A test method for characterizing the web blocking performance of lithium anode material after pulping

Abstract

The application discloses a kind of for the test method for characterizing the plugging performance of lithium battery negative electrode material pulp, including following test content: (1) negative electrode material oil absorption value test, according to the oil absorption value to judge the oil absorption capacity index of the negative electrode material to be tested;(2) slurry longitudinal viscosity test and / or relaxation time test of negative electrode material pulp, according to slurry longitudinal viscosity value and / or relaxation time value to evaluate whether the negative electrode material to be tested will be blocked in use Processing performance index.The application can be applied before the negative electrode material leaves the factory or when the negative electrode material enters the factory of lithium battery manufacturer, by comparing the performance of the negative electrode material graphite made into slurry, it can be confirmed whether the processing performance of the negative electrode material is abnormal.Especially, for abnormal materials, isolation can be carried out in advance before graphite delivery, so as to avoid production abnormalities caused by delivery to customers.

Description

Technical fields:

[0001] This invention relates to a testing method, and more particularly to a testing method for characterizing the screen blockage performance of lithium battery anode materials after slurry preparation. Background technology:

[0002] Lithium-ion batteries, or lithium batteries for short, are a type of rechargeable battery that achieves charging and discharging through the directional movement of lithium ions (Li+) between the positive and negative electrodes. Lithium-ion batteries can be classified into energy storage, power, and consumer batteries according to their application areas. Power batteries are primarily used in the power sector, serving markets such as new energy vehicles and electric forklifts.

[0003] As is well known, the manufacturing of lithium batteries requires the separate preparation and coating of positive and negative electrode slurries, which are then assembled with separators, electrolytes, and other components to form a battery. Therefore, issues related to the slurry often pose significant challenges to battery manufacturing.

[0004] For manufacturers of anode materials, although there are relatively mature testing procedures and methods for graphite (GB / T2533-2019), such as particle size, specific surface area, tap density, loose density, and compacted density, these indicators provide good characterization of the processing performance of graphite itself. Trace elements and magnetic substances clearly characterize the safety performance of batteries made from anode materials, while capacity and efficiency clearly characterize electrical performance. However, the processing performance of slurries made from graphite anodes is rarely tested, especially tests related to screen blockage, which are almost non-existent. If screen blockage occurs during the coating of anode slurries, the prepared slurries cannot be used normally, leading to production line shutdowns, severely impacting normal production, and inevitably causing customer complaints. This necessitates multi-party coordination to investigate the cause, analyze the situation, determine responsibility, and pursue claims.

[0005] Therefore, there are currently no reports from lithium-ion battery anode material manufacturers testing the screen-clogging performance of their anode materials after they leave the factory. Only lithium-ion battery processing manufacturers test viscosity to evaluate the uniformity and stability of the slurry. However, firstly, since the slurry is a non-Newtonian fluid, its viscosity is directly related to the shear rate. Therefore, the rotational viscometers currently used cannot characterize its true viscosity and can only serve as a reference for apparent viscosity. Secondly, changes in slurry viscosity can indicate that the slurry may have experienced sedimentation, agglomeration, or uneven dispersion, which can affect processes such as coating, leading to a series of problems such as battery voltage decline, reduced cycle life, and poor battery consistency. However, it is impossible to definitively determine whether the slurry will cause screen clogging. Thirdly, because the preparation of the slurry involves many influencing factors, including the materials used, the proportions, the stirring conditions at the time, and even environmental factors, analysis and attribution become extremely difficult.

[0006] Therefore, it is both necessary and urgent to conduct reasonable characterization and testing of lithium battery anode materials to determine whether they will experience screen clogging. Summary of the Invention:

[0007] The purpose of this invention is to provide a test method for characterizing the screen blocking performance of lithium battery anode materials after slurry preparation.

[0008] This invention is implemented by the following technical solution: a test method for characterizing the screen blocking performance of lithium battery anode materials after slurry preparation, characterized by including the following test contents.

