Qualitative and quantitative detection method for difluoroethylene carbonate in electrolyte

Abstract

The invention relates to a qualitative and quantitative detection method for difluoroethylene carbonate in electrolyte, which comprises the following steps: preparing a plurality of DFEC standard solutions, selecting a chromatographic column, setting test parameters of a gas chromatograph-mass spectrometer, and detecting the prepared DFEC standard solutions. Determining a standard curve, a detection limit and a quantitation limit according to the concentration of the standard solution and the detected peak area, and forming a standard curve equation according to the standard curve; detecting the pretreated to-be-detected electrolyte to obtain the peak area of the to-be-detected electrolyte, and searching according to the standard curve to obtain the concentration of the DFEC in the to-be-detected electrolyte, or calculating according to a standard curve equation to obtain the concentration of the DFEC; according to the method disclosed by the invention, high-sensitivity and high-selectivity detection on trace DFEC in the electrolyte is realized through the synergistic effect of the gas chromatography and the mass spectrum and setting of specific test parameters.

Description

Technical Field

[0001] This invention relates to the field of battery electrolyte detection technology, and in particular to a method for qualitative and quantitative detection of difluoroethylene carbonate in electrolyte. Background Technology

[0002] Electrolyte is an important component of lithium-ion batteries, generally composed of lithium salts, solvents, and additives. Among these, the solvent is the main component of the electrolyte, directly affecting the battery's performance, safety, and lifespan.

[0003] In recent years, with the rapid development of lithium-ion battery technology, fluorinated solvents, due to their unique chemical properties, have gradually become a research hotspot in the field of electrolytes and have been widely used in lithium-ion batteries. Among them, fluorinated cyclic carbonates have higher oxidation stability, improving the low-temperature performance of electrolytes and the wettability between electrolytes and electrodes. Difluoroethylene carbonate (also known as 4,5-difluoro-1,3-dioxane-2-one, abbreviated as DFEC), with the molecular formula C3H2F2O3, is a novel electrolyte additive, mainly used as a film-forming additive in lithium-ion batteries to improve battery performance. Its excellent performance stems from the introduction of two fluorine atoms, which enhances molecular stability, conductivity, and thermal stability, forming a more uniform solid electrolyte interphase (SEI) film and extending battery life.

[0004] In the prior art, gas chromatography (GC) is widely used to detect the impurity content in electrolytes. For example, Chinese invention patent CN115323412A (published on November 11, 2022) discloses a method for preparing difluoroethylene carbonate, using gas chromatography to determine the purity of the compound. Gas chromatography monitors the content of products and impurities in the reaction mixture to ensure the final product meets the required high purity standard. However, this patent only briefly mentions the use of gas chromatography for detection, and because it targets the purity of DFEC (difluoroethylene carbonate), with a product purity exceeding 99.95%, the DFEC content in the detected components is very high, making it unsuitable for detecting trace amounts of DFEC.

[0005] Currently, DFEC is used as an additive in electrolytes. Even in trace amounts (below 0.2 wt%), it can improve the electrolyte's cycle characteristics, high-temperature storage and high-temperature use characteristics, and maintain a high capacity retention rate. Therefore, DFEC is only added in trace amounts to electrolytes. Current detection methods for DFEC in electrolytes rely on direct injection via gas chromatography, which cannot quantitatively determine trace and ultra-trace levels. Furthermore, gas chromatography detection of difluoroethylene carbonate peak area has low reproducibility and is easily masked by electrolyte solvent peaks, resulting in high detection difficulty and low quantitative accuracy.

[0006] Therefore, there is an urgent need to develop and design detection methods for trace and ultra-trace levels of DFEC in electrolytes, so as to enable the research and optimization of electrolyte formulations and the performance testing of electrolyte products to match cell design. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for the qualitative and quantitative detection of difluoroethylene carbonate in electrolytes.

[0008] This invention achieves highly sensitive and selective detection of low concentrations of DFEC by combining gas chromatography (GC) and mass spectrometry (MS) with specific test parameters.

[0009] This invention first utilizes the partitioning effect of the stationary phase and mobile phase in a gas chromatography column to completely separate DFEC from other components, especially interfering components, in complex electrolyte samples. Then, specific ion fragments are generated by electron ionization in a mass spectrometer, and the specific ion signals of DFEC are amplified and collected. This allows for the accurate detection of ultra-low concentrations of DFEC in the electrolyte with high precision.

[0010] To achieve the above objectives, the present invention provides a method for the qualitative and quantitative detection of difluoroethylene carbonate in electrolytes, the detection method comprising: Step S1 involves preparing multiple difluoroethylene carbonate standard solutions with gradient concentrations, specifically by dissolving difluoroethylene carbonate in organic solvents at different ratios to prepare multiple difluoroethylene carbonate standard solutions.

[0011] Step S2: Select a chromatographic column; the stationary phase of the chromatographic column is 5% phenyl and 95% dimethyl polysiloxane, the column length is 25m to 60m, the inner diameter is 0.25mm to 0.50mm, and the inner coating thickness is 0.25μm to 1.0µm.

[0012] Step S3: Set the test parameters for the gas chromatography-mass spectrometry (GC-MS) instrument; wherein the test parameters include: gas chromatography parameters, column temperature program and mass spectrometry parameters.

[0013] The gas chromatography parameters include: carrier gas, column flow rate, split ratio, injection port temperature, injection volume, and purge flow rate; the carrier gas is helium, the column flow rate is 1.20 mL / min to 1.40 mL / min, the split ratio is 10:1 to 20:1, the injection port temperature is 180℃ to 240℃, the injection volume is 1.5 uL to 2.0 uL, and the purge flow rate is 3 mL / min to 5 mL / min.

[0014] The column temperature program includes: maintaining an initial temperature of 35℃~40℃ for 1min~7min, increasing the temperature to 200℃~220℃ at a rate of 8℃~10℃ / min, and maintaining the temperature for 3min~4min.

[0015] The mass spectrometry parameters include: ion source, ion source temperature, transmission line interface temperature, scan mode, and solvent delay time; the ion source is an electron ionization source, the ion source temperature is 230℃~250℃, and the transmission line interface temperature is 250℃~270℃; the scan mode is selected ion monitoring mode, and the ions monitored include: quantitative ions with a mass-to-charge ratio of m / z=124, and reference ions with mass-to-charge ratios of m / z=61 and m / z=80; the solvent delay time is 2.0 min~3.0 min.

[0016] Step S4: The multiple difluoroethylene carbonate standard solutions with gradient concentrations prepared in step S1 are detected using the test parameters of step S3. The instrument response value, i.e., peak area, corresponding to each difluoroethylene carbonate standard solution is recorded. A standard curve is determined based on the concentration and peak area of ​​difluoroethylene carbonate in each difluoroethylene carbonate standard solution, as well as the detection limit and quantitation limit under the test conditions. The standard curve equation is then formed based on the standard curve.

