Analysis Method of Organic Additives in Lithium-Ion Battery Electrolyte

Abstract

The present invention provides an analytical method for organic additives in a lithium-ion battery electrolyte. The analytical method includes: Step S1, separating the lithium-ion battery electrolyte by anti-solvent method using a solvent to obtain a supernatant containing the organic additive and a precipitate containing lithium hexafluorophosphate; Step S2, performing HPLC analysis on the supernatant. Wherein, the lithium-ion battery electrolyte contains lithium hexafluorophosphate, the fluoride ion concentration in the supernatant is ≤ 1 ppm, and the solvent is a non-polar solvent. The above method of the present application makes the fluoride ion concentration in the supernatant ≤ 1 ppm, and avoids the corrosion of the chromatographic column by fluoride ions and the destruction of the structure of the organic additive. Therefore, the supernatant can be directly taken for qualitative and quantitative analysis of the organic additive. Moreover, the above method is simple and effective, and does not affect the peak appearance effect of the organic additive in liquid chromatography after separation, so that the measurement result is relatively accurate.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion battery electrolytes, and more particularly, to an analytical method for organic additives in a lithium-ion battery electrolyte. Background Art

[0002] Trace additives in the electrolyte can effectively improve the performance of lithium-ion batteries. With the development and application of electrolyte formulations, the types of trace organic additives in lithium-ion batteries are increasing. Currently, the main methods for detecting organic additives in the electrolyte are qualitative analysis of the additives in the electrolyte using a gas chromatography-mass spectrometry (GC-MS) instrument and quantitative analysis of the organic additives in the electrolyte using gas chromatography (GC). However, since some trace organic additives have a low peak emergence effect in gas chromatography or a high boiling point (when the boiling point of a general organic additive is higher than 300 °C), they cannot be detected in gas chromatography. Therefore, in order to improve the detection method for trace organic additives in the electrolyte, a liquid chromatography (LC) instrument is introduced to perform qualitative and quantitative analysis of the organic additives in the electrolyte by liquid chromatography, so as to make up for the deficiency that high-boiling organic additives cannot be measured by gas chromatography in electrolyte analysis.

[0003] Currently, liquid chromatography of organic additives in the electrolyte usually uses a C 18 chromatographic column. The C 18 chromatographic column is a commonly used reversed-phase chromatographic column, which is synthesized by long-chain alkyl bonds, has a high carbon content and better hydrophobicity, making the C 18 chromatographic column suitable for separating non-polar organic solvents. However, the C 18 chromatographic column is not resistant to corrosion by hydrofluoric acid (HF). Therefore, when testing an electrolyte sample by liquid chromatography, the sample cannot contain HF.

[0004] Lithium hexafluorophosphate (LiPF6) in the lithium-ion battery electrolyte is prone to hydrolysis, and it is inevitable to entrain hydrofluoric acid into the final product during the electrolyte preparation process. The industry standard "HG.50871-2015 Lithium Hexafluorophosphate Electrolyte" requires that the content of hydrofluoric acid in the finished electrolyte is less than 0.005%. Generally, the content of hydrofluoric acid in the electrolyte is controlled by controlling the water content of the electrolyte, but LiPF6 will continuously react with water to produce hydrofluoric acid. The mobile phase of liquid chromatography contains an aqueous phase. If the electrolyte containing LiPF6 is injected into the liquid chromatography, the LiPF6 in it will continuously react with the water in the chromatographic mobile phase to produce HF, and the HF will corrode the C 18 chromatographic column and its flow path pipeline, thereby causing irreversible damage to the liquid chromatography. Therefore, it is necessary to develop a method to separate lithium hexafluorophosphate (LiPF6) from the electrolyte.

[0005] In addition, although there are some methods for removing lithium hexafluorophosphate from lithium-ion battery electrolytes in the prior art, these methods often have problems such as too high a concentration of fluoride ions (greater than 1 ppm) and the structure of organic additives being easily damaged, resulting in the inability to accurately qualitatively and quantitatively analyze the organic additives in lithium-ion battery electrolytes. Summary of the Invention

[0006] The main object of the present invention is to provide an analytical method for organic additives in lithium-ion battery electrolytes to solve the problems in the prior art of being unable to accurately qualitatively and quantitatively analyze high-boiling organic additives in lithium-ion battery electrolytes and the chromatographic column being easily damaged.

