ultrapure water to make up the volume, and dissolving them by ultrasonication to obtain the mobile phase.

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