Method for detecting content of anion impurities in bis (trifluoromethanesulfonyl) imide sodium

Abstract

The invention relates to a method for detecting the content of anion impurities in sodium bis (trifluoromethanesulfonyl) imide. The method comprises the following steps: preparing a regeneration solution and a gradient eluent; preparing a 100mg / L mixed standard solution of fluorine ions, acetate radicals, methanesulfonate radicals and trifluoromethanesulfonate radicals; the method comprises the following steps: preparing mixed standard solutions of fluorine ions, acetate radicals, methanesulfonate radicals and trifluoromethanesulfonate radicals with the concentrations of 0.00 mg / L, 0.05 mg / L, 0.25 mg / L, 1.25 mg / L and 6.25 mg / L; respectively carrying out anion chromatographic analysis on the mixed standard solutions with the concentrations of 0.0 mg / L, 0.05 mg / L, 0.25 mg / L, 1.25 mg / L and 6.25 mg / L by adopting an ion chromatograph, and drawing standard curves of four anions; the method comprises the following steps: diluting sodium bis (trifluoromethylsulfonyl) imide with high-purity water, carrying out anion chromatographic analysis on the diluted sample, and recording the peak area. The method is simple in experimental process, high in operability, high in analysis speed, high in detection sensitivity, good in reproducibility, low in cost and capable of detecting various anion impurities at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of anion impurity content detection, and in particular to a method for detecting the anion impurity content in sodium bistrifluoromethanesulfonimide. Background Art

[0002] In the process of rapid development of new energy industry, the market demand for lithium-ion batteries is increasing, but the resources of lithium-ion batteries are limited. Sodium-ion batteries have a very similar working principle to lithium-ion batteries and are one of the alternative industries to lithium-ion batteries. With the rapid development of the sodium-ion battery industry in recent years, sodium bis(trifluoromethylsulfonyl)imide and sodium hexafluorophosphate are both raw materials for sodium battery electrolytes. Among them, sodium bis(trifluoromethylsulfonyl)imide has good electrochemical stability, high anion charge dispersion and easy ionization. It has the advantages of large dissociation degree, high ion mobility and high conductivity in the solution. Compared with sodium hexafluorophosphate, it has great advantages and is therefore a high-quality sodium battery electrolyte. However, acetate, fluoride, trifluoromethanesulfonate and methanesulfonate will reduce the number of cycles of sodium batteries and seriously affect the service life of sodium batteries.

[0003] Chinese patent CN117250291A discloses a method for determining lithium difluorooxalate borate and lithium dioxalate borate in lithium battery electrolyte, comprising the following steps: preparing BF 4- Standard solution stock solution; preparation of BF 4- Standard solution; Preparation of lithium battery electrolyte BF 4- Solution to be tested; Preparation of C2O4 2- Standard solution stock solution; preparation of C2O4 2- Standard solution; Preparation of lithium battery electrolyte C2O4 2- Solution to be tested; Instrumental analysis: Anion chromatography was used, the regeneration solution was sulfuric acid aqueous solution, and the eluent was Na2CO3, NaHCO3 acetonitrile water system; BF 4- Standard solution, C2O4 2- Standard solution, lithium battery electrolyte BF 4- C2O4 in the test solution and lithium battery electrolyte 2- The solution to be tested is subjected to anion chromatography analysis, and the peak area is recorded; the contents of lithium difluorooxalatoborate and lithium dioxalatoborate are calculated.

[0004] Chinese patent CN113030287B, a method for determining TSED-2 in a lithium ion battery electrolyte containing lithium hexafluorophosphate, comprises: preparing a regeneration solution, a leaching solution, a standard solution, and a sample solution to be tested, wherein the leaching solution is an acetonitrile aqueous solution of sodium carbonate and sodium bicarbonate, wherein the volume percentage of acetonitrile is 23.1%, and the molar concentrations of sodium carbonate and sodium bicarbonate are 3.69 mmol / L and 1.23 mmol / L, respectively; using an anion chromatograph, chromatographically analyzing the standard solution and the sample solution to be tested, respectively, and recording the peak areas; and using an external standard method to calculate the mass percentage of TSED-2 in the electrolyte sample to be tested.

