Editor's note As a lithium-ion battery company, the raw material is ultimately presented as a product in front of consumers. When a negative electrode material is obtained, how can the material be used well and the performance of the material itself can be exerted? The responsibility is. As a lithium-ion battery company, the raw material is ultimately presented as a product in front of consumers. When a negative electrode material is obtained, how can the material be used well and the performance of the material itself can be exerted? The responsibility of the work, and as an important part of the lithium-ion battery - graphite anode material, what are the test indicators in the process? The third part of this series will take you through to find relevant answers. 1, homogenization process As the first step of the negative electrode material, it is also an important process. Once the first step has problems, it is useless to remedy it later. Therefore, there are many relevant detection parameters in the homogenization process, which will be briefly introduced below. (1) Solid content: the percentage of active material, conductive agent and binder in the total mass of the slurry in the slurry. The measurement method is also relatively simple. A small amount of slurry is weighed on the copper foil and dried. Weigh and then calculate it. However, there are already related automatic equipments, which are self-contained and weighed. As long as the sample is put in, the relevant parameters are input and the result is automatically calculated. (2) Fineness: the degree of dispersion of the powdery particles in the solvent, the slurry with good dispersion, the solid particles can be well wetted, the surface of the prepared coating will be flat, and the particles will be stored during storage. It is not easy to precipitate and has good storage stability. When the slurry is not dispersed, there are problems such as large particles and slurry sedimentation. At present, the fineness of the scraper is basically measured. During the measurement, the sample is dropped into the deepest part of the groove, and then the plate is vertically contacted with a doctor blade to pull the slurry through the entire length of the groove at an appropriate speed, and then the particles in the groove are uniformly exposed in the direction of the incident angle of 30°. The scale of the sample indicates the fineness of the sample. Generally, the fineness should be below 20 μm. (3) Viscosity: Viscosity is a physical and chemical property of a substance. It is defined as a pair of parallel plates with an area of ​​A, a distance of dr, and a liquid filled between the plates. Now a thrust F is applied to the upper plate to produce a velocity. The force required for change. Generally measured by a rotational viscometer, the unit is poise. Coatings of different viscosities are selected for coating depending on the coating equipment. It should be noted that if the slurry shows sedimentation, the viscosity of the upper and lower layers of the homogenization tank will be different. At the same time, the viscosity of the slurry will change after being placed for a period of time. In the actual production process, it is necessary to collect relevant The data is aggregated and analyzed to determine the viscosity range that suits you and the storage time of the slurry. 1 poise (1P) = 100 centipoise (100 cP) 1 centipoise (1 cP) = 1 mPas s (1 mPa s) 1 mPa s (1 mPa s) = 1000 micropascal seconds (1000 μ Pa.s) ) (4) Rheology: Rheology appeared in the 1920s and has been widely used in the coatings industry. The meaning is that under the action of external force, the deformation and flow of the object are also widely used in the slurry of lithium ion batteries. The slurry of a lithium ion battery is a shear-thin non-Newtonian fluid, and the viscosity decreases as the shear rate increases. The rheological curve represents a plot of material viscosity versus shear stress, as well as specialized test equipment. Through the rheological curve, some properties of the slurry can also be analyzed, which will not be introduced in detail here. If necessary, it can be explained specifically. (5) Slurry stability: With the deepening of research, the stability of the slurry is increasingly valued by researchers in the lithium battery industry. What is the distribution of the internal particle in a finished slurry? How long the stable storage will directly affect the production cycle and batch of the real battery, therefore, the study of slurry stability came into being. The measurement principle utilizes the principle of multiple light scattering. When the particle concentration in the sample is relatively low, after the plurality of particles are scattered, the light that can pass through the sample is projected light, and the light that is not transmitted is scattered light. The device uses two probes to scan from the upper layer of the slurry to be tested to the lower layer and make relevant curves. The curve can be used to characterize the uniformity of the sample, and can be scanned once every time and obtained through the relevant software. The series of curves, which gives the stability dynamics index (TSI) of the slurry. (6) Zeta potential: The potential of the shear plane is an index that characterizes the stability of the colloidal dispersion system and varies with the distance of the surface of the particle. The zeta potential of the negative electrode slurry can be tested by the relevant equipment. The stability of the slurry can be analyzed through relevant data, and it also has certain guiding significance for the addition of additives. It should be understood that the relevant detection parameters of the slurry are related to each other. In the actual application process, it is necessary to synthesize a plurality of data to analyze the negative electrode slurry, in order to obtain a more comprehensive conclusion. 2, the coating process After the simple introduction of the homogenization process, the following is a brief introduction to the coating process. The main inspection points are the thickness of the coating, the difference between the thickness of the two sides, the presence of defects on the surface after drying, etc. A brief introduction. (1) Thickness detection: At present, some lithium battery manufacturers are using online detection systems, and can analyze the data in real time. Once the difference in coating thickness occurs, the device will alarm, and there is not much here. Different batteries, different manufacturers in the thickness control standards and ranges are also different, the difference in thickness will directly cause the difference in battery capacity, so the range is still as small as possible. With the increase of the current capacity, the negative electrode is also coated more and more thick, so due to the influence of the drying rate, the edge of the negative electrode coating will cause thick edges. The general solution is to modify the shape of the coating pad. The speed control, slurry viscosity control and other means, related literature and materials are also more, here are not introduced one by one; (2) Surface state detection: This is currently only visual inspection. Check whether the surface is scratched, large particles, pits, exposed foil, etc. after coating and drying. The general problem is that the slurry is not ideal, it needs The slurry homogenate is improved, including rotation speed, feed sequence, temperature control, additive addition amount, and the like. 3, the rolling process When the negative electrode piece that has passed the homogenization and coating process is completed, the next process is crushing. Why should it be crushed? Because the surface state of the coated pole piece is relatively loose, the thickness is relatively thick, and the bonding force is not necessarily ideal. By rolling, the contact between the particle and the particle is tight, and the thickness is reduced, thereby achieving the design requirement. The parameters to be tested during the rolling process are similar to the coating, mainly the thickness control and the consistency of the thickness. In order to achieve high energy density, the coating density of the negative electrode is now higher and higher, thus deriving two mills. Pressing, heating and rolling, etc., are all designed to make the negative electrode better pressed to the required thickness, and it needs to be applied according to the actual situation. summary: This paper mainly introduces the parameters and detection methods of anode materials in the process of homogenization, coating and rolling. It is believed that with the development of lithium-ion battery technology, the research on related parameters will be more and more in-depth, more Parameters are also introduced into the process detection of lithium-ion batteries. Toolkits For Cutting Mahine and Cutting Materials
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