[0009] (1) Oil absorption value test of negative electrode material: The oil absorption capacity index of the negative electrode material under test is judged based on the measured oil absorption value.

[0010] (2) The longitudinal viscosity test and / or relaxation time test of the slurry of the negative electrode material are used to evaluate the processing performance index of whether the negative electrode material will clog the screen during use based on the longitudinal viscosity value and / or relaxation time value of the slurry.

[0011] The longitudinal viscosity test and relaxation time test of the negative electrode material slurry include the following steps:

[0012] S1. Base material preparation: Mix pure water and thickener, stir at 1800-2200 r / min for 30-60 min, and keep warm at 25-40℃ for 30-60 min to prepare the base material. The mass concentration of thickener in the base material is 0.95-1.15%.

[0013] S2. Slurry preparation: Mix the base material, graphite, and binder, and stir at 800-1500 r / min for 2-10 min to obtain the final slurry; the solid content in the slurry is 42-46% by mass;

[0014] The mass ratio of graphite to binder is 95-98:2-5;

[0015] S3. Longitudinal viscosity and relaxation time test.

[0016] Preferably, the oil absorption value test of the negative electrode material includes the following steps:

[0017] S1. Weigh the sample M1;

[0018] S2. Slowly add NMP (N-methylpyrrolidone) reagent dropwise onto the sample, stirring constantly with a spoon. Observe for any liquid seepage within 20 seconds. If no seepage occurs, continue adding the reagent. Continue until the added NMP is not completely absorbed by the sample within 20 seconds, and liquid seeps out. This indicates the test endpoint has been reached. Weigh the sample after oil absorption and record it as M2. Calculate the oil absorption value using the formula:

[0019] Oil absorption value = (M2-M1) / M1*100%.

[0020] Preferably, the thickener is carboxymethyl cellulose.

[0021] Preferably, the adhesive is styrene-butadiene rubber.

[0022] Regarding the research on the screen clogging phenomenon of negative electrode slurry, no reports have been found on longitudinal viscosity, relaxation time, and oil absorption value.

[0023] This paper infers from experiments conducted that, given the same specific surface area (nitrogen adsorption method) for the aforementioned materials, their relaxation time and oil absorption value differ, ultimately resulting in different longitudinal viscosities of the slurry. The main reason is that the negative electrode material may possess some small pores or functional groups on its surface. When testing the specific surface area using the nitrogen adsorption method, N2 molecules are relatively large (0.35 μm) and only undergo physical adsorption, thus failing to accurately characterize the true specific surface area of ​​various materials. The oil absorption value test indicates that for the same material, a larger liquid absorption volume suggests a greater number of pores on the surface or more functional groups capable of binding with NMP. Specifically, the negative electrode material corresponding to the screen-clogging slurry exhibits a larger oil absorption value than the normal material. Further analysis of the negative electrode material into a slurry revealed that the screen-clogging slurry also exhibits a larger wetting specific surface area than the normal non-screen-clogging slurry, simultaneously increasing the longitudinal viscosity and leading to screen clogging during sieving.

[0024] In summary, the negative electrode material contains a large number of pores <0.35nm on its surface, or contains a small number of functional groups, which leads to an increase in the wettable specific surface area of ​​the slurry after pulping, as well as an increase in longitudinal viscosity, ultimately resulting in slurry clogging.

[0025] Advantages of this invention:

[0026] 1. This invention can be applied before the negative electrode material leaves the factory or when the negative electrode material arrives at the lithium battery manufacturer's factory. By comparing the performance of the graphite in the negative electrode material slurry, it can be confirmed whether the processing performance of the negative electrode material is abnormal. In particular, abnormal materials can be isolated in advance before graphite delivery, thereby avoiding production abnormalities and economic losses such as production stoppages caused by shipment, as well as the adverse effects on suppliers due to customer complaints. At the same time, for negative electrode material graphite with abnormal shipments, the oil absorption value of the graphite can be tested to determine whether the performance change is due to abnormal graphite structure.

