Pretreatment method of imidodisulfuryl fluoride and detection method of chloride ion content

Abstract

The invention discloses a pretreatment method of imidodisulfuryl fluoride and a detection method of chloride ion content, belongs to the technical field of ion detection, and mainly researches a pretreatment method of imidodisulfuryl fluoride (HFSI), i.e., before detection, imidodisulfuryl fluoride is treated by using a sodium hydroxide solution, then the pH value of the solution is regulated to 7 by using nitric acid, and the pH value of the solution is regulated to 7 by using nitric acid; the treated imidodisulfuryl fluoride can be directly subjected to an ion chromatography test, the content of chloride ions in imidodisulfuryl fluoride is preliminarily tested by a mercury titration method, and the acid content of a system is tested by a triethylamine titration method so as to determine the use amount of sodium hydroxide for treating an imidodisulfuryl fluoride sample. According to the invention, the problems of strong acidity and corrosivity of the HFSI and chlorine loss caused by HClSI reaction in HFSI treatment are solved, so that the HFSI can be used for accurately and quantitatively testing chloride ions in the HFSI by using an ion chromatography.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion detection, and specifically relates to a pretreatment method for bis(fluorosulfonyl)imide and a detection method for chloride ion content. Background Art

[0002] Bis(fluorosulfonyl)imide (HFSI) is a raw material for lithium bis(fluorosulfonyl)imide salt (LiFSI) in lithium batteries. The quality of HFSI has a great impact on the quality of synthesized LiFSI. Generally, HFSI is obtained by fluorination of bis(chlorosulfonyl)imide (HClSI). Therefore, one of the indicators for controlling the quality of HFSI is placed on chloride ions. Higher chloride ions in HFSI may be directly introduced into the lithium salt during the synthesis of LiFSI, affecting the quality of LiFSI and having a great impact on the performance of lithium batteries. Therefore, the detection of trace chloride ions in HFSI is particularly important, and an accurate detection method for chloride ions in HFSI needs to be developed.

[0003] Currently, for the determination of chloride ions in HFSI, the most commonly used methods are titration methods, such as silver nitrate titration method and mercury nitrate titration method. These methods are relatively simple, but there are large errors in testing low-concentration chloride ions. Moreover, the unfluorinated HClSI remaining in HFSI will react violently with water to generate hydrogen chloride and escape, which will cause certain deviation in the test of chloride ions.

[0004] Ion chromatography is suitable for the determination of trace chloride ions. However, HFSI has strong acidity, slowly reacts with water to generate acids such as HF, and has a strong reactivity with residual HClSI, so it cannot be directly used for ion chromatography testing. It needs to be pretreated before ion chromatography testing, but there is currently no standard pretreatment method for HFSI to be used for ion chromatography testing.

[0005] CN114924019A discloses a method for testing chlorides in bis(fluorosulfonyl)imide. Bis(fluorosulfonyl)imide is added to ice water to control the decomposition rate of bis(chlorosulfonyl)imide at low temperature, and then it reacts with sodium hydroxide. Although this treatment method can meet the requirement of ion chromatography testing, there will still be a part of bis(chlorosulfonyl)imide decomposed and volatilized, resulting in inaccurate test results. Summary of the Invention

[0006] The purpose of the present invention is to provide a pretreatment method for bis(fluorosulfonyl)imide (HFSI) and a detection method for chloride ion content. The main research is on a pretreatment method for HFSI to solve the problems of strong acidity, corrosiveness of HFSI, and chlorine loss due to the reaction of HClSI during HFSI treatment, so that it can be used for ion chromatography to accurately quantify the chloride ions in HFSI.

[0007] Based on the above purpose, the present invention adopts the following technical solutions:

[0008] A pretreatment method for bis(fluorosulfonyl)imide is as follows:

[0009] (1) Initially test the chloride ion content and acid content in bis(fluorosulfonyl)imide;

[0010] (2) Weigh bis(fluorosulfonyl)imide and put it into a reaction flask with a side tube. Connect a balloon to the side tube of the reaction flask.

