The present invention discloses a
lithium ion battery composite separation membrane and a preparation method thereof, and belongs to the technical field of
lithium ion batteries, wherein at least a surface of a
polyolefin separation membrane is coated with a modified
natural rubber polymer coating. According to the invention, the
polyolefin separation membrane and the modified
natural rubber are combined to form the composite separation membrane, such that mechanical properties of the
natural rubber can be improved, and the original pore closing characteristic of the
polyolefin separation membrane can be maintained and utilized so as to improve safety of the battery, enhance bonding force between the separation membrane and the positive
electrode and bonding force between the separation membrane and the negative
electrode, eliminate the interface effect, and improve cycle stability of the battery; and the
inorganic nanoparticles are added to the modified
natural rubber latex, such that the
crystallinity of the
polymer can be reduced to a certain extent, the
mechanical strength of the separation membrane and the carrier concentration can be increased, the interface compatibility between the separation membrane and the
lithium electrode can be effectively improved, and the interface is stable.