Date: 2024-08-15 hits: 165
This article reveals the key factors leading to membrane wrinkling through analysis of various aspects such as polarizer materials, winding processes, and membrane characteristics. Further proposed corresponding solutions provide important theoretical basis and practical reference for improving the performance and stability of lithium batteries,
Preface
Lithium batteries still face some challenges in practical applications, among which wrinkling of the separator is a common problem. Wrinkled film not only affects the performance and safety of batteries, but may also lead to serious consequences such as battery short circuits and thermal runaway. It is of great significance to conduct in-depth research on the causes of wrinkling of lithium battery separators and take effective solutions to improve the quality and reliability of lithium batteries.
Reasons for wrinkling of lithium battery separators
1、Uneven polar material
The unevenness of the polarizer material is an important reason for the wrinkling of the diaphragm. The differences in physical properties such as thickness, density, and elasticity of the polarizer will result in uneven stress distribution during the winding process, leading to wrinkles in the diaphragm.
2、Inappropriate winding tension
The winding tension has a crucial impact on the flatness of the pole piece, and excessive tension may lead to the pole piece being too tight and causing cracks; If the tension is too low, it may cause the pole piece to loosen and wrinkle.
3、Insufficient drying of polarizer
The polarizer needs to undergo sufficient drying treatment before winding to remove residual moisture inside. If the drying is not sufficient, moisture may cause the diaphragm to wrinkle during the winding process.
4、Inappropriate winding speed
The winding speed determines the force situation of the polarizer during the winding process. Excessive winding speed may cause uneven force on the polarizer, resulting in wrinkles; A too slow winding speed may cause excessive deformation of the polarizer during the winding process and also lead to the formation of wrinkles.
5、 Improper edge treatment of polarizer
Burrs, bends, and other issues at the edge of the polarizer may cause stress concentration during the winding process, leading to wrinkles in the diaphragm.
6、 Microscopic defects at the interface between the diaphragm and the polarizer
The uneven micro distribution of electrolyte in the crystalline and amorphous regions of the diaphragm can cause stress accumulation or relaxation at the micro scale, leading to macroscopic wrinkles in the diaphragm.
7、The internal structure of the diaphragm
The difference in microstructure of polyolefin membranes prepared by stretching method may be the main reason for wrinkles. The uneven micro distribution of electrolyte in the crystalline and amorphous regions of the membrane can also lead to stress accumulation or relaxation at the micro scale, resulting in macroscopic wrinkles of the membrane.
8、The wettability of electrolytes varies
The electrolyte has different wetting properties on the positive and negative electrode plates and the separator, which may lead to wrinkling of the separator during charging and discharging processes.
9、Thickness of diaphragm
Increasing the thickness of the membrane can to some extent regulate the number of folds on the flow path of the solution, but it is difficult to completely eliminate the generation of folds.
10、contact angle
The contact angle of electrolyte on the surface of the diaphragm may affect the wetting process, thereby affecting the formation of wrinkles on the diaphragm.
11、Capillary action
When droplets penetrate the micropores inside the membrane along the thickness direction, it may cause periodic adhesion between the membrane and the electrode, resulting in wrinkles,
12、The adhesion between the diaphragm and the polarizer
There is an alternating process of tight and non tight adhesion between the membrane and the polarizer, which may be related to the unique microporous structure of the membrane,.
Solve the lithium battery separator wrinkle strategy
1、Optimize polarizer materials
Select electrode material with good uniformity, control the physical properties such as thickness, density, and elasticity of the electrode to reduce uneven stress distribution during the winding process.
2、Adjust the winding process
Reasonably adjust the winding tension and speed to ensure even force distribution on the polarizer during the winding process and avoid wrinkles.
3、Fully dry the polarizer
Before winding, the polarizer should be thoroughly dried to remove any residual moisture inside and reduce the impact of moisture on the membrane wrinkling.
4、Optimize polar edge processing
Smooth the edges of the polarizer to reduce burrs and bends, and lower the risk of stress concentration.
5、Improve the micro defects at the interface between the diaphragm and the polarizer
By optimizing the electrolyte formula and improving the membrane preparation process, the micro defects at the interface between the membrane and the electrode are improved, reducing stress accumulation or relaxation at the micro scale.
6、Optimize the internal structure of the diaphragm
Choose diaphragm materials with uniform microstructure or adopt new diaphragm preparation processes to reduce structural differences inside the diaphragm and minimize the possibility of wrinkles.
7、Adjust electrolyte wettability
By optimizing the electrolyte formula, the wettability of the electrolyte to the positive and negative electrode plates and separator can be improved, reducing the risk of wrinkling of the separator during charging and discharging processes.
8、Control diaphragm thickness
On the premise of meeting the performance requirements of the battery, the thickness of the separator should be appropriately controlled to reduce the number of wrinkles on the solution flow track
9、Optimize contact angle
By surface treatment and other methods, optimize the contact angle of the electrolyte on the surface of the diaphragm, improve the uniformity of the wetting process, and reduce the formation of diaphragm wrinkles.
10、Reduce capillary action
By using appropriate membrane materials and structures, the possibility of liquid droplets infiltrating the micropores inside the membrane along the thickness direction is reduced, and the influence of capillary action on membrane wrinkles is minimized.
11、Optimize the adhesion between the diaphragm and the polarizer
By improving the microporous structure of the membrane or using special bonding techniques, the bonding process between the membrane and the electrode sheet can be optimized to reduce the alternation of tight and non tight bonding and lower the risk of wrinkles.
Conclusion
The wrinkling of lithium battery separators is a complex problem that involves multiple aspects such as electrode material, winding process, and separator characteristics. Through in-depth analysis of these factors, corresponding solutions can be adopted to effectively reduce the occurrence of membrane wrinkling and improve the performance and stability of lithium batteries.