[0011] (3) According to the chloride ion content and acid content obtained in step (1), determine the volume of sodium hydroxide solution that reacts with the bis(fluorosulfonyl)imide in step (2), and add it dropwise to the sealed reaction flask; adjust the pH value of the solution after the reaction with nitric acid.

[0012] Furthermore, when testing the chloride ion content in bis(fluorosulfonyl)imide, first treat it with sodium hydroxide solution at 0 - 5 °C until the pH of bis(fluorosulfonyl)imide is 6 - 7, and then adjust the pH of the solution to 2.5 - 3.5 with nitric acid. Use the mercurimetric titration method to detect the chloride ion content and chloride ion concentration in the bis(fluorosulfonyl)imide after adjusting the pH.

[0013] Specifically, the calculation method for the chloride ion content is as follows:

[0014]

[0015] n Cl = C×(V2 - V1)×10 -3

[0016] C Cl - Chloride ion concentration (mg / L) in the bis(fluorosulfonyl)imide sample,

[0017] n Cl - Amount of chloride ions in moles (mol) in the bis(fluorosulfonyl)imide sample,

[0018] V2 - Volume of mercuric nitrate consumed by the test solution (mL),

[0019] V1 - Volume of mercuric nitrate consumed by the blank sample (mL),

[0020] C - Concentration of mercuric nitrate solution (mol / L),

[0021] V - Volume of the test solution used (mL),

[0022] V3 - Dilution factor from the bis(fluorosulfonyl)imide sample to the test solution.

[0023] The chloride ion concentration serves as the basis for dilution during detection.

[0024] Furthermore, dilute bis(fluorosulfonyl)imide with distilled water at 0 - 5 °C, and use the triethylamine titration method to detect the acid content in the diluted bis(fluorosulfonyl)imide.

[0025] Specifically, the acid content in bis(fluorosulfonyl)imide is calculated according to the following formula:

[0026] n H = C×(V2 - V1)×10 -3

[0027] n H - Acid content in bis(fluorosulfonyl)imide (mol),

[0028] V2 - Volume of triethylamine consumed by the bis(fluorosulfonyl)imide titrant (mL),

[0029] V1 - Volume of triethylamine consumed by the blank sample (mL),

[0030] C - Concentration of the triethylamine solution (mol / L).

[0031] Furthermore, the amount of the sodium hydroxide solution used in step (3) is 1.2 - 1.5 times its theoretical molar amount.

[0032] Specifically, considering the test error of chloride ions during titration, when actually weighing the amount of the sodium hydroxide solution used, multiply the theoretical amount by the amplification factor of 1.2 - 1.5 to ensure that the unfluorinated HClSI reacts completely. The volume of the sodium hydroxide solution is calculated through the following formula:

[0033] V NaOH = (n Cl + n H )×(1.2 - 1.5)÷C NaOH ×1000,

[0034] V NaOH - Volume of the sodium hydroxide solution used to treat bis(fluorosulfonyl)imide (mL),

[0035] n Cl - Chloride ion content in bis(fluorosulfonyl)imide obtained by the mercuric titration method (mol),

[0036] n H - Acid content in bis(fluorosulfonyl)imide by the triethylamine titration method (mol),

[0037] C NaOH - Concentration of the sodium hydroxide solution used to treat bis(fluorosulfonyl)imide (mol / L).

[0038] Furthermore, the concentration of the sodium hydroxide solution is 0.1 - 0.5 mol / L, and the concentration of nitric acid is 0.1 - 1 mol / L.

[0039] Further, in step (3), when adding the sodium hydroxide solution, stop adding the sodium hydroxide solution when the balloon bulges significantly. Let it stand until the balloon deflates, then add the sodium hydroxide solution again until all the sodium hydroxide solution is added. Shake the reaction flask to make it contact with the upper-layer gas, and let it stand for 0.5 - 1 h.