[0017] Step S5: Select the electrolyte to be tested, pretreat the electrolyte, and test the pretreated electrolyte using the same method as the difluoroethylene carbonate standard solution in step S4 to obtain the peak area of ​​the electrolyte. Then, find the concentration of difluoroethylene carbonate in the electrolyte according to the standard curve obtained in step S4, or calculate the concentration of difluoroethylene carbonate in the electrolyte according to the standard curve equation.

[0018] Preferably, in step S1, the concentrations of the plurality of difluoroethylene carbonate standard solutions with gradient concentrations are selected between 0.80 mg / L and 160.0 mg / L.

[0019] The organic solvent is chromatographically pure dichloromethane.

[0020] More preferably, the concentrations of the plurality of difluoroethylene carbonate standard solutions with gradient concentrations include: 0.80 mg / L, 1.60 mg / L, 8.00 mg / L, 40.0 mg / L, 80.0 mg / L, 120.0 mg / L, and 160.0 mg / L.

[0021] Preferably, in step S2, the chromatographic column is a capillary chromatographic column SH-I-5Sil MS, with a column length of 30m, an inner diameter of 0.25mm, and an inner coating thickness of 1.0µm.

[0022] Preferably, in step S3, the injection port temperature is 200°C, the split ratio is 20:1, and the injection volume is 2.0 μL.

[0023] The column temperature program includes: maintaining a constant temperature of 40°C for 1 minute, increasing the temperature to 200°C at a rate of 10°C / min, and maintaining the temperature for 3 minutes.

[0024] The ionization energy of the gas chromatography-mass spectrometry system is 70 eV; the ion source temperature is 230℃; the transmission line interface temperature is 250℃; and the solvent delay time is 2.5 min.

[0025] Preferably, in step S4, the detection limit is below 0.5 mg / L and the quantitation limit is below 1 mg / L; wherein, the detection limit refers to the sample concentration when the peak generation signal is 3 times the baseline noise standard, that is, the corresponding sample concentration when the signal-to-noise ratio is 3:1; the quantitation limit refers to the sample concentration when the peak generation signal is 10 times the baseline noise standard, that is, the corresponding sample concentration when the signal-to-noise ratio is 10:1.

[0026] Preferably, the lower limit of detection is 0.25 mg / L and the lower limit of quantitation is 0.8 mg / L.

[0027] Preferably, in step S4, the coefficient of determination R of the standard curve 2 >0.999; the standard curve equation is Y = 199.2367X + 257.0345, where X is the peak area of ​​difluoroethylene carbonate and Y is the concentration of difluoroethylene carbonate in the electrolyte.

[0028] Preferably, in step S5, the pretreatment specifically includes: diluting the electrolyte to be tested with chromatographically pure dichloromethane, such that the mass concentration of difluoroethylene carbonate in the diluted electrolyte is less than or equal to 100 mg / L.

[0029] The step of finding the concentration of difluoroethylene carbonate in the electrolyte to be tested based on the standard curve obtained in step S4 is specifically as follows: by performing multiple tests on the electrolyte to be tested, multiple measured peak areas are obtained. Based on the multiple measured peak areas, corresponding values ​​are found on the standard curve to obtain multiple concentrations of difluoroethylene carbonate in the electrolyte to be tested. The average value is calculated to obtain the concentration of DFEC in the electrolyte to be tested.

[0030] Preferably, the mass concentration of difluoroethylene carbonate in the electrolyte to be tested is 0.001wt% to 0.2wt%.

[0031] The present invention provides a method for qualitative and quantitative detection of difluoroethylene carbonate in electrolyte, which has the following beneficial effects.

[0032] (1) The qualitative and quantitative detection method for difluoroethylene carbonate (DFEC) in electrolyte provided by this invention firstly involves preparing multiple DFEC standard solutions, then selecting a chromatographic column, setting specific test parameters for a gas chromatography-mass spectrometry (GC-MS) instrument, and then detecting the prepared DFEC standard solutions. A standard curve, detection limit, and quantitation limit are determined based on the concentrations of the multiple standard solutions and the detected peak areas. Based on the standard curve equation, the pretreated electrolyte is quantitatively detected using a GC-MS instrument with specific test parameters to obtain the peak area of ​​the electrolyte. The concentration of DFEC in the electrolyte is then determined by finding the standard curve or by calculating the concentration of DFEC based on the standard curve equation. This detection method is for the detection of trace and ultra-trace levels of DFEC.

[0033] Specifically, this invention utilizes a gas chromatography column. Through the distribution of the stationary and mobile phases, and by optimizing process parameters such as column flow rate (1.20 mL / min~1.40 mL / min), split ratio (10:1~20:1), injection port temperature (180℃~240℃), injection volume (1.5 uL~2.0 uL), initial column temperature program temperature (35℃~40℃), and ramp temperature, extremely low concentrations of DFEC in complex multi-component electrolyte systems can be completely separated from other components (such as coexisting solvents and matrix interference substances). This results in the extraction of symmetrical, well-separated ion chromatographic peaks free from impurity interference.

[0034] After separation by gas chromatography, DFEC molecules enter the mass spectrometer. By optimizing the ion source temperature and transfer line interface temperature, condensation of the sample during the transfer from GC to MS is prevented. The target analytes are identified by full-scan mass spectra, and the characteristic ions are selected based on retention time and fragment ions. Then, specific ion fragments (e.g., molecular ion m / z=124, characteristic fragment m / z=61) are generated by electron ionization (EI). The mass spectrometer is then used in selected ion monitoring (SIM) mode to amplify and acquire only the specific ion signals of DFEC, avoiding background noise interference and enabling the detection of trace and ultra-trace levels of DFEC.

[0035] Therefore, the detection results of this invention are highly accurate, providing an important reference for the optimization analysis and research and development of electrolytes.

[0036] (2) The qualitative and quantitative detection method of difluoroethylene carbonate in electrolyte provided by the present invention utilizes gas chromatography-mass spectrometry to detect DFEC in electrolyte and sets specific detection parameters. Its detection limit reaches the ppm level, with high sensitivity and good repeatability. Moreover, the method is simple to operate, has high testing efficiency and low cost.

[0037] (3) The qualitative and quantitative detection method of difluoroethylene carbonate in electrolyte provided by the present invention provides an effective detection method for trace additives in battery electrolytes, fills the gap in trace additive detection methods, enables the research and development and optimization of electrolyte formulations, and enables the performance testing of electrolyte products to match cell design, which has important practical significance. Attached Figure Description

[0038] Figure 1 The flowchart illustrates the preparation method of the detection method provided in this embodiment of the invention.

[0039] Figure 2 The chromatograms of DFEC standard solutions prepared using acetonitrile, methanol, n-hexane, and dichloromethane as organic solvents, respectively, are provided for embodiments of the present invention.

