Method for determining the solids content of an oil-based conductive paste and use

Abstract

The application provides a determination method and application of solid content of an oily conductive paste, and relates to the technical field of lithium ion batteries. The determination method comprises the following steps: taking a required amount of the oily conductive paste, determining the moisture content of the oily conductive paste, extracting solvent A in the remaining amount of the oily conductive paste by using solvent B, diluting the solvent A, and then performing gas chromatography-mass spectrometry analysis to obtain the content of the solvent A in the oily conductive paste; and the solid content of the oily conductive paste is calculated by using the relationship between the solid content of the oily conductive paste and the moisture content and the content of the solvent A. In the determination method, the solvent A in the oily conductive paste does not need to be dried through an oven, so that the pollution to the environment is reduced, the time required in the whole determination process is short, and the production efficiency is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method and application for determining the solid content of an oily conductive slurry. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in the field of rechargeable batteries due to their advantages such as high energy density, long lifespan, and environmental friendliness. The main materials of a lithium-ion battery include four parts: the positive electrode, the negative electrode, the separator, and the electrolyte. The positive electrode sheet is mainly made by dissolving and dispersing active materials, conductive agents, and binders in a solvent to form a slurry, which is then coated onto a foil and dried. The conductive agent's main function is to improve electronic conductivity; commonly used materials include carbon nanotubes, conductive carbon black (SP), or graphene. However, these conductive agents have a large specific surface area, and direct dispersion in the positive electrode slurry can easily lead to agglomeration, affecting the battery's cycle performance and rate performance. Therefore, the conductive agent is usually first prepared as a conductive slurry before being added to the positive electrode slurry.

[0003] Conductive pastes are mainly composed of conductive agents, dispersants, and solvents. The solid components are the conductive agents and dispersants. The solid content of conductive pastes is closely related to their conductivity. Theoretically, a higher solid content is beneficial for improving the conductivity of the battery cell. However, exceeding the critical volume concentration does not improve conductivity; instead, it reduces the cell capacity. Therefore, accurately determining the solid content of conductive pastes is essential. Based on the different solvents in the conductive paste, it can generally be divided into water-based and oil-based conductive pastes, with oil-based conductive pastes being more commonly used. Currently, the common method for testing the solid content of oil-based conductive pastes is the drying method. The drying method utilizes the difference in volatility between the solid substances and the solvent in the conductive paste. During the heating process, the solvent evaporates first, leaving the conductive medium and other solid substances behind. The solid content of the sample can be calculated based on the mass change of the conductive paste. The specific steps are as follows: first, weigh and tare a piece of foil; then, evenly coat 1-5g of conductive paste onto the foil; and finally, bake it in a forced-air oven at 120-150℃ for 2-3 hours. After baking, weigh the sample and calculate the solid content. However, the solvents volatilized from the prolonged baking of the paste in the above method will pollute the environment, and the time required is relatively long, which is not conducive to improving production efficiency.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the solid content of oily conductive paste, which can accurately determine the solid content of oily conductive paste without causing environmental pollution, and in a short time.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for determining the solid content of an oily conductive paste, comprising the following steps:

[0008] (a) Providing an oil-based conductive slurry, said oil-based conductive slurry comprising a conductive agent, a dispersant, and solvent A;

[0009] Take the required amount of oily conductive paste and determine its moisture content w1 using a moisture analyzer.

[0010] (b) Solvent B is added to the remaining amount of oily conductive slurry for ultrasonic extraction, then centrifugation is performed to obtain the supernatant, and the supernatant is filtered to obtain a mixed solution containing solvent A.

[0011] (c) Take the required amount of the mixed solution and dilute it with solvent B to obtain the solution to be tested;

[0012] (d) Gas chromatography-mass spectrometry analysis was performed on the test solution to obtain the content w2 of solvent A in the oily conductive slurry. The solid content of the oily conductive slurry was calculated according to the following formula (1):

[0013] w0 = 100% - w1 - w2 (1),

[0014] Where w0 is the solid content of the oily conductive slurry, %; w1 is the moisture content of the oily conductive slurry, %; and w2 is the content of solvent A in the oily conductive slurry, %.

[0015] Furthermore, based on the above technical solution of the present invention, in step (a), the conductive agent includes carbon nanotubes and / or graphene.

[0016] And / or, the solvent A comprises N-methylpyrrolidone and / or dimethyl sulfoxide.

[0017] Furthermore, based on the above technical solution of the present invention, in step (a), the temperature of the moisture analyzer is set to 150-180℃;

[0018] And / or, the gas flow rate of the moisture analyzer is set to 50-60 mL / min.

[0019] Furthermore, based on the above technical solution of the present invention, in step (b), the solvent B includes at least one of methanol, n-hexane or dichloromethane;

[0020] And / or, the mass-to-volume ratio of the remaining oily conductive slurry to solvent B is (3-5) g: (30-50) mL;

[0021] And / or, the ultrasonic extraction time is 3-10 min;

[0022] And / or, the frequency of the ultrasonic extraction is 30-50 kHz;

[0023] And / or, the power of the ultrasonic extraction is 200-300W.

[0024] Furthermore, based on the above technical solution of the present invention, in step (b), the centrifugation time is 3-5 minutes;

[0025] And / or, the centrifugation speed is 10000-15000 rpm;

[0026] And / or, the filter membrane used for filtration is an oil-based filter membrane with a pore size of 0.22 μm or 0.45 μm.

