A method for detecting electrolyte

Abstract

The present invention provides a method for detecting an electrolyte, which comprises: a calibration step: performing calibration using a calibration cell that has not been subjected to an operating condition to determine the type, amount, and mixing ratio of an extractant; an injection step: injecting the extractant into the cell after the operating condition with the initial mass using the type, amount, and mixing ratio of the extractant determined in the calibration step; a mixing step: sealing and preserving the cell after the operating condition into which the extractant has been injected and processing it to obtain a mixed solution; an extraction step: taking out the mixed solution from the cell after the operating condition; and a component testing step: performing a sub-test on the mixed solution to determine the mass fraction C of each component of the electrolyte in the mixed solution. i , where i = 1, 2, ..., n, and the total mass fraction C0 of the extractant components in the mixed solution; analysis step: calculating the absolute mass of the electrolyte components of the battery cell after the operating condition using the data obtained in the component testing step. The electrolyte detection method proposed in the present invention enables accurate analysis.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for detecting an electrolyte. Background Art

[0002] With the rapid development of smart grids, electric vehicles, and portable electronics, secondary batteries, primarily lithium-ion and sodium-ion batteries, have become one of the most widely used electrochemical energy storage devices. In secondary batteries, the electrolyte plays a crucial role in conducting ions. Electrolyte components can be categorized as solvents, lithium / sodium salts, and additives. During secondary battery operation, the electrolyte is consumed as operating conditions change. Therefore, understanding electrolyte dynamics is crucial to battery cell design.

[0003] Electrolyte consumption analysis in lithium- and sodium-ion batteries primarily involves extracting electrolyte from the battery using centrifugation or pressure extrusion. Consumption analysis is then performed by measuring the mass fractions of various components in the electrolyte. However, current electrolyte extraction methods cannot completely remove the electrolyte from the cell. A large amount of electrolyte can be adsorbed and infiltrated into the pores of the electrode and separator, making it impossible to separate and extract. For example, during R&D and production, when examining the changes in electrolyte composition before and after a cell's operating conditions, all electrolyte components may be consumed after a certain number of charge and discharge cycles, resulting in a decrease in the total electrolyte volume. However, the consumption rates of various electrolyte components vary, potentially leading to an increase in the relative mass percentage of a component whose absolute consumption decreases. Furthermore, even when the overall electrolyte consumption rate is high, a component with a similarly high absolute consumption rate may show little change in mass fraction. These phenomena can affect the interpretation of electrolyte composition analysis results and render the investigation of the impact of battery operating conditions on electrolyte composition ineffective. In other words, although the mass fraction of each component can be measured, the total amount of electrolyte cannot be accurately known, making it impossible to quantify the components in the electrolyte. This affects the judgment of the electrolyte composition analysis results and makes the work of examining the impact of battery operating conditions on electrolyte composition lack of practical reference value. Summary of the Invention

[0004] The present invention proposes a method for detecting an electrolyte. Through the method for detecting an electrolyte provided by the present invention, the absolute mass of the components in the electrolyte can be accurately detected and analyzed, the detection method can be simplified, and the detection efficiency can be improved.

[0005] To solve the above technical problems, the present invention proposes a method for detecting an electrolyte, which is used to detect the absolute mass of each component in the electrolyte of a battery cell after operation, and at least includes:

[0006] Calibration step: using a cell that is completely consistent with the cell before the working condition and has not been subjected to the working condition as a calibration cell, the calibration cell has an electrolyte with an initial mass I0, adding a specific type and mass of an extractant to the calibration cell, the total mass of the extractant is m, the electrolyte and the extractant are fully mixed to obtain a mixed solution, extracting the mixed solution and measuring the total mass fraction C of each component of the extractant, based on which the calibration mass I=m / Cm of the electrolyte is reversed, and by comparing the relationship between the calibration mass I of the electrolyte and the initial mass I0, the k components used as the extractant and the amount w of each component can be determined. j , where j = 1, 2 ... k, and the initial amount of the extractant m0 ​​= w1 + w2 ... w k ;

[0007] Injection step: injecting the extractant and the amount of each component determined by the calibration step into the battery cell after the working condition;

[0008] Mixing step: sealing and preserving the working condition battery cell injected with the extractant and then treating it to obtain a mixed solution, wherein the mixed solution includes all components of the electrolyte and the extractant;

[0009] Extraction step: taking out the mixed liquid in the battery cell after the working condition;

[0010] Component testing steps: Analyze the mixed solution and calculate the mass fraction C of each component of the electrolyte in the mixed solution. i , wherein i=1, 2, ... n, and the total mass fraction C0 of the components of the extractant in the mixed solution; and

[0011] Analysis step: Calculate the absolute mass m of each of the n components in the electrolyte of the battery cell after the working condition using the data obtained in the component testing step. i , where i = 1, 2, 3…n.

