Determination of 1, 2, 3, 4, 5, 6-hexa (2-cyanoethoxy) hexane in lithium ion battery electrolyte

Abstract

The invention discloses a method for determining 1, 2, 3, 4, 5, 6-hexa (2-cyano ethyoxyl) hexane in lithium ion battery electrolyte, which comprises the following steps: preparing a standard solution: taking a 1, 2, 3, 4, 5, 6-hexa (2-cyano ethyoxyl) hexane standard substance, diluting with propylene carbonate to obtain a standard solution mother solution, and diluting with a mobile phase to obtain the standard solution; a mobile phase is an acetonitrile water solution with the volume percentage content of 57.5%-59.0%; preparing a to-be-detected sample solution: taking a to-be-detected lithium ion battery electrolyte sample, and diluting the to-be-detected lithium ion battery electrolyte sample with the mobile phase solution to obtain the to-be-detected sample solution; determining: using a liquid chromatograph with a differential refraction detector, wherein two chromatographic columns are connected in series; respectively performing chromatographic analysis on the standard solution and the sample solution to be detected, and recording peak areas; and calculating by adopting an external standard method and single standard correction to obtain the mass percentage content of the 1, 2, 3, 4, 5, 6-hexa (2-cyano ethyoxyl) hexane. The method has the advantages of reliability, stability, simple and easy analysis process and high accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of determination of additives in lithium ion battery electrolyte, and in particular to a method for determining 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane. Background Art

[0002] The structural formula of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane is:

[0003]

[0004] 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane is a new type of additive. When added to the electrolyte in an appropriate amount, it can not only stabilize the transition metal on the surface of the positive electrode active material of the lithium-ion battery and reduce the oxidizability of the high-valent transition metal, but also oxidize into a film, thereby forming a double protection for the electrode, inhibiting the decomposition of the electrolyte, inhibiting the high-temperature gas production, and improving the high-temperature storage performance, cycle performance, floating charge performance and overcharge performance of the lithium-ion battery, so that the lithium-ion battery can maintain good high-temperature storage performance, cycle performance, floating charge performance and overcharge performance while having a higher energy density.

[0005] 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane will also work together with other additives in the electrolyte to further improve the various properties of lithium-ion batteries, such as: it can alleviate the impact of the solubility and viscosity of the electrolyte; reduce costs to achieve a balance between performance and cost; and assist in enhancing the stability of SEI film formation. 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane provides lithium-ion batteries with excellent high-temperature properties, high-temperature stability, low-temperature properties, and life characteristics at room temperature, so that lithium-ion batteries achieve a lower storage expansion rate and a better capacity retention rate, which maintains the stability of battery performance to a certain extent, improves the battery's cycle performance, extends the battery's life, and ensures the safety of the battery.

[0006] 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane has a boiling point that is too high, exceeding 300°C, so it cannot produce peaks on GC. It cannot hydrolyze in aqueous solution to produce ions, so it does not produce peaks on ICS. As the electrolyte formula to which 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane is added becomes more and more complex, the results will be inaccurate during detection due to the influence of some other components in the formula, which in turn affects the quality of the electrolyte, and the electrolyte is equivalent to the blood of lithium-ion batteries. Therefore, in order to effectively ensure the quality and performance of lithium batteries, it is urgently needed to develop a simple and easy determination method that can accurately analyze and quantify 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in any complex electrolyte formula. Summary of the invention

[0007] The purpose of the present invention is to provide a method for determining 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in a lithium ion battery electrolyte, wherein the method has good stability, high accuracy and strong applicability.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: the determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in lithium ion battery electrolyte includes the following steps: preparing a standard solution: taking a 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane standard, diluting and dissolving it with propylene carbonate to obtain a standard solution mother liquor, and then diluting the standard solution mother liquor with a mobile phase to obtain a standard solution; the mobile phase is an acetonitrile aqueous solution, wherein the volume percentage of acetonitrile is 57.5% to 59.0%; preparing a sample solution to be tested: taking a lithium ion battery electrolyte sample to be tested, and diluting it with a mobile phase solution according to the theoretical concentration value of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane therein to obtain a sample solution to be tested; the 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution mother liquor is 1,2,3,4,5 ,6-hexa(2-cyanoethoxy)hexane concentration = (1±5%) × theoretical concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium ion battery electrolyte sample to be tested; the theoretical concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the sample solution to be tested = (1±5%) × concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution; Determination: using a liquid chromatograph with a differential refractive index detector, two chromatographic columns are connected in series; chromatographic analysis is performed on the standard solution and the sample solution to be tested, respectively, and the peak area is recorded; using the external standard method and single standard correction, the mass percentage of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the electrolyte sample to be tested is obtained according to the calculation formula; the calculation formula is as follows:

[0009]

[0010] Wherein, Y1% is the mass percentage of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium ion battery electrolyte sample to be tested; Y2 is the peak area of ​​1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the sample solution to be tested, in μS·min; B1 is the content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution, in ppm; B2 is the peak area of ​​1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution, in μS·min; A is the dilution multiple of the sample solution to be tested; 10000 is the unit conversion constant.

[0011] Furthermore, in the determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the aforementioned lithium-ion battery electrolyte, a Waters liquid chromatograph with a differential refractive index detector was used, and the column model of each chromatographic column was Inertsil ODS-SP 5μm, 4.6*250mm.

[0012] Further, the determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the aforementioned lithium-ion battery electrolyte, wherein the steps of instrument preparation include: connecting the prepared mobile phase to the instrument, turning on the instrument host, detector, column oven power and computer; opening the Breeze software, selecting the GPC system and the corresponding project folder, and clicking the flow icon in the running sample column to set the pump flow rate to 0.5 mL / min; clicking Temp °C on the detector panel, setting the detector and column oven temperatures to 40 °C, then clicking Home to return to the main interface, and then clicking Shift and 1 in sequence to enter the Purge flow path to flush the sample pool and reference pool for 2 to 3 hours; clicking the Balance System / Monitor Baseline icon in the software interface to call the instrument method and clicking Balance / Monitor to monitor the baseline; after the baseline is stable, clicking Shift and 1 on the detector panel to cancel Purge and return to the normal sampling flow path, and sample analysis can be performed after balancing for 3 to 5 minutes.

[0013] Furthermore, in the determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the aforementioned lithium-ion battery electrolyte, during the preparation of the mobile phase, acetonitrile is filtered using a 0.22 μm organic phase filter membrane.

[0014] Furthermore, in the aforementioned determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium ion battery electrolyte, the volume percentage of acetonitrile in the mobile phase is 58%.

[0015] Furthermore, in the determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the aforementioned lithium-ion battery electrolyte, acetonitrile is of HPLC grade.

[0016] The advantages of the present invention are as follows: the method for determining 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in a lithium ion battery electrolyte of the present invention comprises: (1) using an acetonitrile-water mobile phase with an acetonitrile volume percentage of 57.5% to 59.0% and connecting two chromatographic columns in series, so that the peaks of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane and any other components in the lithium ion battery electrolyte product to be determined can be completely separated, and the influence of other components in the product to be determined on the determination of the content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane can be effectively eliminated, thereby greatly improving the accuracy of the determination; and (2) using propylene carbonate solvent to prepare a standard solution mother liquor, which greatly simplifies the preparation process of the standard solution and is more conducive to storage and use, thereby greatly improving the work efficiency. Regardless of the content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the electrolyte product to be tested, the measured data are accurate and stable, which greatly facilitates the quantitative analysis of various components in the lithium battery electrolyte, thereby ensuring the quality of the lithium-ion battery electrolyte and the performance of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a chromatogram showing the separation of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane from 2-fluoroethyl acetate and ethyl acetate peaks when two chromatographic columns are connected in series and an acetonitrile-water mobile phase with an acetonitrile volume percentage of 57.5% to 59.0% is used.

[0018] Figure 2 This is a chromatogram showing the interaction between the peaks of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane and 2-fluoroethyl acetate when two chromatographic columns are connected in series and an acetonitrile-water mobile phase with a volume ratio of 1:1 is used.

[0019] Figure 3 This is a chromatogram showing overlapping peaks of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane and ethyl acetate when two chromatographic columns are connected in series and an acetonitrile-water mobile phase with a volume ratio of 5.5:4.5 is used.