[0027] Furthermore, based on the above technical solution of the present invention, in step (c), the required volume of the mixed solution is 5-20 μL;

[0028] And / or, the dilution factor is 100-200 times.

[0029] Furthermore, based on the above-mentioned technical solution of the present invention, in step (d), during the gas chromatography-mass spectrometry analysis, the SIM / SACN mixed mode is used to detect the solution to be tested, the peak area of ​​solvent A is obtained, and the content of solvent A in the oily conductive slurry is obtained by combining the linear equation of the standard curve of solvent A.

[0030] Furthermore, based on the above-described technical solution of this invention, in step (d), the method for obtaining the linear equation of the standard curve of solvent A includes:

[0031] Solvent A is added to solvent B and mixed evenly to obtain mixed solution I. The required amount of mixed solution I is diluted with solvent B to obtain multiple standard solutions of solvent A with progressively varying concentrations.

[0032] The SIM / SCAN mode was used to detect standard solutions of solvent A at different concentrations to obtain the peak area of ​​solvent A at different concentrations. The concentration of solvent A in the standard solutions of different concentrations and the peak area of ​​solvent A in the corresponding standard solutions were used to plot the standard curve to obtain the linear equation of the standard curve of solvent A.

[0033] Alternatively, in step (d), the method for obtaining the linear equation of the standard curve of solvent A includes:

[0034] Multiple masses of solvent A are added to the same volume of solvent B and mixed thoroughly to obtain mixed solutions I of different concentrations. The required amount of each concentration of mixed solution I is diluted with solvent B by the same factor to obtain multiple standard solutions of solvent A with progressively varying concentrations. The amount of solvent B used to prepare mixed solutions I of different concentrations is the same as the amount of solvent B used in step (b) when preparing the mixed solution containing solvent A. The required amount of each concentration of mixed solution I is the same and the same as the required amount of the mixed solution in step (c). The dilution factor of mixed solution I is the same as the dilution factor of the mixed solution in step (c).

[0035] The standard solutions of solvent A at different concentrations were detected using the SIM / SCAN mode to obtain the peak areas of solvent A at different concentrations. A standard curve was plotted using the mass of solvent A in mixed solution I of different concentrations and the peak areas of solvent A in the standard solutions formed by the corresponding mixed solution I, so as to obtain the linear equation of the standard curve of solvent A.

[0036] Furthermore, based on the above-described technical solution of this invention, in step (c), the chromatographic determination conditions in the SIM / SACN mixed mode include at least one of the following operating parameters:

[0037] The chromatographic column was an Rtx-MS column with a length of 30 m, an inner diameter of 0.25 mm, and a film thickness of 0.25 μm.

[0038] And / or, the carrier gas is helium with a purity of 99.999%;

[0039] And / or, injection volume 1 μL, split ratio 10-30:1;

[0040] And / or, the number of times solvent B is rinsed before injection is 1-5 times; the number of times solvent B is rinsed after injection is 1-5 times; the number of times the sample is rinsed is 1-5 times;

[0041] And / or, the injection port temperature is 230-260℃;

[0042] And / or, heating program: initial temperature 80-120℃, hold for 3-5 min; increase temperature to 100-150℃ at a rate of 5-10℃ / min, and increase temperature to 200-250℃ at a rate of 5-15℃ / min.

[0043] And / or, the mass spectrometry conditions are: EI source, ion source temperature of 200-230℃, and interface temperature of 230-260℃.

[0044] The present invention also provides the application of the above-mentioned method for determining the solid content of oily conductive slurry in the field of lithium-ion batteries.

[0045] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0046] (1) This invention provides a method for determining the solid content of an oily conductive slurry. First, a required amount of oily conductive slurry is taken and its moisture content is determined. Then, solvent A in the remaining amount of oily conductive slurry is extracted using solvent B to obtain a mixed solution containing solvent A. The required amount of the mixed solution is then diluted with solvent B and subjected to gas chromatography-mass spectrometry analysis to obtain the content of solvent A in the oily conductive slurry. The solid content of the oily conductive slurry is calculated using the relationship between the solid content of the oily conductive slurry, its moisture content, and the content of solvent A. This method does not require drying solvent A in the oily conductive slurry in an oven during the determination process, reducing environmental pollution. The entire determination process is also short, greatly improving production efficiency.

[0047] (2) The present invention provides the application of the above-mentioned method for determining the solid content of oily conductive slurry. Given the advantages of the above-mentioned method, it has good application prospects in the field of lithium-ion batteries. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0049] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0050] According to a first aspect of the present invention, a method for determining the solid content of an oily conductive paste is provided, comprising the following steps:

[0051] (a) Providing an oil-based conductive slurry, said oil-based conductive slurry comprising a conductive agent, a dispersant, and solvent A;

[0052] Take the required amount of oily conductive paste and determine its moisture content w1 using a moisture analyzer.

[0053] (b) Solvent B is added to the remaining amount of oily conductive slurry for ultrasonic extraction, then centrifugation is performed to obtain the supernatant, and the supernatant is filtered to obtain a mixed solution containing solvent A.

[0054] (c) Take the required amount of the mixed solution and dilute it with solvent B to obtain the solution to be tested;

[0055] (d) Gas chromatography-mass spectrometry analysis was performed on the test solution to obtain the content w2 of solvent A in the oily conductive slurry. The solid content of the oily conductive slurry was calculated according to the following formula (1):

[0056] w0 = 100% - w1 - w2 (1),

[0057] Where w0 is the solid content of the oily conductive slurry, %; w1 is the moisture content of the oily conductive slurry, %; and w2 is the content of solvent A in the oily conductive slurry, %.