[0040] Figure 3 The chromatograms of DFEC were obtained by detecting the injection port temperatures at 180℃, 200℃, 220℃, and 240℃, respectively, according to the embodiments of the present invention.

[0041] Figure 4 The chromatograms of FEMC and DFEC separation at an initial temperature of 35°C are provided for embodiments of the present invention.

[0042] Figure 5 The chromatograms of FEMC and DFEC separation at an initial temperature of 40°C are provided for embodiments of the present invention.

[0043] Figure 6 The chromatograms of FEMC and DFEC separation at an initial temperature of 45°C are provided for embodiments of the present invention.

[0044] Figure 7 The chromatograms of FEMC and DFEC separation at an initial temperature of 50°C are provided for embodiments of the present invention.

[0045] Figure 8 The chromatograms of FEMC and DFEC separation at an initial temperature of 55°C are provided for embodiments of the present invention.

[0046] Figure 9 The DFEC standard curve diagram provided for embodiments of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0048] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0049] To facilitate a better understanding of the present invention, some technical terms will be explained below.

[0050] "Detection limit" refers to the sample concentration at which the peak generation signal is 3 times the baseline noise standard, that is, the corresponding concentration at a signal-to-noise ratio of 3:1.

[0051] "Limit of Quantification" refers to the sample concentration at which the peak height signal is 10 times the baseline noise standard, i.e., the corresponding concentration at a signal-to-noise ratio of 10:1.

[0052] This invention provides a qualitative and quantitative detection method for difluoroethylene carbonate (DFEC) in electrolytes, which can be used for the effective detection of trace and ultra-trace amounts in electrolytes. The content of DFEC additives in electrolyte systems is extremely low; typically, an addition of less than 0.2 wt% is sufficient to improve the electrolyte's cycling characteristics, high-temperature storage and use characteristics, and maintain a high capacity retention rate. However, the detection of trace substances in solution systems is exceptionally difficult, and conventional detection methods are insufficient. Gas chromatography also presents challenges, primarily because DFEC is difficult to distinguish from conventional solvent components in the electrolyte, and their chromatographic peaks easily overlap. Furthermore, the high proportion of solvent components in the electrolyte causes DFEC peaks to be masked by solvent peaks. In addition, the low DFEC content in the electrolyte leads to low peak area reproducibility. Therefore, the detection of difluoroethylene carbonate in electrolytes is challenging, and its qualitative and quantitative accuracy is low.

[0053] This invention employs a combination of chromatography and mass spectrometry. First, by improving the process conditions of gas chromatography, DFEC can be effectively separated from other interfering components in the electrolyte. Then, by combining the selective generation of specific ion fragments through electron ionization in mass spectrometry, the specific ion signals of DFEC are amplified and collected, thereby enabling the accurate detection of ultra-low concentrations of DFEC in the electrolyte. This achieves the detection of trace and ultra-trace amounts of DFEC additives in electrolytes.

[0054] This invention provides a method for the qualitative and quantitative detection of difluoroethylene carbonate (DFEC) in electrolytes, such as... Figure 1 As shown, the specific steps include:

[0055] Step S1: Prepare multiple difluoroethylene carbonate standard solutions with gradient concentrations.

[0056] Specifically, the process of preparing the standard solution includes: dissolving ethylene difluorocarbonate in organic solvents in different proportions to prepare multiple ethylene difluorocarbonate standard solutions with gradient concentrations.

[0057] In this step, chromatographically pure dichloromethane was used as the organic solvent. For the selection of organic solvents, acetonitrile, methanol, n-hexane, and dichloromethane were used respectively to prepare 10 mg / L DFEC standard solutions, which were then analyzed using gas chromatography-mass spectrometry (GC-MS). The test result curves are shown below. Figure 2 As shown, the horizontal axis represents time (in minutes), and the vertical axis represents absolute intensity. Figure 2 The test results showed that DFEC chromatographic peaks exhibited low symmetry and poor peak shape when acetonitrile was used as a solvent, while methanol and n-hexane produced higher base peaks, which masked the DFEC signal of the target compound. Dichloromethane, however, provided a better peak shape for DFEC. Therefore, dichloromethane was used as the organic solvent in the preparation of the DFEC standard solution in this invention.

[0058] This step uses chromatographically pure dichloromethane as the organic solvent to prepare multiple difluoroethylene carbonate standard solutions with gradient concentrations ranging from 0.80 mg / L to 160.0 mg / L. Preferably, the following seven concentration gradient difluoroethylene carbonate standard solutions can be prepared: 0.80 mg / L, 1.60 mg / L, 8.00 mg / L, 40.0 mg / L, 80.0 mg / L, 120.0 mg / L, and 160.0 mg / L. Subsequently, gas chromatography-mass spectrometry (GC-MS) analysis is performed on the above seven standard solutions to obtain the standard curve equation.

[0059] Step S2: Select the chromatographic column.

[0060] The chromatographic column used in this invention has a stationary phase of 5% phenyl and 95% dimethyl polysiloxane, a column length of 25m to 60m, an inner diameter of 0.25mm to 0.50mm, and an inner coating thickness of 0.25μm to 1.0µm.

[0061] The chromatographic column of the present invention is preferably a capillary chromatographic column (model SH-I-5Sil MS), with a column length of 30m, an inner diameter of 0.25mm, and an inner coating thickness of 1.0µm.

[0062] Step S3: Set the test parameters for the gas chromatography-mass spectrometry (GC-MS) instrument; the test parameters include: gas chromatography parameters, column temperature program, and mass spectrometry parameters.

[0063] Specifically, the ionization energy of the gas chromatography-mass spectrometry instrument is 70 eV.

[0064] The gas chromatography parameters include: carrier gas, column flow rate, split ratio, injection port temperature, injection volume, and purge flow rate; wherein, the carrier gas is helium, the column flow rate is 1.20 mL / min to 1.40 mL / min, the split ratio is 10:1 to 20:1, the injection port temperature is 180℃ to 240℃, the injection volume is 1.5 μL to 2.0 μL, and the purge flow rate is 3 mL / min to 5 mL / min; preferably, the injection port temperature is 200℃, the split ratio is 20:1, and the injection volume is 2.0 μL.

[0065] The column temperature program includes: holding the initial temperature of 35℃~40℃ for 1min~7min, increasing the temperature to 200℃~220℃ at a heating rate of 8℃~10℃ / min, and holding the temperature for 3min~4min; the preferred column temperature program is: holding the initial temperature of 40℃ for 1min, increasing the temperature to 200℃ at a heating rate of 10℃ / min, and holding the temperature for 3min.

[0066] The mass spectrometry parameters include: ion source, ion source temperature, transmission line interface temperature, scan mode, and solvent delay time; the ion source is an electron ionization source, the ion source temperature is 230℃~250℃, and the transmission line interface temperature is 250℃~270℃; preferably, the ion source temperature is 230℃; the transmission line interface temperature is 250℃; and the solvent delay time is 2.5 min.