[0020] Figure 4 The chromatogram is a graph showing the mutual influence of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane and ethyl acetate peaks when a mobile phase of acetonitrile with a volume percentage of 57.5% to 59.0% of acetonitrile is used under the condition of a single chromatographic column.

[0021] Figure 5 The standard curve of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane concentration and peak area is shown in FIG. 1 when two chromatographic columns are connected in series and an acetonitrile-water mobile phase with an acetonitrile volume percentage of 58% is used. DETAILED DESCRIPTION

[0022] The method for determining 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in a lithium ion battery electrolyte comprises the following steps.

[0023] Preparation of mobile phase: The mobile phase is an acetonitrile aqueous solution, wherein the volume percentage of acetonitrile is 58.0%. The preparation steps include: first, placing a clean brown empty reagent bottle with a capacity of 4L on a 6kg electronic scale and peeling it, then filtering the acetonitrile with a 0.22μm organic phase filter membrane, then adding the filtered acetonitrile (1811.9±0.5)g into the reagent bottle, peeling the electronic scale, and finally slowly injecting distilled water (1680±0.5)g into the reagent bottle, mixing well and then ultrasonically degassing to prepare the required mobile phase.

[0024] Prepare the mother liquor of standard solution No. 1: Take the standard solid 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane, the purity value is 99.0%. The theoretical content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium-ion battery electrolyte component index in the product application is 1.0%. Use a 1 / 10,000 balance to weigh 1.0167g of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane standard, dilute it to 100.9764g with propylene carbonate, seal and shake until completely dissolved, and obtain the mother liquor of standard solution No. 1 with a concentration of 9968.0ppm. The standard solid 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane is purchased.

[0025] Prepare 1# standard solution: weigh a certain amount of 1# standard solution mother liquor respectively, and dilute it with mobile phase solution to obtain three 1# standard solutions with concentrations of 508.8ppm, 946.9ppm, and 2013.8ppm.

[0026] Instrument preparation: Waters liquid chromatograph, differential refractometer, chromatographic column model Inertsil ODS-SP5μm, 4.6*250mm, two columns connected in series; the steps of instrument preparation include: connecting the prepared mobile phase to the instrument, turning on the instrument host, detector, column oven power and computer; opening Breeze software, selecting the GPC system and the corresponding project folder, and clicking the flow icon in the running sample column to set the pump flow rate to 0.5mL / min; clicking Temp℃ on the detector panel, setting the detector and column oven temperatures to 40℃, then clicking Home to return to the main interface, and then clicking Shift and 1 in sequence to enter the Purge flow path to flush the sample pool and reference pool for 2~3h; clicking the Balance System / Monitor Baseline icon in the software interface to call the instrument method and clicking Balance / Monitor to monitor the baseline; after the baseline is stable, clicking Shift and 1 on the detector panel to cancel Purge and return to the normal sampling flow path, and after balancing for 3~5min, perform chromatographic analysis on the standard solution and the sample solution to be tested respectively.

[0027] Three concentrations of 1# standard solution were taken respectively, and after being fully mixed, they were analyzed and tested, and their peak areas were recorded, as shown in Table 1. The standard curve of the standard solution concentration and peak area of ​​1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane under the mobile phase condition was obtained, as shown in Table 1. Figure 5 shown.

[0028] Table 1:

[0029] Standard sample name Dilution multiple Concentration (ppm) Peak area (μV*sec) blank / 0 0 Standard 1 19.6 508.8 99206 Standard 2 10.5 946.9 200560 Standard three 4.9 2013.8 405872

[0030] From Table 1 and Figure 5 It shows that under the conditions of two chromatographic columns connected in series and under the conditions of the mobile phase (acetonitrile aqueous solution, in which the volume percentage of acetonitrile is 57.5% to 59.0%), the concentration of the standard solution prepared by the standard substance 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane is proportional to its peak area and has good linearity.

[0031] Considering that the multiples of dilution of the mother solution required to prepare standard solutions of various concentrations vary greatly, the density of each injection may be inconsistent and some errors may occur. In order to facilitate operation, save detection time and improve work efficiency, under the premise of good linearity between 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane concentration and peak area, a single standard calibration method is used to calibrate and calculate the content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the electrolyte sample.