[0005] As can be seen from the above, there are some studies on the determination method of anion content in other electrolytes in China, but there is no study on the detection method of acetate, fluoride, trifluoromethanesulfonate and methanesulfonate content in sodium bistrifluoromethanesulfonyl imide. Therefore, the present invention proposes a method for detecting the anion impurity content in sodium bistrifluoromethanesulfonyl imide. Summary of the invention

[0006] The invention aims to provide a method for detecting the content of anionic impurities in sodium bistrifluoromethanesulfonyl imide. The method has the advantages of simple operation, fast detection speed and low cost, and can simultaneously determine the contents of acetate, fluoride, trifluoromethanesulfonate and methanesulfonate in sodium bistrifluoromethanesulfonyl imide.

[0007] To achieve the purpose of the present invention, the specific technical solutions provided by the present invention are as follows:

[0008] A method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide comprises the following steps:

[0009] S1, preparing a regeneration solution and a gradient eluent, wherein the gradient eluent includes an eluent A and an eluent B;

[0010] S2. Prepare a 100 mg / L mixed standard solution of fluoride ion, acetate, methanesulfonate, and trifluoromethanesulfonate;

[0011] S3, prepare standard solutions of fluoride ion, acetate, methanesulfonate and trifluoromethanesulfonate with mixed concentrations of 0.00 mg / L, 0.05 mg / L, 0.25 mg / L, 1.25 mg / L and 6.25 mg / L;

[0012] S4. Perform anion chromatography analysis on standard solutions with mixed concentrations of 0.0 mg / L, 0.05 mg / L, 0.25 mg / L, 1.25 mg / L and 6.25 mg / L, respectively, using an ion chromatograph to draw standard curves for the four anions;

[0013] S5. Dilute sodium bis(trifluoromethylsulfonyl)imide with high-purity water, perform anion chromatography analysis on the diluted sample, and record the peak area.

[0014] Preferably, in step S1, the eluent A is an acetonitrile aqueous solution of Na2CO3 and NaHCO3, wherein the volume percentage of acetonitrile is 10%, and the concentrations of Na2CO3 and NaHCO3 are 0.339 mg / L and 0.084 mg / L, respectively; the eluent B is an acetonitrile aqueous solution of Na2CO3 and NaHCO3, wherein the volume percentage of acetonitrile is 40%, and the concentrations of Na2CO3 and NaHCO3 are 0.339 mg / L and 0.084 mg / L, respectively; the regeneration liquid is an aqueous sulfuric acid solution, and the volume ratio of high-purity water to concentrated sulfuric acid in the aqueous sulfuric acid solution is 1000:15.

[0015] Preferably, in step S3, 0.0g, 0.05g, 0.25g, 1.25g, and 6.25g of a mixed standard solution with a concentration of 100mg / L are accurately weighed, transferred to a clean beaker, and diluted with high-purity water to a total weight of 100g to obtain 5 mixed standard solutions for use. The concentrations of the mixed standard solutions are 0.00mg / L, 0.05mg / L, 0.25mg / L, 1.25mg / L, and 6.25mg / L, respectively, and the weighing error is less than 3%.

[0016] Preferably, the ion chromatograph uses a Swiss Metrohm 940 ion chromatograph, and selects Metrosep A Supp5-250 / 4.0 as an anion chromatographic column; instrument detection conditions: ion chromatographic column temperature is 45°C, eluent flow rate is 0.7mL / min, ion chromatographic column maximum pressure is 16.0MPa, and injection volume is 20uL.

[0017] Preferably, before performing the detection in step S4, the ion chromatograph is turned on and preheated, and the eluent A is used to draw the baseline, and the sample analysis is performed after the baseline is stable for 1 hour.