[0007] To achieve the above object, according to one aspect of the present invention, there is provided an analytical method for organic additives in lithium-ion battery electrolytes, the analytical method comprising: Step S1, separating the lithium-ion battery electrolyte by the anti-solvent method using a solvent to obtain a supernatant containing the organic additive and a precipitate containing lithium hexafluorophosphate; Step S2, performing HPLC analysis on the supernatant, wherein the lithium-ion battery electrolyte contains lithium hexafluorophosphate, the fluoride ion concentration in the supernatant is ≤1 ppm, and the solvent is a non-polar solvent.

[0008] Further, the above non-polar solvent is selected from any one or more of C6-C 10 normal alkane solvents, preferably n-decane.

[0009] Further, the volume ratio of the above solvent to the lithium-ion battery electrolyte is ≥1:1.

[0010] Further, the volume ratio of the above solvent to the lithium-ion battery electrolyte is 1:1 to 9:1.

[0011] Further, the volume ratio of the above solvent to the lithium-ion battery electrolyte is 4:1 to 9:1, preferably 9:1.

[0012] Further, the mass content of lithium hexafluorophosphate in the above lithium-ion battery electrolyte is 5-20%.

[0013] Further, the mass content of the organic additive in the above lithium-ion battery electrolyte is 0.1-8%.

[0014] Further, the process of the anti-solvent method separation includes: oscillating and mixing the solvent with the lithium-ion battery electrolyte and then standing to obtain a standing system including a supernatant and a precipitate; preferably, the standing time is 3-5 h.

[0015] Further, the above-mentioned organic additive is selected from any one or more of fluorobenzene, vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, ethylene fluoroethylene carbonate, and ethylene sulfite.

[0016] Further, C 18 chromatographic column is used for the above HPLC analysis.

[0017] Applying the technical solution of the present invention, since lithium hexafluorophosphate is a polar substance, while other components in the lithium ion battery electrolyte are mostly non-polar substances, in this application, the lithium ion battery electrolyte is separated by the anti-solvent method using a non-polar solvent, so that lithium hexafluorophosphate precipitates out as a precipitate, and the components other than lithium hexafluorophosphate remain in the supernatant, and the fluoride ion concentration in the supernatant ≤ 1 ppm, thus greatly reducing the probability that lithium hexafluorophosphate will continuously react with water in the chromatographic mobile phase to produce HF, and further reducing the production amount of HF. Further, it avoids the corrosion of the chromatographic column by fluoride ions and the damage to the structure of the organic additive. Therefore, the supernatant can be directly taken for qualitative and quantitative analysis of the organic additive. And the above method is simple and effective, does not affect the peak appearance effect of the organic additive in liquid chromatography, so that the measurement result is relatively accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0019] Figure 1 Shows the chromatographic overlay diagram of fluoride ions and hexafluorophosphate ions of sample 1 obtained according to Preparation Example 1 of the present application, supernatant 1 obtained according to Test Example 1, lower layer liquid obtained according to Test Comparative Example 1, and 1 ppm fluoride ion standard sample;

[0020] Figure 2 Shows the liquid chromatographic overlay diagram of fluorobenzene in supernatant 1 obtained according to Test Example 1 of the present application and lower layer liquid obtained according to Test Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0022] As analyzed in the background art, lithium hexafluorophosphate in the electrolyte of a lithium-ion battery will hydrolyze when encountering the aqueous phase of liquid chromatography to produce HF: LiPF6 + H2O = POF3 + 2HF + LiF, thereby increasing the concentration of fluoride ions in the electrolyte of the lithium-ion battery. Furthermore, it is likely to corrode the liquid chromatography column, causing damage to the chromatography column and destroying the structure of the high-boiling organic additives in the electrolyte of the lithium-ion battery. To solve this problem, the present invention provides an analytical method for organic additives in the electrolyte of a lithium-ion battery.