[0032] The following is an example of a lithium ion battery electrolyte with a theoretical content of 1.00% of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane. The lithium ion battery electrolyte with a content of 1.00% of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane is numbered 5#.

[0033] Prepare 5# sample solution to be tested: theoretical content 1.00%, take 2.012g of 5# lithium ion battery electrolyte sample, add mobile phase to dilute to 20.736g and shake well to obtain 5# sample solution to be tested.

[0034] Take the 5# sample solution to be tested, analyze and detect it, record its peak area, select the 1# standard solution with a concentration of 946.9ppm as the standard sample, use the external standard method and single standard calibration to calculate the mass percentage of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the electrolyte sample to be tested; the calculation formula is as follows:

[0035]

[0036] Among them, Y1% is the mass percentage of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium ion battery electrolyte sample to be tested; Y2 is the peak area of ​​1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the sample solution to be tested, in μS·min; B1 is the content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution, in ppm; B2 is the peak area of ​​1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution, in μS·min; A is the dilution multiple of the sample solution to be tested; 10000 is the unit conversion constant. The specific calculation results are shown in Table 2 below.

[0037] Table 2:

[0038]

[0039] The following is an example of a lithium ion battery electrolyte with a theoretical content of 0.50% of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane. The number of the lithium ion battery electrolyte with a theoretical content of 0.50% of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane is 4#.

[0040] Preparation of 2# standard solution mother liquor: Take the standard 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane solid, the purity value is 99.0%. According to the theoretical content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the product application of lithium ion battery electrolyte component index of 0.50%, weigh 0.5083g of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane standard with a 1 / 10,000 balance, dilute to 100.4678g with propylene carbonate, seal and shake until completely dissolved, and obtain 2# standard solution mother liquor with a concentration of 5008.7ppm.

[0041] Preparation of 2# standard solution: Take 2.066 g of 2# standard solution mother liquor and dilute it to 20.589 g with mobile phase solution to obtain 2# standard solution with a concentration of 502.6 ppm.

[0042] Preparation of 4# test sample solution: Based on the theoretical content of 0.50%, take 2.025 g of 4# lithium ion battery electrolyte sample, add mobile phase to dilute to 20.078 g and shake well to obtain 4# test sample solution.

[0043] Take the 4# sample solution to be tested, analyze and detect it, record its peak area, use the 2# standard solution with a concentration of 502.6ppm as the standard sample, use the external standard method and single standard calibration to calculate the mass percentage of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the electrolyte sample to be tested; the calculation formula is the same as above. The calculation results are shown in Table 3.

[0044] Table 3:

[0045]

[0046] The following parallel analysis was performed on the 4# sample solution and the 5# sample solution, and the mass percentage content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane obtained by detection is shown in Table 4.

[0047] Table 4:

[0048]

[0049] The data in Table 4 show that the relative standard deviation (RSD) of the parallel analysis results of the mass percentage content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane meets the requirements and has good reproducibility.

[0050] A spike recovery experiment was conducted on this method. A certain amount of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane was added to the 4# and 5# electrolyte samples, respectively. The mass percentage content of the spiked electrolyte was analyzed according to the above-mentioned 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane electrolyte detection method. The detection data are shown in Table 5.

[0051] Table 5:

[0052]

[0053]

[0054] The data analysis of Table 5 shows that the recovery rates of the detection method of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the electrolyte product of the present invention are between 95% and 105%, and the analysis accuracy is good.

[0055] The determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium ion battery electrolyte of the present invention is further described in detail below.

[0056] First examine the mobile phase.

[0057] The most commonly used C18 reverse phase column in liquid chromatography usually uses an acetonitrile-water system as the mobile phase. Under the commonly used acetonitrile-water mobile phase concentration conditions (usually the volume ratio of acetonitrile to water is 1:1), the peaks of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane will overlap with those of common solvents 2-fluoroethyl acetate and ethyl acetate and cannot be separated or will affect each other, making it impossible to accurately quantify the content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the corresponding electrolyte product.