[0018] Preferably, in step S4, four anion standard curves Y=KX+C are drawn respectively, wherein: X is the concentration of the element corresponding to the standard solution, K is the slope of the working curve, C is the background concentration, and Y is the corresponding conductivity of the solution to be tested in the ion chromatograph. The standard curve fitting degree of the four anions is greater than 0.999.

[0019] Preferably, in step S5, firstly, an aqueous solution of sodium bis(trifluoromethylsulfonyl)imide is prepared, and then the sodium bis(trifluoromethylsulfonyl)imide sample is diluted 95-105 times for anion chromatography analysis.

[0020] Preferably, the sodium carbonate and sodium bicarbonate used in preparing the eluent are both of reference reagent grade, the acetonitrile is of analytical grade, and the sulfuric acid is of premium grade.

[0021] The method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide of the present invention has the following beneficial effects:

[0022] 1. This method has clear steps and is easy to operate. It does not require complicated pre-treatment steps, which greatly shortens the detection time and improves work efficiency. Due to the clear steps and standardized operation, the test results have good reproducibility, ensuring the stability and reliability of the test results.

[0023] 2. This method uses an ion chromatograph for analysis, which can accurately and sensitively detect extremely low concentrations of anionic impurities, ensuring the accuracy and reliability of the test results. A gradient eluent is used, in which eluent A is more likely to elute fluoride ions and acetate, and eluent B is more likely to elute bistrifluoromethylsulfonyl imide and trifluoromethanesulfonate, so that the ion chromatograph can simultaneously determine a variety of anionic impurities such as acetate, fluoride, trifluoromethanesulfonate and methanesulfonate in sodium bistrifluoromethylsulfonyl imide, thereby improving the comprehensiveness and accuracy of the test. This method is not only suitable for the detection of anionic impurities in newly produced sodium salt sodium bistrifluoromethylsulfonyl imide, but can also be widely used in the quality control and detection of other similar sodium salt products, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The ion chromatogram is of fluoride, acetate, methanesulfonate and trifluoromethanesulfonate in sodium bis(trifluoromethanesulfonyl)imide of the present invention. DETAILED DESCRIPTION

[0025] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the present invention are described in detail below in combination with the preferred embodiments.

[0026] Example 1

[0027] A method for detecting the content of anionic impurities in sodium bistrifluoromethanesulfonyl imide, using gradient ion chromatography to detect the contents of fluoride ion, acetate, methanesulfonate and trifluoromethanesulfonate in sodium bistrifluoromethanesulfonyl imide, using Swiss Metrohm 940 ion chromatograph as ion chromatograph, selecting Metrosep A Supp5-250 / 4.0 as anion chromatographic column; instrument detection conditions are as follows: ion chromatographic column temperature is 45°C, eluent flow rate is 0.7mL / min, ion chromatographic column maximum pressure is 16.0MPa, injection volume is 20uL, and specifically comprises the following steps:

[0028] S1, configuration of regeneration solution and gradient eluent, the gradient eluent includes eluent A and eluent B;

[0029] The regeneration liquid is a sulfuric acid aqueous solution, in which the volume ratio of high-purity water to concentrated sulfuric acid is 1000:15;

[0030] The eluent is an acetonitrile aqueous solution of Na2CO3 and NaHCO3. For eluent A, take 0.3392g of Na2CO3 and 0.0842g of NaHCO3 into a 1000mL beaker, then pour in 100mL of acetonitrile, add a small amount of high-purity water to dissolve, and transfer to a 1000mL volumetric flask to make up the volume. Eluent A is easier to elute fluoride ions and acetate ions;

[0031] Eluent B, take 0.3392g of Na2CO3 and 0.0842g of NaHCO3 into a 1000mL beaker, then pour in 400mL of acetonitrile, add a small amount of high-purity water to dissolve, transfer to a 1000mL volumetric flask to make up the volume, eluent B is easier to elute bistrifluoromethylsulfonyl imide and trifluoromethanesulfonate.