[0012] In one embodiment of the present invention, the solvent and additives in the electrolyte are completely dissolved in the extractant.

[0013] In one embodiment of the present invention, the solubility of the lithium salt in the electrolyte in the extractant is greater than or equal to 0.1 wt %.

[0014] In one embodiment of the present invention, the extractant includes one or a combination of at least two of nitriles, carboxylates, carbonates, ethers, tetrahydrofuran, amides, alkanes, halogenated alkanes, alcohols, ketones, benzene and its homologues or halides, and carbon disulfide, whose main chains contain more than 2 carbon atoms.

[0015] In one embodiment of the present invention, the extractant and the electrolyte do not chemically react during each step of the detection method.

[0016] In one embodiment of the present invention, the initial amount m0 ​​of the extractant is 10%-200% of the initial mass I0 of the electrolyte of the battery cell after the working condition.

[0017] In one embodiment of the present invention, after the battery cells after working condition are sealed and stored for 1 hour to 72 hours, the mixed liquid is extracted from the battery cells after working condition by centrifugation or squeezing the battery cells after working condition.

[0018] In one embodiment of the present invention, in the mixing step, after the extractant is added to the working condition battery cell and the battery cell is sealed and stored, the working condition battery cell is subjected to ultrasonic treatment for 5 minutes to 2 hours.

[0019] In one embodiment of the present invention, in the calibration step, when the relative deviation ω = |I-I0| / I0*100% between the inferred calibration mass I of the electrolyte and the initial mass I0 of the electrolyte is greater than 20%, the type and amount of the extractant and the processing conditions of the mixing step are adjusted, and calibration is performed again until ω is less than 20%.

[0020] In one embodiment of the present invention, the absolute mass M of the electrolyte of the battery cell after the working condition is obtained by the following formula:

[0021] M=m0 / C0-m0.

[0022] In one embodiment of the present invention, the mass m of any component in the electrolyte of the battery cell after the working condition is i Obtained by the following formula:

[0023] m i =C i ×m0 / C0.

[0024] In summary, the present invention proposes a method for detecting an electrolyte, which can reduce the influence of an extractant on the electrolyte, improve the accuracy of subsequent analysis, simplify the analysis method, improve analysis efficiency, and reduce the influence of the extractant factor on the test results. The detection materials provided by the present invention are easy to obtain, the operation method is simple, and the operating cost is reduced. At the same time, it can overcome the problem that the electrolyte in the battery cell is difficult to extract after a long period of charge and discharge cycle or storage test, and improve the accuracy and reliability of the analysis results. The absolute mass of each component in the electrolyte can be obtained, which can be used to study the changes in the absolute mass of each component before and after the battery cell working condition, so that the analysis of the changes in the electrolyte components before and after the battery cell working condition has more practical reference significance.

[0025] Of course, it is not necessary to achieve all the advantages mentioned above at the same time in any one of the modes of implementing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 Flowchart of a method for detecting electrolyte in one embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0029] It should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art. Unless otherwise specified, "%" and "parts" shown in the following examples refer to "mass %" and "mass parts" respectively.

[0030] The technical solutions of the present invention are further described in detail below with reference to specific embodiments and accompanying drawings. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0031] Secondary batteries have advantages such as high specific energy, no memory effect, and long cycle life, and have been gradually applied to multiple fields. Secondary batteries include a positive electrode, a negative electrode, an electrolyte, and a separator. The electrolyte is prepared from raw materials such as a high-purity organic solvent, a metal ion salt, and a small amount of additives. The metal ion salt is, for example, a lithium salt or a sodium salt, and is selected according to the type of secondary battery. After the battery undergoes processes such as formation, storage, or circulation, the electrolyte is continuously consumed, which directly affects the actual performance of the battery. Therefore, accurate analysis of the electrolyte composition and absolute mass after actual operating conditions in the battery has important guiding significance for battery cell design. The present invention provides a method for detecting electrolytes, which can accurately analyze the absolute mass of electrolyte components and has the advantages of simple operation, low analysis cost, high accuracy, and high safety. It can be widely used in the design process of different secondary batteries to improve the performance of secondary batteries.

