Lithium-ion battery separator, preparation method thereof, and lithium-ion battery prepared therefrom

A method for preparing a separator for a lithium-ion battery having temperature resistance, comprising:

• mixing, melting, and plasticizing, in mass percentage, 20%-60% of a polypropylene main material, 2%-10% of a solubilizer, 30%-80% of a solvent, 0.1%-5% of a nucleating aid and/or 0.1%-1% of an antioxidant, carrying out twin-screw extrusion, and carrying out thermally induced phase separation to obtain a cast sheet;
• and
• carrying out cast sheet stretching, extraction, and post-treatment, or
• directly carrying out extraction and post-treatment,
• wherein a pre-extrusion feeding mode is synchronous feeding and asynchronous feeding;
• wherein, during the twin-screw extrusion process, a screw temperature is 140° C.-240° C., a melt pipe temperature is 190° C.-230° C., and a die head temperature is 180° C.-220° C.;
• wherein, the cast sheet stretching comprises maintaining an air temperature of 130° C.-165° C. and a film surface temperature of 124° C.-140° C., and stretching at a stretching speed of 3 m/min-60 m/min by 1-30 times in a Machine Direction (MD), by 1-30 times in a transverse direction (TD), and/or by (1-30)*(1-30) times in a biaxial synchronous direction;
• wherein, the post-treatment comprises successively performing a dry film MD-TD biaxial stretching, an MD-TD biaxial retracting, and a heat-setting, wherein the dry film MD-TD biaxial stretching comprises maintaining the air temperature of 130° C.-175° C. and the film surface temperature of 125° C.-150° C., and stretching at the stretching speed of 3 m/min-40 m/min by (1-30) times in the MD, by (1-30) times in the TD, and/or by (1-30)*(1-30) times in the biaxial synchronous direction;
• the MD-TD biaxial retracting comprises maintaining wind temperature of 130° C.-175° C. and the film surface temperature of 125° C.-150° C., and retracting at a retraction speed of 3 m/min-20 m/min by 1-3 times in the MD retraction, by 1-3 times in the TD retraction and/or (1-3)*(1-3) times in the biaxial synchronous direction;
• wherein, the polypropylene is a single component with a melt index of less than 2 g/10 min or a mixture of the component and a polypropylene with a melt index of less than 0.5 g/10 min;
• wherein, the nucleating aid comprises one or more of adipic acid, calcium stearate, aluminum stearate, sorbitol benzylidene derivatives, sodium benzoate, and aluminum bis (p-tert-butylbenzoate) carboxylate;
• wherein, the solubilizer comprises one or more of a polyethylene/propylene copolymer, a polypropylene/ethylene-butene copolymer, a polypropylene/ethylene-hexene copolymer, a polyethylene wax, a polypropylene wax, and a polyester wax;
• and
• wherein, the separator has a thickness of 3.5-30 μm, a porosity of 30-80%, an adjustable pore size of 20-2000 nm, a biaxial tensile strength of ≥50 MPa, an air permeability of ≤400 s/100 cc, and a breaking temperature of ≥160° C.