Method for analyzing residual electrolyte of failed lithium battery

Abstract

The invention relates to the technical field of lithium battery detection, in particular to a method for analyzing residual electrolyte of a failed lithium battery. The method comprises the following steps: after a failed cell is discharged, opening a shell, injecting an extracting agent, sealing, and standing; after standing, carrying out solid-liquid separation on a mixed system in the shell to obtain a roll core and a mixed solution; weighing the roll core, and recording the weight as G1; the roll core is weighed after being dried, and the weight is recorded as G1; weighing the mixed solution, and recording the weight as G2; distilling the mixed solution to remove the extracting agent to obtain an electrolyte, weighing the electrolyte, and recording the weight as G2; and analyzing the total amount of the residual electrolyte: calculating the total amount of the residual electrolyte according to the formula G = G2 + (G1-G1) * G2 / G2. The invention provides a new thought for analyzing the total amount of the residual electrolyte, the total amount of the residual electrolyte comprises the electrolyte amount in the directly separated mixed solution and the electrolyte amount in the mixed solution adsorbed by the roll core, and calculation of the total amount of the residual electrolyte is complete and accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery detection, and in particular to a method for analyzing residual electrolyte in a failed lithium battery. Background Art

[0002] Lithium-ion batteries may fail with a certain probability during use or storage, including increased polarization, damage to positive and negative electrode materials, electrolyte consumption, lithium precipitation, loss of intercalated and deintercalated lithium, etc., which seriously affect the performance, consistency, reliability and safety of lithium-ion batteries. Accurately diagnosing lithium-ion battery failures and quickly finding the main factors causing failures have far-reaching significance for the performance improvement and technological development of lithium-ion batteries.

[0003] When doing failure analysis of the electrolyte plate, it is necessary to analyze the total amount of residual electrolyte, as well as the components of the residual electrolyte and the proportion of each component. The total amount of residual electrolyte is worthy of attention during failure analysis: free electrolyte refers to the electrolyte part of the battery that is not completely bound by the diaphragm or other structures and can move freely inside the battery. It has high fluidity and can freely transmit ions inside the battery. It is a key component for the normal operation of the battery. Residual electrolyte is the free electrolyte remaining in the battery after the battery is lost due to chemical reactions, evaporation, leakage, etc. during use or storage. By understanding the total amount of residual electrolyte, the amount of free electrolyte loss can be understood, thereby analyzing the cause of battery failure. The components of the residual electrolyte and the proportion of each component are also worthy of attention during failure analysis: the residual electrolyte may contain more impurities or reaction products, which may block the channels inside the battery and affect the transmission of ions; at the same time, the chemical substances in the residual electrolyte may continue to react with the electrode material, resulting in further degradation of battery performance. By analyzing the components and proportions in the residual electrolyte, impurities or reaction products can be understood, thereby analyzing the cause of battery failure.

[0004] In the prior art, there are physical methods and chemical methods for analyzing electrolytes, but there are large errors in the analysis of the total amount of residual electrolyte. For example, the physical method, the patent document with publication number CN114543956A discloses a device and method for collecting and detecting the amount of free electrolyte in soft-pack lithium batteries, which collects free electrolyte by puncturing and squeezing. On the one hand, this method requires the addition of extrusion equipment to increase costs, and may also cause contamination to the electrolyte, thereby affecting the qualitative and quantitative analysis of the electrolyte; on the other hand, for batteries with dried free electrolytes and severe internal lithium deposition, physical extrusion is used to collect electrolytes, which may cause internal short-circuit safety failures and inability to collect enough electrolytes for analysis.

[0005] Another example is the chemical method. The patent document with the publication number CN116297939A discloses a method for testing the residual amount of electrolyte in lithium-ion batteries, which includes the following steps: S1. Disassemble the lithium-ion battery to obtain the pole group, and soak the pole group in acetonitrile to obtain the soaking solution; S2. Perform GC-MS test and / or IC test on the soaking solution to obtain the content of each component in the soaking solution; S3. Calculate the residual amount of electrolyte. Since acetonitrile has a high boiling point and cannot be separated from the solvent component in the electrolyte, the mass of each component in the soaking solution is specifically calculated by the mass of acetonitrile, and then the mass of the solvent, lithium salt and additive is the mass of the residual electrolyte. However, there will be some impurities and reaction products in the residual electrolyte. This calculation method does not and is difficult to calculate these components, so that the amount of residual electrolyte obtained has a large error. Summary of the invention

[0006] The present invention aims to solve the above-mentioned problem and provide an accurate analysis method for the total amount of residual electrolyte.