[0058] In the present invention, under the premise of two chromatographic columns connected in series, the mobile phase is an acetonitrile aqueous solution, and the volume percentage of acetonitrile is 57.5% to 59.0%. Under the mobile phase conditions of this concentration, the peak of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane is completely separated from the peaks of other components in the electrolyte product. Figure 1 As shown, the mobile phase is an acetonitrile aqueous solution with a volume percentage of 57.5% to 59.0%. When the mobile phase is used for analysis, the peaks of 2-fluoroethyl acetate or ethyl acetate and 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane are completely separated.

[0059] See also Figure 2 , Figure 3As shown in the figure, the same premise is that two chromatographic columns are connected in series, and when the acetonitrile aqueous solution of the mobile phase is used at other concentrations, the peak conditions of 2-fluoroethyl acetate or ethyl acetate and 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane are as follows: Figure 2 The volume ratio of acetonitrile and water in the acetonitrile aqueous solution is 1:1. Figure 3 The volume ratio of acetonitrile to water in the acetonitrile aqueous solution is 5.5:4.5. Figure 2 , Figure 3 It can be seen that under other concentrations of acetonitrile aqueous solution conditions, the peaks of 2-fluoroethyl acetate or ethyl acetate and 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane will overlap and affect each other.

[0060] In addition, if Figure 4 As shown, under the condition of a single chromatographic column, the mobile phase is an acetonitrile aqueous solution with a volume percentage of 57.5% to 59.0%, and the peaks of ethyl acetate and 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane will affect each other.

[0061] Secondly, the standard solution was examined.

[0062] Liquid chromatographs use quantitative loop injection. Since the injection volume is fixed when analyzing the standard solution and the electrolyte sample to be tested, if the density difference between the two is large, the concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane will be inconsistent, which will cause a certain error and affect the accuracy of the detection. Therefore, it is necessary to prepare a small sample of electrolyte with the same formula as the electrolyte sample to be tested as the mother solution of the standard solution, so that there is no difference in the density of the electrolyte sample to be tested and the mother solution of the standard solution.

[0063] At present, there are more and more different electrolyte products containing 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane, and there are more than ten components in the product formula. It is very time-consuming and cumbersome to prepare standard solution mother liquors of different formulas. It is found that the density of most electrolyte products containing 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane is about 1.18g / ml, as shown in Table 6, which is closest to the density of the commonly used solvent propylene carbonate of about 1.20g / ml.

[0064] Table 6:

[0065]

[0066] Therefore, it is considered to use propylene carbonate to dissolve and dilute pure 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane as the mother liquor of the standard solution, and make the concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane therein equivalent to the theoretical concentration value of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the electrolyte product, and then dilute this mother liquor with the mobile phase by the same multiple as the sample solution to be tested for analysis and calibration.

[0067] In addition, considering the simplicity and feasibility of preparing the standard solution, an attempt was made to directly dissolve the 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane solid in the mobile phase solution to obtain a standard solution mother liquor with the same concentration as the theoretical content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the electrolyte product, and then dilute it to obtain the required standard solution for analysis and calibration.

[0068] The following is an example of three common lithium-ion battery electrolyte products with known 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane contents. The mass percentages of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane are 0.51%, 1.03% and 0.98% respectively, and they are numbered 1#, 2# and 3# respectively. The mother solutions of the standard solutions under different systems are diluted by the same multiple with the mobile phase, and the obtained standard solutions are analyzed and calibrated to compare the 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane content data in the above electrolyte samples to be tested, as shown in Table 7.

[0069] Table 7:

[0070]

[0071] The data in Table 7 show that when detecting the content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the same sample solution, the calibration results of the standard solution in the propylene carbonate mother solution system are very close to the calibration results of the standard solution in the mother solution system of the same electrolyte formula, while the calibration results of the standard solution in the mobile phase mother solution system are quite different from the former two. It is thus obtained that the standard solution in the propylene carbonate mother solution system can completely replace the standard solution in the mother solution system of the same electrolyte formula, and because propylene carbonate is relatively stable and not easy to volatilize and deteriorate, it is more conducive to the preservation of the mother solution of the standard solution, which makes the use of this system greatly save the time of preparing the standard solution and makes the detection simple and efficient.

