Relating to the technical field of
lithium ion batteries, the invention discloses a preparation method of a
lithium ion battery composite diaphragm. The method includes the steps of: preparation of modified
graphene, preparation of modified
graphene dispersion liquid, preparation of a modified
graphene /
organic polymer, and preparation of the diaphragm. According to the invention, the modified graphene /
organic polymer is precipitated on the surface of a
polyolefin diaphragm, the prepared composite diaphragm has the
chemical stability, electrochemical stability, thermodynamic stability, flexibility and high
porosity of an
organic polymer modified diaphragm and the high
mechanical strength, fast heat dissipation and other characteristics of graphene, the modifying phenylcarboxyl on graphene can interact with
lithium ions in the
electrolyte solution, the
desolvation degree of lithium ions can be enhanced to improve the
lithium ion conduction rate, the hydrophilic group carboxyl also can improve the wettability of a base membrane to the
electrolyte solution, and the prepared lithium
ion composite diaphragm can improve the safety performance and electrochemical performance of lithium ionbatteries.