[0040] Further, in step (3), adjust the pH value of the solution after the reaction to 6 - 7 with nitric acid.

[0041] A method for detecting the chloride ion content in bis(fluorosulfonyl)imide. Use the liquid obtained by the above pretreatment method as the test solution or dilute it as the test solution for ion chromatography testing to obtain the chloride ion content, and calculate the chloride ion content in bis(fluorosulfonyl)imide from the chloride ion content in the test solution.

[0042] Further, dilute the test sample obtained by the pretreatment method to a concentration range of 0 - 20 mg / L as the test solution.

[0043] Specifically, prepare a blank sample and a series of standard solutions with a chloride ion concentration range of 0 - 20 mg / L. Conduct ion chromatography testing on the standard solutions, the blank sample, and the test solution. Draw a standard curve based on the peak area and chloride ion concentration in the standard solutions to obtain the standard curve equation. Calculate the chloride ion content in the test solution according to the standard curve equation, and calculate the chloride ion content in bis(fluorosulfonyl)imide from the chloride ion content in the test solution.

[0044] Further, when conducting ion chromatography testing, use a Dionex IonPac AS11-HC chromatographic column, with the eluent being 12 mmol / L sodium carbonate solution, the flow rate being 1 mL / min, the column temperature being 30 °C, the injection volume being 25 μL, and the detector being a conductivity detector.

[0045] Further, calculate the chloride ion content in bis(fluorosulfonyl)imide from the chloride ion content in the test solution according to the following formula:

[0046]

[0047] u - the chloride ion content in bis(fluorosulfonyl)imide, unit ppm,

[0048] t2 - the chloride ion content in the test solution detected by ion chromatography, unit mg / L,

[0049] t1 - the chloride ion content in the blank sample detected by ion chromatography, unit mg / L,

[0050] v - the volume of the bis(fluorosulfonyl)imide sample taken originally, unit mL,

[0051] m - the mass of the bis(fluorosulfonyl)imide sample taken originally, unit g,

[0052] r - Dilution factor of the original difluorosulfonylimide to the test solution.

[0053] Further, the gradient concentrations of the standard solution are 0.00 mg / L, 2.00 mg / L, 4.00 mg / L, 10.00 mg / L, and 20.00 mg / L in sequence.

[0054] Further, the standard curve equation is y = 0.08701 + 1.090601×10 -6 x, and the linear correlation coefficient R 2 ≥0.999.

[0055] The present invention mainly studies a pretreatment method for HFSI, solves the problems of strong acidity, corrosiveness of HFSI, and chlorine loss in the reaction of HClSI during the treatment of HFSI, enables it to be directly used in ion chromatography, accurately measures the chloride ions in HFSI, and the test results are accurate and reliable. Description of the Drawings

[0056] Figure 1 It is the standard working curve diagram of Example 1 of the present invention. Detailed Embodiments

[0057] Before the experiment, prepare 0.2 mol / L sodium hydroxide solution and 1 mol / L nitric acid solution for use.

[0058] Example 1

[0059] A method for detecting the chloride ion content in difluorosulfonylimide is as follows:

[0060] (1) Determination of the dosage of sodium hydroxide for treating the difluorosulfonylimide sample

