Lithium battery separator pore size and lithium battery separator process -Lithium - Ion Battery Equipment
Lithium-ion battery separator pore size and lithium-ion battery separator process. The separator is an important part of the lithium-ion battery. Its important purpose is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and causing a short circuit. In addition, it also has the function of allowing electrolyte ions to pass through. The lithium-ion battery separator itself has a microporous structure, and the uniformity of pore size and distribution directly affects the performance of the battery. This article will introduce the pore size of lithium-ion battery separator and the lithium-ion battery separator process.
Lithium-ion battery separator pore size
Generally speaking, in order for the separator to prevent direct contact of electrode particles, it is very important to prevent the electrode particles from passing directly through the separator. The electrode particles currently used are generally on the order of 10 microns, while the conductive additives used are on the order of 10 nanometers. Fortunately, carbon black particles generally tend to agglomerate to form large particles. Generally speaking, a separator with submicron pores is enough to prevent the direct passage of electrode particles. Of course, it does not rule out that some electrodes have poor surface treatment and excessive dust, such as micro short circuits.(Lithium - Ion Battery Equipment)
In order for the battery to operate continuously and stably, the current density in the battery is required to be uniform and stable, so the separator is required to have a suitable pore size and pore size distribution. If the pore size is too small, the permeability of lithium ions will be limited, thereby increasing the internal resistance of the battery and reducing the overall performance of the battery; if the pore size is too large, while increasing the permeability of lithium ions, it will also be susceptible to damage. The growth of lithium ion dendrites can pierce the separator, causing safety issues such as short circuit or even explosion. The pore size of the separator should be smaller than the particle size of other components such as electrode active materials, conductive agents, etc., in order to effectively prevent particles from blocking the micropores, thereby improving the safety performance of lithium-ion batteries.
Lithium-ion battery separator process
At present, the main methods for preparing lithium-ion battery separators are wet method and dry method. The wet method is also called phase separation method or thermally induced phase separation method. Liquid hydrocarbons or small molecular substances are mixed with polyolefin resin. After heating and melting, a uniform mixture is formed. The temperature is then cooled for phase separation, and the membrane is pressed to obtain a membrane. The sheet is heated to a temperature close to the melting point and stretched biaxially to orient the molecular chains. Finally, it is kept warm for a certain period of time, and the remaining solvent is eluted with volatile substances to prepare an interconnected microporous membrane. In the dry method, polyolefin resin is melted, extruded, and blown into a crystalline polymer film. After crystallization and annealing, a highly oriented multilayer structure is obtained, which is further stretched at high temperatures to peel off the crystalline surfaces. , forming a porous structure, which can increase the pore size of the film.
At present, domestic separators and battery manufacturers using separators often use scanning electron microscopy and mercury porosimeter for characterization. Scanning electron microscopy can only see the microstructure of the surface, and only characterizes the pore size of the pore port, rather than the pores that actually serve the purpose of filtration. The pore diameter at the narrowest point in the pore channel. In addition, SEM testing requires a certain statistical distribution to calculate the pore size distribution, and the test area is quite small, making it difficult to characterize the macroscopic properties of the material. The mercury porosimeter uses mercury as the test medium. , there are certain safety issues, and the test needs to be conducted under high pressure (400MPa), which will cause certain damage to the microporous structure. Therefore, both are not suitable for the characterization of microporous separators.
In terms of product performance, compared with dry separators, wet separators have certain advantages in mechanical properties, air permeability, and physical and chemical properties. By coating adhesives such as ceramic alumina, PVDF, and aramid on the base film, it can It greatly improves the thermal stability of the separator, reduces the shrinkage rate at high temperatures, and prevents the pole pieces from being exposed due to large shrinkage of the separator.
Lithium-ion battery separator pore size
Generally speaking, in order for the separator to prevent direct contact of electrode particles, it is very important to prevent the electrode particles from passing directly through the separator. The electrode particles currently used are generally on the order of 10 microns, while the conductive additives used are on the order of 10 nanometers. Fortunately, carbon black particles generally tend to agglomerate to form large particles. Generally speaking, a separator with submicron pores is enough to prevent the direct passage of electrode particles. Of course, it does not rule out that some electrodes have poor surface treatment and excessive dust, such as micro short circuits.(Lithium - Ion Battery Equipment)
In order for the battery to operate continuously and stably, the current density in the battery is required to be uniform and stable, so the separator is required to have a suitable pore size and pore size distribution. If the pore size is too small, the permeability of lithium ions will be limited, thereby increasing the internal resistance of the battery and reducing the overall performance of the battery; if the pore size is too large, while increasing the permeability of lithium ions, it will also be susceptible to damage. The growth of lithium ion dendrites can pierce the separator, causing safety issues such as short circuit or even explosion. The pore size of the separator should be smaller than the particle size of other components such as electrode active materials, conductive agents, etc., in order to effectively prevent particles from blocking the micropores, thereby improving the safety performance of lithium-ion batteries.
Lithium-ion battery separator process
At present, the main methods for preparing lithium-ion battery separators are wet method and dry method. The wet method is also called phase separation method or thermally induced phase separation method. Liquid hydrocarbons or small molecular substances are mixed with polyolefin resin. After heating and melting, a uniform mixture is formed. The temperature is then cooled for phase separation, and the membrane is pressed to obtain a membrane. The sheet is heated to a temperature close to the melting point and stretched biaxially to orient the molecular chains. Finally, it is kept warm for a certain period of time, and the remaining solvent is eluted with volatile substances to prepare an interconnected microporous membrane. In the dry method, polyolefin resin is melted, extruded, and blown into a crystalline polymer film. After crystallization and annealing, a highly oriented multilayer structure is obtained, which is further stretched at high temperatures to peel off the crystalline surfaces. , forming a porous structure, which can increase the pore size of the film.
At present, domestic separators and battery manufacturers using separators often use scanning electron microscopy and mercury porosimeter for characterization. Scanning electron microscopy can only see the microstructure of the surface, and only characterizes the pore size of the pore port, rather than the pores that actually serve the purpose of filtration. The pore diameter at the narrowest point in the pore channel. In addition, SEM testing requires a certain statistical distribution to calculate the pore size distribution, and the test area is quite small, making it difficult to characterize the macroscopic properties of the material. The mercury porosimeter uses mercury as the test medium. , there are certain safety issues, and the test needs to be conducted under high pressure (400MPa), which will cause certain damage to the microporous structure. Therefore, both are not suitable for the characterization of microporous separators.
In terms of product performance, compared with dry separators, wet separators have certain advantages in mechanical properties, air permeability, and physical and chemical properties. By coating adhesives such as ceramic alumina, PVDF, and aramid on the base film, it can It greatly improves the thermal stability of the separator, reduces the shrinkage rate at high temperatures, and prevents the pole pieces from being exposed due to large shrinkage of the separator.