[0007] The technical solution to the problem of the present invention is to provide a method for analyzing residual electrolyte of a failed lithium battery, comprising the following steps: S1. After the failed battery cell is discharged, the shell is opened, the extractant is injected, and the shell is sealed and allowed to stand; after standing, the solid-liquid mixed system in the shell is separated to obtain a core and a mixed liquid; S2. Weigh the core, the weight is recorded as G1; weigh the core after drying, the weight is recorded as G1`; S3. The mixed solution is weighed, and the weight is recorded as G2; the mixed solution is distilled to remove the extractant to obtain an electrolyte, and the electrolyte is weighed, and the weight is recorded as G2`; S4. Analysis of the total amount of residual electrolyte: Calculate the total amount of residual electrolyte G = G2` + (G1- G1`) × G2` / G2.

[0008] In this application, a new idea for analyzing the total amount of residual electrolyte is provided: first, an extractant that can be removed by distillation is used, and secondly, on this basis, the weight of the mixed liquid G2 and its mass G2' after removing the extractant are used to obtain the concentration of the electrolyte in the mixed liquid G2' / G2, and then the amount of electrolyte that should be in the mixed liquid adsorbed by the core (i.e., G1-G1') can be calculated. The total amount of residual electrolyte in this application includes the amount of electrolyte in the directly separated mixed liquid and the amount of electrolyte in the mixed liquid adsorbed by the core, and the calculation of the total amount of residual electrolyte is complete and accurate.

[0009] The lowest boiling point in the electrolyte is its solvent, and most of its solvents are carbonate compounds, such as ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. The boiling points of these compounds are all above 90°C. By selecting an extractant with a boiling point not exceeding 90°C, the extractant can be distilled off without affecting the amount of solvent in the electrolyte, thereby ensuring the accuracy of the analysis of the residual electrolyte. Of course, the components of the extractant should also be different from any components in the failed battery cell.

[0010] In order to more effectively remove the extractant without affecting the solvent of the residual electrolyte, as a preferred embodiment of the present invention, the boiling point of the extractant does not exceed 80° C. Further preferably, the boiling point of the extractant does not exceed 60° C. On the basis of ensuring the extraction effect, the greater the difference between the boiling point of the extractant and the boiling point of the electrolyte solvent, the better.

[0011] As a preferred embodiment of the present invention, the extractant is used in a pure solution without being mixed with other solvents to ensure the removal of the extractant.

[0012] As a preferred embodiment of the present invention, the extractant is selected from one of ether, methyl formate, acetone, dichloromethane and methyl acetate. The boiling point of ether is 34.5°C, the boiling point of methyl formate is 31.5°C, the boiling point of acetone is 56°C, the boiling point of dichloromethane is 39.8°C, and the boiling point of methyl acetate is 57°C. The extractant is preferably ether or methyl formate.

[0013] In addition to the selection of the extractant, other steps also affect the final analysis amount of the residual electrolyte to a certain extent.

[0014] As a preferred embodiment of the present invention, in step S1, the standing conditions are: temperature 20-30°C, dew point ≤-10°C, and standing for 24-36 hours.

[0015] The temperature may be 20°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 30°C, preferably 25°C.

[0016] The dew point can be -10°C, -11°C, -12°C, -13°C, -14°C, -15°C, etc. The lower the better. The lower the dew point, the less water vapor content in the air, which can prevent moisture in the air from entering the battery and affecting the quality of the mixed system in the shell.

[0017] The standing time can be 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, preferably 30 h. If the standing time is too short, the extraction effect will be affected, resulting in less electrolyte content in the mixed solution obtained by solid-liquid separation, and its mass will be small after the subsequent distillation to remove the extractant, which will affect the weighing accuracy and thus affect the calculation result of the total amount of residual electrolyte; in addition, the amount of electrolyte is too small, so that it cannot be used for the qualitative and quantitative detection of the components therein. If the standing time is too long, the components in the core may be dissolved therein, resulting in a higher total amount of residual electrolyte obtained by analysis, and also affecting the subsequent qualitative and quantitative detection results of the components therein.