[0032] See also Figure 1 As shown, the present invention provides a method for detecting an electrolyte, and the detection method at least includes steps S11-S16.

[0033] Step S11, calibration step: calibrate with a calibration cell that has not been subjected to the working condition and is completely consistent with the cell after the working condition before the working condition, so as to determine the type, amount and mixing ratio of the extractant.

[0034] Step S12, injection step: injecting the extractant and the amount of each component determined by the calibration step into the battery cell after the working condition.

[0035] Step S13, mixing step: the battery cell after injection of the extractant is sealed and stored, and then processed to obtain a mixed solution, which includes all components of the electrolyte and the extractant.

[0036] Step S14, extraction step: taking out the mixed liquid in the battery cell after the working condition.

[0037] Step S15, component testing step: Analyze the mixed solution and calculate the mass fraction C of each component of the electrolyte in the mixed solution. i And the total mass fraction C0 of each component of the extractant in the mixed solution.

[0038] Step S16, analysis step: calculate the absolute mass m of each of the n components in the electrolyte of the battery cell after the working condition through the data obtained in the component testing step i .

[0039] See also Figure 1As shown, in one embodiment of the present invention, in step S11, before the absolute mass of the electrolyte components is analyzed and tested, the extractant needs to be calibrated to determine the type, amount, and mixing ratio of the extractant due to different injection volumes, different electrode coil liquid retention capabilities, and different electrolyte systems in different battery systems. Specifically, a cell that is completely consistent with the cell before the working condition and has not been subjected to the working condition is selected as the calibration cell. The calibration cell is, for example, a newly assembled cell that has not been subjected to the working condition. The initial mass of the electrolyte in the calibration cell is known to be I0. The calibration cell has not been subjected to the working condition, which is equivalent to the electrolyte not being consumed. Then, an extractant of a specific type and mass is added to the calibration cell and sealed for storage. The initial mass of the extractant in the calibration cell is m. The extractant is injected, for example, by puncturing the cell air bag with a syringe, or by puncturing the edge of the cell, and then the injection port is sealed by reheating the aluminum-plastic film, applying sealing tape or AB glue, etc. In other embodiments, other methods may be used for injecting and sealing the extractant to reduce the exposure time of the interior of the battery cell.

[0040] See also Figure 1 As shown, in one embodiment of the present invention, in step S11, after the extractant is injected into the calibration cell, the sealed storage time is, for example, 1h-72h to ensure that the extractant and the electrolyte are fully mixed to obtain a mixed solution, and then the mixed solution is taken out by centrifugation or pressure extrusion. Among them, the centrifugation process of the cell is specifically to take out the cell pole roll or diaphragm-pole sheet assembly in an inert atmosphere and quickly put it into a sealed centrifuge tube, and centrifuge it at a speed of, for example, less than 10000rpm to obtain a mixed solution. Pressurized extrusion refers to squeezing the cell with a force of, for example, less than 500kN under a clamp of appropriate size to obtain a mixed solution. The mass fractions of the solvent and additives in the mixed solution are determined by gas chromatography (GC), and the mass fraction of the metal ion salts are determined by ion chromatography (IC) to obtain the mass fractions of each component in the mixed solution. Among them, the total mass fraction of the components of the extractant in the mixed solution is C, and the calibrated mass I of the electrolyte is inferred by the formula I=m / Cm. The relative deviation ω between the calibrated mass I of the electrolyte and the initial mass I0 of the electrolyte is calculated as |I-I0| / I0*100%. When the relative deviation ω is greater than 20%, the type and amount of the extractant and the processing conditions of the mixing step are adjusted, and calibration is performed again until ω is less than 20%. Through calibration, the k components of the extractant and the amount of each component w can be determined. j , where j = 1, 2...k, and the initial amount of extractant m0 ​​= w1 + w2...w kThe initial amount of extractant, m0, is 10%-200% of the initial mass of the electrolyte, I0. During calibration, the test mass of other components in the electrolyte can be measured using other components, ensuring the deviation between the measured mass and the actual added mass does not exceed ±20%, thereby improving the accuracy of subsequent testing and analysis.