[0067] The scanning mode is selected ion monitoring mode. The ions monitored include: quantitative ions with a mass-to-charge ratio of m / z=124, and reference ions with mass-to-charge ratios of m / z=61 and m / z=80.

[0068] The solvent delay time is 2.0 min to 3.0 min.

[0069] Step S4: The multiple difluoroethylene carbonate standard solutions with gradient concentrations prepared in step S1 are detected using the test parameters of step S3. The instrument response value, i.e., peak area, corresponding to each difluoroethylene carbonate standard solution is recorded. The standard curve is determined based on the concentration and peak area of ​​difluoroethylene carbonate in each difluoroethylene carbonate standard solution, as well as the detection limit and quantitation limit under the test conditions. The standard curve equation is then formed based on the standard curve.

[0070] The detection limit is below 0.5 mg / L, and the quantitation limit is below 1 mg / L; the lower limit of detection is preferably 0.25 mg / L, and the lower limit of quantitation is preferably 0.8 mg / L.

[0071] The limit of detection refers to the sample concentration when the peak signal is 3 times the baseline noise standard, i.e., the corresponding sample concentration with a signal-to-noise ratio of 3:1; the limit of quantitation refers to the sample concentration when the peak signal is 10 times the baseline noise standard, i.e., the corresponding sample concentration with a signal-to-noise ratio of 10:1.

[0072] The coefficient of determination R of the standard curve 2 >0.999.

[0073] The standard curve equation is Y = 199.2367X + 257.0345, where X is the abscissa of the standard curve, representing the peak area of ​​difluoroethylene carbonate; and Y is the ordinate of the standard curve, representing the concentration of difluoroethylene carbonate in the electrolyte.

[0074] Step S5: Select the electrolyte to be tested, pretreat the electrolyte, and test the pretreated electrolyte using the same method as the difluoroethylene carbonate standard solution in step S4 to obtain the peak area of ​​the electrolyte. Then, find the concentration of difluoroethylene carbonate in the electrolyte according to the standard curve obtained in step S4, or calculate the concentration of difluoroethylene carbonate in the electrolyte according to the standard curve equation.

[0075] The pretreatment specifically includes diluting the electrolyte to be tested with chromatographically pure dichloromethane, ensuring that the mass concentration of difluoroethylene carbonate in the diluted electrolyte is less than or equal to 100 mg / L. Extraction is the preferred method for sample pretreatment, with dichloromethane as the extraction solvent and a final volume of 2 mL being suitable for the determination of trace DFEC additives.

[0076] Specifically, step S5 involves finding the concentration of ethylene difluorocarbonate in the electrolyte to be tested based on the standard curve obtained in step S4. This includes: performing multiple tests on the electrolyte to be tested to obtain multiple measured peak areas; searching on the standard curve according to the measured peak areas to obtain the concentrations of ethylene difluorocarbonate in multiple electrolytes to be tested; and calculating the average value to obtain the concentration of DFEC in the electrolyte to be tested.

[0077] In step S5, the mass concentration of difluoroethylene carbonate in the electrolyte to be tested is selected within the range of 0.001 wt% to 0.2 wt%, and can be any value within this range, such as 0.001 wt%, 0.002 wt%, 0.003 wt%, 0.004 wt%, 0.005 wt%, 0.006 wt%, 0.007 wt%, 0.008 wt%, 0.009 wt%, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, 0.16 wt%, 0.17 wt%, 0.18 wt%, 0.19 wt%, 0.20 wt%, etc. However, this does not apply to all values ​​listed; other unlisted values ​​within this range also apply.

[0078] In step S3 of this invention, setting the test parameters of the gas chromatography-mass spectrometry (GC-MS) instrument is intended to ensure effective adsorption and desorption of DFEC on the chromatographic column. The chromatographic test parameters need to ensure effective separation of DFEC from other components in the electrolyte, especially interfering components, thereby facilitating subsequent mass spectrometry testing, achieving high sensitivity, high efficiency, high reproducibility, and ensuring the accuracy of the test results. The setting of the GC-MS test parameters is particularly important for the detection results of DFEC. Specific improvements to the chromatographic test parameters provided in this embodiment are as follows.

[0079] (1) In the chromatographic test of this invention, the column flow rate is 1.20 mL / min to 1.40 mL / min, which can be any value within the above range, such as 1.20 mL / min, 1.25 mL / min, 1.30 mL / min, 1.35 mL / min, 1.40 mL / min, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. By limiting the column flow rate within the above range, it is possible to ensure that DFEC has a suitable retention time and resolution, thereby facilitating the effective separation of DFEC from other phases in subsequent processes. Because DFEC contains fluorine groups and exhibits strong adsorption, if the retention time on the chromatographic column is too long, it will be difficult to separate it from other phases. Considering that the column flow rate directly affects the peak shape and retention time, the inventors ensured increased ionization efficiency and improved detection sensitivity by selecting an appropriate column flow rate. This invention compares the changes in analysis time and resolution under different column flow rates, as detailed in Table 1.

[0080] Table 1 shows a comparison of flow rate tests for different columns, as follows.

[0081] A comparison of the gas chromatography-mass spectrometry (GC-MS) results in Table 1 shows that DFEC has an excessively long residence time on the column at flow rates of 0.8 mL / min and 1.0 mL / min, resulting in a resolution <1.5. However, at flow rates of 1.20 mL / min to 1.60 mL / min, the residence time is reasonable, and the resolution >1.5. Furthermore, in the reproducibility test (n=6), the peak area RSD was <1% at flow rates of 1.20 mL / min to 1.40 mL / min and >9% at 1.6 mL / min. Therefore, the column flow rate range provided in this embodiment is 1.20 mL / min to 1.40 mL / min.

[0082] (2) In the chromatographic test of this invention, the split ratio is 10:1 to 20:1, which can be any value within the above range, such as 10:1, 12:1, 15:1, 18:1, 20:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The split ratio directly affects the amount of sample entering the chromatographic column, affecting the peak area and detection sensitivity. In this invention, based on the consideration of DFEC trace component analysis, the split ratio is set to ensure that all samples enter the chromatographic column to improve detection sensitivity. The tailing factor (T) is a key parameter for evaluating the symmetry of chromatographic peaks. It is defined as the ratio of the peak width at 5% peak height (W0.05h) to the distance from the peak apex to the leading edge (d1). This invention uses the tailing factor to determine the symmetry of chromatographic peaks by comparing flow ratios of 80:1, 40:1, 20:1, 10:1, and 5:1. The closer the value is to 1.0, the more symmetrical the peak shape is and the more Gaussian the distribution, thus ensuring the accuracy of the analytical results. The results are detailed in Table 2.

[0083] Table 2 shows a comparison of tests with different split ratios.

