Method for detecting content of N-methyl pyrrolidone in battery pole piece

Abstract

The invention provides a method for detecting the content of N-methyl pyrrolidone in a battery pole piece, which comprises the following steps: carrying out first crushing treatment on the battery pole piece to obtain a first crushed material, putting the first crushed material and a solvent into a headspace bottle, and sealing to obtain a sample to be detected; baking the battery pole piece at the temperature not lower than 200 DEG C for more than 24 hours, and carrying out second crushing treatment to obtain a second crushed material; preparing a standard solution containing N-methyl pyrrolidone and a solvent, filling the second crushed material and the standard solution into a headspace bottle, and sealing to obtain a control sample; testing the control sample and the sample to be detected by headspace-gas chromatography, obtaining a standard curve by an external standard method, obtaining the mass content of the N-methyl pyrrolidone in the sample to be detected according to the standard curve, and further calculating to obtain the content of the N-methyl pyrrolidone in the battery pole piece. According to the method, extraction and filtration are not needed in the testing process, the testing steps are simplified, the detection time is shortened, and the detection efficiency can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of detection and analysis, and relates to a method for detecting the content of N-methylpyrrolidone in a battery pole piece. Background Art

[0002] Lithium-ion batteries are widely used in many fields, including electric vehicles, mobile devices, aerospace, energy storage systems, etc., due to their advantages such as high energy density, long life, no memory effect and green environmental protection. The main components of lithium-ion batteries include positive electrode sheets, negative electrode sheets, diaphragms and electrolytes. Among them, the preparation process of the electrode sheets often requires the preparation of active slurries, and the solvent in the active slurry is indispensable. It mainly plays the role of dispersing active materials, conductive agents and adhesives. The commonly used solvent is mainly N-methylpyrrolidone (NMP). Most of the NMP can be volatilized during the baking process of the electrode sheets, but some residues will inevitably remain, and the residual NMP will affect the performance of lithium-ion batteries, such as affecting the film-forming reaction of the electrolyte and reducing the cycle efficiency and capacity of the battery. Therefore, it is necessary to monitor the residual NMP content on the electrode sheets.

[0003] At present, the detection procedure of NMP content in battery electrodes usually requires organic solvent extraction and filtration before detection. However, the NMP adsorbed inside the particles during the extraction process is difficult to extract, and there are problems such as cumbersome and time-consuming processing steps.

[0004] Therefore, it is necessary to develop a new testing method to simplify the processing steps, shorten the detection time, and improve the detection efficiency. Summary of the invention

[0005] In view of the above defects, the present invention provides a method for detecting the content of N-methylpyrrolidone in a battery electrode. This method does not require extraction and filtration of the electrode during the test process, which greatly simplifies the test steps, shortens the detection time, and can effectively improve the detection efficiency.

[0006] The present invention provides a method for detecting the content of N-methylpyrrolidone in a battery pole piece, comprising the following steps:

[0007] 1) performing a first crushing process on the battery electrode to obtain a first crushed material; placing the first crushed material and a solvent into a headspace bottle, sealing the bottle, and obtaining a sample to be tested;

[0008] 2) baking the battery electrode at a temperature not lower than 200° C. for more than 24 hours, and then performing a second crushing process to obtain a second crushed material; preparing a standard solution containing N-methylpyrrolidone and a solvent, and placing the second crushed material and the standard solution into a headspace bottle, sealing the bottle, and obtaining a control sample;

[0009] 3) testing the control sample by headspace-gas chromatography, and using the external standard method to draw a standard curve based on the measured chromatographic peak area;

[0010] 4) Using headspace-gas chromatography to detect the sample to be tested, obtaining the chromatographic peak area, obtaining the mass content of N-methylpyrrolidone in the sample to be tested according to the standard curve, and calculating the N-methylpyrrolidone content in the battery electrode according to Formula 1,

[0011] Formula 1

[0012] In Formula 1, x is the mass content of N-methylpyrrolidone in the battery electrode, in micrograms / gram; C is the mass content of N-methylpyrrolidone in the sample to be tested obtained according to the standard curve, in micrograms / milliliter; V is the volume of the sample to be tested, in milliliters; and m is the mass of the battery electrode, in grams.