[0023] In a typical embodiment of the present application, an analytical method for organic additives in the electrolyte of a lithium-ion battery is provided. The analytical method includes: Step S1, separating the electrolyte of the lithium-ion battery by the anti-solvent method using a solvent to obtain a supernatant containing the organic additive and a precipitate containing lithium hexafluorophosphate; Step S2, performing HPLC analysis on the supernatant. Among them, the electrolyte of the lithium-ion battery contains lithium hexafluorophosphate, the fluoride ion concentration in the supernatant is ≤ 1 ppm, and the solvent is a non-polar solvent.

[0024] Since lithium hexafluorophosphate is a polar substance, while most of the other components in the electrolyte of the lithium-ion battery are non-polar substances, in this application, the electrolyte of the lithium-ion battery is separated by the anti-solvent method using a non-polar solvent, so that lithium hexafluorophosphate precipitates out from it, while the components other than lithium hexafluorophosphate continue to remain in the supernatant, and the fluoride ion concentration in the supernatant is ≤ 1 ppm. Thus, the probability that lithium hexafluorophosphate will continuously react with water in the chromatographic mobile phase to produce HF is greatly reduced, and further, the production amount of HF is reduced. Furthermore, the corrosion of the chromatographic column by fluoride ions and the destruction of the structure of the organic additive are avoided. Therefore, the supernatant can be directly taken for qualitative and quantitative analysis of the organic additive. And the above method is simple and effective, does not affect the peak appearance effect of the separated organic additive in liquid chromatography, so that the measurement result is relatively accurate.

[0025] The above anti-solvent method is to use a solvent with low or insoluble solubility for the target substance to treat the object to be treated in the art, and utilize the difference in solubility to separate and treat the target substance in the form of a precipitate. Therefore, based on the above principle, those skilled in the art can screen solvents to separate lithium hexafluorophosphate in the electrolyte of a lithium-ion battery. On the basis of a large number of experiments in this application, to further improve the separation efficiency of the anti-solvent method, it is preferred that the above non-polar solvent is selected from any one or more of the normal alkane solvents of C6 - C 10 and is preferably n-decane.

[0026] In an embodiment of the present application, the volume ratio of the above solvent to the electrolyte of the lithium-ion battery is ≥ 1:1.

[0027] It has been found through experiments that in order to separate and remove lithium hexafluorophosphate in the lithium-ion battery electrolyte as much as possible, so that the fluoride ion concentration in the obtained supernatant is ≤ 1 ppm, and then the organic additives in the supernatant can be accurately qualitatively and quantitatively analyzed, it is preferred that the volume ratio of the above solvent to the lithium-ion battery electrolyte is at least 1:1.

[0028] To balance the separation effect of lithium hexafluorophosphate in the lithium-ion battery electrolyte and the cost of the solvent used, it is preferred that the volume ratio of the above solvent to the lithium-ion battery electrolyte is 1:1 to 9:1.

[0029] On the basis of controlling the cost of the solvent used, to further improve the separation efficiency of lithium hexafluorophosphate, it is preferred that the volume ratio of the above solvent to the lithium-ion battery electrolyte is 4:1 to 9:1, and preferably 9:1.

[0030] Usually, the mass content of lithium hexafluorophosphate in the lithium-ion battery electrolyte is 5-20%, and the above analysis method of the present application has excellent applicability to the lithium-ion battery electrolyte with lithium hexafluorophosphate within the above range.

[0031] Usually, the mass content of the organic additives in the lithium-ion battery electrolyte is 0.1-8%, and the above analysis method of the present application can accurately qualitatively and quantitatively analyze the lithium-ion battery electrolyte with the content of organic additives within the above range.

[0032] In an embodiment of the present application, the process of separating by the above antisolvent method includes: oscillating and mixing the above solvent and the lithium-ion battery electrolyte and then standing still to obtain a standing system including a supernatant and a precipitate; preferably, the standing time is 3-5 h.

