Preparation method of battery separator

    The preparation methods of diaphragm are divided into dry method and wet method.

    The dry method is to melt, extrude and blow the polyolefin resin into a crystalline polymer film. After crystallization treatment and annealing, a highly oriented multilayer structure is obtained. After further stretching at high temperature, the crystalline interface is peeled off to form a porous structure, which can increase the pore size of the film. There are two ways of dry stretching: unidirectional stretching and biaxial stretching.

    Wet process is also known as phase separation method or thermally induced phase separation method. Liquid hydrocarbon or some small molecular substances are mixed with polyolefin resin, heated and melted to form a uniform mixture, then cooled for phase separation, and pressed to obtain a membrane. Then the membrane is heated to a temperature close to the melting point, and the molecular chain is oriented by bi-directional stretching. Finally, it is kept for a certain time, and the residual solvent is eluted with volatile substances to prepare interconnected microporous membrane materials.