[0058] Specifically, the solid substances in oily conductive slurry are conductive agents and dispersants. Since solvent A in oily conductive slurry may absorb some water, when determining the solid content in oily conductive slurry, it is only necessary to determine the content of solvent A and water in oily conductive slurry. Then, the solid content of oily conductive slurry can be obtained by using the formula: solid content of oily conductive slurry = 100% - content of solvent A in oily conductive slurry - water content in oily conductive slurry.

[0059] Step (a) involves using a moisture analyzer to measure the moisture content in the oily conductive slurry.

[0060] Step (b) mainly involves first extracting solvent A from the oily conductive slurry into the mixed solution, and then diluting it in step (c) so that the resulting test solution can meet the requirements of gas chromatography-mass spectrometry analysis.

[0061] Step (d) involves gas chromatography-mass spectrometry analysis of the test solution. First, the concentration of solvent A in the test solution is obtained. Then, based on the amount of solvent B used in preparing the mixed solution in step (b), the dilution factor in step (c), and the concentration of solvent A in the test solution, the mass of solvent A in the remaining amount of oily conductive slurry in step (b) is calculated. The content of solvent A in the oily conductive slurry is obtained by dividing the mass of solvent A in the remaining amount of oily conductive slurry in step (b) by the mass of the remaining amount of oily conductive slurry in step (b). Finally, the solid content of the oily conductive slurry is calculated using formula (1).

[0062] This invention provides a method for determining the solid content of an oily conductive slurry. First, a required amount of oily conductive slurry is taken, and its moisture content is determined. Then, solvent A is extracted from the remaining amount of oily conductive slurry using solvent B. After dilution, the extracted solvent A is analyzed by gas chromatography-mass spectrometry to obtain the solvent A content in the oily conductive slurry. The solid content of the oily conductive slurry is calculated using the relationship between its solid content, moisture content, and solvent A content. This method eliminates the need for drying solvent A in an oven, reducing environmental pollution. Furthermore, it is faster, taking only 1 / 10 to 1 / 3 of the time required by the drying method, thus improving production efficiency.

[0063] In an optional embodiment of the present invention, in step (a), the conductive agent includes carbon nanotubes and / or graphene. Here, "and / or" means that the conductive agent may include only carbon nanotubes, only graphene, or both carbon nanotubes and graphene.

[0064] Solvent A for the oily conductive paste can be any type of solvent commonly used in the art. As an optional embodiment of the present invention, solvent A includes N-methylpyrrolidone (NMP) and / or dimethyl sulfoxide (DMSO).

[0065] As an optional embodiment of the present invention, the temperature of the moisture analyzer is set to 150-180°C, and the typical but non-limiting temperature is 150°C, 160°C, 170°C, 180°C or any numerical range formed by two points.

[0066] In the process of measuring moisture using a moisture analyzer, a certain amount of gas (e.g., air) is introduced to remove the evaporated moisture. As an optional embodiment of the present invention, the gas flow rate of the moisture analyzer is set to 50-60 mL / min, with typical but non-limiting gas flow rates being 50 mL / min, 52 mL / min, 54 mL / min, 55 mL / min, 56 mL / min, 58 mL / min, 60 mL / min, or any range formed by any two points.

[0067] As an optional embodiment of the present invention, a Karl Fischer moisture analyzer is selected as the moisture analyzer.

[0068] As an optional embodiment of the present invention, in step (b), solvent B includes at least one of methanol, n-hexane or dichloromethane, and its purity level can be selected as chromatographic grade.

[0069] By further restricting solvent B, it is made to have good dissolving ability for solvent A, which can fully extract solvent A from the remaining amount of oily conductive slurry, thereby improving the accuracy of test results.

[0070] It should be noted that the remaining amount of oily conductive paste refers to the oily conductive paste from the same batch as the amount required in step (a) that has not undergone moisture content determination. That is, the oily conductive paste provided in step (a) is divided into two parts: one part is the required amount of oily conductive paste used to determine the moisture content, and the other part is the remaining amount of oily conductive paste used to determine the content of solvent A.

[0071] As an optional embodiment of the present invention, in step (b), the mass-to-volume ratio of the remaining amount of oily conductive slurry to solvent B is (3-5) g:(30-50) mL, and typical but non-limiting mass-to-volume ratios are 3 g:30 mL, 3 g:40 mL, 3 g:50 mL, 4 g:30 mL, 4 g:40 mL, 4 g:50 mL, 5 g:30 mL, 5 g:40 mL, or 5 g:50 mL, etc.

[0072] As an optional embodiment of the present invention, in step (b), the ultrasonic extraction time is 3-10 min; typically but not limitingly, the ultrasonic extraction time is 3 min, 5 min, 6 min, 8 min, 10 min or any range of values ​​formed by two points.

[0073] As an optional embodiment of the present invention, in step (b), the frequency of ultrasonic extraction is 30-50 kHz; typically but not limitingly, the frequency of ultrasonic extraction is 30 kHz, 40 kHz, 50 kHz or any numerical range formed by two point values.

[0074] As an optional embodiment of the present invention, in step (b), the power of ultrasonic extraction is 200-300W. Typical but non-limiting power is 200W, 220W, 240W, 250W, 260W, 280W, 300W, or any range of values ​​formed by two points.

[0075] As an optional embodiment of the present invention, in step (b), the centrifugation time is 3-5 minutes. Typical but non-limiting centrifugation times are 3 minutes, 4 minutes, or 5 minutes.

