Quantitative analysis method for electrolyte solvent component content variation, electrolyte and application

Abstract

The invention provides an electrolyte solvent component content variation quantitative analysis method, an electrolyte and application, and relates to the technical field of battery preparation. The quantitative analysis method for the electrolyte solvent component content variation comprises the following steps: providing an electrolyte, adding a benchmarking substance into the electrolyte, uniformly mixing and stirring to obtain a standby electrolyte, measuring the solvent component content of the standby electrolyte and the benchmarking substance content, recording as a first detection value, and preparing a battery by using the standby electrolyte; discharging the battery after the battery is tested; taking a to-be-detected electrolyte and obtaining the to-be-detected electrolyte at the dew point temperature of less than or equal to-34 DEG C; detecting each solvent component of the electrolyte to be detected and the content of the benchmarking substance, and recording the content as a second detection value; performing conversion processing on the second detection value according to a formula 1, and recording a converted value as a converted value; and calculating the content change value of each solvent component according to a formula 2. According to the method, the electrolyte solvent component content variation in the battery testing process can be quantitatively analyzed.

Description

Technical Field

[0001] The invention relates to the technical field of battery preparation, and in particular to a quantitative analysis method for changes in the content of electrolyte solvent components, an electrolyte and applications. Background Art

[0002] Currently, lithium-ion batteries are widely used in various consumer electronic products, including mobile phones, laptops and power tools, due to their high energy, power density, fast charging capability and long cycle life. They are also used in electric vehicles, grid energy storage markets, and aerospace and marine applications. Lithium-ion batteries include positive electrodes, negative electrodes, separators and electrolytes, among which the electrolyte plays a decisive role in the performance of lithium-ion batteries. However, during use, the electrolyte will be consumed or decomposed to form various types of decomposition products, resulting in changes in the content of electrolyte solvent components, and the content of solvent components will affect the service life of the battery and safety during use. Therefore, it is necessary to understand the change in the content of electrolyte solvent components after charging and discharging.

[0003] However, the existing detection method of the content of electrolyte solvent components is a method for analyzing electrolyte testing by gas chromatography-mass spectrometry (GC-MS). Its principle is that after a multi-component mixed sample enters a chromatographic column, the difference in the distribution coefficient or adsorption coefficient of each component in the mobile phase and the stationary phase is separated from each other in the chromatographic column. Each gaseous molecule separated by gas chromatography is bombarded by an ion source, electrolytically decomposed into ions, and separated according to the m / z size under the combined action of an electric field and a magnetic field, and detected, recorded and sorted by a detector to obtain a mass spectrum, and to achieve qualitative and quantitative analysis of samples. Therefore, this test method can only test the content of electrolyte components, but cannot measure the variation of the electrolyte solvent component content in the battery. Therefore, how to quantitatively analyze the variation of the electrolyte solvent component content becomes a technical problem that those skilled in the art need to solve urgently. Summary of the invention

[0004] 1. Technical issues to be solved

[0005] In view of the deficiencies in the prior art, the present invention provides a method for quantitatively analyzing the change in the content of a solvent component in an electrolyte, an electrolyte and applications, and solves the technical problem of how to quantitatively analyze the change in the content of a solvent component in an electrolyte.

[0006] (II) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] In one aspect, the present invention provides a method for quantitatively analyzing the change in the content of electrolyte solvent components, comprising the following steps:

[0009] S1. providing an electrolyte, adding a reference substance to the electrolyte, mixing and stirring to obtain a standby electrolyte, measuring the contents of each solvent component and the reference substance in the standby electrolyte, recording them as first detection values, and preparing a battery using the standby electrolyte;

[0010] S2, testing the battery and then performing a discharge process;

[0011] S3, taking out the electrolyte inside and outside the battery roll core as the electrolyte to be tested;

[0012] S4, detecting the content values ​​of each solvent component and the reference substance of the electrolyte to be tested, and recording them as the second detection value;

[0013] S5, converting the second detection value according to formula 1, and recording the converted value as the converted value,

[0014]

[0015] S6. Calculate the change value of each solvent component content

[0016] According to formula 2, the change value of each solvent component content is calculated.