[0018] As a preferred embodiment of the present invention, in step S2, the drying conditions are: temperature 80-120°C, vacuum ≤-90Kpa, and baking 12-24h.

[0019] The drying temperature can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, preferably 100°C. The baking time can be 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, preferably 18 h. Too low a drying temperature or too low a baking time may result in incomplete drying, affecting the mass of the mixed solution adsorbed by the core, and further affecting the measurement of the residual electrolyte. Too high a drying temperature or too long a baking time may result in the decomposition and loss of certain components in the core, resulting in a larger mass of the mixed solution adsorbed by the core, and further affecting the measurement of the residual electrolyte.

[0020] The vacuum can be -90 Kpa, -95 Kpa, -100 Kpa, -105 Kpa, -110 Kpa, etc. The lower the better to avoid the influence of components in the air.

[0021] As a preferred embodiment of the present invention, in step S3, the distillation conditions are: temperature 40-80° C., and distillation 24-36 hours.

[0022] Further preferably, the temperature is 40-60°C, and can be 40°C, 45°C, 50°C, 55°C, 60°C, and the specific temperature depends on the boiling point of the extractant. The distillation time can be 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, preferably 30 h. Too high a distillation temperature or too long a distillation time will cause the volatilization of the electrolyte components, and too low a temperature or too low a time will not completely remove the extractant, which will affect the analysis results of the residual electrolyte.

[0023] As a preferred embodiment of the present invention, during the distillation process, the separation effect of the extractant can be improved by condensation reflux, and the extractant can be recovered for reuse.

[0024] As a preferred embodiment of the present invention, in step S3, the mixed solution is sampled every 1 to 3 hours to detect whether the mixed solution contains the extractant. When it is detected that the mixed solution does not contain the extractant component, the distillation is completed and the electrolyte and the extract can be completely separated.

[0025] As a preferred embodiment of the present invention, in step S3, the recovery mass of the extractant is recorded. When the recovery mass reaches the injection amount of the extractant in step S1, the distillation is completed and the electrolyte and the extract can be completely separated.

[0026] The above method can completely and accurately calculate the total amount of residual electrolyte. As a preferred embodiment of the present invention, the following steps are also included: S5. Analysis of components and proportions of residual electrolyte: The electrolyte obtained in step S3 is subjected to qualitative and quantitative analysis.

[0027] In the present application, since an extractant that can be removed by distillation is used, a pure electrolyte can be obtained, and the components and their proportions therein can be directly qualitatively and quantitatively analyzed without the need for secondary calculations, and the analysis method is simpler and more accurate.

[0028] There is no limitation on the qualitative and quantitative analysis of the electrolyte. As a preferred embodiment of the present invention, in step S5, the GCMS external standard method is used to perform qualitative and quantitative analysis on the solvent and additives in the electrolyte. MS can accurately identify each component, and GC measures the peak area of ​​each component to calculate the mass content of each component according to the regression equation.

[0029] As the preferred embodiment of the present invention, the gas phase detection conditions of GCMS are as follows: chromatographic column: Rtx-5MS capillary chromatographic column, 30m×0.25mm, 0.25μm; high-purity helium is selected as the carrier gas, with a constant flow rate of 1.0mL / min; the feed inlet temperature is 280°C, and the chromatographic column adopts a programmed temperature increase method, the temperature increase program: from 35°C to 260°C; keep below 35°C for 3.5min, increase to 220°C at a rate of 10°C / min, increase to 280°C at a rate of 20°C / min and keep for 5min; adopt split mode injection, the split ratio is set to 20:1, and the injection volume is set to 1μL; the ion source temperature is set to 220~240°C, and the chromatography-mass spectrometry interface temperature is set to 280°C.

[0030] As a preferred embodiment of the present invention, the quantitative analysis includes the following steps: prepare a mixed standard solution of known electrolyte solvents, additives, and diluents according to their types and proportions. Dilute each component into a standard solution of several concentrations, draw a standard curve based on the peak area and concentration of each component, and obtain a linear regression equation for each component based on the standard curve; wherein the concentration range of the high-content component is 100~1000ppm, and the concentration range of the low-content component is 10~400ppm. Take the electrolyte sample obtained in step S3, dilute it with a diluent to a reasonable multiple, and then measure the peak area of ​​each component by GCMS, and calculate the mass content of each component according to the linear regression equation.