[0076] As an optional embodiment of the present invention, in step (b), the centrifugation speed is 10,000-15,000 rpm. Typical but non-limiting centrifugation speeds are 10,000 rpm, 11,000 rpm, 12,000 rpm, 13,000 rpm, 14,000 rpm, 15,000 rpm, or any range of values ​​formed by any two points.

[0077] As an optional embodiment of the present invention, in step (b), the filter membrane used for filtration is an oil-based filter membrane with a pore size of 0.22 μm or 0.45 μm.

[0078] By limiting the specific process parameters in the extraction, centrifugation, and filtration processes, solvent A can be extracted more fully.

[0079] As an optional embodiment of the present invention, in step (c), the required volume of the mixed solution is 5-20 μL, typically but not limitingly, 5 μL, 10 μL, 15 μL, 20 μL or any range of values ​​formed by two points.

[0080] In an optional embodiment of the present invention, in step (c), the dilution factor is 100-200 times. Typical but non-limiting factors are 100 times, 120 times, 140 times, 150 times, 160 times, 180 times, 200 times, or any numerical range formed by two point values. By performing the above dilution, the concentration of solvent A can be reduced, preventing column supersaturation and improving the lifespan and accuracy of the GCMS.

[0081] As an optional embodiment of the present invention, in step (d), during the gas chromatography-mass spectrometry analysis, the SIM / SACN mixed mode is used to detect the test solution, obtain the peak area of ​​solvent A, and calculate the content of solvent A in the oily conductive slurry by combining the linear equation of the standard curve of solvent A.

[0082] As an optional embodiment of the present invention, in step (d), the method for obtaining the linear equation of the standard curve of solvent A includes:

[0083] Solvent A is added to solvent B and mixed evenly to obtain mixed solution I. The required amount of mixed solution I is diluted with solvent B to obtain multiple standard solutions of solvent A with progressively varying concentrations.

[0084] The SIM / SCAN mode was used to detect standard solutions of solvent A at different concentrations to obtain the peak area of ​​solvent A at different concentrations. A standard curve was plotted using the concentration of solvent A in the standard solutions of different concentrations and the peak area of ​​solvent A in the corresponding standard solutions to obtain the linear equation of the standard curve of solvent A.

[0085] It should be noted that when preparing standard solutions of solvent A at different concentrations, if the amount of solvent B used in preparing mixed solution I is different from the amount of solvent B used in step (b), and the dilution factor of mixed solution I is different from the dilution factor of the mixed solution in step (c), then the concentration of solvent A in the test solution should be obtained first by gas chromatography-mass spectrometry analysis. Then, based on the amount of solvent B used in preparing the mixed solution in step (b), the dilution factor in step (c), and the concentration of solvent A in the test solution, the mass of solvent A in the mixed solution should be calculated (this mass is the mass of solvent A in the remaining amount of oily conductive slurry). Finally, based on the mass of the remaining amount of oily conductive slurry in step (b), the content of solvent A in the oily conductive slurry should be calculated.

[0086] As another optional embodiment of the present invention, in step (d), the method for obtaining the linear equation of the standard curve of solvent A includes:

[0087] Solvent A of various masses is added to the same volume of solvent B and mixed evenly to obtain mixed solutions I of different concentrations. The required amount of each concentration of mixed solution I is taken and diluted with solvent B by the same factor to obtain multiple standard solutions of solvent A with progressively varying concentrations. The amount of solvent B used to prepare mixed solutions I of different concentrations is the same as the amount of solvent B used in step (b) to prepare the mixed solution containing solvent A. The required amount of each concentration of mixed solution I is the same as the required amount of the mixed solution in step (c). The dilution factor of mixed solution I is the same as the dilution factor of the mixed solution in step (c).

[0088] The standard solutions of solvent A at different concentrations were detected using the SIM / SCAN mode to obtain the peak areas of solvent A at different concentrations. A standard curve was plotted using the mass of solvent A in mixed solution I of different concentrations and the peak areas of solvent A in the standard solutions formed by the corresponding mixed solution I, so as to obtain the linear equation of the standard curve of solvent A.

[0089] When the amount of solvent B used to prepare mixed solutions I of different concentrations is the same as the amount of solvent B used in preparing mixed solutions containing solvent A in step (b), and the dilution factor of mixed solution I is the same as the dilution factor of the mixed solution in step (c), the dilution factor can be simultaneously canceled out when applying the linear relationship with the standard curve equation, and the content (concentration) of solvent A in the mixed solution in step (b) can be directly obtained. Then, based on the content (concentration) of solvent A in the mixed solution in step (b), the amount of solvent B used in preparing the mixed solution, and the mass of the remaining oily conductive slurry in step (b), the content of solvent A in the oily conductive slurry can be calculated. Alternatively, when applying the linear relationship with the standard curve equation, the dilution factor and the amount of solvent B used in preparing the mixed solution (mixed solution I) can be simultaneously canceled out, and the mass of solvent A in the mixed solution in step (b) can be directly obtained (this mass is the mass of solvent A in the remaining oily conductive slurry). Then, based on the mass of the remaining oily conductive slurry in step (b), the content of solvent A in the oily conductive slurry can be calculated.

[0090] Therefore, a standard curve can be plotted using the concentration of solvent A in standard solutions of different concentrations and the peak area of ​​solvent A in standard solutions of corresponding concentrations, and the corresponding linear equation of the standard curve of solvent A can be obtained. Alternatively, a standard curve can be plotted using the mass of solvent A in mixed solution I of different concentrations and the peak area of ​​solvent A in the standard solution formed by mixed solution I of corresponding concentrations, and the corresponding linear equation of the standard curve of solvent A can be obtained.