[0013] The method for detecting the content of N-methylpyrrolidone in a battery pole piece as described above, wherein the mass of the first crushed material in step 1) is consistent with the mass of the second crushed material in step 2);

[0014] The volume of the solvent in step 1) is consistent with the volume of the standard solution in step 2).

[0015] In the above-mentioned method for detecting the content of N-methylpyrrolidone in a battery pole piece, in step 1), the mass of the first crushed material is 0.02-1 g, and the volume of the solvent is 0.1-2 ml.

[0016] The method for detecting the content of N-methylpyrrolidone in the battery pole piece as described above, wherein the size of the first crushed material is (2 mm~5 mm)*(2 mm~5 mm);

[0017] And / or, the size of the second crushed material is (2 mm~5 mm)*(2 mm~5 mm).

[0018] In the method for detecting the content of N-methylpyrrolidone in a battery pole piece as described above, the solvent includes at least one of dimethylacetamide, ethyl acetate, methanol, ethanol, N,N-dimethylformamide, toluene, and tetrahydrofuran.

[0019] The method for detecting the content of N-methylpyrrolidone in a battery pole piece as described above, wherein in step 1), after the first crushed material and the solvent are loaded into a headspace bottle, the bottle is sealed within 8 to 12 seconds;

[0020] In step 2), after the second crushed material and the standard solution are placed in the headspace bottle, the bottle is sealed within 8 to 12 seconds.

[0021] In the method for detecting the content of N-methylpyrrolidone in a battery electrode as described above, the preparation of the standard solution in step 2) comprises: using a solvent to set the volume of N-methylpyrrolidone to obtain a reserve solution; then weighing a portion of the reserve solution and diluting it step by step to obtain the standard solution.

[0022] In the above-mentioned method for detecting the content of N-methylpyrrolidone in a battery pole piece, the concentration of the standard solution is 5-1000 μg / ml.

[0023] The method for detecting the content of N-methylpyrrolidone in the battery pole piece as described above, wherein the headspace procedure in the headspace-gas chromatography test is: constant temperature at 120-180°C for 20-40 minutes, the transmission line temperature is 150-190°C, and the injection time is 0.1-0.2 minutes.

[0024] The method for detecting the content of N-methylpyrrolidone in the battery pole piece as described above, wherein, in the headspace-gas chromatography test, the gas chromatography conditions are: polar chromatography column HP-INNOWAX: 3 mm*0.25 mm*0.25 μm; inlet temperature: 200~250°C; split ratio: 10:1~50:1; flow rate: 1 ml / min.

[0025] The method for detecting the content of N-methylpyrrolidone in the battery pole piece of the present invention is as follows: first, the crushed material of the battery pole piece is mixed with a solvent to dissolve the residual N-methylpyrrolidone (NMP) in the pole piece to obtain a sample to be tested; then, the electrode pole piece is baked under specific conditions to completely volatilize the NMP therein, and the baked electrode pole piece is crushed, and the obtained crushed material is mixed with the prepared standard solution and tested by headspace-gas chromatography, and a standard curve is obtained by the external standard method; finally, the aforementioned sample to be tested is tested by headspace-gas chromatography, and the obtained standard curve is combined to obtain the mass content of NMP in the sample to be tested, and the value is substituted into formula 1 to obtain the content of N-methylpyrrolidone in the battery pole piece. This method does not require extraction and filtration, so it can greatly simplify the processing steps, improve the detection efficiency, and the method has high detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The chromatogram is a control sample having a standard solution mass concentration of 25 μg / ml in Example 1 of the present invention;

[0027] Figure 2 The chromatogram is a control sample having a standard solution mass concentration of 125 μg / ml in Example 1 of the present invention;

[0028] Figure 3The chromatogram is a control sample having a standard solution mass concentration of 500 μg / ml in Example 1 of the present invention;

[0029] Figure 4 The chromatogram is a control sample with a standard solution mass concentration of 1000 μg / ml in Example 1 of the present invention;