[0041] In one embodiment of the present invention, the extractant includes, for example, one or a combination of at least two of nitriles, carboxylates, carbonates, ethers, tetrahydrofuran, amides, alkanes, alkyl halides, alcohols, ketones, benzene, its homologues or halides, and carbon disulfide, with a main chain carbon number greater than 2. The solvent and additives in the electrolyte are completely soluble in the extractant. For example, the lithium salt in the electrolyte for a lithium-ion battery is one or a combination of at least two of LiPF6, LiFSI, LiTFSI, LiODFP, LiODFB, LiBF4, LiBOB, or LiSO3F, and the solubility of the lithium salt in a single extractant or a combination of multiple solvents is greater than or equal to 0.1 wt%. In this embodiment, the selected extractant does not chemically react with the components of the electrolyte during each step of the detection method, nor does it react with the positive and negative electrodes of the battery cell, thereby reducing the extractant's impact on the electrolyte and improving the accuracy of the detection method.

[0042] See also Figure 1 As shown, in one embodiment of the present invention, in step S12, the battery cell after the working condition is provided as the battery cell to be tested, and the battery cell after the working condition is completely consistent with the calibration battery cell before the working condition, and the battery cell after the working condition is, for example, a battery cell after formation, storage or circulation. According to the type, amount and mixing ratio of the extractant determined in step S11, an initial amount of extractant m0 ​​is injected into the battery cell after the working condition. The extractant is, for example, a single solvent or a combination of solvents, and the initial amount of the extractant m0 ​​is, for example, 10%-200% of the initial mass of the electrolyte of the battery cell after the working condition.

[0043] See also Figure 1 As shown, in one embodiment of the present invention, in step S12-step S13, after the extractant is injected, the post-working condition battery cell is sealed and stored, and then processed to obtain a mixed liquid. In this embodiment, the method of injecting the extractant into the post-working condition battery cell and sealing the post-working condition battery cell is the same as the injection and sealing method of the extractant of the calibration battery cell, and will not be elaborated here. After the post-working condition battery cell is sealed, it is sealed and stored for 1h-72h. In one embodiment of the present invention, after the post-working condition battery cell is sealed and stored, the post-working condition battery cell can be ultrasonically treated, and the time of ultrasonic treatment is, for example, 5min-2h, so as to shorten the time for the extractant and the electrolyte to be fully mixed and improve the analysis efficiency.

[0044] See also Figure 1As shown, in one embodiment of the present invention, in step S14, after the extractant and the electrolyte of the post-operation battery cell are evenly mixed, the mixed liquid in the post-operation battery cell is removed. In this embodiment, the mixed liquid is removed by, for example, centrifugation or pressurized extrusion. The removal method is the same as the removal method of the mixed liquid in the calibration battery cell described above, and will not be elaborated here.

[0045] See also Figure 1 As shown, in one embodiment of the present invention, in step S15, after the mixed liquid is taken out, the mass of the mixed liquid is weighed and recorded as M0, the mass fractions of the solvent and additives in the mixed liquid are determined by gas chromatography, and the content of metal ion salts is determined by ion chromatography to obtain the mass fractions of each component in the mixed liquid. In this application, the total mass fraction of each component of the extractant in the mixed liquid of the battery cell after the working condition is measured as C0, and the mass fraction of each component of the electrolyte in the mixed liquid is C i , i represents the number of components in the electrolyte, i = 1, 2, ... n.

[0046] See also Figure 1 As shown, in one embodiment of the present invention, in step S16, after obtaining the mass of the mixed liquid extracted from the battery cell after the working condition, and the mass fraction of each component in the mixed liquid, the absolute mass of the electrolyte of the battery cell after the working condition, and the absolute mass of each component in the electrolyte are obtained by calculation. In this embodiment, the absolute mass of the electrolyte is obtained by formula (I), formula (I): M=m0 / C0-m0; wherein, M is the absolute mass of the electrolyte in the battery cell after the working condition, m0 is the initial amount of the extractant, and C0 is the total mass fraction C0 of each component of the extractant. The absolute mass of each of the n components in the electrolyte is obtained by formula (II), formula (II): m i =C i ×m0 / C0, where C i is the mass fraction of any component in the electrolyte in the mixed solution, m i is the absolute mass of any component in the electrolyte. The absolute mass of each component in the electrolyte can be obtained by calculating the mass fraction of each component in the mixed solution, the initial mass of the extractant, and the mass fraction of the extractant in the mixed solution. Since the extractant does not react in the electrolyte and the total mass of the extractant in the mixed solution remains unchanged, the absolute mass of the remaining electrolyte in the cell after the operating condition can be derived based on the total mass fraction of the extractant. Simultaneously, the absolute mass of each component in the electrolyte can be calculated using a simple formula. This can be used to study the changes in the absolute mass of each component before and after the cell operating condition, making the analysis of changes in electrolyte composition before and after the cell operating condition more practical.