[0031] As a preferred embodiment of the present invention, the diluent used for the standard solution and the electrolyte sample is selected from at least one of ether, acetone, methyl formate or dichloromethane. Further preferably, the diluent is selected from one of ether, acetone, methyl formate or dichloromethane, that is, the diluent is a pure solution.

[0032] As a preferred embodiment of the present invention, in step S5, IC ion chromatography is used to perform qualitative and quantitative analysis on the lithium salt in the electrolyte.

[0033] As a preferred embodiment of the present invention, the detection conditions of IC are: the eluent is an acetonitrile aqueous solution of sodium carbonate, or a methanol aqueous solution of sodium carbonate, or an acetone aqueous solution of sodium carbonate, wherein the molar concentration of sodium carbonate is 10 mmol / L, and the volume percentage of acetonitrile, methanol or acetone is 25% to 40%; the regeneration liquid is a sulfuric acid aqueous solution with a molar concentration of 100 mmol / L, the column temperature is 30°C, the injection volume is 20 μL, the flow rate is 0.7 ml / min, the chromatographic column is a Metromone supp-5-250, and the correlation coefficient R ≥ 0.999.

[0034] As a preferred embodiment of the present invention, the quantitative analysis includes the following steps: lithium salt, lithium salt additive, and diluent are configured into a mixed standard solution according to their types and proportions. The concentration of the configured standard mixed solution is 200-2000ppm for lithium salt, and 10-200ppm for other lithium salt additives; sample analysis is performed under the selected chromatographic conditions, and a standard curve is established based on the peak area and concentration of each component, and a linear regression equation of each component is obtained based on the standard curve; the electrolyte sample obtained in step S3 is taken, and diluted with a diluent to a reasonable multiple so that the concentration of the measured solution is equivalent to the concentration of the standard solution component, and the peak area of ​​each component is measured by IC, and the mass content of each component is calculated based on the regression equation.

[0035] As a preferred embodiment of the present invention, when the lithium salt in the electrolyte is subjected to qualitative and quantitative analysis, the test sample and the standard sample are both weakly alkaline. Specifically, the diluent used for the standard solution and the electrolyte sample is a weakly alkaline diluent, so that the sample to be tested is in a weakly alkaline environment, which is conducive to inhibiting the hydrolysis of the lithium salt, thereby ensuring the qualitative and quantitative test accuracy of the lithium salt. As a preferred embodiment of the present invention, the diluent is selected from one of a methanol aqueous solution of sodium carbonate, an acetone aqueous solution of sodium carbonate, and an acetonitrile aqueous solution of sodium carbonate.

[0036] Beneficial effects of the present invention: 1. The present application provides a new idea for analyzing the total amount of residual electrolyte: an extractant that can be removed by distillation is used, and on this basis, the weight G2 of the mixed liquid and its mass G2` after removing the extractant are used to obtain the concentration G2` / G2 of the electrolyte in the mixed liquid, and then the amount of electrolyte that should be in the mixed liquid adsorbed by the core (i.e., G1-G1`) can be calculated. The total amount of residual electrolyte in the present application includes the amount of electrolyte in the directly separated mixed liquid and the amount of electrolyte in the mixed liquid adsorbed by the core, and the calculation of the total amount of residual electrolyte is complete and accurate. In some embodiments, the error of the total amount of residual electrolyte obtained by the analysis method of the present application is within 0.1%, the error is small, and the analysis result is accurate.

[0037] 2. In the present application, an extractant that can be removed by distillation is used, so a pure electrolyte can be obtained, and the components and their proportions therein can be directly qualitatively and quantitatively analyzed without the need for secondary calculations, and the analysis method is simpler and more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is the peak area of ​​each component in the solvent and additive standard solution of Example 2; Figure 2 is the standard curve of the peak area and concentration of solvent DMC in the standard sample listed in Example 2; Figure 3 is the peak area of ​​each component in the lithium salt standard solution of Example 2; Figure 4 This is the standard curve of the peak area and concentration of the lithium salt LiPF6 in the standard sample listed in Example 2. DETAILED DESCRIPTION

[0039] The following are specific implementations of the present invention, and in conjunction with the accompanying drawings, the technical solution of the present invention is further described, but the present invention is not limited to these embodiments.