[0033] The above oscillation is beneficial to the more sufficient dissolution of the components in the lithium-ion battery electrolyte except lithium hexafluorophosphate in the solvent, and standing still is beneficial to the precipitation of lithium hexafluorophosphate and its stratification with the liquid. The oscillation in the present application is selected from manual oscillation or ultrasonic oscillation. For the convenience of operation, manual oscillation is preferred. Of course, those skilled in the art can also select other operation methods that can achieve a uniform mixing effect of the solvent and the lithium-ion battery electrolyte according to the actual situation, which will not be elaborated here.

[0034] The present application preferably samples directly from the supernatant for testing. Of course, those skilled in the art can also separate the supernatant and the precipitate by solid-liquid separation, such as separating the supernatant and the precipitate by filtration or vacuum filtration, and then sampling from the supernatant for testing.

[0035] To further improve the accurate qualitative and quantitative analysis of the above organic additives by the above analysis method, it is preferred that the above organic additives are selected from any one or more of fluorobenzene, vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, ethylene carbonate ethyl ester, and ethylene sulfite.

[0036] Of course, those skilled in the art can also analyze the types and contents of other organic additives in the lithium-ion battery electrolyte according to actual needs by using the above test method, which will not be elaborated here.

[0037] To improve the analysis effect of the organic additives in this application, it is preferred to use a C 18 chromatographic column for the above HPLC analysis.

[0038] In addition, the above HPLC analysis of this application is as follows: The contents of fluoride ions and hexafluorophosphate ions in the supernatant solution are tested by an ion chromatograph. The content of the electrolyte organic additives in the supernatant is tested by liquid chromatography, and the recovery rate and relative error of the organic additives are calculated. To improve the HPLC analysis efficiency of the supernatant, the specific HPLC analysis conditions for the supernatant are preferably: the mobile phase of the ion chromatograph is a mixture of acetonitrile and pure water in a volume ratio of 4:4 to 6, and the flow rate of the mobile phase is 0.7 mL / min. In the liquid chromatography, the mobile phase A is a mixture of pure water and methanol in a volume ratio of 7 to 9:1, the mobile phase B is acetonitrile, and the two phases A and B are mixed in a volume ratio of 1:1, and the flow rate of the mobile phase is 1 mL / min. Of course, those skilled in the art can also perform the above HPLC analysis with reference to the analysis conditions in the existing relevant technologies, which will not be elaborated here.

[0039] Hereinafter, the beneficial effects of this application will be described in conjunction with specific examples and comparative examples.

[0040] Preparation Examples 1 to 7 of Lithium-Ion Battery Electrolyte

[0041] Preparation Example 1

[0042] Prepare a lithium-ion battery electrolyte in a glove box filled with nitrogen (nitrogen purity is 99.999%, moisture ≤ 5 ppm). Weigh ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate respectively and mix them evenly according to the mass ratio of 1:1:1 to obtain Mixture 1. By mass percentage, Mixture 1 is 76%. Add 0.5% of vinylene carbonate organic additive and 3.5% of fluorobenzene organic additive to Mixture 1, and then slowly add 18% of lithium hexafluorophosphate and 2% of lithium difluoro(oxalato)borate and mix them evenly. Denote it as Sample 1. The chromatograms of fluoride ions and hexafluorophosphate ions in Sample 1 are as Figure 1 shown.

[0043] Preparation Example 2

[0044] Prepare the lithium-ion battery electrolyte in a glove box filled with nitrogen (nitrogen purity is 99.999% and moisture ≤ 5 ppm). Weigh ethylene carbonate, dimethyl carbonate, and diethyl carbonate respectively and mix them evenly according to the mass ratio of 1:1:1 to obtain Mixture 2. By mass percentage, Mixture 2 is 80%. Add 5% of fluorobenzene organic additive to Mixture 2, and then slowly add 15% of lithium hexafluorophosphate and mix well to obtain Sample 2.

[0045] Preparation Example 3

[0046] Prepare the lithium-ion battery electrolyte in a glove box filled with nitrogen (nitrogen purity is 99.999% and moisture ≤ 5 ppm). Weigh ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate respectively and mix them evenly according to the mass ratio of 1:1:1:1 to obtain Mixture 3. By mass percentage, Mixture 3 is 82.5%. Add 2.5% of fluorobenzene organic additive to Mixture 3, and then slowly add 12% of lithium hexafluorophosphate and 3% of lithium bis(fluorosulfonyl)imide and mix well to obtain Sample 3.

