The invention discloses a separator for a
lithium ion battery and belongs to the technical field of
lithium ion batteries. The separator comprises a
polymer microporous film substrate, wherein the surface of the substrate and the internal wall of a micropore duct of the substrate are coated with nano-
oxide layers. The preparation method comprises the following steps: (1) performing oxidation treatment on the
polymer microporous film with an acid solution, then washing the film successively with an alkali solution and deionized water and
drying the film; (2) putting the film on an
atomic layer deposition apparatus or a continuous
atomic layer deposition device, then vacuumizing, heating to 50-100 DEG C and keeping for 1-30min; (3) introducing trimethylaluminum as a first precursor; (4) adding
nitrogen or
inert gas for purging; (5) introducing a second precursor; (6) adding
nitrogen or
inert gas for purging; (7) repeating steps (3)-(6); and (8) performing
heat setting treatment. The separator disclosed by the invention is small in thickness and heat shrinkage, and is good in
wetting property with
electrolyte. The preparation process temperature is low, a formed
coating is dense, and the thickness of the
coating can be precisely controlled.