Composite diaphragm for lithium ion battery and preparation method thereof

The invention relates to the research field of lithium ion batteries, and discloses a composite diaphragm for lithium ion batteries and a preparation method thereof. Firstly, PVDF-HFP and PDMS are dissolved in a diluent to obtain a mixed system with uniform characters; secondly, a dispersant is added into the mixed system to obtain a dispersion system; finally, the mixture of PVDF-HFP and PDMS is prepared into a film, and the film is extracted by an extractant and is dried to obtain a porous PVDF-HFP and PDMS composite diaphragm. The composite diaphragm prepared by the invention has high a liquid absorption rate, conductivity, and uniform pore distribution. The composite diaphragm has an electrolyte absorptivity of 175-185%, room temperature conductivity of 1.3 mS/cm, and porosity of 60%-75%.