[0061] Use a pipette to transfer two portions of 1.0 mL of difluorosulfonylimide sample (1.90 g). One portion is treated with 0.2 mol / L sodium hydroxide solution at 5°C until the pH of the difluorosulfonylimide solution is 7, and then adjusted to pH 3 with 1 mol / L nitric acid. Use a pipette to transfer 10 mL of the treated solution; another 0.2 mol / L sodium hydroxide solution equal to the amount for treating 1 mL of difluorosulfonylimide is taken, adjusted to pH 3 with 1 mol / L nitric acid, and 10 mL is taken out as a blank sample. Add 5 drops of diphenylcarbazone-bromophenol blue as an indicator to the treated difluorosulfonylimide solution and the blank sample, shake well, and titrate the solution with 0.01 mol / L mercuric nitrate until it turns blue-violet (this is the end point), and record the volume of mercuric nitrate consumed. At this time, the volumes of mercuric nitrate consumed by the test sample and the blank sample are 7.43 mL and 0.22 mL respectively. Calculate the chlorine content and concentration according to the formula. After calculation, in the difluorosulfonylimide sample, the chlorine content n Cl is 7.21*10 -5 mol, and the chloride ion concentration (CCl ) is 2560 mg / L, n Cl = C × (V2 - V1) × 10 -3

[0062] In the above formula, V2 = 7.43 mL, V1 = 0.22 mL, C = 0.01 mol / L, V3 = 10, V = 10 mL.

[0063] Another solution of bis(fluorosulfonyl)imide is treated with distilled water at 5 °C, diluted to 10 mL, and a 10 mL sample of distilled water is taken as a blank. 3 drops of neutral red - methylene blue are added as an indicator to the treated bis(fluorosulfonyl)imide solution and the blank respectively. After shaking well, it is titrated to the end point with 0.2 mol / L triethylamine (stop titrating when it changes from the initial blue - purple to green). At this time, the volumes of triethylamine consumed by the sample to be measured and the blank are 52.32 mL and 0.11 mL respectively. Calculate the acid content in bis(fluorosulfonyl)imide according to the following formula:

[0064] n H = C × (V2 - V1) × 10 -3

[0065] In the above formula, V2 = 52.32 mL, V1 = 0.11 mL, C = 0.2 mol / L.

[0066] After calculation, the acid content n H is 1.04 × 10 -2 mol.

[0067] Then, according to the formula V NaOH = (n Cl + n H ) × 1.5 ÷ C NaOH × 1000, calculate the volume of 0.2 mol / L sodium hydroxide solution required to treat bis(fluorosulfonyl)imide. After calculation, the amount of sodium hydroxide used is 78.59 mL.

[0068] (2) Treating the bis(fluorosulfonyl)imide sample with sodium hydroxide

[0069] Using a pipette, transfer 1 mL of bis(fluorosulfonyl)imide into a 100 mL Schlenk flask with a side arm connected to a balloon. Then, use a pipette to transfer 78.59 mL of 0.2 mol / L sodium hydroxide solution into a 100 mL constant-pressure funnel. Connect the constant-pressure funnel to the mouth of the Schlenk flask and slowly drip the sodium hydroxide solution. Control the dripping of sodium hydroxide by observing the inflation of the balloon. When the balloon bulges significantly during the dripping of the sodium hydroxide solution, stop adding the sodium hydroxide solution. Let it stand until the balloon inflation is not obvious, and then resume dripping the sodium hydroxide solution until it is completely added. Shake the reaction flask to allow the upper gas to come into contact. Let the entire apparatus stand for 0.5 h and shake it 2 - 3 times during this process to fully absorb the gas. Adjust the pH of the solution to 7 with 1 mol / L nitric acid. Separately, take 78.59 mL of sodium hydroxide solution with the same volume as that used to treat bis(fluorosulfonyl)imide and adjust its pH to 7 with 1 mol / L nitric acid solution as the untreated blank sample.

[0070] (3) Dilute and process the bis(fluorosulfonyl)imide sample to obtain the sample to be measured

[0071] Using a pipette, separately take out 7.64 mL of the bis(fluorosulfonyl)imide sample treated with sodium hydroxide in (2) and the untreated blank sample and transfer them to a 25 mL volumetric flask. Make up the volume to obtain the sample to be measured and the blank sample. Finally, dilute the chlorine content of bis(fluorosulfonyl)imide measured by titration, which is 2560 mg / L, to approximately 7 mg / L. Specifically, according to the above method, process three identical samples to obtain three parallel samples.