[0030] Figure 5 is the standard curve in Example 1 of the present invention;

[0031] Figure 6 is a chromatogram of the sample to be tested in Example 1 of the present invention;

[0032] Figure 7 The chromatogram is a control sample with a standard solution mass concentration of 5 μg / ml in Example 2 of the present invention;

[0033] Figure 8 The chromatogram is a control sample with a standard solution mass concentration of 10 μg / ml in Example 2 of the present invention;

[0034] Fig. 9 The chromatogram is a control sample with a standard solution mass concentration of 20 μg / ml in Example 2 of the present invention;

[0035] Fig.10 The chromatogram is a control sample of the standard solution with a mass concentration of 50 μg / ml in Example 2 of the present invention;

[0036] Fig.11 is the standard curve in Example 2 of the present invention;

[0037] Fig.12 This is the chromatogram of the sample to be tested in Example 2 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. 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.

[0039] In the process of preparing battery pole pieces, it is often necessary to prepare active slurry, which mainly includes active materials (including positive electrode active materials or negative electrode active materials), conductive agents, binders and solvents. The solvent mainly plays a dispersing role. The main solvent currently used is N-methylpyrrolidone (NMP). In the drying process after the pole piece is coated with the active slurry, most of the NMP solvent in the slurry can be removed, but some of it will still remain in the pole piece, which will have a negative impact on the battery's cycle performance and capacity. Therefore, in the process of pole piece preparation, it is necessary to monitor the mass content of NMP in the pole piece to ensure the quality of the battery.

[0040] At present, the existing monitoring methods generally extract and filter the electrode to obtain the filtrate, and then use gas chromatography, gas mass spectrometry and liquid chromatography to test the filtrate to detect the content of NMP in the electrode. However, this method has complicated steps and low detection efficiency; and the NMP adsorbed inside the active particles is difficult to extract. Therefore, how to simplify the processing steps and improve the test accuracy is a technical problem that needs to be solved in this field.

[0041] Based on the above problems, the inventors found that the extraction and filtration steps can be omitted by using headspace-gas chromatography testing. This is because the test temperature of the sample can be controlled during the headspace-gas chromatography test to volatilize the solvent and NMP in the sample, and the volatiles can be directly tested to obtain the NMP content therein, which can greatly simplify the test steps, shorten the sample processing time, and improve the detection efficiency. At the same time, controlling the temperature during the test process also helps to dissolve the NMP adsorbed inside the active particles, thereby improving the accuracy of the test.

[0042] Based on the above analysis, the present invention provides a method for detecting the content of N-methylpyrrolidone in a battery electrode, comprising the following steps:

[0043] 1) performing a first crushing process on the battery electrode to obtain a first crushed material; placing the first crushed material and a solvent into a headspace bottle, sealing the bottle, and obtaining a sample to be tested;

[0044] 2) baking the battery pole piece at a temperature not lower than 200° C. for more than 24 hours, and then performing a second crushing treatment to obtain a second crushed material; preparing a standard solution containing N-methylpyrrolidone and a solvent, and placing the second crushed material and the standard solution into a headspace bottle, sealing the bottle, and obtaining a control sample;

[0045] 3) Use headspace-gas chromatography to test the control sample, and use the external standard method to draw a standard curve based on the measured chromatographic peak area;

[0046] 4) Use headspace-gas chromatography to detect the sample to be tested, obtain the chromatographic peak area, obtain the mass content of N-methylpyrrolidone in the sample to be tested according to the standard curve, and calculate the N-methylpyrrolidone content in the battery electrode according to formula 1.

[0047] Formula 1

[0048] In formula 1, x is the mass content of N-methylpyrrolidone in the battery electrode, in micrograms / gram; C is the mass content of N-methylpyrrolidone in the sample to be tested obtained according to the standard curve, in micrograms / ml; V is the volume of the sample to be tested, in milliliters; and m is the mass of the battery electrode, in grams.

