Method for detecting concentration of chlorine ion in lithium battery electrolyte by ultraviolet spectrum

Abstract

The application discloses a kind of lithium battery electrolyte chloride ion concentration UV spectrum detection method, comprising the following steps: accurately take the electrolyte sample to be measured, electrolyte sample is heated and burned to no liquid, and residue is obtained;Deionized water is added to the residue, continue to heat reflux and burn for a set time, then the remaining liquid is transferred to constant volume;The liquid after constant volume is detected using ultraviolet spectrophotometry, and the measurement band is 190-250nm.Organic matter in electrolyte hydroxyl and other functional groups have absorption in deep ultraviolet region, which will interfere with the measurement of chloride ion, so by burning electrolyte, organic matter can be removed, thereby avoiding the interference of organic matter on the measurement of chloride ion, and improving the accuracy of chloride ion detection.

Description

Technical Field

[0001] This invention belongs to the field of chloride ion concentration detection technology, specifically relating to an ultraviolet spectral detection method for chloride ion concentration in lithium battery electrolyte. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Lithium-ion battery electrolytes contain chloride salts, which gradually decompose over time to form chloride ions. The presence of chloride ions negatively impacts battery performance. First, chloride ions react with the surface of the cathode material, causing corrosion and impurity formation. These impurities not only reduce battery efficiency but also negatively affect battery stability and lifespan. Second, chloride ions affect the battery's current density. Higher chloride ion levels decrease the current density, impairing the battery's output capacity. Finally, the presence of chloride ions can induce bubble formation within the battery, creating voids and reducing output capacity and stability. Therefore, accurate and sensitive chloride ion detection in the electrolyte is crucial to ensure that the chloride ion content is controlled at a very low level.

[0004] Currently, commonly used methods for chloride ion detection include turbidimetry, potentiometric titration, and ion chromatography. However, turbidimetry produces a white suspension that is prone to sedimentation, which can significantly affect the interpretation of results. Other methods for chloride ion concentration using ultraviolet spectroscopy employ a novel integral model that removes interference from other impurity ions; however, in practice, baseline imbalances in the ultraviolet light can easily lead to errors in the calculated data. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide an ultraviolet spectral detection method for chloride ion concentration in lithium battery electrolytes.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] A method for detecting chloride ion concentration in lithium battery electrolyte using ultraviolet spectroscopy, comprising the following steps:

[0008] Accurately weigh the electrolyte sample to be tested, heat the electrolyte sample until no liquid remains, and obtain the residue.

[0009] Add deionized water to the residue, continue heating under reflux for a set time, and then transfer the remaining liquid to a final volume.

[0010] The liquid after being brought to a constant volume was tested using ultraviolet spectrophotometry, with a measurement wavelength of 190-250 nm.

[0011] In this invention, the chloride ion begins to absorb in the 200nm wavelength range and has strong absorption in the deep ultraviolet region at 195nm and below in the spectral absorption method. Since there is no barium sulfate in the detection liquid, there is no ultraviolet absorption by barium sulfate, thus avoiding interference from barium sulfate.

[0012] In addition, the electrolyte also contains organic matter. The inventors discovered that the functional groups such as hydroxyl groups in the organic matter in the electrolyte have absorption in the deep ultraviolet region, which will interfere with the measurement of chloride ions. Therefore, the organic matter can be removed by burning the electrolyte, thereby avoiding the interference of organic matter with the measurement of chloride ions.

[0013] Adding deionized water to the residue and continuing to heat it helps to dissolve the residue more completely, which facilitates subsequent testing. Cooling the remaining liquid before testing can effectively improve the accuracy of chloride ion detection.

[0014] In some embodiments, the electrolyte sample is heated and ignited at a temperature of 200-250°C.

[0015] In some embodiments, after adding deionized water to the residue, the temperature of the reflux heating is 200-250°C, and the reflux heating time is 20-40 minutes.

[0016] In practice, the electrolyte is heated and burned to allow the organic matter to evaporate. After burning dry, about 20 ml of water is added directly. The experiment uses a 50 ml polytetrafluoroethylene beaker with a lid. The bottom area of ​​the 50 ml polytetrafluoroethylene beaker is very small. During the heating and reflux process, about 10 ml of water is lost, leaving about 10 ml remaining. Therefore, it will not burn dry in the actual process.

[0017] Preferably, the heating and reflux calcination temperature is 230°C and the heating and reflux calcination time is 30 min.

[0018] In some embodiments, when transferring the remaining liquid to a fixed volume, the step of simultaneously transferring the cleaning solution from the original container is also included. This is to prevent chloride ions from adhering to the walls of the original container, thereby reducing the amount of chloride ions and improving the accuracy of chloride ion concentration detection.