[0017] The change value of each solvent component content = (the converted value of each solvent component content - the first detected value of each solvent component content) × 100% - Formula 2.

[0018] The above-mentioned quantitative analysis method adopts the existing GC-MS test method for the content of electrolyte solvent components. By adding a reference substance to the electrolyte and then converting it, the change in the content of the electrolyte solvent component during the battery test is calculated, thereby quantitatively analyzing the change in the content of each solvent component of the electrolyte during the battery test, providing a decision-making basis for the electrolyte formulation research.

[0019] Preferably, the reference substance is compound 1, and the compound 1 is shown in structural formula 1:

[0020]

[0021] And / or, the quantitative analysis method further comprises an extraction process, wherein after S2, at a dew point temperature of ≤-34°C, an extractant of 0.8-1.2 times the mass of the electrolyte is added to the battery after the discharge process, the battery is sealed, and placed at a dew point temperature of ≤-34°C for 24-48 hours; after the extraction process, S3 is performed to obtain the electrolyte to be tested;

[0022] And / or, the S3, taking the electrolyte to be tested includes taking out the electrolyte outside the battery core under the condition of dew point temperature ≤ -34°C, recorded as the first electrolyte to be tested, and then taking out the electrolyte inside the core, recorded as the second electrolyte to be tested, and mixing the first electrolyte to be tested with the second electrolyte to be tested to obtain the electrolyte to be tested.

[0023] After the above extraction treatment, the electrolyte absorbed by the electrode sheet can be extracted from the electrode sheet, thereby reducing the test error of the electrolyte solvent content caused by the electrode sheet absorbing the electrolyte.

[0024] Preferably, the added amount of the compound 1 accounts for 1%-5% of the mass of the electrolyte.

[0025] The amount of compound 1 added is controlled within an appropriate range. If the added amount is less than 1%, the calibration material content will be too small, resulting in a large error in the result; if the added amount is greater than 5%, the battery performance may be affected.

[0026] Preferably, said routine testing comprises cycling and / or storage.

[0027] Carry out routine cycle and storage tests to simulate the consumption of each component in the normal electrical performance test of the battery cell.

[0028] Preferably, the cycle test condition is 0.5-1C cycle, the voltage range is 2.0-3.65V, the cycle test temperature range is 25-55°C, and the storage test time is ≤28 days.

[0029] Preferably, the battery is selected from a square or cylindrical lithium-ion battery or a soft-pack lithium-ion battery, and the positive electrode active material of the battery is lithium iron phosphate, and the voltage range of lithium iron phosphate is 2.0-3.65V. If the voltage is too high, the internal standard may partially participate in the battery reaction. The preset current of the battery is 0.5-1C, and the preset cut-off voltage is 2.0V. If the cut-off voltage is lower than 2.0V, it may cause over-discharge and the battery performance will decrease.

[0030] Preferably, the method for obtaining the second electrolyte to be tested includes centrifuging the core in a centrifugal manner, collecting the centrifuged liquid to obtain the second electrolyte to be tested.

[0031] The core is centrifuged and the centrifuge liquid is collected. Centrifugation can fully remove the electrolyte inside the core, making the calibration of the internal standard more accurate. Other methods may result in the failure to completely remove the internal electrolyte, resulting in errors in the test results.

[0032] Preferably, the centrifugal speed is 2500r / min-7500r / min.

[0033] Control the centrifugal speed within an appropriate range. If the speed is too low, the electrolyte will not be completely removed. If the speed is too high, the active substances in the core may come out together, affecting the test accuracy.

[0034] On the other hand, the present invention also provides an electrolyte, wherein the electrolyte components include compound 1.

[0035] The electrolyte components include compound 1, which does not participate in the battery reaction within the operating voltage range of the iron-lithium battery, and its content in the electrolyte does not change after the battery test, so that the change in the content of the electrolyte component can be quantitatively analyzed.

[0036] On the other hand, the present invention also provides an application of compound 1 in quantitatively analyzing the change in the content of a solvent component in an electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 paying creative work.