[0072] As can be seen from the above, the method for determining 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium ion battery electrolyte of the present invention has the following advantages: First, due to the use of an acetonitrile water mobile phase with a volume concentration of 57.5% to 59.0%, and two chromatographic columns connected in series, the peaks of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane and any other components in the lithium ion battery electrolyte product to be measured are completely separated, which effectively eliminates the influence of other components in the lithium ion battery electrolyte to be measured on the determination of the content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane. Second, the use of a standard solution of a propylene carbonate mother liquor system greatly simplifies the preparation process of the standard solution and improves work efficiency. Regardless of the concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the product to be tested, the measured data are accurate, stable, and applicable, providing great assistance to the quantitative analysis of various components in lithium-ion battery electrolytes, thereby providing reliable guarantees for the quality of lithium-ion battery electrolytes and the performance of lithium-ion batteries.

Claims

1. The determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in lithium ion battery electrolyte comprises the following steps: preparing a standard solution: taking a 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane standard, diluting and dissolving it with propylene carbonate to obtain a standard solution mother liquor, and then diluting the standard solution mother liquor with a mobile phase to obtain a standard solution; the mobile phase is an acetonitrile aqueous solution, wherein the volume percentage of acetonitrile is 57.5% to 59.0%; preparing a sample solution to be tested: taking a lithium ion battery electrolyte sample to be tested, and diluting it with a mobile phase solution according to the theoretical concentration value of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane therein to obtain a sample solution to be tested; the 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution mother liquor is 0.04477%; the 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution mother liquor is 0.02477%; the 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution mother liquor is 0.01 ... The concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane = (1±5%) × the theoretical concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium ion battery electrolyte sample to be tested; the theoretical concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the sample solution to be tested = (1±5%) × the concentration of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution; Determination: using a liquid chromatograph with a differential refractive index detector, two chromatographic columns are connected in series; performing chromatographic analysis on the standard solution and the sample solution to be tested respectively and recording the peak area; using the external standard method and single standard correction, according to the calculation formula, the mass percentage of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the electrolyte sample to be tested is obtained; the calculation formula is as follows: , in, Y1% is the mass percentage of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium-ion battery electrolyte sample to be tested; Y2 is the peak area of ​​1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the sample solution to be tested, in µS·min; B1 is the content of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution, in ppm; B2 is the peak area of ​​1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the standard solution, in µS·min; A is the dilution multiple of the sample solution to be tested; 10000 is the unit conversion constant.

2. The method of claim 1, wherein the determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in a lithium ion battery electrolyte is characterized in that: A Waters liquid chromatograph with a differential refractometer was used, and the model of each chromatographic column was Inertsil ODS-SP 5 μm, 4.6*250 mm.

3. The method of claim 2, wherein the determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in a lithium ion battery electrolyte is characterized in that: The steps of instrument preparation include: connecting the prepared mobile phase to the instrument, turning on the instrument host, detector, column oven power and computer; opening the Breeze software, selecting the GPC system and the corresponding project folder, and clicking the flow icon in the running sample column to set the pump flow rate to 0.5mL / min; clicking Temp ºC on the detector panel, setting the detector and column oven temperatures to 40 ℃, then clicking Home to return to the main interface, and then clicking Shift and 1 in sequence to enter the Purge flow path to flush the sample pool and reference pool for 2 to 3 hours; clicking the Balance System / Monitor Baseline icon in the software interface to call the instrument method and clicking Balance / Monitor to monitor the baseline; after the baseline is stable, clicking Shift and 1 on the detector panel to cancel Purge and return to the normal sampling flow path, and sample analysis can be performed after balancing for 3 to 5 minutes.

4. The method of claim 1, wherein the amount of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in a lithium ion battery electrolyte is: During the preparation of the mobile phase, acetonitrile was filtered using a 0.22 μm organic phase filter membrane.

5. The determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in the lithium ion battery electrolyte according to claim 1 or 4, characterized in that: The volume percentage of acetonitrile in the mobile phase was 58%.

6. The method of claim 5, wherein the determination of 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane in a lithium ion battery electrolyte is characterized in that: Acetonitrile was of HPLC grade.

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