Composite Separators for Li-ion Batteries

Abstract

The invention discloses a polytetrafluoroethylene composite diaphragm for a lithium ion battery. It includes a diaphragm, the diaphragm is formed by the upper polypropylene microporous membrane and the lower polypropylene microporous membrane or the upper polyethylene microporous membrane and the lower polyethylene microporous membrane, characterized in that the upper polypropylene microporous membrane A polytetrafluoroethylene microporous membrane is arranged between the porous membrane and the lower polypropylene microporous membrane or between the upper polyethylene microporous membrane and the lower polyethylene microporous membrane. The polytetrafluoroethylene composite diaphragm for lithium ion battery of the present invention not only has the low closed cell temperature of the lithium ion battery diaphragm, but also has the performance of high membrane rupture temperature, and effectively guarantees the safety and reliability of the lithium ion battery during use sex. The polytetrafluoroethylene composite separator for the lithium ion battery of the present invention can be used as a separator between the positive electrode and the negative electrode of the lithium ion battery.

Description

Technical field: [0001] The invention relates to a diaphragm for a lithium ion battery, in particular to a polytetrafluoroethylene composite diaphragm for a lithium ion battery. Background technique: [0002] Lithium-ion batteries have become a new generation of batteries widely used due to their advantages of high voltage, high energy, long cycle life and no pollution to the environment. [0003] Electronic products using lithium-ion batteries continue to be miniaturized and their applications are becoming more and more popular. Explosion accidents in notebook computers, digital cameras, mobile phones and other products have made people put forward higher requirements for the safety of lithium-ion batteries. Especially for high-capacity lithium-ion batteries, therefore, improving the safety of lithium-ion battery separators has become a hot research topic. [0004] In lithium-ion batteries, the separator is used to avoid short circuits between the positive and negative ele...

AI Technical Summary

Problems solved by technology

[0008] The closed-cell temperature of the polypropylene microporous membrane used as a lithium-ion battery separator is around 150°C. The disadvantage of this temperature is that it is close to the melting point of lithium, which is obviously unsafe.

The closed cell temperature of polyethylene microporous membrane is relatively low at 130°C, which is more suitable, but its membrane rupture temperature is also low, close to 145°C, that is, the temperature difference between the closed cell temperature and the membrane rupture temperature is only 15°C. That is, its heat resistance is poor, which is very unsafe. Moreover, the elastic recovery of polyethylene microporous membrane is poor, which leads to easy stretching and poor mechanical properties when it is loaded into the battery, so its production performance and use performance are not good. is very low, so polypropylene microporous membranes and polyethylene microporous membranes need to be improved in terms of safety and reliability.

However, the coexistence of low pore closure temperature and high membrane rupture temperature of the diaphragm is important, but it is difficult to achieve a high membrane rupture temperature when the separator has a low pore closure temperature, and vice versa.

In order to improve the performance of a single-layer polypropylene microporous membrane or a single-layer polyethylene microporous membrane, a double-layer polypropylene microporous membrane or a double-layer polyethylene microporous membrane is usually used as a lithium-ion battery composite separator, although a certain effect has been achieved. However, it has not fundamentally improved the lithium-ion battery separator to have both low closed cell temperature and high membrane rupture temperature, so it is necessary to seek the best of both worlds.

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