[0091] As an optional embodiment of the present invention, in step (d), the chromatographic determination conditions in the SIM / SACN mixed mode include at least one of the following operating parameters:

[0092] The chromatographic column was an Rtx-MS column with a length of 30 m, an inner diameter of 0.25 mm, and a film thickness of 0.25 μm.

[0093] And / or, the carrier gas is helium with a purity of 99.999%;

[0094] And / or, the injection volume is 1 μL, and the split ratio is 10-30:1 (including but not limited to 10:1, 20:1 or 30:1);

[0095] And / or, the number of times solvent B is rinsed before injection is 1-5 times (e.g., 1, 2, 3, 4 or 5 times); the number of times solvent B is rinsed after injection is 1-5 times (e.g., 1, 2, 3, 4 or 5 times); the number of times sample is rinsed is 1-5 times (e.g., 1, 2, 3, 4 or 5 times).

[0096] And / or, the injection port temperature is 230-260℃ (including but not limited to 230℃, 240℃, 250℃ or 260℃);

[0097] And / or, the temperature program: initial temperature 80-120℃ (including but not limited to 80℃, 100℃, 110℃, or 120℃), maintain for 3-5 min; increase the temperature at a rate of 5-10℃ / min to 100-150℃ (including but not limited to 100℃, 110℃, 120℃, 140℃, or 150℃), and increase the temperature at a rate of 5-15℃ / min to 200-250℃ (including but not limited to 200℃, 220℃, 230℃, 240℃, or 250℃);

[0098] And / or, the mass spectrometry conditions are: EI source, ion source temperature of 200-230℃ (including but not limited to 200℃, 210℃, 220℃ or 230℃), and interface temperature of 230-260℃ (including but not limited to 230℃, 240℃, 250℃ or 260℃).

[0099] By further limiting the chromatographic determination conditions described above, the accuracy of the determination results and the lifespan of the GCMS can be improved.

[0100] In the method of this invention, the determination of moisture content in the oily conductive slurry takes approximately 3-5 minutes, ultrasonic extraction takes approximately 3-10 minutes, centrifugation takes 3-5 minutes, and the dilution of the mixed solution and gas chromatography-mass spectrometry analysis take approximately 10-20 minutes. The total time taken is 19-40 minutes. Therefore, the entire determination process takes less time than conventional baking, significantly improving production efficiency.

[0101] According to a second aspect of the present invention, the application of the above-described method for determining the solid content of oily conductive slurry in the field of lithium-ion batteries is also provided.

[0102] Given the advantages of the above-mentioned method for determining the solid content of oily conductive slurry, it has good application prospects in the field of lithium-ion batteries.

[0103] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0104] Example 1

[0105] This embodiment provides a method for determining the solid content of an oily conductive paste, including the following steps:

[0106] (a) Provide an oily conductive slurry; wherein the oily conductive slurry includes a conductive agent, a dispersant and a solvent A, the conductive agent being carbon nanotubes (0.5-2 μm in length and about 50 nm in diameter), the dispersant being DIS-NMP, and the solvent A being NMP.

[0107] The Karl Fischer moisture analyzer was set to a measuring temperature of 150℃ and a gas flow rate of 50 mL / min.

[0108] The sample bottles and blank bottles used to hold the oily conductive paste were placed in the same environment for drying treatment, specifically: vacuum baking at 110℃ for 6 hours, and then placed in a room temperature environment with less than 3% humidity for 3 hours.

[0109] Weigh the required amount of oily conductive paste and determine its moisture content w1 using a moisture analyzer. Specifically, weigh approximately 0.2g of oily conductive paste into five sample bottles using an electronic balance. Place the blank bottle in position 1, and place the five sample bottles in positions 2, 3, 4, 5, and 6 respectively, labeling them Sample 1, Sample 2, Sample 3, Sample 4, and Sample 5. Input the actual mass of the oily conductive paste and press the start button on the instrument to perform the moisture test, obtaining the moisture content w1 of the oily conductive paste. It should be noted that the purpose of setting up the blank bottle is to measure the moisture in the blank bottle as a blank experiment. When the moisture analyzer measures the moisture in Samples 1-6, the moisture mass in the blank bottle will be automatically subtracted. The specific test results are shown in Table 1.

[0110] Table 1

[0111] Sample Name Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Mass (g) 0.2125 0.2006 0.2350 0.2169 0.2113 Moisture content (ppm) 512.04 536.43 548.26 521.56 519.20

[0112] Based on the moisture content of samples 1-5 in Table 1, the average moisture content in the oily conductive slurry was calculated to be 527.498 ppm.

[0113] (b) Weigh out 5 portions of 5g oily conductive slurry from the remaining amount of oily conductive slurry, add 50mL of solvent B (n-hexane, chromatographic grade) to each portion for ultrasonic extraction, then centrifuge to obtain the supernatant, and filter the supernatant to obtain a mixed solution containing solvent A (NMP).

[0114] The ultrasonic extraction time was 5 min, the frequency was 40 kHz, and the power was 250 W; the centrifugation time was 5 min, and the centrifugation speed was 10000 rpm; the filter membrane used for filtration was a 0.22 μm oil-based filter membrane.