[0019] In some embodiments, the method further includes the steps of preparing chloride ion solutions with gradient concentrations, detecting them using ultraviolet spectrophotometry, and fitting a model formula for absorbance versus chloride ion concentration.

[0020] Preferably, when constructing the model formula, the integral area of ​​chloride ions between 190-200 nm is used as the absorption area of ​​chloride ions.

[0021] Preferably, the concentration of the chloride ion solution with gradient concentration is 0.01-0.2 mg / L.

[0022] Preferably, pyridine is added to the chloride ion solution with gradient concentrations, and the concentration of pyridine is 0.03-0.07 mg / L. Pyridine serves as a reference substance, does not react with other reagents, and is chemically stable. Pyridine acts as another signal to verify the stability of the background signal in each experiment.

[0023] In some embodiments, when using ultraviolet spectrophotometry for detection, a measurement is performed every 0.1 nm wavelength.

[0024] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0025] In this invention, by selecting the measurement band of ultraviolet spectrophotometry, the interference problem of barium sulfate can be effectively eliminated, and by calcination, the influence of organic functional groups can be removed, thereby improving the accuracy of the test.

[0026] Adding an internal reference solution allows for real-time monitoring of the test system's stability, effectively mitigating the impact of curve fluctuations on data. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0028] Figure 1 It is the standard curve corresponding to the model formula of absorbance and chloride ion concentration constructed in the embodiments of the present invention. Detailed Implementation

[0029] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] The present invention will be further described below with reference to the embodiments.

[0031] Example

[0032] The method for detecting chloride ion concentration in electrolyte includes the following steps:

[0033] Establish a model for chloride ion absorbance and concentration at 190 nm:

[0034] (1) Estimate the actual chloride ion concentration in the electrolyte from industry standards. According to HG / T4067-2015 "Lithium Hexafluorophosphate Electrolyte", the chloride ion concentration is <1ppm. This is used as a basis for estimation. If 5g of electrolyte is taken, the chloride ion mass in 5g is 5ug. If the electrolyte is thoroughly mixed with 50mL of deionized water, the chloride ion mass fraction is 0.1mg / L. This concentration is used as the concentration parameter standard for the calibration solution.

[0035] (2) Prepare chloride ion concentration solutions within a certain range. Based on the chloride ion concentration calibration in (1), prepare chloride ion concentrations of 0.01 mg / L, 0.02 mg / L, 0.04 mg / L, 0.08 mg / L, 0.1 mg / L, 0.12 mg / L, 0.16 mg / L, and 0.2 mg / L in a stepwise manner.

[0036] (3) Establish an internal reference chloride ion concentration gradient solution. Add a quantitative amount of pyridine solution to each chloride ion concentration solution prepared in (2). The concentration of pyridine in each chloride ion solution is 0.05 mg / L.

[0037] (4) The absorption spectra of the standard solutions of each concentration in (3) were recorded under ultraviolet spectrophotometer measurement. The instrument used was a Purkinje TU-1901 spectrometer (190-900nm), and the measurement band was 250-190nm. A slow scan method was used, and a measurement was performed every 0.1nm band.

[0038] (5) Construct a chloride ion absorbance and concentration model, using the integral area method. First, select the absorbance in the 190nm to 200nm range, and use the integral area of ​​chloride ions in the 190-200nm range as the chloride ion absorbance value.

[0039] The following values ​​were obtained for seven concentrations and their calculated absorbance integrals: 0.02 g / L 1.15, 0.04 g / L 1.67, 0.08 g / L 5.434, 0.1 g / L 6.37, 0.2 g / L 7.71, and 0.2 g / L 10.124.

[0040] Plotting concentration and absorbance, and using the least squares method for linear fitting, the model formula was obtained: Y = 58.304*x + 0.6199, R0 2 =0.9988, where Y is absorbance (unitless) and x is chloride ion concentration (unit mg / L).

[0041] The electrolyte sample to be tested was then analyzed.

[0042] (1) Pretreatment of the electrolyte sample: When this method is applied to the measurement of chloride ion concentration in the electrolyte, it is necessary to ignite the sample to remove the influence of organic matter in the electrolyte. Specifically, using an electronic balance, accurately measure 5.0 g of the electrolyte to be tested, pour it into a 50 ml PTFE beaker, and heat it at 230°C until no liquid remains. The electrolyte composition is relatively complex; UV measurement only measures the content of one substance. A matrix-based sample is easier to test, reduces background interference, and improves detection accuracy.

[0043] (2) Add 20 ml of deionized water to the polytetrafluoroethylene beaker (with lid) that has been burned off the electrolyte, continue heating at 230°C for 30 minutes, and then cool to room temperature.

[0044] (3) Pour the remaining liquid into a 50mL volumetric flask, rinse the beaker three times with deionized water and bring it to the mark.