[0038] Figure 1 This is a flow chart of a method for extracting an electrolyte to be tested according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0041] Example

[0042] This embodiment provides a method for quantitatively analyzing the change in the content of a solvent component in an electrolyte, comprising the following steps:

[0043] S1. Preparation of batteries

[0044] In a glove box filled with argon, compound 1 accounting for 3% of the mass of the electrolyte was added to a conventional lithium-ion battery electrolyte, and the mixture was stirred evenly to obtain a standby electrolyte. The GC-MS detection method was used to detect the contents of each solvent component and compound 1 in the standby electrolyte, which was recorded as the first detection value, as shown in Table 1. The standby electrolyte was injected into a soft-pack battery with a rated capacity of 3Ah (5g / Ah injection coefficient), and then a conventional chemical composition process was performed.

[0045] S2, perform routine testing, and perform discharge treatment after the test is completed;

[0046] The prepared lithium-ion battery was cycled for 400 cycles at 45°C to complete the cycle experiment;

[0047] The cycled lithium-ion battery is discharged at a current of 3A to 2.0V to complete the discharge process.

[0048] S3. Extraction treatment

[0049] Under the protection of argon gas, cut a small hole above the discharged battery, add chloroform with a mass 1.0 times the mass of the electrolyte, seal it, and place it at a dew point temperature ≤-34℃ for 24 hours to ensure that the electrolyte absorbed by the electrode sheet is completely extracted from the electrode sheet.

[0050] S4. Obtain the electrolyte to be tested

[0051] like Figure 1 , cut open the lithium-ion battery after extraction under the protection of argon gas, take out the electrolyte in the soft-pack battery with a syringe, record it as the first electrolyte to be tested, and take out the core and place it in a centrifuge tube, centrifuge it at 5000r / min for 5min, collect the electrolyte centrifuged from the core, record it as the second electrolyte to be tested, and mix the first electrolyte to be tested with the second electrolyte to be tested, which is the electrolyte to be tested.

[0052] S5. Detecting the content of each solvent component and compound 1 in the electrolyte to be tested

[0053] After testing, the content values ​​of each solvent component and compound 1 of the electrolyte to be tested are obtained, which are recorded as the second test value, as shown in Table 1 for details.

[0054] S6. Convert the second detection value according to Formula 1, and record the converted value as the converted value.

[0055]

[0056] S7. Calculate the change value of each solvent component content

[0057] The change value of each solvent component content is calculated according to Formula 2, so as to quantitatively analyze the change amount of the solvent component content of the electrolyte during the battery test, and provide a decision-making basis for the electrolyte formulation research.

[0058] Change value of each solvent component content = (converted value of each solvent component content - first detected value of each solvent component content) × 100%

[0059] ——Formula 2.

[0060] Table 1: Content and change of electrolyte solvent components in Example 1

[0061]

[0062] Comparative Example

[0063] The difference between this comparative example and the example is that in S1, compound 1 is not added to the conventional lithium-ion battery electrolyte; S4 is not included. Others are the same as in the example. The first test value and the second test value are shown in Table 2.

[0064] Table 2 Solvent component content in the electrolyte in the comparative example

[0065] Solvent Name The first detection value The second detection value EC 23.73％ 22.28％ PC 4.75％ - EMC 28.48％ 31.67％ DMC 37.97％ 46.05％ FEC 3.38％ - VC 1.69％ -

[0066] As can be seen from Table 2, in the first test value column, the sum of the contents of the six solvents EC, PC, EMC, DMC, FEC, and VC is 100%. After the battery is tested, only three solvents EC, EMC, and DMC can be detected in the electrolyte. From the second test value column, the sum of the second test values ​​of the three solvents EC, EMC, and DMC is still 100%, which shows that the content of the analyte measured by the existing electrolyte solvent component content detection method is essentially the relative content of each analyte. If the component of the analyte changes, the relative content of the analyte will also change. Therefore, the second test value of the three solvents EC, EMC, and DMC in the comparative example minus the first test value of the three solvents EC, EMC, and DMC does not get the change in the three solvents EC, EMC, and DMC. Therefore, the existing test method can only test the content of the electrolyte components, but cannot measure the change in the content of the electrolyte solvent components in the battery.