[0049] Specifically, in step 1), the battery pole piece is weighed and subjected to a first crushing treatment to obtain a first crushed material, the first crushed material is placed in a headspace bottle, a solvent is added to the headspace bottle, and then the headspace bottle is sealed to obtain a sample to be tested. The purpose of sealing is to prevent the solvent or N-methylpyrrolidone therein from volatilizing and negatively affecting the accuracy of the results.

[0050] The present invention does not specifically limit the method of the first crushing treatment, and the first crushing treatment may be performed by conventional methods in the art, for example, using scissors to cut the battery pole pieces to obtain crushed materials.

[0051] The present invention does not specifically limit the type of solvent, and a suitable solvent can be selected according to actual conditions. It should be noted that a solvent that is miscible with N-methylpyrrolidone needs to be selected.

[0052] The present invention does not specifically limit the source of the solvent, and any commercially available product or a product prepared by a conventional preparation method well known to those skilled in the art may be used.

[0053] In step 2), the electrode plate is baked at a temperature not lower than 200° C. for a baking time of not less than 24 hours, and then the baked electrode plate is subjected to a second crushing treatment to obtain a second crushed material; a standard solution containing N-methylpyrrolidone and a solvent is prepared, and the second crushed material and the standard solution are placed together in a headspace bottle, which is sealed to obtain a control sample.

[0054] Preferably, the baking temperature is 200-300° C., and the baking time is 24-48 hours.

[0055] It should be noted that the electrode plate in step 2) is consistent with the electrode plate in step 1). At the same time, in order to ensure the accuracy of the test results, the type of solvent in the control sample must be consistent with the type of solvent in the sample to be tested, and the volume of the solvent in the control sample must be consistent with the volume of the standard solution in the sample to be tested.

[0056] The present invention does not specifically limit the baking method, and the baking can be performed using conventional methods in the art. In one embodiment, the baking can be performed using a vacuum baking oven.

[0057] The present invention does not specifically limit the source of N-methylpyrrolidone, and any commercially available product or a product prepared by a conventional preparation method well known to those skilled in the art may be used.

[0058] In step 3), the control sample is tested by headspace-gas chromatography to obtain a chromatogram; and a standard curve is obtained by using an external standard method based on the mass concentration (μg / ml) of N-methylpyrrolidone in the standard solution and the corresponding chromatographic peak area.

[0059] In step 4), the sample prepared in step 1) is subjected to headspace-gas chromatography to obtain the corresponding chromatographic area; the mass content of N-methylpyrrolidone in the sample is obtained according to the standard curve obtained in step 3); then the mass content of N-methylpyrrolidone obtained above is substituted into formula 1 to calculate the content of N-methylpyrrolidone in the battery electrode.

[0060] Formula 1

[0061] In formula 1, x is the mass content of N-methylpyrrolidone in the battery electrode, in micrograms / gram; C is the mass content of N-methylpyrrolidone in the sample to be tested obtained according to the standard curve, in micrograms / ml; V is the volume of the sample to be tested, in milliliters; and m is the mass of the battery electrode, in grams.

[0062] It should be noted that the headspace-gas chromatography test conditions in step 4) should be consistent with the test conditions in step 3) to ensure the consistency of the test results.

[0063] The detection method of the present invention is firstly to mix the crushed material of the battery pole piece with a solvent to promote the dissolution of N-methylpyrrolidone therein, and obtain a sample to be tested; then the battery pole piece is baked at a temperature not less than 200°C for more than 24 hours to remove the N-methylpyrrolidone therein as much as possible, and the baked electrode pole piece is crushed, and the crushed material obtained is mixed with a standard solution and added to a headspace bottle, which is sealed to obtain a control sample; then the above-mentioned control sample is tested by headspace-gas chromatography; the chromatographic peak area obtained by the test is associated with the mass content of N-methylpyrrolidone in the control sample by an external standard method, and a standard curve is drawn; then, under the same test conditions, the sample to be tested is tested by headspace-gas chromatography, and the chromatographic peak area obtained by the test is substituted into the above standard curve to obtain the mass content of N-methylpyrrolidone in the sample to be tested, and then the mass content is substituted into the above formula 1 to obtain the content of N-methylpyrrolidone in the battery pole piece. In this detection method, there is no need to extract and filter the battery pole piece, which can effectively reduce the processing time and improve the detection efficiency.