[0045] (4) The absorbance of the diluted solution was measured using a UV spectrophotometer. A Purkinje TU-1901 spectrometer (190-900 nm) was used, with the measurement band being 190-200 nm. A slow scan was employed, with measurements taken at 0.1 nm intervals. The test intervals were consistent with the calibrated intervals. The absorbance of the diluted solution was measured to be 6.4503, corresponding to a concentration of 0.1 mg / L.

[0046] (5) The mass fraction of chloride ions in the electrolyte sample was calculated to be 1 ppm, which meets the industry standard requirements for chloride ion testing in electrolytes.

[0047] Two electrolyte samples were randomly selected and subjected to ultraviolet detection and ion chromatography tests using the above method. The results are shown in Table 2 below:

[0048] Ion chromatography sample preparation: Weigh 5g of the same electrolyte sample, accurate to 0.0001g, pour it into a 50mL volumetric flask, and dilute to the mark with pure water.

[0049] Cl - Standard solution: Purchase chromatographic grade Cl directly. - The standard solutions all had a concentration of 1000 mg / L.

[0050] Cl - Preparation of standard solution (10 mg / L): Measure Cl... - Add 1 mL of the standard solution (1000 mg / L) to a final volume of 100 mL.

[0051] Cl - Preparation of a series of standard solutions: accurately prepare Cl- solutions separately. -Dispense 0.50 mL, 1 mL, 2 mL, 5.00 mL, and 10 mL of the standard solution (10 mg / L) into five 100 mL volumetric flasks, dilute to the mark with pure water, and shake well.

[0052] The operating conditions for ion chromatography are shown in Table 1.

[0053] Table 1

[0054] Rinse solution concentration <![CDATA[5.0 mmol / L Na2CO3 + 4.0 mmol / L NaHCO3 + 27% acetonitrile]]> Rinse fluid flow rate 1.2 mL / min regenerated liquid flow rate 1.2 mL / min Column temperature (30±1)℃ Temperature of the detection pool (35±1)℃ regenerated liquid 0.2% sulfuric acid (v / v) Suppressor current none Suppressor ASRS 300, 4mm chromatographic column IonPac AS22 analytical column + IonPac AG22 Injection volume 25μl

[0055] The blank reagent (pure water) and the series of standard solutions were sequentially injected into the syringe to establish the anion assay curve. Next, the sample to be tested was directly measured using the same method. The results were corrected by subtracting the blank value, and the final result after subtracting the blank value is the Cl. - content.

[0056] Table 2

[0057]

[0058] As shown in Table 2, when using ion chromatography for detection, the presence of background interference reduces the concentration of Cl in the electrolyte. - Undetectable, severely affecting the Cl in the electrolyte. - The accuracy of content detection.

[0059] The detection method of this invention can successfully detect Cl in the electrolyte. - The low concentration of Cl in the electrolyte, and the small RSD of the three parallel measurements, indicate that the detection method of this invention can detect low concentrations of Cl in the electrolyte. - The content is accurately measured, and the detection accuracy is good.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 detecting chloride ion concentration in lithium battery electrolyte using ultraviolet spectroscopy, characterized in that: Includes the following steps: Accurately weigh the electrolyte sample to be tested, heat the electrolyte sample until no liquid remains, and obtain the residue; the temperature for heating the electrolyte sample is 200-250℃; Add deionized water to the residue, continue heating and refluxing for a set time, and then transfer the remaining liquid to a fixed volume; after adding deionized water to the residue, continue heating and refluxing at a temperature of 200-250℃ for 20-40 minutes; or heat to reflux at a temperature of 230℃ for 30 minutes. The liquid after volume adjustment was tested using ultraviolet spectrophotometry, with a measurement wavelength of 190-250 nm. When transferring the remaining liquid to a fixed volume, the process also includes the step of simultaneously transferring the cleaning solution from the original container; it also includes the step of preparing chloride ion solutions with gradient concentrations, detecting them using ultraviolet spectrophotometry, and fitting a model formula for absorbance and chloride ion concentration. Pyridine is added to the chloride ion solution with a gradient concentration of 0.03-0.07 mg / L.

2. The ultraviolet spectral detection method for chloride ion concentration in lithium battery electrolyte according to claim 1, characterized in that: When constructing the model formula, the integral area of ​​chloride ions in the range of 190-200 nm is used as the absorption area of ​​chloride ions.

3. The ultraviolet spectral detection method for chloride ion concentration in lithium battery electrolyte according to claim 1, characterized in that: The concentration of the chloride ion solution with the gradient concentration is 0.01-0.2 mg / L.

4. The ultraviolet spectral detection method for chloride ion concentration in lithium battery electrolyte according to claim 1, characterized in that: When using ultraviolet spectrophotometry for detection, a measurement is performed every 0.1 nm wavelength.

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