[0040] Example 1 A method for analyzing residual electrolyte in a failed lithium battery comprises the following steps: S1. Take a battery, and in order to compare the accuracy of the analysis method of this application, analyze a standard battery instead of a failed battery. It is known that the amount of liquid injected into the battery cell of the standard battery is 700.8g.

[0041] The battery is discharged at 0.5C+0.02C until the cut-off voltage is fully discharged. At a temperature of 25±2℃ and a dew point of ≤-10℃, the shell is opened and 500g of ether extractant is injected; then the opening is sealed and allowed to stand for 30 hours at a temperature of 25±2℃ and a dew point of ≤-10℃. After standing, the battery is disassembled to obtain a solid core and a liquid mixture.

[0042] S2. Weigh the core, weight G1 = 5066.281 g. Then bake the core at 100°C, -90 KPa vacuum environment for 18 hours, weigh the baked core, weight G1` = 4997.952 g.

[0043] S3. The mixed solution was weighed, and the weight G2 = 1132.195 g. Then the mixed solution was distilled in a water bath at 50°C for 30 hours to remove the ether extractant in the mixed solution to obtain an electrolyte, which was weighed, and the weight G2` = 660.627 g.

[0044] S4. Analysis of the total amount of residual electrolyte: Calculate the total amount of residual electrolyte G = G2` + (G1- G1`) × G2` / G2 = 700.496g. The error with the injection amount is 0.04%.

[0045] Example 2 This embodiment is basically the same as the embodiment 1, except that it also includes the following steps: S5. Analysis of residual electrolyte components and proportions: Take the electrolyte obtained in step S3 for qualitative and quantitative analysis.

[0046] It is known that in the above-mentioned standard batteries, the electrolyte solvents and additives are: EC (ethylene carbonate), PC (propylene carbonate), DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), DEC (diethyl carbonate), EA (ethyl acetate), VC (vinylene carbonate), FEC (fluoroethylene carbonate), DTD (vinyl sulfate), FB (fluorobenzene), PS (1,3-propane sultone); the lithium salt is: LiPF6 (lithium hexafluorophosphate); the lithium salt additives are LiBF4 (lithium tetrafluoroborate), LiODFB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), and LiFSI (lithium bis(fluorosulfonyl)imide).

[0047] The GCMS external standard method is used to perform qualitative and quantitative analysis of solvents and additives in the electrolyte: The gas phase detection conditions of GCMS are as follows: chromatographic column: Rtx-5MS capillary chromatographic column, 30m×0.25mm, 0.25μm; high-purity helium was selected as the carrier gas with a constant flow rate of 1.0mL / min; the inlet temperature was 280℃, and the chromatographic column was programmed to heat up, with the heating program as follows: from 35℃ to 260℃; kept below 35℃ for 3.5min, increased to 220℃ at a rate of 10℃ / min, and increased to 280℃ at a rate of 20℃ / min and kept for 5min; the split mode was used for injection, the split ratio was set to 20:1, and the injection volume was set to 1μL; the ion source temperature was set to 230℃, and the chromatography-mass spectrometry interface temperature was set to 280℃.

[0048] The determination of the content of solvents and additives was carried out according to the following steps: according to the electrolyte formula of the standard battery used, the solvents and additives were prepared into standard solutions according to their types and proportions, and ether was used as a diluent to prepare the standard solutions into 4 groups of standard solutions with different concentrations of solvents and additives. The peak area of ​​each component was obtained by GCMS, such as Figure 1 Then, a standard curve is established based on the peak area and concentration, and the linear regression equation of each component is obtained based on the standard curve, as shown in Figure 2 Then, the electrolyte sample obtained in step S3 of Example 1 was taken and diluted with ether to a reasonable multiple, and each component was qualitatively analyzed by MS, and the peak area of ​​each component was measured by GC, and the mass content of each component was calculated according to the regression equation.