[0072] (4) Establish the ion chromatography standard curve

[0073] Accurately weigh 1.6584 g of sodium chloride and transfer it in full to a 1000 mL volumetric flask. Dilute it with water to the mark and make up the volume. Then, using a pipette, transfer 0.00 mL, 0.20 mL, 0.40 mL, 1.00 mL, and 2.00 mL of the above made-up solution into a set of 100 mL volumetric flasks respectively. Dilute them with water to the mark to prepare a set of standard series, namely: standard solutions of 0.00 mg / L, 2.00 mg / L, 4.00 mg / L, 10.00 mg / L, and 20.00 mg / L.

[0074] Inject the 0.00 mg / L, 2.00 mg / L, 4.00 mg / L, 10.00 mg / L, and 20.00 mg / L standard solutions into the ion chromatography in sequence. The ion chromatography test conditions are as follows: Dionex IonPac AS11-HC chromatographic column, the eluent is 12 mmol / L sodium carbonate solution, the flow rate is 1 mL / min, the column temperature is 30 °C, the injection volume is 25 μL, and the detector is a conductivity detector. Plot the working curve with the chloride ion concentration in the working curve as the abscissa and the corresponding peak area as the ordinate, as Figure 1As shown, the standard curve equation is y = 0.08701 + 1.090601×10 -6 x, and the linear correlation coefficient R 2 is 0.99973.

[0075] (5) Ion chromatography test

[0076] Using the ion chromatography test conditions in step (4), test the three parallel samples and the blank sample prepared above. According to the peak area obtained from the test, obtain the concentration of the test sample, and calculate the chloride ion concentration in the original bis(fluorosulfonyl)imide sample based on the dilution situation during the process. The calculation method for the chloride ion content in the original sample is as follows:

[0077]

[0078] In this example, v = 1 mL, m = 1.90 g, r = (78.59 + 1) ÷ 1 × (25 ÷ 5.44) ≈ 366. The specific results are shown in Table 1 below. Table 1

[0079]

[0080] As can be seen from Table 1, when testing three samples in parallel, the RSD is 1%, indicating that the determination of chloride ions in bis(fluorosulfonyl)imide by the present invention has good precision and stability.

[0081] Example 2:

[0082] A method for detecting the chloride ion content in bis(fluorosulfonyl)imide, the process is as follows:

[0083] Prepare a mixed solution with a chlorine content of 7994 ppm using dichlorosulfonylimide and bis(fluorosulfonyl)imide with a purity of 99.5%. Specifically, accurately weigh 0.241 g (molecular weight 214.05) of dichlorosulfonylimide and 9.759 g (molecular weight 181.141) of bis(fluorosulfonyl)imide in a glove box, put them into a 20 mL flask and shake well, and take 1 g (0.53 mL) of the mixed solution and put it into a 100 mL Schlenk flask with a balloon connected to the side tube.

[0084] Measure the corresponding amount of sodium hydroxide solution. Specifically, according to the sodium hydroxide dosage algorithm in step (1) of Example 1, calculate the dosage of sodium hydroxide to be 42.94 mL based on the theoretical amounts of dichlorosulfonylimide and bis(fluorosulfonyl)imide in the mixed solution. Use a 50 mL pipette to transfer 42.94 mL of the pre-prepared 0.2 mol / L sodium hydroxide solution to a 100 mL constant pressure funnel and place it in the glove box.

[0085] Connect a constant pressure funnel to a Schlenk flask, slowly add sodium hydroxide solution dropwise, observe the state of the balloon to control the dropping rate. After adding the sodium hydroxide solution dropwise, let it stand for 0.5 h, and shake the Schlenk flask 2 to 3 times during this period to fully absorb the gas. After the reaction is complete, measure the pH value of the solution with a pH test paper and adjust it to about 7 with 1 mol / L nitric acid.