[0047] Preparation Example 4

[0048] Prepare the lithium-ion battery electrolyte in a glove box filled with nitrogen (nitrogen purity is 99.999% and moisture ≤ 5 ppm). Weigh ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate respectively and mix them evenly according to the mass ratio of 1:1:1 to obtain Mixture 4. By mass percentage, Mixture 4 is 85%. Add 2% of 1,3 - propane sultone organic additive and 1% of fluorobenzene organic additive to Mixture 4, and then slowly add 10% of lithium hexafluorophosphate and 3% of lithium bis(fluorosulfonyl)imide and mix well to obtain Sample 4.

[0049] Preparation Example 5

[0050] Prepare the lithium-ion battery electrolyte in a glove box filled with nitrogen (nitrogen purity is 99.999% and moisture ≤ 5 ppm). Weigh ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate respectively and mix them evenly according to the mass ratio of 1:1:1 to obtain Mixture 5. By mass percentage, Mixture 5 is 87.25%. Add 2% of 1,3 - propane sultone organic additive, 1% of vinylene carbonate organic additive, and 0.75% of fluorobenzene organic additive to Mixture 5, and then slowly add 8% of lithium hexafluorophosphate and 1% of lithium tetrafluoroborate and mix well to obtain Sample 5.

[0051] Preparation Example 6

[0052] Prepare the lithium-ion battery electrolyte in a glove box filled with nitrogen (nitrogen purity is 99.999%, moisture ≤ 5 ppm). Weigh ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate respectively and mix them evenly according to the mass ratio of 1:1:1 to obtain mixture 6. By mass percentage, mixture 6 is 70%. Add 4.5% of vinylene carbonate organic additive and 3.5% of fluorobenzene organic additive to mixture 6, then slowly add 20% of lithium hexafluorophosphate and 2% of lithium difluoro(oxalato)borate and mix well, denoted as sample 6.

[0053] Preparation Example 7

[0054] Prepare the lithium-ion battery electrolyte in a glove box filled with nitrogen (nitrogen purity is 99.999%, moisture ≤ 5 ppm). Weigh ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate respectively and mix them evenly according to the mass ratio of 1:1:1 to obtain mixture 7. By mass percentage, mixture 7 is 80%. Add 0.1% of fluorobenzene organic additive to mixture 7, then slowly add 17.9% of lithium hexafluorophosphate and 2% of lithium difluoro(oxalato)borate and mix well, denoted as sample 7.

[0055] Test Examples 1 to 13 of Lithium-Ion Battery Electrolyte

[0056] Test Example 1

[0057] Use a pipette to take 10 mL of sample 1 into a 100 mL volumetric flask, then pour 90 mL of n-decane into the volumetric flask to make up the volume, shake well up and down and let it stand for 3 h to obtain the standing system. Filter the standing system to obtain the supernatant 1 and lithium hexafluorophosphate precipitate. Among them, the chromatograms of fluoride ions and hexafluorophosphate ions in the supernatant 1 are as Figure 1 shown, and the liquid chromatogram of fluorobenzene in the supernatant 1 is as Figure 2 shown.

[0058] Test Example 2

[0059] The difference between Test Example 2 and Test Example 1 is that

[0060] Use a pipette to take 20 mL of sample 1 into a 100 mL volumetric flask, then pour 80 mL of n-decane into the volumetric flask to make up the volume, shake well up and down and let it stand for 3 h to obtain the standing system. Filter the standing system to obtain the supernatant 2 and lithium hexafluorophosphate precipitate.

[0061] Test Example 3

[0062] The difference between Test Example 3 and Test Example 1 is that

[0063] Use a pipette to take 12.5 mL of Sample 1 into a 100 mL volumetric flask. Then pour 87.5 mL of n-decane into the volumetric flask, make up the volume, shake well up and down, and let it stand for 3 h to obtain the standing system. Filter the standing system to obtain the supernatant 3 and lithium hexafluorophosphate precipitate.