[0027] 2. This invention can also be used to test after slurry screen blockage occurs, testing the oil absorption value of the negative electrode material used in the negative electrode slurry, which can help analyze whether the slurry screen blockage is caused by abnormal structure of the negative electrode material, and facilitate the determination of responsibility for the slurry screen blockage. Detailed implementation method:

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] In this embodiment, normal negative electrode graphite with no grid blockage and abnormal negative electrode graphite with grid blockage were selected from feedback by lithium battery manufacturers for testing. Four samples of normal negative electrode graphite were selected and named Sample 1-4 respectively; four samples of abnormal graphite were selected and named Sample 5-8 respectively.

[0030] For the samples provided by lithium battery manufacturers, we first tested the longitudinal viscosity and relaxation time of normal and abnormal slurries. Then, we tested the oil absorption value of the graphite used in the normal and abnormal slurries.

[0031] Example 1:

[0032] This embodiment tests the oil absorption value of samples 1-8, and the steps are as follows:

[0033] ① Weigh out the aluminum foil boat and spoon, and measure their mass M0;

[0034] ② Weigh the sample M1;

[0035] ③ Use a pipette to slowly add 10-100 μL of NMP reagent to the sample each time, stirring constantly with a spoon. Observe for any liquid seepage within 20 seconds. If no seepage occurs, continue adding the reagent.

[0036] ④ If the added NMP is not completely absorbed by the sample within 20 seconds and liquid seeps out, the test endpoint is reached. The total mass of the aluminum foil boat, spoon, and sample is recorded as M2. The oil absorption value is calculated using the formula:

[0037] Oil absorption value = (M3 - M0 - M1) / M1 * 100%

[0038] Testing equipment: 0.01% balance, pipette, aluminum foil boat (φ=7.7cm), horn spoon;

[0039] The test results are shown in Table 1.

[0040] Table 1. Oil absorption value test results for samples 1-5

[0041]

[0042] As shown in Table 1, the oil absorption values ​​(52.54%-54.42%) of normal material samples 1-4 reported by lithium battery manufacturers are lower than those of abnormal material samples 5-8 (57.65%-59.35%). Therefore, the oil absorption value test can be used as a standard to determine whether the negative electrode material is blocked when it is prepared into a slurry. For example, in this embodiment, the oil absorption value threshold can be set to 56%.

[0043] Example 2:

[0044] In this embodiment, longitudinal viscosity testing was performed on samples 1-8 after slurry preparation. The steps are as follows:

[0045] Weigh 305g of pure water into a 500ml beaker using a 0.1g balance. Then weigh 3.0g (±0.1g) of CMC and add it to the 500ml beaker. Stir at 2000r / min for 30-60min until the liquid is clear and free of white lumps. Transfer the liquid to a constant temperature water bath and keep it at 30℃ for 30min. During the test, the temperature of the base material should be controlled at 28℃.

[0046] Weigh 123g of the base material using a 0.1g balance and add it to the dispersion cup. Continue to weigh 97.7g of the sample and add it to the weighed base material. Use a glass rod to initially disperse the graphite to prevent clumping. Place it in a Simida degassing mixer and stir according to the set parameters: 850rpm for 1min; 2000rpm for 10min. After stirring, add 2.2ml of SBR and place it back in the mixer. Stir at 800rpm for 30s; 1500rpm for 2min to complete the stirring and obtain the slurry sample.

[0047] Specific proportions of solids:

[0048] CMC (2200 large-diameter silica gel): Sample: SBR (BASF 21-11) = 1.2:97.7:1.1 Solids to water ratio:

[0049] Solid matter: H2O=100:122

[0050] Equipment used: Vacuum stirring degassing machine (Simaida TMV-700TT), sand mill dispersion mixer (Zhongshi ZMD-550), 0.1% balance, water cooling circulation equipment.