[0084] A comparison of the gas chromatography-mass spectrometry (GC-MS) results in Table 2 revealed slight tailing at high split ratios of 80:1 and 40:1, caused by discrimination or adsorption. Tailing factors were smaller at split ratios of 20:1 and 10:1, very close to 1.0. Further reducing the split ratio to 5:1 resulted in severe tailing, indicating column overload due to the larger sample volume. Therefore, considering the purpose of DFEC trace detection, the optimal range for the split ratio in this invention is selected as 20:1–10:1.

[0085] (3) In the chromatographic test of this invention, the injection port temperature is 180℃~240℃, which can be any value within the above range, such as 180℃, 200℃, 220℃, 240℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. This is because the injection port temperature setting needs to ensure that the sample is completely vaporized to avoid peak tailing and splitting caused by incomplete vaporization. At the same time, excessively high temperatures should also be avoided to prevent degradation of thermally unstable components. Figure 3 As shown, this invention compares the tailing of the target peak and the tailing factor when the injection port temperatures are 180℃, 200℃, 220℃, and 240℃. The tailing factor is 1.031 at 180℃, 1.019 at 200℃, 1.072 at 220℃, and 1.041 at 240℃. It can be seen that the change in tailing factor is small when the injection port temperature is between 180℃ and 240℃, and no obvious tailing is observed in the spectrum. Therefore, the injection port temperature range of this invention is selected as 180℃ to 240℃.

[0086] (4) The injection volume is 1.5uL to 2.0uL, which can be any value within the above range, such as 1.5uL, 1.6uL, 1.7uL, 1.8uL, 1.9uL, 2.0uL, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0087] This invention compares test data with injection volumes of 0.5 μL, 1.0 μL, 1.5 μL, 2.0 μL, and 2.5 μL, and observes the changes in retention time and tailing factor, as detailed in Table 3.

[0088] Table 3 shows a comparison of tests with different injection volumes, as follows.

[0089] A comparison of the gas chromatography-mass spectrometry (GC-MS) results in Table 3 revealed that the tailing factor was larger when the injection volume was 0.5 μL and 1.0 μL, while the tailing factor was smaller when the injection volume was 1.5 μL to 2.5 μL. In particular, the RSD of the reproducibility test (n=6) for 2.5 μL was >5%. Therefore, the injection volume selected in this invention is 1.5 μL to 2.0 μL.

[0090] (5) The column temperature rise program in the chromatographic test of the present invention is crucial, as it directly affects the residence time of DFEC on the chromatographic column and the separation of each phase.

[0091] To analyze the optimal range of column temperature rise programs in chromatographic testing, this invention prepared a mixed solution using chromatographically pure dichloromethane as solvent and methyltrifluoroethyl carbonate (FEMC) and DFEC as solutes, with a total solute concentration of 100 mg / L. The mass ratio of FEMC to DFEC was 200:1. This solution was used to simulate and study the behavior of trace component DFEC in a high-concentration matrix of FEMC. The separation of substances in the above mixed solution was compared at initial temperatures of 35℃, 40℃, 45℃, 50℃, and 55℃. The separation chromatograms are shown below. Figures 4-8 As shown in the figure, the detection results using gas chromatography-mass spectrometry (GC-MS) indicate that when the initial temperature is 35℃ or 40℃, the separation degree of FEMC and DFEC is >1.5, indicating a very good separation effect. However, when the initial temperature is 45℃, 50℃, and 55℃, the separation degree of FEMC and DFEC is <1.5, and even at 55℃, the peaks of the two substances completely overlap. This shows that the initial temperature is crucial for phase separation and determines the separation of DFEC and the interfering component FEMC.

[0092] The initial temperature of the column temperature program in this invention is 35℃ to 40℃, and can be any temperature value within this range, such as 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, etc., but is not limited to the listed temperature values; other unlisted temperature values ​​within this range are also applicable. Based on the separation situation, this invention preferentially selects an initial temperature of 40℃ to set the temperature condition, as the substance partitions and reaches equilibrium more quickly under this initial temperature condition, resulting in better separation.

[0093] An initial temperature of 40°C was selected, and the effect of holding time at the initial temperature was compared. This invention, by maintaining the temperature at this level for 1 min, 3 min, 5 min, and 7 min respectively, found that the effect of time on the DFEC detection signal was relatively small when a suitable temperature was selected. To improve efficiency, this invention can choose a shorter time, for example, a retention time of 1 min, to allow the target compound DFEC to be fully adsorbed at the column head.

[0094] The above describes specific improvements to chromatographic testing parameters. Mass spectrometry testing parameters are also crucial, primarily because the ion source, mass analyzer, and acquisition mode determine the instrument's sensitivity and resolution, ensuring accurate characterization and quantification of target compounds. This invention, through the selection of mass spectrometry conditions, can guarantee the testing results for trace and ultra-trace DFEC. Specific ion fragments are selected in the mass spectrometry process for precise quantitative detection of DFEC, ensuring the accuracy of the results. The improvements to mass spectrometry testing parameters in this invention are as follows.

[0095] (1) The ion source temperature in the mass spectrometry process of this invention is 230℃~250℃, which can be any temperature value within the above range, such as 230℃, 235℃, 240℃, 245℃, 250℃, etc., but is not limited to the listed temperature values. Other unlisted temperature values ​​within the range are also applicable.

[0096] The transmission line interface temperature is 250℃~270℃, and can be any value within the above temperature range, such as 250℃, 255℃, 260℃, 265℃, 270℃, etc., but is not limited to the listed temperature values. Other unlisted temperature values ​​within this temperature range are also applicable.

[0097] The ion source temperature and transfer line interface temperature of this invention need to be matched. The transfer line interface temperature should be equal to or slightly higher than the maximum programmed temperature of the chromatographic column. This is because the heating line connecting the gas chromatographic column outlet and the mass spectrometer ion source inlet must be set high enough to prevent sample condensation during the transfer from GC to MS.

[0098] This invention compares the response differences of mass spectrometry detection under two conditions: Condition 1 and Condition 2, as well as the response differences between two conditions: Condition 1 and Condition 3. In Condition 1, the ion source temperature is 230°C and the transmission line interface temperature is 250°C; in Condition 2, the ion source temperature is 250°C and the transmission line interface temperature is 270°C; and in Condition 3, the ion source temperature is 240°C and the transmission line interface temperature is 250°C.

[0099] The results show that when the ion source temperature and transmission line interface temperature are matched in conditions 1 and 2, the recovery rates are 106% and 109%, respectively, with little difference. Comparing conditions 1 and 3, the recovery rates are 106% and 114%, respectively, showing a significant difference. A recovery rate close to 100% indicates better recovery performance. This also shows that after matching the ion source temperature and transmission line interface temperature, the temperature has little impact on DFEC. The preferred ion source temperature in this invention is 230℃, and the preferred transmission line interface temperature is 250℃.