[0064] Test Example 4

[0065] The difference between Test Example 4 and Test Example 1 is that

[0066] Use a pipette to take 50 mL of Sample 1 into a 100 mL volumetric flask. Then pour 50 mL of n-decane into the volumetric flask, make up the volume, shake well up and down, and let it stand for 3 h to obtain the standing system. Filter the standing system to obtain the supernatant 4 and lithium hexafluorophosphate precipitate.

[0067] Test Example 5

[0068] The difference between Test Example 5 and Example 1 is that

[0069] Use a pipette to take 60 mL of Sample 1 into a 100 mL volumetric flask. Then pour 40 mL of n-decane into the volumetric flask, make up the volume, shake well up and down, and let it stand for 3 h to obtain the standing system. Filter the standing system to obtain the supernatant 5 and lithium hexafluorophosphate precipitate.

[0070] Test Example 6

[0071] The difference between Test Example 6 and Test Example 1 is that

[0072] Let it stand for 5 h to obtain the standing system. Filter the standing system to obtain the supernatant 6 and lithium hexafluorophosphate precipitate.

[0073] Test Example 7

[0074] The difference between Test Example 7 and Test Example 1 is that

[0075] The solvent is n-hexane, and finally the supernatant 7 and lithium hexafluorophosphate precipitate are obtained.

[0076] Test Example 8

[0077] The difference between Test Example 8 and Test Example 1 is that

[0078] Use a pipette to take 10 mL of Sample 2 into a 100 mL volumetric flask. Finally, the supernatant 8 and lithium hexafluorophosphate precipitate are obtained.

[0079] Test Example 9

[0080] The difference between Test Example 9 and Test Example 1 is that

[0081] Use a pipette to take 10 mL of sample 3 into a 100 mL volumetric flask, and finally obtain the supernatant 9 and lithium hexafluorophosphate precipitate.

[0082] Test Example 10

[0083] The difference between Test Example 10 and Test Example 1 is that

[0084] Use a pipette to take 10 mL of sample 4 into a 100 mL volumetric flask, and finally obtain the supernatant 10 and lithium hexafluorophosphate precipitate.

[0085] Test Example 11

[0086] The difference between Test Example 11 and Test Example 1 is that

[0087] Use a pipette to take 10 mL of sample 5 into a 100 mL volumetric flask, and finally obtain the supernatant 11 and lithium hexafluorophosphate precipitate.

[0088] Test Example 12

[0089] The difference between Test Example 12 and Test Example 1 is that

[0090] Use a pipette to take 10 mL of sample 6 into a 100 mL volumetric flask, and finally obtain the supernatant 12 and lithium hexafluorophosphate precipitate.

[0091] Test Example 13

[0092] The difference between Test Example 13 and Test Example 1 is that

[0093] Use a pipette to take 10 mL of sample 7 into a 100 mL volumetric flask, and finally obtain the supernatant 13 and lithium hexafluorophosphate precipitate.

[0094] Test Comparative Example 1

[0095] Take 10 mL of sample 1 into a 100 mL volumetric flask, add about 80 mL of saturated sodium carbonate solution to the volumetric flask, shake it up and down, open the piston of the volumetric flask and let it stand for 20 min. After observing that there are no more bubbles in the bottle, add 10 mL of dichloromethane to the bottle. After the solution is mixed and stratified, the electrolyte is in the lower layer and the sodium carbonate solution is in the upper layer. Shake the solution well, let it stand for about 10 minutes until the upper and lower layers are clearly stratified. Pour out the upper layer solution, then pour sodium carbonate solution into the volumetric flask, shake it well and let it stand, and then pour out the upper layer supernatant. Repeat the above operation 9 times, pour out the upper layer liquid, and obtain the lower layer liquid. Use an ion chromatograph to inject the lower layer liquid for testing, and record the peak emergence time and peak area of fluoride ions and hexafluorophosphate ions. Use liquid chromatography to inject the lower layer liquid for testing, and record the fluorobenzene content. The liquid chromatogram of fluorobenzene is as Figure 2 shown, and the chromatograms of fluoride ions and hexafluorophosphate ions are asFigure 1 as shown

[0096] Test Comparative Example 2

[0097] The difference between Test Comparative Example 2 and Test Comparative Example 1 is that 10 mL of dichloromethane was directly poured into the electrolysis, and no precipitate was formed in the electrolyte solution.