[0047] See also Figure 1As shown, in the present application, the absolute mass of each component in the electrolyte can be obtained only by the extractant and the mass fraction of each component after uniform mixing, which simplifies the detection method. Before the analysis and test, calibration is performed first to reduce the influence of the extractant factor on the test results. And the absolute mass of each component in the electrolyte is obtained through simple digital calculation. The materials of the detection method provided by the present invention are easy to obtain, the operation method is simple, and the operating cost is reduced. At the same time, it can overcome the problem that the electrolyte in the battery cell is difficult to extract after a long period of charge and discharge cycle or storage test, improve the detection efficiency, and improve the accuracy and reliability of the analysis results.

[0048] For further understanding the detection method provided by the present invention, citing specific embodiment will explain the present invention in more detail, these embodiments should not be construed as restrictive. In the scope consistent with the gist of the present invention, can make appropriate modifications, it all falls within the technical scope of the present invention.

[0049] Comparative Example

[0050] As an example of the prior art, a 1Ah lithium iron phosphate (LFP)-graphite soft-pack battery cell that was charged to 100% and stored at 60°C for 60 days was used as the battery to be tested. The initial mass of the electrolyte was 3.0g, and the electrolyte included ethylene carbonate (EC), ethyl methyl carbonate (EMC), LiPF6, and vinylene carbonate (VC). The mass fraction of EC was 25wt%, the mass fraction of EMC was 60wt%, the mass fraction of LiPF6 was 12wt%, and the mass fraction of VC was 3wt%. That is, the mass of EC in the electrolyte was 0.75g, the mass of EMC was 1.8g, the mass of LiPF6 was 0.36g, and the mass of VC was 0.09g.

[0051] A syringe was used to poke a hole in the edge of the soft-pack cell. 10g of anhydrous acetonitrile was added and the hole was sealed. After standing for 24 hours, the liquid was opened and removed for testing. After centrifugation, 12.1g of the mixture was collected. Gas chromatography and ion chromatography analyzed the composition of the mixture, revealing 4.38wt% EC, 13.73wt% EMC, 1.23wt% LiPF6, 0% VC, and 80.66wt% anhydrous acetonitrile.

[0052] Based on the initial injection amount of anhydrous acetonitrile being 10 g and the total mass fraction of anhydrous acetonitrile in the mixed solution being 80.66%, it can be inferred that the residual mass of the electrolyte in the battery cell after storage is 2.34 g. The mass of each component of the electrolyte in the battery cell after the working condition can be calculated to be 0.53 g of EC, 1.66 g of EMC, 0.15 g of LiPF6 and 0 g of VC.

[0053] The amount of electrolyte inferred through this analysis process deviates by more than 20% from the actual electrolyte injection volume. Furthermore, the mass deviations of LiPF6 and VC, in particular, are significantly larger than the actual content, making the quality reliability of the test method poor. The reason for this poor reliability is that the amount of extractant added is excessive, and the mixing step is uneven, resulting in the electrolyte components not being evenly incorporated into the mixed solution. Furthermore, the lithium salt has a low solubility and is not well dissolved, while the additive content is too low, making its concentration in a larger amount of the mixed solution insignificant, falling below the instrument's detection limit, resulting in it not being correctly detected.

[0054] The following describes an example of analyzing an electrolyte using the detection method proposed in this application.

[0055] Example

[0056] First, the calibration steps are described.

[0057] A 1Ah LFP-graphite soft-pack dry cell (a dry cell is a cell without electrolyte) was injected with 3.0g of electrolyte, which was used as a calibration cell. The electrolyte consisted of EC, EMC, LiPF6, and VC. The mass fraction of EC was 25wt%, the mass fraction of EMC was 60wt%, the mass fraction of LiPF6 was 12wt%, and the mass fraction of VC was 3wt%.