[0032] S2. Preparation of mixed standard solution: Use a pipette to take 10 mL of 1000 mg / L fluoride ion standard solution into a beaker, then take 10 mL of acetate standard solution, 10 mL of methanesulfonate standard solution, and 10 mL of trifluoromethanesulfonate standard solution into the same beaker in sequence, dilute with high-purity water and transfer to a 100 mL volumetric flask to make up to volume to obtain a 100 mg / L mixed standard solution.

[0033] S3. Preparation of gradient standard solution: Take 0.0000g, 0.0512g, 0.2483g, 1.2535g, and 6.2419g of 100mg / L mixed standard solution respectively, put them into a 100mL beaker, dilute to 100g with high-purity water to obtain 0.000mg / L, 0.0511mg / L, 0.2479mg / L, 1.2516mg / L, and 6.2324mg / L mixed standard solutions.

[0034] S4. Establishment of fitting curve: Turn on the ion chromatograph to preheat, and use eluent A to draw the baseline, and make the baseline stable for 1 hour;

[0035] Anion chromatography was used to analyze the mixed standard solutions with concentrations of 0.000 mg / L, 0.0511 mg / L, 0.2479 mg / L, 1.2516 mg / L, and 6.2324 mg / L, respectively. When the sample was injected and tested, eluent A was used. After 10 minutes of sample testing, eluent B was switched.

[0036] After the sample detection was completed, standard curves of four anions were drawn. The fitting degrees of the standard curves of fluoride, acetate, methanesulfonate and trifluoromethanesulfonate were 0.99911, 0.99974, 0.99935 and 0.99915, respectively.

[0037] S5. Sample detection: Use an electronic balance to accurately weigh 1.0341g of sodium bis(trifluoromethylsulfonyl)imide sample, place it in a 100mL beaker, add high-purity water to 100.2736g, shake well, dilute the sodium bis(trifluoromethylsulfonyl)imide solution again with high-purity water by 96.97 times, shake well for standby use; due to the high content of bis(trifluoromethylsulfonyl)imide, elution is more difficult, so it is necessary to dilute the sample 100 times before detection;

[0038] Under the same chromatographic conditions, the diluted sample was subjected to anion chromatography analysis and detection, the dilution multiple was input, and the diluted sample was tested twice in parallel. The ion chromatogram was as follows: Figure 1 The peak areas were recorded and the results were calculated as shown in Table 1.

[0039] Table 1 Anion peak positions and impurity contents in samples

[0040]

[0041] Verification Example 1: Calculation of method detection limit and quantification limit

[0042] Take 0.1089 g of 100 mg / L mixed standard solution and dilute it to 100.1523 g with 100-fold diluted sodium bis(trifluoromethylsulfonyl)imide solution. The calculated spiked concentration is 0.1087 mg / L. Repeat the above method 7 times to prepare 7 spiked solutions. The same method is repeated for 7 times. The degree of freedom of the sample repeated for 7 times is 3.14. Therefore, 3.14 times the standard deviation is the method detection limit, and 5 times the detection limit is the method quantification limit. The calculation results are shown in Table 2. It can be seen that the method can be experimentally verified to simultaneously detect the contents of fluoride ion, acetate, methanesulfonate and trifluoromethanesulfonate in sodium bis(trifluoromethylsulfonyl)imide, and the method detection limits are 1.05 mg / L, 1.27 mg / L, 1.06 mg / L and 0.61 mg / L, respectively.

[0043] Table 2 Detection limit and quantification limit of the method

[0044]

[0045]

[0046] The calculation results of the spiked recovery are shown in Table 3. The spiked recovery of the four anions is between 82.32% and 99.17%. The spiked recovery is within this range, indicating that the test results are highly accurate.