[0049] IC ion chromatography is used to perform qualitative and quantitative analysis of lithium salts in the electrolyte: The detection conditions of IC are as follows: the eluent is an acetone aqueous solution of sodium carbonate, wherein the molar concentration of sodium carbonate is 10 mmol / L and the volume percentage of acetone is 30%; the regeneration liquid is an aqueous solution of sulfuric acid with a molar concentration of 100 mmol / L, the column temperature is 30°C, the injection volume is 20 μL, the flow rate is 0.7 ml / min, the chromatographic column is Metrom supp-5-250, and the correlation coefficient R ≥ 0.999.

[0050] The determination of lithium salt content is carried out according to the following steps: according to the electrolyte formula of the standard battery used, lithium salt and lithium salt additives are prepared into standard solutions according to their types and proportions, and sodium carbonate acetone solution is used as a diluent to prepare the standard solutions into 4 groups of lithium salt standard solutions with different concentrations. Samples are injected and analyzed under the selected chromatographic conditions to obtain the peak area of ​​each component, such as Figure 3 As shown. A standard curve was established based on the peak area and concentration of each component, and the linear regression equation of each component was obtained based on the standard curve, as shown in Figure 4Take the electrolyte sample obtained in step S3 of Example 1, dilute it with an acetone solution of sodium carbonate to a reasonable multiple, so that the concentration of the measured solution is equivalent to the concentration of the components of the standard solution, measure the peak area of ​​each component by IC, and calculate the mass content of each component according to the regression equation.

[0051] Example 3 A method for analyzing residual electrolyte in a failed lithium battery comprises the following steps: S1. Take the battery from the same batch as Example 1, and the amount of liquid injected into the battery core is 700.8g. Discharge the battery at 0.5C+0.02C until the cut-off voltage is fully discharged. At a temperature of 28±2℃ and a dew point of ≤-10℃, open the shell and inject 500g of acetone extractant; then seal the opening and let it stand for 24h at a temperature of 28±2℃ and a dew point of ≤-10℃. After standing, disassemble the battery to obtain a solid core and a liquid mixture.

[0052] S2. Weigh the core, weight G1 = 5066.787g. Then bake the core at 120°C, -95Kpa vacuum environment for 16h, weigh the baked core, weight G1` = 4996.150g.

[0053] S3. The mixed solution was weighed, and the weight was G2 = 1131.847 g. Then the mixed solution was distilled in a water bath at 80°C for 24 hours to remove the acetone extractant in the mixed solution to obtain an electrolyte, and the electrolyte was weighed, and the weight was G2` = 658.948 g; S4. Analysis of the total amount of residual electrolyte: Calculate the total amount of residual electrolyte G = G2` + (G1- G1`) × G2` / G2 = 700.072g. The error with the injection amount is 0.1%.

[0054] Example 4 A method for analyzing residual electrolyte in a failed lithium battery comprises the following steps: S1. Take the battery from the same batch as Example 1, and the amount of liquid injected into the battery core is 700.8g. Discharge the battery at 0.5C+0.02C until the cut-off voltage is fully discharged. At a temperature of 22±2℃ and a dew point of ≤-10℃, open the shell and inject 500g of dichloromethane extractant; then seal the opening and let it stand for 36h at a temperature of 22±2℃ and a dew point of ≤-10℃. After standing, disassemble the battery to obtain a solid core and a liquid mixture.

[0055] S2. Weigh the core, weight G1 = 5064.657g. Then bake the core at 90°C, -100Kpa vacuum environment for 24h, weigh the core after baking, weight G1` = 4999.172g.

[0056] S3. The mixed solution was weighed, and the weight G2 = 1133.948g. Then the mixed solution was distilled in a water bath at 60°C for 36h to remove the dichloromethane extractant in the mixed solution to obtain an electrolyte, and the electrolyte was weighed, and the weight G2` = 662.091g; S4. Analysis of the total amount of residual electrolyte: Calculate the total amount of residual electrolyte G = G2` + (G1- G1`) × G2` / G2 = 700.326g. The error with the injection amount is 0.07%.

[0057] Example 5 This embodiment is basically the same as the embodiment 1, and the only difference is that the standing time is longer.