[0100] (2) In this invention, the selection of characteristic ions in the mass spectrometry testing process parameters is achieved by qualitatively identifying the target analyte using a full scan (SCAN) mass spectrum, and determining the target analyte based on the retention time and fragment ions. Specifically, the ion scan (SIM) mode is selected, and one molecular ion and two to three characteristic fragment ions are selected based on the target mass spectrum. By directly monitoring the molecular ion and fragment ions, the cost is low and the effect is good.

[0101] This invention establishes a SIM scanning method by determining the retention time and fragment ions of the target analyte DFEC, and finally selects the m / z 61, m / z 80, and m / z 124 with high abundance as characteristic ions, i.e., quantitative ion m / z=124, and reference ions m / z=61 and m / z=80.

[0102] In step S4 of this invention, the limit of detection (LOD) and limit of quantitation (LOQ) are defined according to chromatographic methods: the limit of detection (LOD) is the lowest concentration or amount of analyte that can be reliably detected, determined based on the signal-to-noise ratio (S / N=3); the limit of quantitation (LOQ) is the lowest concentration or amount that can be determined, determined based on the signal-to-noise ratio (S / N=10). This invention uses a blank solution with 10 mg / L DFEC standard solution for serial dilution before analysis. The LOD is set at a sample concentration of 0.25 mg / L (S / N=3.3), and the LOQ is set at a sample concentration of 0.8 mg / L (S / N=10.5).

[0103] The analytical range configured in this invention is in the low concentration range, and seven standard series solutions with concentrations of 0.80 mg / L, 1.60 mg / L, 8.00 mg / L, 40.0 mg / L, 80.0 mg / L, 120.0 mg / L and 160.0 mg / L are prepared respectively.

[0104] The parameters of the gas chromatography-mass spectrometry (GC-MS) instrument were set according to the optimized test parameters described above. The instrument was then used to detect seven standard series solutions to obtain response values ​​(i.e., peak areas). After detection, scatter plots were plotted and fitted to form a standard curve, as shown below. Figure 9 As shown, the horizontal axis represents the DFEC component concentration in the standard series solutions, and the vertical axis represents the peak area. Regression analysis was then performed using the ratio of component concentration to the corresponding instrument response value (peak area) to establish the regression equation for the standard curve. The standard curve equation is Y = 199.2367X + 257.0345, where X is the peak area of ​​difluoroethylene carbonate, Y is the concentration of DFEC in the electrolyte, and R0 is the coefficient of determination of the standard curve. 2 =0.9992, since R 2 A value >0.999 indicates good linearity of the target analyte in the range of 0.8 mg / L to 160.0 mg / L, demonstrating an excellent linear relationship between the standard curve equation of the detection method provided by this invention and the response (peak area) of DFEC and the concentration.

[0105] This invention further verifies the accuracy and precision of the standard curve equation: the method accuracy is expressed as the spike recovery rate; the method precision is expressed as the relative standard deviation; the specific verification is as follows.

[0106] (1) Validation of DFEC dichloromethane standard solutions: Four standard solutions with concentrations of 0.80 mg / L, 10 mg / L, 60 mg / L and 100 mg / L were prepared for spiking and recovery. Six parallel tests were performed at each concentration level to determine the recovery rate of spiked samples at different concentrations and to determine the accuracy and precision of the method. The recovery rates and relative standard deviations of DFEC at each concentration level are shown in Table 4.

[0107] Table 4 shows the DFEC spiked recovery results and relative standard deviations (n=6), as follows.

[0108] As shown in Table 4, the average recoveries of the blank standard samples at the four concentration levels from low to high were 97.8% to 105.7%, with relative standard deviations (n=6) ranging from 0.3% to 1.9%. The blank standard samples demonstrate that the test process parameters and standard curves of this invention have very high accuracy and precision.

[0109] (2) Validation of matrix-spiked samples: The accuracy is expressed as the recovery rate and relative standard deviation of the matrix-spiked samples. Electrolyte matrix samples were prepared using FEMC:FEC = 4:6 as the main solvent, with DFEC contents of 1, 10, and 50 ppm. The accuracy of the method was validated in three segments. Then, three-level tests were conducted by adding 50%, 100%, and 150% of the background concentration of DFEC in the samples, with 6 parallel samples prepared for each level. The average recovery rate and relative standard deviation data are shown in Tables 5, 6, and 7.

[0110] Table 5. Recovery, average recovery, and relative standard deviation (RSD) of electrolyte matrix spiked (DFEC content 1 ppm).

[0111] Table 6 shows the recoveries, average recoveries, and relative standard deviations (RSD) of the electrolyte matrix spiked (DFEC content 10 ppm).

[0112] Table 7 shows the recoveries, average recoveries, and relative standard deviations (RSD) of the electrolyte matrix spiked (DFEC content 50 ppm).

[0113] The matrix spiked recovery results in Tables 5-7 show that: in low-concentration samples (1 ppm), the recovery rate was 95.1%–97.6%, with a relative standard deviation (RSD) of 0.7%–1.3%; in medium-concentration samples (10 ppm), the recovery rate was 98.2%–100.9%, with an RSD of 0.2%–0.9%; and in high-concentration samples (50 ppm), the recovery rate was 95.3%–97.6%, with an RSD of 0.2%–0.5%. This indicates that DFEC can be well separated with high accuracy in electrolytes containing FEMC.

[0114] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0115] The batteries, materials, and reagents used in the embodiments of this invention can all be obtained commercially or in-house. The main reagents and equipment used in this invention include: acetonitrile (Cas No. 75-05-8), chromatographically pure, purchased from Fisher Scientific, USA; methanol (Cas No. 67-56-1), chromatographically pure, purchased from Honeywell Pharmaceuticals, USA; n-hexane (Cas No. 110-54-3), chromatographically pure, purchased from Honeywell Pharmaceuticals, USA; dichloromethane (Cas No. 75-09-2), chromatographically pure, purchased from Fisher Scientific, USA; and 4,5-difluoro-1,3-dioxolane-2-one (DFEC, Cas No. 171730-81-7), 98% pure, purchased from Jiangsu Aikon Biomedical R&D Co., Ltd.

[0116] The gas chromatograph-mass spectrometer is manufactured by Shimadzu Corporation (Shimadzu Japan), model QP2020NX: equipped with an electron impact ionization source (EI), and the chromatographic column is SH-I-5Sil MS (30m×0.25mm i.d, 1.0μm) bonded cross-linked polyarylene, specifically 1,4-di(dimethyl)phenylmethylpolysiloxane.

[0117] Analytical balance: sensitivity 0.0001g (Shimadzu, Japan).

[0118] The main solvent of the electrolyte to be tested is methyltrifluoroethyl carbonate (FEMC) and fluoroethylene carbonate (FEC), wherein the volume ratio of FEMC:FEC is 4:6. The concentration of DFEC in the electrolyte to be tested in Examples 1-6 and Comparative Examples 1-5 is 0.0016 wt%, and the concentration of DFEC in the electrolyte to be tested in Example 7 is 0.2 wt%.