[0051] The rheological properties of the slurry samples were tested using a DT-600 ultrasonic rheometer from the United States. The longitudinal viscosity test results at a frequency of 10.3 MHz were obtained and are listed in Table 2.

[0052] Table 2 Longitudinal viscosity test values

[0053]

[0054] As shown in Table 2, the longitudinal viscosity values ​​(185.7-191.17) cP of the slurry prepared from normal material samples 1-4 reported by lithium battery manufacturers are lower than the longitudinal viscosity values ​​(207.12-219.25) cP of the slurry prepared from abnormal material samples 5-8. Therefore, the longitudinal viscosity test can be used as a standard to determine whether the negative electrode material is blocked when it is prepared into a slurry. For example, in this embodiment, the longitudinal viscosity threshold can be set to 200 cP.

[0055] Example 3:

[0056] In this embodiment, relaxation time tests were performed on samples 1-8 after slurry preparation. The steps are as follows:

[0057] Stir the slurry with a glass rod for 2 minutes, then use a 5mL syringe to draw a small amount of sample and inject the sample into the NMR tube A. The sample volume is 0.7mL. Insert the NMR tube into the wetted particle surface area analyzer for testing.

[0058] Testing equipment: Wetting particle specific surface area analyzer, Xigo Area (USA)

[0059] The test results are listed in Table 3.

[0060] Table 3 Relaxation Time Test Values

[0061]

[0062] As shown in Table 3, the relaxation time values ​​(14.60-15.50) of the slurry prepared from normal material samples 1-4 reported by lithium battery manufacturers are greater than the longitudinal viscosity values ​​(11.10-12.50) of the slurry prepared from abnormal material samples 5-8. Therefore, the relaxation time test can be used as a standard to determine whether the negative electrode material is blocked when it is prepared into a slurry. For example, in this embodiment, the relaxation time threshold can be set to 14ms.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A test method for characterizing the wire blocking performance of a lithium anode material after slurrying, characterized in that, The test contents include (1) negative electrode material oil absorption value test, the oil absorption capacity index of the tested negative electrode material is judged according to the measured oil absorption value; (2) slurry longitudinal viscosity test and / or relaxation time test of negative electrode material slurry preparation, the processing performance index of whether the tested negative electrode material will block the screen during use is evaluated according to the slurry longitudinal viscosity value and / or relaxation time value; The slurry longitudinal viscosity test and relaxation time test of negative electrode material slurry preparation include the following steps: S1. Base material preparation: mix pure water and thickening agent, stir at 1800-2200 r / min for 30-60 min, and keep at 25-40 DEG C for 30-60 min to prepare the base material, the mass concentration of the thickening agent in the base material is 0.95-1.15%; S2. Slurry preparation: mix the base material, graphite and binder, stir at 800-1500 r / min for 2-10 min to obtain the final slurry; the solid content mass fraction in the slurry is 42-46%; The mass ratio of graphite and binder is 95-98:2-5; S3. Longitudinal viscosity and relaxation time test; The negative electrode material oil absorption value test includes the following steps: S1. Weigh the sample weight M1; S2. Slowly drop NMP reagent on the sample, stir evenly with a spoon while dropping, and observe whether there is liquid seepage within 20s, if there is no seepage, continue to drop; until the added NMP is not completely absorbed by the sample within 20s, and seepage liquid appears, the test endpoint is reached, weigh the sample mass after oil absorption as M2, and calculate the oil absorption value by the formula: Oil absorption value = (M2-M1) / M1*100%. 2.The method for characterizing the performance of a lithium anode material in a pulp in terms of the clogging of a screen after the pulp has been prepared, according to claim 1, characterized in that, The thickening agent is carboxymethyl cellulose. 3.The method for characterizing the performance of a lithium anode material in a pulp in clogging a screen after slurry preparation according to claim 1, characterized in that, The binder is butadiene styrene rubber.

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