The performance of wet-coated membranes is excellent and is gradually dominating the industry.
Release time:
2023-03-16 10:05
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Wet method membranes can be divided into base membranes and coated membranes, with coated membranes being wet method membranes that undergo coating processing based on the base membrane. The base membrane is limited by the low melting point of PE, resulting in poor thermal stability. To enhance the performance of the base membrane, a coating membrane is formed by applying inorganic materials, heat-resistant polymer materials, or a mixture of both on the surface, which can greatly optimize the membrane performance. Common coating materials include inorganic coating materials such as aluminum oxide and boehmite; organic coating materials such as PVDF and aramid; as well as various composite coating materials.
Coating can significantly enhance the performance of membranes and largely mitigate the thermal stability shortcomings of wet method membranes, making the wet coating process a prevailing trend in the membrane industry. On one hand, coating materials can reduce the thermal shrinkage rate of membranes. For instance, after heat treatment at 145°C for 30 minutes, the thermal shrinkage rate of a blank base membrane can differ by more than 50% compared to a membrane coated with 6μm aluminum oxide.
Polyolefin membranes have poor high-temperature resistance. As the temperature of lithium batteries continues to rise, the membrane will sequentially undergo three stages: shrinkage, pore closure, and melting. Since the pore closure temperature is lower than the melting temperature, theoretically, when the membrane undergoes pore closure, it can stop the ion exchange between the electrodes, causing the battery to lose functionality while preventing further temperature rise, thus avoiding battery short circuits caused by membrane melting. However, due to the small temperature difference between the melting rupture temperature and the pore closure temperature of polyolefin films (for example, the pore closure temperature of PE membranes is about 135°C, while the rupture temperature is around 147°C), the residual heat generated after pore closure can still cause the membrane temperature to continue rising, potentially leading to membrane rupture and accidents.
After coating treatment, the performance of the membrane is significantly enhanced, allowing the membrane to maintain its original shape even after reaching the melting temperature of polyolefin, preventing short circuits and improving battery safety. On the other hand, the coating materials also greatly improve the puncture resistance of the membrane, further enhancing battery safety. In addition, due to the larger pore size compared to the base membrane, the coating materials can maintain higher wettability with the electrolyte, thereby reducing the internal resistance of the battery and increasing the discharge power. As the coating processes for ceramics, PVDF, aramid, and others gradually mature, wet method coated membranes are gradually dominating the industry due to their superior performance and higher safety advantages.
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2023-03-16
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