Date: 2025-06-06 hits: 103
A. Introduction
Lithium batteries still face some challenges in practical applications, among which diaphragm wrinkling is a common problem. Diaphragm wrinkling not only affects the performance and safety of the battery, but may also lead to serious consequences such as battery short circuit and thermal runaway. In-depth research on the causes of lithium battery diaphragm wrinkling and taking effective solutions are of great significance to improving the quality and reliability of lithium batteries.
B. Causes of lithium battery diaphragm wrinkling
(I) Uneven pole piece material
The unevenness of pole piece material is an important cause of diaphragm wrinkling. Differences in physical properties such as thickness, density, and elasticity of the pole piece will produce uneven stress distribution during the winding process, causing wrinkles in the diaphragm.
(II) Improper winding tension
The winding tension has a vital influence on the flatness of the pole piece. Excessive tension may cause the pole piece to be too tight and crack; too little tension may cause the pole piece to loosen and wrinkle.
(III) Insufficient drying of the pole piece
The pole piece needs to be fully dried before winding to remove residual moisture inside. If the drying is not sufficient, the moisture may cause the diaphragm to wrinkle during the winding process.
(IV) Improper winding speed
The winding speed determines the stress of the pole piece during the winding process. Too fast a winding speed may cause uneven stress on the pole piece, resulting in wrinkles; too slow a winding speed may cause excessive deformation of the pole piece during the winding process, which may also cause wrinkles.
(V) Improper treatment of the pole piece edge
The burrs and bends on the edge of the pole piece may cause stress concentration during the winding process, resulting in wrinkles on the diaphragm.
(VI) Microscopic defects at the interface between the diaphragm and the electrode
The uneven microscopic distribution of the electrolyte in the crystalline and amorphous regions of the diaphragm will cause microscopic stress accumulation or relaxation, and then produce macroscopic wrinkles in the diaphragm.
(VII) Internal structure of the diaphragm
The difference in the microstructure of the polyolefin diaphragm prepared by the stretching method may be the main reason for the wrinkles. The uneven microscopic distribution of the electrolyte in the crystalline and amorphous regions of the diaphragm will also cause microscopic stress accumulation or relaxation, and then produce macroscopic wrinkles in the diaphragm.
(VIII) Different wettability of the electrolyte
The different wettability of the electrolyte to the positive and negative electrodes and the diaphragm may cause wrinkles in the diaphragm during the charge and discharge process.
(IX) Diaphragm thickness
Increasing the thickness of the diaphragm can control the number of wrinkles on the solution flow path to a certain extent, but it is difficult to completely eliminate the generation of wrinkles.
(X) Contact angle
The contact angle of the electrolyte on the diaphragm surface may affect the wetting process, and then affect the formation of wrinkles on the diaphragm.
(XI) Capillary action
When the droplets penetrate into the micropores in the diaphragm along the thickness direction of the diaphragm, it may cause periodic contact between the diaphragm and the electrode, thus generating wrinkles.
(XI) Contact between the diaphragm and the electrode
There is an alternating process of close contact and non-close contact between the diaphragm and the electrode, which may be related to the unique microporous structure of the diaphragm.
C. Optimization scheme for wrinkling of lithium battery diaphragm
(I) Optimize pole piece materials
Select pole piece materials with good uniformity, control the thickness, density and elasticity of the pole piece and other physical properties to reduce the uneven stress distribution during the winding process.
(II) Adjust the winding process
Reasonably adjust the winding tension and winding speed to ensure that the pole piece is evenly stressed during the winding process to avoid wrinkles.
(III) Fully dry the pole piece
Fully dry the pole piece before winding to remove the residual moisture inside and reduce the effect of moisture on the wrinkling of the diaphragm.
(IV) Optimize the edge treatment of the pole piece
Smooth the edge of the pole piece to reduce burrs and bending, and reduce the risk of stress concentration.
(V) Improve the microscopic defects at the interface between the diaphragm and the pole piece
By optimizing the electrolyte formula, improving the diaphragm preparation process and other methods, improve the microscopic defects at the interface between the diaphragm and the pole piece, and reduce the microscopic stress accumulation or relaxation.
(VI) Optimize the internal structure of the diaphragm
Select diaphragm materials with uniform microstructure, or adopt new diaphragm preparation processes to reduce the structural differences inside the diaphragm and reduce the possibility of wrinkles.
(VII) Adjust the wettability of the electrolyte.
By optimizing the electrolyte formula, improve the wettability of the electrolyte to the positive and negative electrodes and the diaphragm, and reduce the risk of wrinkles on the diaphragm during charging and discharging.
(VIII) Control the thickness of the diaphragm.
On the premise of meeting the battery performance requirements, appropriately control the thickness of the diaphragm to reduce the number of wrinkles on the solution flow path.
(IX) Optimize the contact angle
Through surface treatment and other methods, optimize the contact angle of the electrolyte on the diaphragm surface, improve the uniformity of the wetting process, and reduce the formation of diaphragm wrinkles.
(X) Reduce capillary action
Use appropriate diaphragm materials and structures to reduce the possibility of droplets penetrating into the micropores in the diaphragm along the thickness direction of the diaphragm, and reduce the influence of capillary action on diaphragm wrinkles.
(XI) Optimize the fit between the diaphragm and the pole piece
By improving the microporous structure of the diaphragm or adopting a special bonding process, the bonding process between the diaphragm and the pole piece can be optimized, the alternation between close fit and non-close fit can be reduced, and the risk of wrinkles can be reduced.
D. Conclusion
Wrinkling of lithium battery diaphragms is a complex problem, involving multiple aspects such as pole piece materials, winding process, and diaphragm characteristics. Through in-depth analysis of these factors, corresponding solutions can be adopted to effectively reduce the occurrence of diaphragm wrinkling and improve the performance and stability of lithium batteries.