[0064] In addition, this method directly detects volatiles during the test process, so it can also prevent solid matter in the filtrate from entering the gas chromatography system and causing problems such as clogging of the chromatographic column.

[0065] In a specific embodiment, the mass of the first crushed material in step 1) is consistent with the mass of the second crushed material in step 2);

[0066] The volume of the solvent in step 1) is the same as the volume of the standard solution in step 2).

[0067] At this time, the states of the control sample and the sample to be tested can be guaranteed to be consistent, thus improving the accuracy of the test results.

[0068] In order to further improve the dissolution effect of N-methylpyrrolidone in the battery pole piece, the amount of the first crushed material and the solvent, or the size of the crushed material can also be controlled.

[0069] In a specific embodiment, in step 1), the mass of the first crushed material is 0.02-1 g, and the volume of the solvent is 0.1-2 ml. Within this range, the amount of N-methylpyrrolidone dissolved in the first crushed material can be effectively increased, and the accuracy of the test results can be improved.

[0070] Illustratively, in step 1), the mass of the first crushed material is 0.02 g, 0.05 g, 0.10 g, 0.06 g, 0.08 g or 1 g; the volume of the solvent is 0.1 ml, 0.2 ml, 0.4 ml, 0.6 ml, 0.8 ml, 1 ml, 1.5 ml or 2 ml.

[0071] In a specific embodiment, the size of the first crushed material is (2 mm~5 mm)*(2 mm~5 mm);

[0072] The size of the second crushed material is (2 mm~5 mm)*(2 mm~5 mm). Within this range, N-methylpyrrolidone in the battery pole piece can be dissolved better, improving the accuracy of the detection.

[0073] Exemplarily, the size of the first crushed material is 2 mm*2 mm, 3 mm*3 mm, 4 mm*4 mm, 5 mm*5 mm, 2 mm*4 mm or 3 mm*5 mm.

[0074] Exemplarily, the size of the second crushed material is 2 mm*2 mm, 3 mm*3 mm, 4 mm*4 mm, 5 mm*5 mm, 2 mm*4 mm or 3 mm*5 mm.

[0075] In a specific embodiment, the solvent includes at least one of dimethylacetamide, ethyl acetate, methanol, ethanol, N,N-dimethylformamide, toluene, and tetrahydrofuran.

[0076] When the solvent is a mixture of the aforementioned specific compounds, the present invention does not specifically limit the ratio between the specific compounds.

[0077] Furthermore, in order to prevent the volatilization of the solvent and N-methylpyrrolidone in the sample to be tested, the headspace bottle can be sealed immediately after the crushed material and the solvent are loaded into the headspace bottle.

[0078] In a specific embodiment, in step 1), after the first crushed material and the solvent are placed in the headspace bottle, the bottle is sealed within 8 to 12 seconds;

[0079] In step 2), after the second crushed material and the standard solution are placed in the headspace bottle, the bottle is sealed within 8 to 12 seconds. At this time, the solvent in the headspace bottle and the dissolved N-methylpyrrolidone can be effectively prevented from volatilizing, causing quality loss and affecting the accuracy of the test results.

[0080] In a specific embodiment, the preparation of the standard solution in step 2) includes: using a solvent to adjust the volume of N-methylpyrrolidone to obtain a reserve solution; then weighing a portion of the reserve solution and diluting it step by step to obtain a standard solution.

[0081] Specifically, a set mass of N-methylpyrrolidone is weighed, and the volume is fixed to a set volume with a solvent to obtain a stock solution of a specific mass concentration; set volumes of the stock solution are respectively transferred, and the solvent is added for stepwise dilution to obtain standard solutions of different mass concentrations.

[0082] In one specific embodiment, the concentration of the standard solution is 5-1000 μg / ml.

[0083] Illustratively, the concentration of the standard solution is 5 μg / mL, 50 μg / mL, 100 μg / mL, 200 μg / mL, 400 μg / mL, 600 μg / mL, 800 μg / mL, or 1000 μg / mL.