[0058] S1. Take the battery from the same batch as Example 1, and the amount of liquid injected into the battery core is 700.8g. Discharge the battery at 0.5C+0.02C until the cut-off voltage is fully discharged. At a temperature of 25±2℃ and a dew point of ≤-10℃, open the shell and inject 500g of ether extractant; then seal the opening and let it stand for 60h at a temperature of 25±2℃ and a dew point of ≤-10℃. After standing, disassemble the battery to obtain a solid core and a liquid mixture.

[0059] S2. Weigh the core, weight G1 = 5063.346g. Then bake the core at 100°C, -90Kpa vacuum environment for 18h, weigh the core after baking, weight G1` = 4995.058g.

[0060] S3. The mixed solution was weighed, and the weight G2 = 1135.255 g. Then the mixed solution was distilled in a water bath at 50°C for 30 hours to remove the ether extractant in the mixed solution to obtain an electrolyte, and the electrolyte was weighed, and the weight G2` = 663.570 g.

[0061] S4. Analysis of the total amount of residual electrolyte: Calculate the total amount of residual electrolyte G = G2` + (G1- G1`) × G2` / G2 = 703.485g. The error with the injection amount is 0.38%.

[0062] Example 6 This embodiment is basically the same as Embodiment 1, the only difference being that the drying temperature is lower.

[0063] S1. Take the battery from the same batch as Example 1, and the amount of liquid injected into the battery core is 700.8g. Discharge the battery at 0.5C+0.02C until the cut-off voltage is fully discharged. At a temperature of 25±2℃ and a dew point of ≤-10℃, open the shell and inject 500g of ether extractant; then seal the opening and let it stand for 30h at a temperature of 25±2℃ and a dew point of ≤-10℃. After standing, disassemble the battery to obtain a solid core and a liquid mixture.

[0064] S2. Weigh the core, weight G1 = 5065.818 g. Then bake the core at 60°C and -90 KPa vacuum for 18 h, weigh the baked core, weight G1` = 5006.216 g.

[0065] S3. The mixed solution was weighed, and the weight was G2 = 1132.817 g. Then the mixed solution was distilled in a water bath at 50°C for 30 hours to remove the ether extractant in the mixed solution to obtain an electrolyte, and the electrolyte was weighed, and the weight was G2` = 661.017 g; S4. Analysis of the total amount of residual electrolyte: Calculate the total amount of residual electrolyte G = G2` + (G1- G1`) × G2` / G2 = 695.796g. The error with the injection amount is 0.71%.

[0066] Example 7 This embodiment is basically the same as Embodiment 1, the only difference being that the drying temperature is higher.

[0067] S1. Take the battery from the same batch as Example 1, and the amount of liquid injected into the battery core is 700.8g. Discharge the battery at 0.5C+0.02C until the cut-off voltage is fully discharged. At a temperature of 25±2℃ and a dew point of ≤-10℃, open the shell and inject 500g of ether extractant; then seal the opening and let it stand for 30h at a temperature of 25±2℃ and a dew point of ≤-10℃. After standing, disassemble the battery to obtain a solid core and a liquid mixture.

[0068] S2. Weigh the core, weight G1 = 5066.737 g. Then bake the core at 200°C, -90 KPa vacuum environment for 18 hours, weigh the baked core, weight G1` = 4990.584 g.

[0069] S3. The mixed solution was weighed, and the weight was G2 = 1131.979 g. Then the mixed solution was distilled in a water bath at 50°C for 30 hours to remove the ether extractant in the mixed solution to obtain an electrolyte, and the electrolyte was weighed, and the weight was G2` = 660.244 g; S4. Analysis of the total amount of residual electrolyte: Calculate the total amount of residual electrolyte G = G2` + (G1- G1`) × G2` / G2 = 704.661g. The error with the injection amount is 0.55%.

[0070] Example 8 This embodiment is basically the same as Embodiment 1, the only difference being that a mixed solution is used as the extractant.

[0071] S1. Take the battery from the same batch as Example 1, and the amount of liquid injected into the battery cell is 700.8g. Discharge the battery at 0.5C+0.02C until the cut-off voltage is fully discharged. At a temperature of 25±2℃ and a dew point of ≤-10℃, open the shell and inject 500g of an extractant, which is a mixture of ether and acetone in equal mass ratios; then seal the opening and let it stand for 30 hours at a temperature of 25±2℃ and a dew point of ≤-10℃. After standing, disassemble the battery to obtain a solid core and a liquid mixture.