[0115] (c) Take 10 μL of the mixed solution and dilute it 100 times with solvent B (n-hexane, chromatographic grade) to obtain the test solution;

[0116] (d) The SIM / SCAN mixed mode of GCMS was used to detect the test solution and obtain the peak area of ​​NMP. The content of NMP in the oily conductive slurry w2 was calculated by combining the linear equation of the standard curve of NMP. The solid content of the oily conductive slurry was calculated according to the following formula (1):

[0117] w0 = 100% - w1 - w2 (1),

[0118] Where w0 is the solid content of the oily conductive slurry, %; w1 is the moisture content of the oily conductive slurry, %; and w2 is the content of solvent A in the oily conductive slurry, %.

[0119] The chromatographic determination conditions in the SIM / SCAN mixed mode of GCMS include:

[0120] The chromatographic column was an Rtx-MS column with dimensions of 30m (length) × 0.25mm (inner diameter) × 0.25μm (film thickness).

[0121] The carrier gas is helium, with a purity of 99.999%.

[0122] The injection volume was 1 μL, and the split ratio was 30:1.

[0123] The number of rinses with solvent B (before injection) is 3; the number of rinses with solvent B (after injection) is 3; the number of rinses with sample is 2.

[0124] The injection port temperature is 250℃;

[0125] Temperature program: Initial temperature 100℃, hold for 3 min; increase temperature to 120℃ at a rate of 5℃ / min, and increase temperature to 220℃ at a rate of 10℃ / min.

[0126] The mass spectrometry conditions were: EI source, ion source temperature 200℃, and interface temperature 250℃.

[0127] The method for preparing the linear equation of the standard curve of NMP is as follows:

[0128] 2g, 5g, and 10g of NMP were added to 50mL of solvent B (n-hexane) and mixed thoroughly to obtain mixed solution I. Then, 10μL of mixed solution I was diluted 100-fold with n-hexane to prepare NMP standard solutions with progressively varying concentrations. The NMP standard solutions of different concentrations were detected using the SIM / SCAN mixed mode of GCMS. Based on the GCMS peak chromatograms of the NMP standard solutions, the peak areas of NMP at each concentration were obtained, as shown in Table 2.

[0129] Table 2

[0130] Mass of NMP in Mixed Solution I 2g 5g 10g NMP concentration (g / mL) in mixed solution I 0.04 0.1 0.2 NMP concentration (mg / mL) after dilution of mixed solution I 0.4 1 2 Peak area 1122080 3225832 6058247

[0131] Then, a standard curve was plotted using the mass of NMP in mixed solutions of different concentrations I and the peak area of ​​NMP in the standard solutions formed from the corresponding concentrations of mixed solutions I. The resulting standard curve equation for NMP is y = 611864x + 1490.6, R0 2=0.9966. Based on the measured peak area of ​​the sample and the NMP standard curve equation, the results are shown in the table below:

[0132] Table 3

[0133]

[0134] Based on the data in the table, the relative standard deviation of the solid content of the oily conductive slurry determined by the method of this embodiment is 3.91%, which is less than 5%. This indicates that the consistency of the solid content determination of the oily conductive slurry by this method is good and can be used as the test result.

[0135] Example 2

[0136] This embodiment provides a method for determining the solid content of an oily conductive paste, including the following steps:

[0137] (a) Provide an oily conductive slurry; wherein the oily conductive slurry includes a conductive agent, a dispersant and a solvent A, the conductive agent being graphene (with a sheet diameter of 0.5 to 5 μm and a thickness of 0.8 to 1.2 nm), the dispersant being KD1, and the solvent A being NMP.

[0138] The Karl Fischer moisture analyzer was set to a measuring temperature of 150℃ and a gas flow rate of 50 mL / min.

[0139] The sample bottles and blank bottles used to hold the conductive paste were placed in the same environment for drying treatment, specifically: vacuum baking at 110℃ for 6 hours, and then placed in a room temperature environment with less than 3% humidity for 4 hours.

[0140] Weigh the required amount of oily conductive paste and determine its moisture content w1 using a moisture analyzer. Specifically, weigh approximately 0.2g of oily conductive paste into five sample bottles using an electronic balance. Place the blank bottle in position 1, and place the five sample bottles in positions 2, 3, 4, 5, and 6 respectively, labeling them Sample 1, Sample 2, Sample 3, Sample 4, and Sample 5. Input the actual mass of the oily conductive paste and press the start button on the instrument to perform the moisture test, obtaining the moisture content w1 of the oily conductive paste. It should be noted that the purpose of setting up the blank bottle is to measure the moisture in the blank bottle as a blank experiment. When the moisture analyzer measures the moisture in Samples 1-6, the mass in the blank bottle will be automatically subtracted. The specific test results are shown in Table 4.

[0141] Table 4

[0142] Sample Name Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Mass (g) 0.2452 0.2354 0.2015 0.2943 0.2821 Moisture content (ppm) 301.25 334.64 312.76 322.42 300.02

[0143] Based on the moisture content of samples 1-5 in Table 4, the average moisture content w1 in the oily conductive slurry was calculated to be 314.218 ppm.

[0144] (b) Weigh out 5 portions of 5g oily conductive slurry from the remaining amount of oily conductive slurry, add 50mL of solvent B (dichloromethane, chromatographic grade) to each portion for ultrasonic extraction, then centrifuge to obtain the supernatant, and filter the supernatant to obtain a mixed solution containing solvent A (NMP).