[0098] Use a pipette to transfer 100 μL of the national standard solution with a fluoride ion concentration of 1000 ppm into a 100 mL volumetric flask, and dilute it to 100 mL with a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass fraction ratio of 1:1:1 to obtain a 1 ppm fluoride ion standard solution. Prepare a series of standard solutions with fluoride ion contents of 0.2 ppm, 0.5 ppm, and 0.7 ppm according to the above steps. Detect the characteristic peaks of the fluoride ion content in the series of fluoride ion standard solutions by ion chromatography (Metrohm ion chromatography - 883, column model: SUPP - 7250, flow rate 0.7 mL / min, pump pressure 14 MPa, mobile phase is a mixed solution of 0.3816 g of sodium bicarbonate plus 400 mL of acetonitrile plus ultrapure water diluted to 1000 mL, and the regeneration solution is a mixed solution of 5 mL of concentrated sulfuric acid plus ultrapure water diluted to 1000 mL), and perform linear fitting. The linear fitting results of the fluoride ion standard solution are shown in Table 1 below.

[0099] Table 1

[0100]

[0101] It can be seen from Table 1 that the correlation coefficient R of the linear fitting of the fluoride ion standard solution with the peak area of the fluoride ion characteristic peak 2 can reach 0.9905.

[0102] Prepare a lithium - ion battery electrolyte in a glove box filled with nitrogen (nitrogen purity is 99.999%, moisture ≤ 5 ppm). Weigh ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate respectively and mix them evenly in a mass fraction ratio of 1:1:1 to obtain mixture 8. By mass percentage, mixture 8 is 99.375%. Add 0.625% of fluorobenzene organic additive to mixture 8 to obtain a 0.625% mass - fraction fluorobenzene standard solution. Prepare a series of standard solutions with fluorobenzene contents of 1.25%, 2.5%, and 5% according to the above steps. Detect the characteristic peaks of the fluorobenzene content in the series of fluorobenzene standard solutions by liquid chromatography, and perform linear fitting. The linear fitting results of the fluorobenzene standard solution are shown in Table 2 below.

[0103] Table 2

[0104]

[0105] As can be seen from Table 2, the correlation coefficient R of the linear fitting of the peak area of the characteristic peak of the medium-fluorobenzene standard solution 2 can reach 0.9998.

[0106] An ion chromatograph was used to detect the supernatant liquids 1 to 13, the lower layer liquid of Comparative Example 1, and the mixed liquid in Comparative Example 2 respectively, and the elution times and elution areas of fluoride ions (F - ) and hexafluorophosphate ions (PF6 - ) were recorded respectively. The test results are listed in Table 3. A liquid chromatograph (Shimadzu liquid chromatograph LC-20A, chromatographic column C18, scanning ultraviolet wavelength 254 nm, flow rate 1 ml / min, mobile phase A is a mixture of methanol and ultrapure water in a ratio of 1:9, mobile phase B is pure acetonitrile, and the pre-mixing ratio of phases A and B during the test is 1:1) was used to test the fluorobenzene content in the supernatant liquids 1 to 13, the lower layer liquid of Comparative Example 1, and the mixed liquid in Comparative Example 2 respectively, and the test results are listed in Table 4. Among them, the liquid chromatogram of fluorobenzene in the supernatant liquid 1 is as Figure 2 shown.

[0107] Table 3

[0108]

[0109] Table 4

[0110]

[0111]

[0112] As can be seen from Table 3, Tests Examples 1 to 13 show that the method of this application can completely precipitate lithium hexafluorophosphate in the electrolyte, and the residual fluoride ions are all within 1 ppm. For Test Proportions 1 and 2, extracting lithium hexafluorophosphate in the electrolyte with saturated sodium carbonate and using polar dichloromethane result in a residual fluoride ion content > 1 ppm, and the effect is poor.