[0072] S2. Weigh the core, weight G1 = 5066.190 g. Then bake the core at 100°C, -90 KPa vacuum environment for 18 hours, weigh the baked core, weight G1` = 4997.225 g.

[0073] S3. The mixed solution was weighed, and the weight was G2 = 1132.254 g. Then the mixed solution was distilled in a water bath at 50°C for 30 hours to remove the extractant from the mixed solution to obtain an electrolyte, which was weighed, and the weight was G2` = 666.784 g; S4. Analysis of the total amount of residual electrolyte: Calculate the total amount of residual electrolyte G = G2` + (G1- G1`) × G2` / G2 = 707.397g. The error with the injection amount is 0.94%.

[0074] The analysis results and error statistics in Example 1 and Implementations 5 to 8 are shown in Table 1 below.

[0075] Table 1. As shown in Table 1, by comparing Example 1 and Example 5, it can be seen that a standing time that is too long will lead to a high analysis result and an increase in error. This may be caused by the loss of the core when the standing time is high. By comparing Example 1 with Examples 6 and 7, it can be seen that a baking temperature that is too low will lead to a low analysis result and an increase in error. This may be caused by incomplete drying and a small amount of mixed liquid adsorbed by the core; a drying temperature that is too high will lead to a high analysis result and an increase in error. This may be caused by the decomposition of certain components in the core, resulting in a large amount of mixed liquid adsorbed by the core. By comparing Example 1 and Example 8, it can be seen that the analysis results are more accurate when a single pure solution is used as an extractant than when a mixed solution is used as an extractant. This may be because the presence of azeotropy in the mixed solution increases the boiling point, resulting in incomplete removal of the extractant, resulting in a high analysis result.

[0076] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for analyzing residual electrolyte in failed lithium batteries. Features: The following steps are involved: S1. After the failed battery is discharged, the shell is opened, the extractant is injected, and the shell is sealed and allowed to stand; after standing, the solid-liquid separation of the mixed system in the shell is performed to obtain a core and a mixed liquid; S2. Weigh the core, the weight is recorded as G1; weigh the core after drying, the weight is recorded as G1`; S3. The mixed solution is weighed, and the weight is recorded as G2; the mixed solution is distilled to remove the extractant to obtain an electrolyte, and the electrolyte is weighed, and the weight is recorded as G2`; S4. Analysis of the total amount of residual electrolyte: Calculate the total amount of residual electrolyte G = G2` + (G1- G1`) × G2` / G2.

2. A method for analyzing residual electrolyte in a failed lithium battery according to claim 1, Features: The boiling point of the extractant does not exceed 80°C.

3. A method for analyzing residual electrolyte in a failed lithium battery according to claim 2, Features: The extractant is selected from one of ether, methyl formate, acetone, dichloromethane and methyl acetate.

4. A method for analyzing residual electrolyte in a failed lithium battery according to claim 2, Features: In step S3, the distillation conditions are: temperature 40-80° C., and distillation time 24-36 h.

5. The method for analyzing residual electrolyte in a failed lithium battery according to claim 1, Features: In step S1, the standing conditions are: temperature 20-30°C, dew point ≤-10°C, and standing for 24-36 hours.

6. A method for analyzing residual electrolyte in a failed lithium battery according to claim 1, Features: In step S2, the drying conditions are: temperature 80-120°C, vacuum ≤-90Kpa, and baking 12-24h.

7. A method for analyzing residual electrolyte in a failed lithium battery according to claim 1, Features: The following steps are also included: S5. Analysis of components and proportions in the residual electrolyte: Take the electrolyte obtained in step S3 for qualitative and quantitative analysis.

8. A method for analyzing residual electrolyte in a failed lithium battery according to claim 7, Features: In step S5, the GCMS external standard method is used to perform qualitative and quantitative analysis on the solvent and additives in the electrolyte.

9. The method for analyzing residual electrolyte in a failed lithium battery according to claim 7, Features: In step S5, IC ion chromatography is used to perform qualitative and quantitative analysis on the lithium salt in the electrolyte.

10. A method for analyzing residual electrolyte in a failed lithium battery according to claim 9, Features: When performing qualitative and quantitative analysis on lithium salts in electrolyte, both the test sample and the standard sample are weakly alkaline.

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