[0086] Pretreatment of the blank sample: Weigh 0.976 g of pure bis(fluorosulfonyl)imide (the amount of bis(fluorosulfonyl)imide in 1 g of the sample), and add 42.94 mL of sodium hydroxide solution dropwise according to the above method, and adjust the pH of the solution to 7 with 1 mol / L nitric acid.

[0087] Use a 10 mL pipette to transfer 2.00 mL of the treated bis(fluorosulfonyl)imide solution and the pretreated blank sample into a 25 mL volumetric flask respectively, make up the volume to obtain the test sample and the blank sample. Finally, the chlorine content of the test sample is about 15 mg / L, so that the chlorine content falls within the range of the standard solution. Calculate the chloride ion content of the original sample according to the following formula,

[0088]

[0089] In this example, v = 0.53 mL, m = 1.0 g, r = (42.94 + 0.53) ÷ 0.53 × (25 ÷ 2) ≈ 1025.

[0090] Test the blank sample and the test sample respectively with ion chromatography, and calculate the corresponding chloride ion content. The specific results are shown in Table 2.

[0091] Table 2

[0092]

[0093] As can be seen from Table 2, three samples are tested in parallel, and the RSD is 0.68%. The error between the measurement result and the true value is small, indicating that the method for determining chloride ions in bis(fluorosulfonyl)imide of the present invention has good precision and stability.

[0094] Example 3:

[0095] A method for detecting the chloride ion content in bis(fluorosulfonyl)imide is as follows:

[0096] Prepare a mixed solution with a chlorine content of 500 ppm using 99.5% pure dichlorosulfonylimide and bis(fluorosulfonyl)imide. Specifically, accurately weigh 0.121 g of dichlorosulfonylimide and 80.101 g of bis(fluorosulfonyl)imide in a glove box, put them into a 100 mL PFA bottle, mix well, and take out 1 g (0.53 mL) of the mixed solution after mixing, and put it into a 100 mL Schlenk flask with a balloon connected to the side tube.

[0097] Measure the corresponding sodium hydroxide solution. Specifically, according to the sodium hydroxide dosage algorithm in Step 3, calculate the dosage of sodium hydroxide to be 41.50 mL based on the theoretical amounts of dichloro and difluoro in the taken mixed solution. Pipette 41.50 mL of the pre-prepared 0.2 mol / L sodium hydroxide solution with a 50 mL pipette and transfer it to a 100 mL constant pressure funnel, then place it in the glove box.

[0098] Connect the constant pressure funnel to the Schlenk flask, slowly drip the sodium hydroxide solution, observe the state of the balloon to control the dripping speed. After dripping the sodium hydroxide solution, let it stand for 0.5 h, and shake the Schlenk flask 2 to 3 times during this period to fully absorb the gas. After sufficient reaction, measure the pH value of the solution and adjust it to approximately 7 with 1 mol / L nitric acid.

[0099] Prepare the blank sample. Weigh 0.998 g of pure difluoromethanesulfonimide (the amount of difluoromethanesulfonimide in 1 g of the sample), and drip 41.50 mL of sodium hydroxide solution according to the above method, and adjust the pH of the solution to 7 with 1 mol / L nitric acid.

[0100] Use a 10 ml pipette to pipette 9.00 mL of the treated difluoro solution and the pretreated blank sample into a 25 mL volumetric flask respectively, make up the volume to obtain the sample to be measured and the blank sample. Finally, the chlorine content of the sample to be measured is about 4 mg / L, so that its chlorine content falls within the range of the standard solution.

[0101] Calculate the chloride ion content of the original sample according to the following formula,

[0102]

[0103] In this example, v = 0.53 mL, m = 1.0 g, r = (41.50 + 0.53) ÷ 0.53 × (25 ÷ 9) ≈ 221.

[0104] Use ion chromatography to test the blank sample and the sample to be measured respectively, and calculate the corresponding chloride ion content. The specific results are shown in Table 3.