[0145] The ultrasonic extraction time was 5 min, the frequency was 40 kHz, and the power was 250 W; the centrifugation time was 5 min, and the centrifugation speed was 10000 rpm; the filter membrane used for filtration was a 0.22 μm oil-based filter membrane.

[0146] (c) Take 10 μL of the mixed solution and dilute it 100 times with solvent B (dichloromethane, chromatographic grade) to obtain the test solution;

[0147] (d) The SIM / SCAN mixed mode of GCMS was used to detect the test solution and obtain the peak area of ​​NMP. The content of NMP in the oily conductive slurry w2 was calculated by combining the linear equation of the standard curve of NMP. The solid content of the oily conductive slurry was calculated according to the following formula (1):

[0148] w0 = 100% - w1 - w2 (1),

[0149] Where w0 is the solid content of the oily conductive slurry, %; w1 is the moisture content of the oily conductive slurry, %; and w2 is the content of solvent A in the oily conductive slurry, %.

[0150] The chromatographic determination conditions in the SIM / SCAN mixed mode of GCMS include:

[0151] The chromatographic column was an Rtx-MS column with dimensions of 30m (length) × 0.25mm (inner diameter) × 0.25μm (film thickness).

[0152] The carrier gas is helium, with a purity of 99.999%.

[0153] The injection volume was 1 μL, and the split ratio was 30:1.

[0154] The number of rinses with solvent B (before injection) is 3; the number of rinses with solvent B (after injection) is 3; the number of rinses with sample is 2.

[0155] The injection port temperature is 250℃;

[0156] Temperature program: Initial temperature 100℃, hold for 3 min; increase temperature to 120℃ at a rate of 5℃ / min, then increase temperature to 220℃ at a rate of 10℃ / min.

[0157] The mass spectrometry conditions were: EI source, ion source temperature 200℃, and interface temperature 250℃.

[0158] The method for preparing the linear equation of the standard curve of NMP is as follows:

[0159] 2g, 5g, and 10g of NMP were added to 50mL of solvent B, dichloromethane, and mixed thoroughly to obtain mixed solution I. Then, 10μL of mixed solution I was diluted 100-fold with dichloromethane to prepare NMP standard solutions with progressively varying concentrations. The NMP standard solutions of different concentrations were detected using the SIM / SCAN mixed mode of GCMS. Based on the GCMS peak chromatograms of the NMP standard solutions, the peak areas of NMP at each concentration were obtained, as shown in Table 5.

[0160] Table 5

[0161]

[0162]

[0163] Then, a standard curve was plotted using the mass of NMP in mixed solutions of different concentrations I and the peak area of ​​NMP in the standard solutions formed from the corresponding concentrations of mixed solutions I. The resulting standard curve equation for NMP is y = 664137x - 335728, R0 2 =0.9951. Based on the measured peak area of ​​the sample and the NMP standard curve equation, the results are shown in the table below:

[0164] Table 6

[0165]

[0166] Based on the data in the table, the relative standard deviation of the solid content of the oily conductive slurry determined by the method of this embodiment is 4.28%, which is less than 5%. This indicates that the consistency of the solid content determination of the oily conductive slurry by this method is good and can be used as the test result.

[0167] Example 3

[0168] This embodiment provides a method for determining the solid content of an oily conductive slurry. Except for replacing solvent B with an equal amount of methanol instead of hexane, the other steps are the same as in Example 1.

[0169] Similarly, when preparing the linear equation method for the NMP standard curve, solvent B can be replaced with an equal amount of methanol instead of hexane. Based on the GC-MS peak elution chromatogram of the NMP standard solution, the peak areas of NMP at various concentrations are obtained, as shown in Table 7.

[0170] Table 7

[0171]

[0172]

[0173] Then, a standard curve was plotted using the mass of NMP in mixed solutions of different concentrations I and the peak area of ​​NMP in the standard solutions formed from the corresponding concentrations of mixed solutions I. The resulting standard curve equation for NMP is y = 610883x - 167923, R0 2 =0.998. Based on the measured peak area of ​​the sample and the NMP standard curve equation, the results are shown in the table below:

[0174] Table 8

[0175]

[0176] Based on the data in the table, the relative standard deviation of the solid content of the oily conductive slurry determined by the method of this embodiment is 4.35%, which is less than 5%. This indicates that the consistency of the solid content determination of the oily conductive slurry by this method is good and can be used as the test result.

[0177] Comparative Example 1

[0178] This comparative example provides a method for determining the solid content in an existing oily conductive slurry, comprising the following steps:

[0179] (1) First, take a piece of foil, weigh and tare it, and then weigh a portion of the remaining oily conductive paste from step (b) of Example 1 and coat it evenly on the foil.

[0180] (2) Then the foil coated with oily conductive paste was placed in a forced-air oven and baked at 150°C for 3 hours. After baking, the solid content was calculated by weighing. The specific results are shown in Table 9.

[0181] Table 9

[0182]

[0183] Based on the data in the table, the relative standard deviation of the solid content determination of oily conductive slurry using this comparative method is 4.3%.

[0184] As can be seen from the data in the table above, the relative standard deviation of the solid content measured by the examples and comparative examples is less than 5%. However, the drying method of the comparative examples requires the use of an oven, which pollutes the environment and takes a long time (at least 3 hours). In contrast, the measurement method of each example of the present invention only requires 19-40 minutes, less than 1 hour. It can be seen that the measurement method of the present invention has obvious advantages over the existing drying method in terms of reducing pollution and improving production efficiency.