[0058] Use a syringe to poke a hole on the edge of the calibration cell, slowly add 2.0g of a mixture of acetonitrile and ethyl acetate, with a mass ratio of acetonitrile to ethyl acetate of 1:1, and then seal the hole. After standing at room temperature for 12 hours, perform ultrasonic treatment for half an hour, and then stand and store for 24 hours to mix the inside. The soft-pack cell is then opened, and 4.2g of the mixture is collected by centrifugation. The composition of the mixture is tested by gas chromatography and ion chromatography, and the composition of the mixture is as follows: 20.3wt% acetonitrile, 19.7wt% ethyl acetate, 15.2wt% EC, 36.4wt% EMC, 6.3wt% LiPF6 and 2.1wt% VC.

[0059] Based on the initial injection mass of 2.0 g of ethyl acetate and acetonitrile and their combined mass fraction in the mixed solution (40 wt%), we can infer that the mass of the original electrolyte is 2.0 ÷ 40% - 2.0 = 3.0 g, and that the content of each electrolyte component, excluding the two extractants, should be 3 / 5 of its content in the mixed solution. Therefore, the components and their contents in the electrolyte can be calculated to be 25.3 wt% EC, 60.6 wt% EMC, 10.5 wt% LiPF6, and 3.5 wt% VC. By multiplying the inferred total electrolyte volume by the respective content of each component, the absolute masses of each component are calculated to be 0.759 g EC, 1.818 g EMC, 0.315 g LiPF6, and 0.105 g VC, respectively.

[0060] Furthermore, the amount of electrolyte inferred from this analysis process is between 80% and 120% of the initial mass of the electrolyte. Furthermore, the measured mass of each component in the electrolyte obtained during the measurement process deviates from the actual added mass by no more than 20%. Therefore, the composition, addition amount, and mixing steps of the extractant can be used to measure the absolute values ​​of each component in the electrolyte of the battery system.

[0061] The following describes the testing and analysis steps.

[0062] A 1Ah LFP-graphite system soft-pack battery cell charged to 100% and stored at 60°C for 60 days was used as the battery to be tested. The initial mass of the electrolyte was 3.0g. The electrolyte included EC, EMC, LiPF6 and VC, and the mass fraction of EC was 25wt%, the mass fraction of EMC was 60wt%, the mass fraction of LiPF6 was 12wt%, and the mass fraction of VC was 3wt%.

[0063] Use a syringe to poke a hole on the edge of the soft-pack battery cell, slowly add 2.0g of a mixture of acetonitrile and ethyl acetate, with a mass ratio of acetonitrile to ethyl acetate of 1:1, and then seal the hole. After standing at room temperature for 12 hours, ultrasonically treat for half an hour, and then stand for 24 hours. After storage and mixing, open the soft pack, collect 2.7g of the mixed solution after centrifugation, and test the composition of the mixed solution by gas chromatography and ion chromatography. The result shows that the mixed solution includes: 23.2wt% acetonitrile, 23.1wt% ethyl acetate, 12.2wt% EC, 34.8wt% EMC, 6.5wt% LiPF6 and 0.2wt% VC.

[0064] Based on the initial mass of ethyl acetate and acetonitrile injected being 2.0 g, and the total mass fraction of ethyl acetate and acetonitrile in the mixture being 46.3 wt %, it can be inferred that the residual mass of the electrolyte in the battery cell after storage is 2.32 g. The converted mass of each component of the electrolyte is 0.53 g of EC, 1.5 g of EMC, 0.28 g of LiPF6, and 0.01 g of VC.

[0065] In summary, the present invention proposes a method for detecting an electrolyte, by selecting an extractant that does not react with the various components in the electrolyte, nor with the positive and negative electrodes of the battery cell, so as to reduce the influence of the extractant on the electrolyte, improve the accuracy of subsequent analysis, and simplify the detection method. By ultrasonically treating the battery cell after the extractant is injected and sealed, the time for the extractant and the electrolyte to be fully mixed is shortened, thereby improving the analysis efficiency. By first calibrating, the influence of the extractant factor on the test results is reduced. The detection method provided by the present invention has easy-to-obtain materials, a simple operation method, and reduces operating costs. At the same time, it can overcome the problem of difficulty in extracting the electrolyte in the battery cell after the battery cell has undergone long-term charge and discharge cycles or storage tests, and improve the accuracy and reliability of the analysis results. The absolute mass of each component in the electrolyte can be obtained, which can be used to study the changes in the absolute mass of each component before and after the battery cell working condition, making the analysis of the changes in the electrolyte composition before and after the battery cell working condition more practical reference significance.