[0113] As can be seen from Table 4, when qualitative and quantitative analysis (taking fluorobenzene as an example) of the organic additives in the electrolyte after precipitating lithium hexafluorophosphate is carried out by liquid chromatography, when the volume ratio of the antisolvent to the lithium-ion battery electrolyte ≥ 1:1, the sample recovery rate is between 90.05 and 100.00%, and the relative error of the quantitative result < 10%. This shows that after precipitating lithium hexafluorophosphate with n-decane or n-hexane as the antisolvent, the structure of the organic additives in the original electrolyte will not be damaged (which can be further proven from the appendix Figure 2 ), and thus it will not affect the quantitative test of the organic additives by liquid chromatography.

[0114] An ion chromatograph was used to test the fluoride ions and hexafluorophosphate ions in Sample 1, the supernatant liquid 1, the lower layer liquid of Comparative Example 1, and the 1 ppm fluoride ion standard sample respectively. The test results are asFigure 1 as shown

[0115] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0116] Since lithium hexafluorophosphate is a polar substance, while most of the other components in the lithium-ion battery electrolyte are non-polar substances, in this application, an anti-solvent method is used to separate the lithium-ion battery electrolyte with a non-polar solvent, so that lithium hexafluorophosphate precipitates out as a precipitate, and the components other than lithium hexafluorophosphate continue to remain in the supernatant, and the fluoride ion concentration in the supernatant is ≤1 ppm, thus greatly reducing the probability that lithium hexafluorophosphate will continuously react with water in the chromatographic mobile phase to produce HF, and further reducing the production amount of HF. Furthermore, it avoids the corrosion of the chromatographic column by fluoride ions and the damage to the structure of organic additives. Therefore, the supernatant can be directly taken for qualitative and quantitative analysis of organic additives. And the above method is simple and effective, and does not affect the peak appearance effect of the separated organic additives in liquid chromatography, so that the measurement results are relatively accurate.

[0117] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An analytical method for organic additives in a lithium-ion battery electrolyte, characterized in that, The analysis method includes: Step S1: Separating the lithium-ion battery electrolyte by anti-solvent method using a solvent to obtain a supernatant solution dissolving an organic additive and a precipitate containing lithium hexafluorophosphate; Step S2: Performing HPLC analysis on the supernatant solution, wherein the lithium-ion battery electrolyte contains lithium hexafluorophosphate, the fluoride ion concentration in the supernatant solution ≤ 1 ppm, and the solvent is a non-polar solvent; The non-polar solvent is selected from any one or more of C6-C 10 normal alkane solvents; The organic additive is fluorobenzene; The process of the anti-solvent method separation includes: Oscillating and mixing the solvent with the lithium-ion battery electrolyte and then standing still to obtain a post-standing system including the supernatant solution and the precipitate.

2. The analysis method according to claim 1, wherein The non-polar solvent is n-decane.

3. The analysis method according to claim 1 or 2, characterized in that The volume ratio of the solvent to the lithium-ion battery electrolyte ≥ 1:

1.

4. The analysis method according to claim 3, characterized in that The volume ratio of the solvent to the lithium-ion battery electrolyte is 1:1 to 9:

1.

5. The analysis method according to claim 4, characterized in that, The volume ratio of the solvent to the lithium-ion battery electrolyte is 4:1 to 9:

1.

6. The analysis method according to claim 5, characterized in that, The volume ratio of the solvent to the lithium-ion battery electrolyte is 9:

1.

7. The analysis method according to claim 1 or 2, characterized in that The mass content of lithium hexafluorophosphate in the lithium-ion battery electrolyte is 5 - 20%.

8. The analysis method according to claim 1, wherein The mass content of the organic additive in the lithium-ion battery electrolyte is 0.1 - 8%.

9. The analysis method according to claim 1 or 2, characterized in that The standing time is 3 - 5 h.

10. The analysis method according to claim 1, characterized in that Use C 18 chromatographic column for the HPLC analysis described above.

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