[0119] Example 1 The detection method of the present invention is used to detect DFEC additive in the electrolyte to be tested.

[0120] The instrument settings for the gas chromatography-mass spectrometry (GC-MS) system in this embodiment are as follows: GC conditions: SH-I-5Sil MS capillary column (30m × 0.25mm i.d, 1.0μm), column flow rate set to 1.2 mL / min, injection port temperature set to 200℃; split injection, split ratio 20:1, injection volume 2.0μL; temperature program: initial temperature 40℃, hold for 1 min; increase to 200℃ at 10℃ / min, hold for 4 min. GC-MS conditions: ionization energy of the GC-MS system 70 eV, ion source temperature 230℃, transfer line interface temperature 250℃. Quantitative ion m / z = 124, reference ions m / z = 61 and m / z = 80, solvent delay time 2.5 min. Where 30m×0.25mmi.d indicates that the length of the chromatographic column is 30m and the inner diameter is 0.25mm, and 1.0μm indicates the thickness of the stationary phase.

[0121] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 8.

[0122] Table 8 shows the results of the determination of the DFEC additive content in the electrolyte sample of Example 1, as follows.

[0123] Example 2 This embodiment uses the detection method of the present invention to detect DFEC additive in the electrolyte under test. The difference from Embodiment 1 is that the initial temperature of the instrument's temperature rise program is set to 35°C.

[0124] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 9.

[0125] Table 9 shows the DFEC determination results of the additive content in the electrolyte sample of Example 2, as follows.

[0126] Example 3 This embodiment uses the detection method of the present invention to detect the additive DFEC in the electrolyte to be tested. The difference from Example 1 is that the column flow rate of the instrument is set to 1.4 mL / min.

[0127] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 10.

[0128] Table 10 shows the results of the determination of the DFEC additive content in the electrolyte sample of Example 3, as follows.

[0129] Example 4 This embodiment uses the detection method of the present invention to detect the additive DFEC in the electrolyte to be tested. The difference from Example 1 is that the split ratio of the instrument is set to 10:1.

[0130] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 11.

[0131] Table 11 shows the results of the determination of the DFEC additive content in the electrolyte sample of Example 4, as follows.

[0132] Example 5 This embodiment uses the detection method of the present invention to detect the additive DFEC in the electrolyte to be tested. The difference from Example 1 is that the sample injection volume under the instrument conditions is 1.5 μL.

[0133] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 12.

[0134] Table 12 shows the results of the determination of the DFEC additive content in the electrolyte sample of Example 5, as follows.

[0135] Example 6 This embodiment uses the detection method of the present invention to detect DFEC additives in the electrolyte under test. The difference from Embodiment 1 is that the ion source temperature is 250°C and the transmission line interface temperature is 270°C.

[0136] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 13.

[0137] Table 13 shows the results of the determination of the DFEC additive content in the electrolyte sample of Example 6, as follows.

[0138] As shown in Tables 8-13, the electrolytes of Examples 1-6 contained low levels of DFEC, and the RSD values ​​of the detection results were all less than 2%, with Example 1 reaching as low as 0.9%. The above test results indicate that by using the qualitative and quantitative detection method of this invention, and by rationally setting the test parameters in the detection process—that is, determining the key process parameters for the qualitative and quantitative detection of DFEC in the electrolyte—the detection and analysis results for trace and ultra-trace amounts in the electrolyte achieve high accuracy and high sensitivity. This demonstrates that the detection method provided by this invention has higher precision, more stable operation, and more reliable data, making it suitable for the testing of trace additives and the research, design, and analysis of electrolyte components.

[0139] Example 7 This embodiment uses the detection method of the present invention to detect the additive DFEC in the electrolyte to be tested. The instrument conditions are the same as in Example 1, the volume ratio of FEMC to FEC in the electrolyte to be tested is 4:6, and the concentration of DFEC in the electrolyte to be tested is 0.2wt%.

[0140] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 1.

[0141] Table 14 shows the results of the determination of the DFEC additive content in the electrolyte sample of Example 7, as follows.

[0142] As can be seen from Table 14, the addition of 0.2 wt% DFEC to the electrolyte in Example 7 resulted in an RSD value as low as 0.7%, indicating high accuracy and sensitivity in the analysis and detection results.

[0143] Comparative Example 1 This comparative example uses the detection method of the present invention to detect the additive DFEC in the electrolyte under test. The difference from Example 1 is that the initial temperature in the gas chromatography-mass spectrometry test parameters is set to 45°C.

[0144] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 15.

[0145] Table 15 shows the results of the determination of the DFEC additive content in the electrolyte sample of Comparative Example 1.

[0146] Comparative Example 2 This comparative example uses the detection method of the present invention to detect the additive DFEC in the electrolyte to be tested. The difference from Example 1 is that the column flow rate in the gas chromatography-mass spectrometry test parameters is set to 1.6 mL / min.

[0147] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 16.

[0148] Table 16 shows the results of the determination of the DFEC additive content in the electrolyte sample of Comparative Example 2.

[0149] Comparative Example 3 This comparative example uses the detection method of the present invention to detect the additive DFEC in the electrolyte under test. The difference from Example 1 is that the split ratio in the gas chromatography-mass spectrometry test parameters is set to 40:1.

[0150] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 17.

[0151] Table 17 shows the results of the determination of the DFEC additive content in the electrolyte sample of Comparative Example 3.

[0152] Comparative Example 4 This comparative example uses the detection method of the present invention to detect the additive DFEC in the electrolyte to be tested. The difference from Example 1 is that the injection volume in the gas chromatography-mass spectrometry test parameters is 2.5 μL.

[0153] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 18.

[0154] Table 18 shows the results of the determination of the DFEC additive content in the electrolyte sample of Comparative Example 4.

[0155] Comparative Example 5 This comparative example uses the detection method of the present invention to detect the additive DFEC in the electrolyte under test. The difference from Example 1 is that the ion source temperature in the gas chromatography-mass spectrometry test parameters is 260°C.

[0156] Analysis of the electrolyte sample: Weigh 0.1 g of the electrolyte sample (accuracy 0.0001 g) and place it in a 10 mL sample vial. Dissolve and dilute to 2 mL with dichloromethane, vortex extract for 1 min, then inject into a liquid chromatography vial and directly inject into a gas chromatography-mass spectrometry (GC-MS) instrument for detection. Analyze the DFEC content using the standard curve method based on the measured peak area. The test results are shown in Table 19.

[0157] Table 19 shows the results of the determination of the DFEC additive content in the electrolyte sample of Comparative Example 5, as follows.