[0066] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by replacing the above features with (but not limited to) technical features with similar functions disclosed in this application. In addition to the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be repeated here.

Claims

1. A method for detecting an electrolyte, for detecting the absolute mass of each component in the electrolyte of a battery cell after operation, characterized in that: At least include: Calibration step: using a cell that is completely consistent with the cell before the working condition and has not been subjected to the working condition as a calibration cell, the calibration cell has an electrolyte with an initial mass I0, adding a specific type and mass of an extractant to the calibration cell, the total mass of the extractant is m, the electrolyte and the extractant are fully mixed to obtain a mixed solution, the mixed solution is extracted and the total mass fraction C of each component of the extractant is measured, and the calibration mass I=m / Cm of the electrolyte is reversely deduced based on this, and by comparing the relationship between the calibration mass I of the electrolyte and the initial mass I0, the k components used as the extractant and the amount w of each component can be determined. j , where j = 1, 2...k, and the initial amount of the extractant m0 ​​= w1 + w2...w k When the relative deviation ω=|I-I0| / I0*100% between the inferred calibrated mass I of the electrolyte and the initial mass I0 of the electrolyte is greater than 20%, the type and amount of the extractant and the treatment conditions of the mixing step are adjusted, and calibration is performed again until ω is less than 20%; Injection step: injecting the extractant and the amount of each component determined by the calibration step into the battery cell after the working condition; Mixing step: sealing and preserving the working condition battery cell injected with the extractant and then treating it to obtain a mixed solution, wherein the mixed solution includes all components of the electrolyte and the extractant; Extraction step: taking out the mixed liquid in the battery cell after the working condition; Component testing steps: Analyze the mixed solution and calculate the mass fraction C of each component of the electrolyte in the mixed solution. i , wherein i=1, 2, ... n, and the total mass fraction C0 of the components of the extractant in the mixed solution; and Analysis step: Calculate the absolute mass m of each of the n components in the electrolyte of the battery cell after the working condition using the data obtained in the component testing step. i , where i=1, 2, 3…n.

2. The method for detecting an electrolyte according to claim 1, wherein: The solvent and additives in the electrolyte are completely dissolved in the extractant.

3. The method for detecting an electrolyte according to claim 1 or 2, wherein: The solubility of the lithium salt in the electrolyte in the extractant is greater than or equal to 0.1 wt %.

4. The method for detecting an electrolyte according to claim 2, wherein: The extractant includes tetrahydrofuran, benzene and its homologues or halides, carbon disulfide, and one or a combination of at least two of nitriles, carboxylates, carbonates, ethers, amides, alkanes, halogenated alkanes, alcohols or ketones whose main chains contain more than 2 carbon atoms.

5. The method for detecting an electrolyte according to claim 4, wherein: The extractant and the electrolyte do not chemically react in each step of the detection method.

6. The method for detecting an electrolyte according to claim 1, wherein: The initial amount m0 ​​of the extractant is 10%-200% of the initial mass I0 of the electrolyte of the battery cell after the working condition.

7. The method for detecting an electrolyte according to claim 1, wherein: After the battery cell after working condition is sealed and stored for 1 hour to 72 hours, the mixed liquid is extracted from the battery cell after working condition by centrifugation or squeezing the battery cell after working condition.

8. The method for detecting an electrolyte according to claim 1, wherein: In the mixing step, after the extractant is added to the working condition battery cell and the battery cell is sealed and stored, the working condition battery cell is subjected to ultrasonic treatment for 5 minutes to 2 hours.

9. The method for detecting an electrolyte according to claim 1, wherein: The absolute mass M of the electrolyte of the battery cell after the working condition is obtained by the following formula: M=m0 / C0-m0.

10. The method for detecting an electrolyte according to claim 1, wherein: The mass mi of any component in the electrolyte of the battery cell after the working condition is obtained by the following formula: m i =C i ×m0 / C0。

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