[0105] Table 3

[0106]

[0107] As can be seen from Table 3, when testing three samples in parallel, the RSD is 1.42%, and the error between the measurement result and the true value is small, indicating that the determination of chloride ions in difluoromethanesulfonimide by the present invention has good precision and stability.

[0108] Comparative Example 1

[0109] Take 10 mL of the sample to be tested (without final dilution) treated with sodium hydroxide in Example 2 and the corresponding pre-treatment blank sample into a 50 mL conical flask, add 5 drops of diphenylcarbazone-bromophenol blue mixed indicator and shake well, and adjust the pH values of the sample to be tested and the blank sample to 3.0 with 1 mol / L nitric acid solution. At this time, the solution is yellow. Titrate the sample to be tested and the blank sample with 0.01 mol / L mercuric nitrate solution until the solution turns blue-violet, and record the amounts of mercuric nitrate consumed by the blank sample and the sample to be tested.

[0110] The amounts of mercuric nitrate consumed by the blank sample and the sample to be tested in three parallel titrations are as follows: blank sample: 0.02 mL, parallel sample 1: 4.92 mL, parallel sample 2: 5.04 mL, parallel sample 3: 5.04 mL. According to the formula V2 = 4.92 mL, 5.04 mL, 5.04 mL, V1 = 0.02 mL, C = 0.01 mol / L, V3 = (42.94 + 0.53) ÷ 0.53 ≈ 82, calculate the chloride ion concentration in the original sample;

[0111] According to the formula U = C Cl ×V÷m

[0112] U - the chloride ion content in the sample to be tested, unit ppm,

[0113] V - the volume of the bis(fluorosulfonyl)imide sample taken originally, unit mL,

[0114] m - the mass corresponding to the bis(fluorosulfonyl)imide sample taken originally, unit g,

[0115] In this comparative example, V = 0.53 mL, m = 1 g, calculate the chloride ion content in the original sample, and the results are shown in Table 4 below.

[0116] Table 4

[0117]

[0118] As can be seen from Table 4, for the three samples in parallel tests, the RSD is 5.75%, and the error between the measurement result and the true value is large.

[0119] Comparative Example 2

[0120] Take 20 mL of the sample to be tested treated with sodium hydroxide in Example 3 and the corresponding blank sample into a 50 mL conical flask, add 5 drops of diphenylcarbazone-bromophenol blue mixed indicator and shake well, and adjust the pH values of the sample to be tested and the blank sample to 3.0 with 1 mol / L nitric acid solution. At this time, the solution is yellow. Titrate the sample to be tested and the blank sample with 0.01 mol / L mercuric nitrate solution until the solution turns blue-violet, and record the amounts of mercuric nitrate consumed by the blank sample and the sample to be tested

[0121] The amounts of mercury nitrate consumed in three parallel titrations of the blank sample and the sample to be tested are as follows: blank sample: 0.04 mL, parallel sample 1: 0.60 mL, parallel sample 2: 0.54 mL, parallel sample 3: 0.64 mL. According to the formula V2 = 0.60 mL, 0.54 mL, 0.64 mL, V1 = 0.04 mL, C = 0.01 mol / L, V3 = (41.50 + 0.53) ÷ 0.53 ≈ 79. Calculate the chloride ion concentration in the original sample;

[0122] According to the formula U = C Cl ×V ÷ m

[0123] U - the chloride ion content in the sample to be tested, unit ppm,

[0124] V - the volume of the bis(fluorosulfonyl)imide sample taken originally, unit mL,

[0125] m - the mass corresponding to the bis(fluorosulfonyl)imide sample taken originally, unit g. In this comparative example, V = 0.53 mL, m = 1 g. Calculate the chloride ion content in the original sample. The results are shown in Table 5 below.

[0126] Table 5

[0127]

[0128] As can be seen from Table 5, for the three samples in parallel tests, the RSD is 9.10%, and the error between the measurement result and the true value is large.