[0185] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the solid content of an oily conductive paste, characterized in that, Includes the following steps: (a) Providing an oily conductive slurry, the oily conductive slurry comprising a conductive agent, a dispersant and solvent A; wherein solvent A comprises N-methylpyrrolidone and / or dimethyl sulfoxide; Take the required amount of oily conductive paste and determine its moisture content w1 using a moisture analyzer. (b) Solvent B is added to the remaining amount of oily conductive slurry for ultrasonic extraction, followed by centrifugation to obtain the supernatant, and the supernatant is filtered to obtain a mixed solution containing solvent A; wherein, solvent B includes at least one of methanol, n-hexane or dichloromethane; (c) Take the required amount of the mixed solution and dilute it with solvent B to obtain the test solution; (d) Gas chromatography-mass spectrometry analysis was performed on the test solution to calculate the content w2 of solvent A in the oily conductive slurry. The solid content of the oily conductive slurry was calculated according to the following formula (1): w0=100%- w1- w2 (1) Where w0 is the solid content of the oily conductive paste, %; w1 is the moisture content of the oily conductive paste, %; and w2 is the content of solvent A in the oily conductive paste, % In the gas chromatography-mass spectrometry analysis, the SIM / SCAN mixed mode is used to detect the test solution, obtain the peak area of ​​solvent A, and combine it with the linear equation of the standard curve of solvent A to obtain the content of solvent A in the oily conductive slurry.

2. The method for determining the solid content of oily conductive paste according to claim 1, characterized in that, In step (a), the conductive agent includes carbon nanotubes and / or graphene.

3. The method for determining the solid content of oily conductive paste according to claim 1, characterized in that, In step (a), the temperature of the moisture analyzer is set to 150-180℃; And / or, the gas flow rate of the moisture analyzer is set to 50-60 mL / min.

4. The method for determining the solid content of oily conductive paste according to claim 1, characterized in that, In step (b), the mass-to-volume ratio of the remaining oily conductive slurry to solvent B is (3-5) g: (30-50) mL; And / or, the ultrasonic extraction time is 3-10 min; And / or, the frequency of the ultrasonic extraction is 30-50 kHz; And / or, the power of the ultrasonic extraction is 200-300W.

5. The method for determining the solid content of oily conductive paste according to claim 1, characterized in that, In step (b), the centrifugation time is 3-5 minutes; And / or, the centrifugation speed is 10000-15000 rpm; And / or, the filter membrane used for filtration is an oil-based filter membrane with a pore size of 0.22 μm or 0.45 μm.

6. The method for determining the solid content of oily conductive paste according to claim 1, characterized in that, In step (c), the required volume of the mixed solution is 5-20 μL; And / or, the dilution factor is 100-200 times.

7. The method for determining the solid content of oily conductive paste according to claim 1, characterized in that, In step (d), the method for obtaining the linear equation of the standard curve of solvent A includes: Solvent A is added to solvent B and mixed evenly to obtain mixed solution I. The required amount of mixed solution I is diluted with solvent B to obtain multiple standard solutions of solvent A with progressively varying concentrations. The SIM / SCAN mode was used to detect standard solutions of solvent A at different concentrations to obtain the peak area of ​​solvent A at different concentrations. The concentration of solvent A in the standard solutions of different concentrations and the peak area of ​​solvent A in the corresponding standard solutions were used to plot the standard curve to obtain the linear equation of the standard curve of solvent A. Alternatively, in step (d), the method for obtaining the linear equation of the standard curve of solvent A includes: Solvent A of various masses is added to the same volume of solvent B and mixed thoroughly to obtain mixed solutions I of different concentrations. The required amount of each concentration of mixed solution I is diluted with solvent B by the same factor to obtain multiple standard solutions of solvent A with progressively varying concentrations. The amount of solvent B used to prepare mixed solutions I of different concentrations is the same as the amount of solvent B used in step (b) when preparing the mixed solution containing solvent A. The required amount of each concentration of mixed solution I is the same and the same as the required amount of the mixed solution in step (c). The dilution factor of mixed solution I is the same as the dilution factor of the mixed solution in step (c). The standard solutions of solvent A at different concentrations were detected using the SIM / SCAN mode to obtain the peak areas of solvent A at different concentrations. A standard curve was plotted using the mass of solvent A in mixed solution I of different concentrations and the peak areas of solvent A in the standard solutions formed by the corresponding mixed solution I, so as to obtain the linear equation of the standard curve of solvent A.

8. The method for determining the solid content of oily conductive paste according to claim 1, characterized in that, In step (d), the chromatographic determination conditions in the SIM / SCAN mixed mode include at least one of the following operating parameters: The chromatographic column was an Rtx-MS column with a length of 30 m, an inner diameter of 0.25 mm, and a film thickness of 0.25 μm. And / or, the carrier gas is helium with a purity of 99.999%; And / or, injection volume 1 μL, split ratio 10-30:1; And / or, the number of times solvent B is rinsed before injection is 1-5 times; the number of times solvent B is rinsed after injection is 1-5 times; the number of times the sample is rinsed is 1-5 times; And / or, the injection port temperature is 230-260℃; And / or, heating program: initial temperature 80-120℃, hold for 3-5 min; increase temperature to 100-150℃ at a rate of 5-10℃ / min, and increase temperature to 200-250℃ at a rate of 5-15℃ / min. And / or, the mass spectrometry conditions are: EI source, ion source temperature of 200-230℃, and interface temperature of 230-260℃.

9. The application of the method for determining the solid content of oily conductive slurry according to any one of claims 1-8 in the field of lithium-ion batteries.

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