[0084] Furthermore, the test conditions in the headspace-gas chromatography test can also be controlled to improve the accuracy of the test results.

[0085] In a specific embodiment, the headspace program in the headspace-gas chromatography test is: constant temperature at 120-180° C. for 20-40 minutes, the transfer line temperature is 150-190° C., and the injection time is 0.1-0.2 minutes.

[0086] In a specific embodiment, in the headspace-gas chromatography test, the gas chromatography conditions are: polar chromatographic column HP-INNOWAX: 3 mm*0.25 mm*0.25 μm; inlet temperature: 200~250°C; split ratio: 10:1~50:1; flow rate: 1 ml / min.

[0087] Hereinafter, the method for detecting the content of N-methylpyrrolidone in a battery electrode provided by the present invention is described in detail through specific examples.

[0088] Example 1

[0089] 1) Sample preparation

[0090] Weigh 0.0500 g (accurate to 0.0001 g) of lithium-ion battery electrode sample, cut it into 2 mm * 2 mm pieces with scissors to obtain the first crushed material, and put all of it into a headspace bottle; add 0.1 ml of N,N-dimethylformamide (DMF), seal the headspace bottle within 10 seconds, and obtain the sample to be tested.

[0091] 2) Preparation of standard solution and drawing of standard curve

[0092] Take the pole piece fragments cut out in step 1), bake them at 220° C. for 30 hours to remove the N-methylpyrrolidone in the pole piece, and divide them into 4 portions, each with 0.0500 g, to obtain the second crushed material;

[0093] Weigh 0.1 g (accurate to 0.0001 g) of N-methylpyrrolidone (NMP, mass fraction is 99.8%), dilute to 25 ml with DMF, and obtain a stock solution with a mass concentration of 4 mg / ml; pipette 4 portions of the stock solution, dilute stepwise, and prepare standard solutions with mass concentrations of 25 μg / ml, 125 μg / ml, 500 μg / ml, and 1000 μg / ml, respectively;

[0094] Four portions of the second crushed material were added to four headspace bottles respectively, and 0.1 ml of the standard solution of different concentrations prepared above were respectively taken and added to the four headspace bottles, and sealed within 10 seconds. The chromatograms of the four standard solutions of different mass concentrations were obtained by using a headspace-gas chromatograph, and the chromatographic peak areas were obtained, such as Figure 1-Figure 4 As shown; According to the peak area obtained from the test and the concentration data of the standard solution, the standard curve is obtained: Y=15.5980X+363.831, as shown Figure 5 As shown, Figure 5 Where X represents the mass concentration of NMP in the standard solution, and Y represents the chromatographic peak area;

[0095] Figure 1 The chromatogram of the control sample with a standard solution mass concentration of 25 μg / ml in Example 1 is shown in FIG. Figure 2 The chromatogram of the control sample with a standard solution mass concentration of 125 μg / ml in Example 1 is shown in FIG. Figure 3 The chromatogram of the control sample with a standard solution mass concentration of 500 μg / ml in Example 1 is shown in FIG. Figure 4 The chromatogram of the control sample with a standard solution mass concentration of 1000 μg / ml in Example 1 is shown in FIG. Figure 5 This is the standard curve in Example 1.

[0096] 3) Test samples

[0097] The sample to be tested in step 1) is tested by a headspace-gas chromatograph to obtain a corresponding chromatogram, and then the chromatographic peak area is obtained; Figure 6 is the chromatogram of the sample to be tested in Example 1, Figure 6 In the figure, the chromatographic peak area of ​​the sample to be tested is 3192.

[0098] 4) According to the standard curve obtained in step 2), the chromatographic peak area measured in step 3) is substituted into the standard curve equation, and the NMP concentration in the sample to be tested is obtained as 181.316 μg / ml according to the peak area of ​​NMP in the sample to be tested, and the mass content of NMP in the sample is determined as 362.632 μg / g according to formula 1.

