Multi-layer microporous membrane and preparation method thereof

Abstract

The invention provides a preparation method thereof of multi-layer microporous membrane. The preparation method includes melting and mixing a first high-boiling-point diluent and first polymer resin to form a first mixture; melting and mixing a second high-boiling-point diluent and second polymer resin to form a second mixture; melting and mixing the first mixture and the second mixture through anextruder to form a thick sheet with three-layer structure; drawing the thick sheet into membrane, washing out the diluents from the membrane, and carrying out thermoforming to obtain the multi-layermicroporous membrane; wherein the first polymer resin comprises 90 wt% or above polyethylene resin, the second polymer resin comprises 5 wt%-15 wt% of polyvinylidene fluoride resin and 85 wt%-95 wt% of polyethylene resin, melt of the first mixture serves as an intermediate layer, and melt of the second mixture serves as a surface layer. Compared with the prior art, the multi-layer microporous membrane has excellent heat resistance, high-imbibition retainability and good low-temperature cell closing property.

Description

technical field [0001] The invention relates to the technical field of microporous membranes, in particular to a multilayer microporous membrane and a preparation method thereof. Background technique [0002] At present, polyolefin microporous membranes are widely used in the manufacture of various separation membranes, capacitor diaphragms and lithium-ion battery diaphragms. Among the existing disclosed technical methods, there are mainly two methods for producing polyolefin microporous membranes: melt extrusion stretching method (MECUS) and thermally induced phase separation method (TIPS). The thermally induced phase separation method, commonly known as the wet method, is a method that melts and mixes polyolefins and high-boiling point pore-forming agents in a high-temperature environment to form a homogeneous system. During the cooling process, the system undergoes phase separation, and finally uses the corresponding volatile solvent The pore-forming agent is washed away...

AI Technical Summary

Problems solved by technology

However, this method tends to cause problems such as deterioration of melt-mixing ability due to addition of inorganic materials, generation of pinholes and non-uniform quality due to deterioration of melt-mixing ability at the time of stretching, and possible problems due to the interaction of inorganic materials and polymers. Lack of compatibility at the interface between resins leads to deterioration of physical properties of the film such as puncture strength, although thermal stability improves with the addition of inorganic materials

Separators using inorganic materials will always have the above disadvantages

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