[0047] Table 3 Spiked recovery

[0048]

[0049] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide, characterized in that: The following steps are involved: S1, preparing a regeneration solution and a gradient eluent, wherein the gradient eluent includes an eluent A and an eluent B; S2. Prepare a 100 mg / L mixed standard solution of fluoride, acetate, methanesulfonate and trifluoromethanesulfonate; S3, prepare mixed standard solutions with concentrations of 0.00 mg / L, 0.05 mg / L, 0.25 mg / L, 1.25 mg / L and 6.25 mg / L respectively; S4, using an ion chromatograph to perform anion chromatography analysis on mixed standard solutions with concentrations of 0.0 mg / L, 0.05 mg / L, 0.25 mg / L, 1.25 mg / L and 6.25 mg / L, respectively, and draw standard curves for the four anions; S5. Dilute sodium bis(trifluoromethylsulfonyl)imide with high-purity water, perform anion chromatography analysis on the diluted sample, and record the peak area.

2. A method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide according to claim 1, characterized in that: In step S1, the eluent A is an acetonitrile aqueous solution of Na2CO3 and NaHCO3, wherein the volume percentage of acetonitrile is 10%, and the concentrations of Na2CO3 and NaHCO3 are 0.339 mg / L and 0.084 mg / L respectively; the eluent B is an acetonitrile aqueous solution of Na2CO3 and NaHCO3, wherein the volume percentage of acetonitrile is 40%, and the concentrations of Na2CO3 and NaHCO3 are 0.339 mg / L and 0.084 mg / L respectively; the regeneration liquid is a sulfuric acid aqueous solution, and the volume ratio of high-purity water to 98% concentrated sulfuric acid in the sulfuric acid aqueous solution is 1000:

15.

3. A method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide according to claim 1, characterized in that: In step S3, accurately weigh 0.0g, 0.05g, 0.25g, 1.25g, and 6.25g of a mixed standard solution with a concentration of 100mg / L, transfer it to a clean beaker, and dilute it with high-purity water to a total weight of 100g to obtain 5 mixed standard solutions for use. The concentrations of the mixed standard solutions are 0.00mg / L, 0.05mg / L, 0.25mg / L, 1.25mg / L, and 6.25mg / L, respectively, and the weighing error is less than 3%.

4. A method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide according to claim 1, characterized in that: The ion chromatograph used was a Swiss Metrohm 940 ion chromatograph, and Metrosep A Supp5-250 / 4.0 was selected as the anion chromatographic column; Instrument detection conditions: ion chromatography column temperature is 45°C, eluent flow rate is 0.7mL / min, ion chromatography column maximum pressure is 16.0MPa, and injection volume is 20uL.

5. A method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide according to claim 1, characterized in that: Before performing the detection in step S4, the ion chromatograph was turned on and preheated, and the eluent A was used to draw the baseline. The sample analysis was performed after the baseline was stable for 1 hour.

6. A method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide according to claim 1, characterized in that: In step S4, four anion standard curves Y=KX+C are drawn respectively, where: X is the concentration of the element corresponding to the standard solution, K is the slope of the working curve, C is the background concentration, and Y is the corresponding conductivity of the solution to be tested in the ion chromatograph. The fitting degree of the standard curves of the four anions is greater than 0.

999.

7. A method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide according to claim 1, characterized in that: In step S5, firstly, an aqueous solution of sodium bis(trifluoromethylsulfonyl)imide is prepared, and then a sodium bis(trifluoromethylsulfonyl)imide sample is diluted 95-105 times and anion chromatography analysis is performed.

8. A method for detecting the content of anionic impurities in sodium bis(trifluoromethanesulfonyl)imide according to claim 1, characterized in that: The sodium carbonate and sodium bicarbonate used in the preparation of the eluent were both of reference reagent grade, the acetonitrile was of analytical grade, and the sulfuric acid was of premium grade.

Images