A kind of multilayer polyolefin microporous membrane with asymmetric structure and its preparation method and application

Abstract

The application discloses a multilayer polyolefin microporous membrane with an asymmetric structure, its preparation method and application. The multilayer polyolefin microporous membrane of the present application comprises A film layer, B film layer and C film layer laminated in sequence; A film layer is made of polypropylene with high melt index and low weight average molecular weight; B film layer is made of high It is made of density polyethylene; the C film layer is made of polypropylene with low melt index and high weight average molecular weight. The multi-layer polyolefin microporous film of the present application has three film layers organically combined, has almost no flow marks in appearance, good product consistency, greatly improved mechanical properties, and avoids tearing when assembling batteries. When used as a separator, the C film layer is attached to the negative electrode, which can resist the puncture of lithium dendrites. In the multi-layer polyolefin microporous membrane of the present application, the A membrane layer has a large pore size as the inner layer and has strong ion migration ability; the C membrane layer has a small pore size as the outer layer, the membrane surface is rough, the contact angle is small, and the wettability to the electrolyte is good; The cooperation of the former avoids the defect of macropores, and improves the cycle performance and charge-discharge efficiency of the battery.

Description

technical field [0001] The present application relates to the field of lithium-ion battery separators, in particular to a multilayer polyolefin microporous membrane with an asymmetric structure and its preparation method and application. Background technique [0002] Lithium battery separator is one of the core components of lithium-ion batteries, and its cost accounts for about 20% to 30% of the cost of the entire lithium battery. It plays an important role in isolating the positive and negative electrodes of the battery and allowing lithium-ion current to pass through during charging and discharging. The battery separators currently on the market are mainly made of polyethylene and polypropylene. Although the pure polyethylene battery separator has a lower closed cell temperature, the rupture temperature is also low. If the internal temperature of the battery exceeds the closed cell temperature and continues to rise to a certain temperature range, the polyethylene film wil...

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Problems solved by technology

Typical polypropylene and polyethylene multilayer composite diaphragms are PP / PE / PP three-layer composite diaphragms produced by Celgard in the United States using dry technology. Difficulties, however, the mechanical properties of the diaphragm are poor, the surface of the membrane has serious flow marks, the surface energy of the membrane surface is low, the wettability to the electrolyte is low, and the pore size distribution is uneven and the consistency is poor

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