[0067] It can be seen from Table 2 that in the second detection value column, there are only detection values ​​of three solvents: EC, EMC, and DMC. This is because there is no step S4, and the amount of electrolyte to be tested is small, resulting in the PC, FEC, and VC solvent contents being lower than the detection limit of the existing electrolyte solvent component content detection method, and therefore cannot be detected.

[0068] Compared with the prior art, the quantitative analysis method of the change in the content of electrolyte solvent components of the present invention can safely and effectively extract the tested lithium-ion battery electrolyte, and accurately and quantitatively analyze the change in the content of solvent components in the electrolyte, which is helpful for studying the failure mechanism of lithium-ion batteries and has great research significance.

[0069] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention is described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Anything not described in detail in the present invention is a well-known technology to those skilled in the art.

Claims

1. A method for quantitatively analyzing the change in the content of electrolyte solvent components, characterized in that: The steps include: S1. providing an electrolyte, adding a reference substance to the electrolyte, mixing and stirring to obtain a standby electrolyte, measuring the contents of each solvent component and the reference substance in the standby electrolyte, recording them as first detection values, and preparing a battery using the standby electrolyte; S2, testing the battery and then performing a discharge process; S3, taking out the electrolyte inside and outside the battery roll core as the electrolyte to be tested; S4, detecting the content values ​​of each solvent component and the reference substance of the electrolyte to be tested, and recording them as the second detection value; S5, converting the second detection value according to formula 1, and recording the converted value as the converted value, S6. Calculate the change value of each solvent component content According to formula 2, the change value of each solvent component content is calculated. The change value of each solvent component content = (the converted value of each solvent component content - the first detected value of each solvent component content) × 100% - Formula 2.

2. The quantitative analysis method according to claim 1, characterized in that The reference substance is compound 1, and the compound 1 is shown in structural formula 1: And / or, the quantitative analysis method further comprises an extraction process, wherein after S2, at a dew point temperature of ≤-34°C, an extractant of 0.8-1.2 times the mass of the electrolyte is added to the battery after the discharge process, the battery is sealed, and placed at a dew point temperature of ≤-34°C for 24-48 hours; after the extraction process, S3 is performed to obtain the electrolyte to be tested; And / or, the S3, taking the electrolyte to be tested includes taking out the electrolyte outside the battery core under the condition of dew point temperature ≤ -34°C, recorded as the first electrolyte to be tested, and then taking out the electrolyte inside the core, recorded as the second electrolyte to be tested, and mixing the first electrolyte to be tested with the second electrolyte to be tested to obtain the electrolyte to be tested.

3. The quantitative analysis method according to claim 2, characterized in that: The added amount of the compound 1 accounts for 1%-5% of the mass of the electrolyte.

4. The quantitative analysis method according to claim 1, characterized in that The testing may include cycling and / or storage.

5. The quantitative analysis method according to claim 4, characterized in that: The cycle test conditions are 0.5-1C cycle, the voltage range is 2.0-3.65V, the cycle test temperature range is 25-55°C, and the storage test time is ≤28 days.

6. The quantitative analysis method according to claim 1, characterized in that: The battery is selected from a cylindrical lithium-ion battery or a soft-pack lithium-ion battery, the positive electrode active material of the battery is lithium iron phosphate, the preset current of the battery is 0.5-1C, and the preset cut-off voltage is 2.0V.

7. The quantitative analysis method according to claim 2, characterized in that: The method for obtaining the second electrolyte to be tested includes centrifuging the core and collecting the centrifuged liquid to obtain the second electrolyte to be tested.

8. The quantitative analysis method according to claim 7, characterized in that: The centrifugal speed is 2500r / min-7500r / min.

9. An electrolyte, characterized in that: The electrolyte components include the compound 1 described in any one of claims 2-8.

10. Use of the compound 1 according to any one of claims 2 to 8 for quantitatively analyzing the change in the content of a solvent component in an electrolyte.

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