[0099] The above headspace-gas chromatography test conditions are:

[0100] Headspace conditions: sample temperature: 180°C, equilibration time: 20 minutes, valve box temperature: 190°C, transfer line temperature: 190°C, injection time 0.1 minutes; gas chromatography conditions: chromatographic column: polar chromatographic column HP-INNOWAX (3 mm*0.25 mm*0.25 μm), injection port temperature: 250°C, split ratio: 10:1, flow rate: 1 ml / min, heating program: initial temperature 80°C, constant temperature for 4 minutes, heating to 220°C at 10°C / min, and constant temperature for 3 minutes.

[0101] Example 2

[0102] 1) Sample preparation

[0103] Weigh 1.0000 g (accurate to 0.0001 g) of lithium-ion battery electrode sample, cut it into 5 mm*5 mm pieces with scissors to obtain the first crushed material, and put all of it into a headspace bottle; add 2 ml of ethyl acetate, seal the headspace bottle within 10 seconds, and obtain the sample to be tested;

[0104] 2) Preparation of standard solution and drawing of standard curve;

[0105] Take the pole piece fragments cut out in step 1), heat them at 200° C. for 48 hours to remove the N-methylpyrrolidone in the pole piece, and divide them into 4 portions, each weighing 1.0000 g, to obtain a second crushed material;

[0106] Weigh 0.1 g (accurate to 0.0001 g) of N-methylpyrrolidone (NMP, mass fraction is 99.8%), dilute to 25 ml with ethyl acetate, and obtain a stock solution with a mass concentration of 4 mg / ml; pipette 4 portions of the stock solution, dilute stepwise, and prepare standard solutions with mass concentrations of 5 μg / ml, 10 μg / ml, 20 μg / ml, and 50 μg / ml, respectively;

[0107] 4 portions of the second crushed material were added to 4 headspace bottles respectively, 2 ml of the standard solution of different concentrations prepared above were respectively taken and added to the above 4 headspace bottles, and sealed within 10 seconds, and tested by headspace-gas chromatograph respectively to obtain chromatograms of 4 portions of standard solutions of different mass concentrations, and then the chromatographic peak area was obtained, such as Figure 7-10 As shown; Based on the peak area obtained from the test and the concentration data of the standard solution, the standard curve is obtained: Y=58.6724X-57.6416, as shown Fig.11 As shown, Fig.11 Where X represents the mass concentration of NMP in the standard solution, and Y represents the chromatographic peak area;

[0108] Figure 7 The chromatogram of the control sample with a standard solution mass concentration of 5 μg / ml in Example 2 is shown in FIG. Figure 8The chromatogram of the control sample with a standard solution mass concentration of 10 μg / ml in Example 2 is shown in FIG. Fig. 9 The chromatogram of the control sample with a standard solution mass concentration of 20 μg / ml in Example 2 is shown in FIG. Fig.10 The chromatogram of the control sample with a standard solution mass concentration of 50 μg / ml in Example 2 is shown in FIG. Fig.11 This is the standard curve in Example 2.

[0109] 3) Test samples

[0110] The sample to be tested in step 1) is tested by a headspace-gas chromatograph to obtain a corresponding chromatogram, and then the chromatographic peak area is obtained; Fig.12 is the chromatogram of the sample to be tested in Example 2, Fig.12 In the figure, the chromatographic peak area of ​​the sample to be tested is 820.

[0111] 4) According to the standard curve obtained in step 2), the chromatographic peak area measured in step 3) is substituted into the standard curve equation, and the NMP concentration in the sample to be tested is obtained as 14.958 μg / ml according to the peak area of ​​NMP in the sample to be tested, and the mass content of NMP in the sample is determined as 29.916 μg / g according to formula 1;

[0112] The above headspace-gas chromatography test conditions are:

[0113] Headspace conditions: sample temperature: 120°C, equilibration time: 40 minutes, valve box temperature: 150°C, transfer line temperature: 150°C, injection time 0.1 minute; gas chromatography conditions: chromatographic column: polar chromatographic column HP-INNOWAX (3 mm*0.25 mm*0.25 μm), injection port temperature: 200°C, split ratio: 50:1, flow rate: 1 ml / min, heating program: initial temperature 100°C, constant temperature for 3 minutes, heating to 220°C at 10°C / min, and constant temperature for 3 minutes.