[0158] As shown in Tables 15-19, the DFEC content in the electrolytes of Comparative Examples 1-5 is the same as that in Examples 1-6, all being trace amounts of DFEC. However, the parameters of the qualitative and quantitative detection methods for DFEC in the electrolytes are not within the range of process parameters provided in this invention. The test results deviate significantly from the actual content, and the RSD value is greater than 3%, indicating that the detection methods provided in Comparative Examples 1-5 have low precision and unreliable data. Therefore, the test process parameter range provided in this invention has a better detection effect.

[0159] As can be seen from the above embodiments and comparative examples, the detection method provided by the present invention has good versatility, high detection accuracy, and is easy to promote. It can be applied to the detection of electrode samples, as well as the original and cycled electrode sheets of various types of cells such as soft-pack cells, hard-shell cells, and cylindrical cells. It is of great significance for the optimized analysis of electrode sheets mixed with solid electrolytes.

[0160] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for qualitative and quantitative detection of difluoroethylene carbonate in an electrolyte, characterized in that, The detection method includes: Step S1, preparing multiple difluoroethylene carbonate standard solutions with gradient concentrations, specifically includes: dissolving difluoroethylene carbonate in organic solvents at different proportions to prepare multiple difluoroethylene carbonate standard solutions. Step S2: Select a chromatographic column; the stationary phase of the chromatographic column is 5% phenyl and 95% dimethyl polysiloxane, the column length is 25m to 60m, the inner diameter is 0.25mm to 0.50mm, and the inner coating thickness is 0.25μm to 1.0µm; Step S3: Set the test parameters for the gas chromatography-mass spectrometry (GC-MS) instrument; wherein, the test parameters include: gas chromatography parameters, column temperature program and mass spectrometry parameters; The gas chromatography parameters include: carrier gas, column flow rate, split ratio, injection port temperature, injection volume, and purge flow rate; the carrier gas is helium, the column flow rate is 1.20 mL / min to 1.40 mL / min, the split ratio is 10:1 to 20:1, the injection port temperature is 180℃ to 240℃, the injection volume is 1.5 uL to 2.0 uL, and the purge flow rate is 3 mL / min to 5 mL / min. The column temperature program includes: holding the initial temperature of 35℃~40℃ for 1min~7min, heating to 200℃~220℃ at a heating rate of 8℃~10℃ / min, and holding the temperature for 3min~4min. The mass spectrometry parameters include: ion source, ion source temperature, transmission line interface temperature, scan mode, and solvent delay time; the ion source is an electron ionization source, the ion source temperature is 230℃~250℃, and the transmission line interface temperature is 250℃~270℃; the scan mode is selected ion monitoring mode, and the ions monitored include: quantitative ions with a mass-to-charge ratio of m / z=124, and reference ions with mass-to-charge ratios of m / z=61 and m / z=80; the solvent delay time is 2.0 min~3.0 min. Step S4: The multiple difluoroethylene carbonate standard solutions with gradient concentrations prepared in step S1 are detected using the test parameters of step S3. The instrument response value, i.e., peak area, corresponding to each difluoroethylene carbonate standard solution is recorded. A standard curve is determined based on the concentration and peak area of ​​difluoroethylene carbonate in each difluoroethylene carbonate standard solution, as well as the detection limit and quantitation limit under the test conditions. The standard curve equation is then formed based on the standard curve. Step S5: Select the electrolyte to be tested, pretreat the electrolyte, and test the pretreated electrolyte using the same method as the difluoroethylene carbonate standard solution in step S4 to obtain the peak area of ​​the electrolyte. Then, find the concentration of difluoroethylene carbonate in the electrolyte according to the standard curve obtained in step S4, or calculate the concentration of difluoroethylene carbonate in the electrolyte according to the standard curve equation.

2. The detection method according to claim 1, characterized in that, In step S1, the concentrations of the plurality of difluoroethylene carbonate standard solutions with gradient concentrations are selected between 0.80 mg / L and 160.0 mg / L. The organic solvent is chromatographically pure dichloromethane.

3. The detection method according to claim 2, characterized in that, The concentrations of the plurality of difluoroethylene carbonate standard solutions with gradient concentrations include: 0.80 mg / L, 1.60 mg / L, 8.00 mg / L, 40.0 mg / L, 80.0 mg / L, 120.0 mg / L, and 160.0 mg / L.

4. The detection method according to claim 1, characterized in that, In step S2, the chromatographic column is a capillary chromatographic column SH-I-5Sil MS, with a column length of 30m, an inner diameter of 0.25mm, and an inner coating thickness of 1.0µm.

5. The detection method according to claim 1, characterized in that, In step S3, the injection port temperature is 200℃, the split ratio is 20:1, and the injection volume is 2.0μL. The column temperature program includes: holding the initial temperature of 40°C for 1 minute, heating to 200°C at a heating rate of 10°C / min, and holding the temperature for 3 minutes. The ionization energy of the gas chromatography-mass spectrometry system is 70 eV; the ion source temperature is 230℃; the transmission line interface temperature is 250℃; and the solvent delay time is 2.5 min.

6. The detection method according to any one of claims 1-4, characterized in that, In step S4, the detection limit is below 0.5 mg / L, and the quantitation limit is below 1 mg / L; wherein, the detection limit refers to the sample concentration when the peak generation signal is 3 times the baseline noise standard, that is, the corresponding sample concentration when the signal-to-noise ratio is 3:1; the quantitation limit refers to the sample concentration when the peak generation signal is 10 times the baseline noise standard, that is, the corresponding sample concentration when the signal-to-noise ratio is 10:

1.

7. The detection method according to claim 6, characterized in that, The lower limit of detection is 0.25 mg / L, and the lower limit of quantitation is 0.8 mg / L.

8. The detection method according to any one of claims 1-6, characterized in that, In step S4, the coefficient of determination R of the standard curve 2 >0.999; the standard curve equation is Y = 199.2367X + 257.0345, where X is the peak area of ​​difluoroethylene carbonate and Y is the concentration of difluoroethylene carbonate in the electrolyte.

9. The detection method according to claim 1, characterized in that, In step S5, the pretreatment specifically includes: diluting the electrolyte to be tested with chromatographically pure dichloromethane, such that the mass concentration of difluoroethylene carbonate in the diluted electrolyte is less than or equal to 100 mg / L. The step of finding the concentration of difluoroethylene carbonate in the electrolyte to be tested based on the standard curve obtained in step S4 is specifically as follows: by performing multiple tests on the electrolyte to be tested, multiple measured peak areas are obtained. Based on the multiple measured peak areas, corresponding values ​​are found on the standard curve to obtain multiple concentrations of difluoroethylene carbonate in the electrolyte to be tested. The average value is calculated to obtain the concentration of DFEC in the electrolyte to be tested.

10. The detection method according to any one of claims 1-9, characterized in that, The mass concentration of difluoroethylene carbonate in the electrolyte to be tested is 0.001wt% to 0.2wt%.

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