[0129] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various modifications and decorations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A pretreatment method for bis(fluorosulfonyl)imide, characterized in that: The process is as follows: (1) Preliminary testing of chloride ion content and acid content in bis(fluorosulfonyl)imide; (2) Weigh bis(fluorosulfonyl)imide and place it in a reaction bottle with a branch tube, and connect a balloon to the branch tube of the reaction bottle; (3) According to the chloride ion content and acid content obtained in step (1), the volume of the sodium hydroxide solution to be reacted with the bis(fluorosulfonyl)imide in step (2) is determined and added dropwise to the sealed reaction bottle; and the pH value of the solution after the reaction is adjusted with nitric acid.

2. The pretreatment method of bis(fluorosulfonyl)imide according to claim 1, characterized in that: When testing the chloride ion content in bis(fluorosulfonyl)imide, first treat it with 0~5℃ sodium hydroxide solution until the pH of the bis(fluorosulfonyl)imide is 6~7, then adjust the pH of the solution to 2.5~3.5 with nitric acid, and use mercury titration to detect the chloride ion content in the bis(fluorosulfonyl)imide after adjusting the pH.

3. The pretreatment method of bis(fluorosulfonyl)imide according to claim 1, characterized in that: Dilute the bis(fluorosulfonyl)imide with distilled water at 0-5°C, and detect the acid content in the diluted bis(fluorosulfonyl)imide by triethylamine titration.

4. The pretreatment method of bis(fluorosulfonyl)imide according to claim 1, characterized in that: The amount of sodium hydroxide solution used in step (3) is 1.2 to 1.5 times its theoretical amount.

5. The pretreatment method of bis(fluorosulfonyl)imide according to any one of claims 1 to 3, characterized in that: The concentration of sodium hydroxide solution is 0.1~0.5 mol / L, and the concentration of nitric acid is 0.1~1 mol / L.

6. The pretreatment method of bis(fluorosulfonyl)imide according to claim 1, characterized in that: In step (3), when adding sodium hydroxide solution, when the balloon swells significantly, stop adding sodium hydroxide solution, let it stand until the balloon swelling disappears, then add sodium hydroxide solution again until the sodium hydroxide solution is added completely, shake the reaction bottle to contact the upper gas, and leave it for 0.5 to 1 hour.

7. The pretreatment method of bis(fluorosulfonyl)imide according to claim 1, characterized in that: In step (3), the pH value of the solution after the reaction is adjusted to 6-7 with nitric acid.

8. A method for detecting the chloride ion content in bis(fluorosulfonyl)imide, characterized in that: The liquid obtained by the pretreatment method according to claim 1 is used as the test liquid or diluted as the test liquid for ion chromatography test to obtain the chloride ion content, and the chloride ion content in the bisfluorosulfonyl imide is calculated from the chloride ion content in the test liquid.

9. The method for detecting the chloride ion content in bis(fluorosulfonyl)imide according to claim 8, characterized in that: In the ion chromatography test, a Dionex IonPac AS11-HC column was used, a 12 mmol / L sodium carbonate solution was used as the eluent, the flow rate was 1 mL / min, the column temperature was 30°C, the injection volume was 25 μL, and the detector was a conductivity detector.

10. The method for detecting the chloride ion content in bis(fluorosulfonyl)imide according to claim 8, characterized in that: The chloride ion content in the bis(fluorosulfonyl)imide is calculated from the chloride ion content in the test solution according to the following formula: The chloride ion content in u-bis(fluorosulfonyl)imide, in ppm, t2- Ion chromatography test of chloride ion content in the test solution, unit: mg / L, t1-chloride ion content in blank sample of ion chromatography test, unit: mg / L, v-the original volume of the bis(fluorosulfonyl)imide sample, in mL, m-the original mass of the bis(fluorosulfonyl)imide sample, in g, r- dilution factor of the original bis(fluorinated) sulfonyl imide to the test solution.

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