[0114] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting the content of N-methylpyrrolidone in a battery pole piece, characterized in that: The following steps are involved: 1) performing a first crushing process on the battery electrode to obtain a first crushed material; placing the first crushed material and a solvent into a headspace bottle, sealing the bottle, and obtaining a sample to be tested; 2) baking the battery electrode at a temperature not lower than 200° C. for more than 24 hours, and then performing a second crushing process to obtain a second crushed material; preparing a standard solution containing N-methylpyrrolidone and a solvent, and placing the second crushed material and the standard solution into a headspace bottle, sealing the bottle, and obtaining a control sample; 3) testing the control sample by headspace-gas chromatography, and using the external standard method to draw a standard curve based on the measured chromatographic peak area; 4) Using headspace-gas chromatography to detect the sample to be tested, obtaining the chromatographic peak area, obtaining the mass content of N-methylpyrrolidone in the sample to be tested according to the standard curve, and calculating the N-methylpyrrolidone content in the battery electrode according to Formula 1, Formula 1 In Formula 1, x is the mass content of N-methylpyrrolidone in the battery electrode, in micrograms / gram; C is the mass content of N-methylpyrrolidone in the sample to be tested obtained according to the standard curve, in micrograms / milliliter; V is the volume of the sample to be tested, in milliliters; and m is the mass of the battery electrode, in grams.

2. The method for detecting the content of N-methylpyrrolidone in a battery pole piece according to claim 1, characterized in that: The mass of the first crushed material in step 1) is consistent with the mass of the second crushed material in step 2); The volume of the solvent in step 1) is consistent with the volume of the standard solution in step 2).

3. The method for detecting the content of N-methylpyrrolidone in a battery pole piece according to claim 2, characterized in that: In step 1), the mass of the first crushed material is 0.02-1 g, and the volume of the solvent is 0.1-2 ml.

4. The method for detecting the content of N-methylpyrrolidone in a battery pole piece according to claim 1, characterized in that: The size of the first crushed material is (2 mm~5 mm)*(2 mm~5 mm); And / or, the size of the second crushed material is (2 mm~5 mm)*(2 mm~5 mm).

5. The method for detecting the content of N-methylpyrrolidone in a battery pole piece according to claim 1, characterized in that: The solvent includes at least one of dimethylacetamide, ethyl acetate, methanol, ethanol, N,N-dimethylformamide, toluene and tetrahydrofuran.

6. The method for detecting the content of N-methylpyrrolidone in a battery pole piece according to claim 1, characterized in that: In step 1), after the first crushed material and the solvent are placed in a headspace bottle, the bottle is sealed within 8 to 12 seconds; In step 2), after the second crushed material and the standard solution are placed in the headspace bottle, the bottle is sealed within 8 to 12 seconds.

7. The method for detecting the content of N-methylpyrrolidone in a battery pole piece according to any one of claims 1 to 6, characterized in that: The preparation of the standard solution in step 2) includes: using a solvent to adjust the volume of N-methylpyrrolidone to obtain a reserve solution; then weighing a portion of the reserve solution and diluting it step by step to obtain the standard solution.

8. The method for detecting the content of N-methylpyrrolidone in a battery pole piece according to claim 7, characterized in that: The concentration of the standard solution is 5-1000 μg / ml.

9. The method for detecting the content of N-methylpyrrolidone in a battery pole piece according to claim 1, characterized in that: The headspace procedure in the headspace-gas chromatography test is: constant temperature at 120-180° C. for 20-40 minutes, the transmission line temperature is 150-190° C., and the injection time is 0.1-0.2 minutes.

10. The method for detecting the content of N-methylpyrrolidone in a battery pole piece according to claim 1, characterized in that: In the headspace-gas chromatography test, the gas chromatography conditions are: polar chromatography column HP-INNOWAX: 3 mm*0.25 mm*0.25 μm; injection port temperature: 200-250°C; split ratio: 10:1-50:1; Flow rate: 1 ml / min.

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