The invention discloses a
lithium ion battery composite diaphragm and a preparation method and an application thereof, belonging to the technical field of
lithium ion batteries. The composite diaphragm comprises a
polyolefin microporous membrane, a
polymer microsphere based
coating on one side surface of the
polyolefin microporous membrane, and an inorganic
ceramic-based
coating on the other side surface of the
polyolefin microporous membrane. The
lithium ion battery composite diaphragm has good air permeability, liquid retaining capability and high-
temperature resistance and can remarkably improve the security and the circulation property of the battery. The
melting point or
softening point of the
polymer microsphere-based
coating in the composite diaphragm is 90-140 DEG C, and when the temperature of the battery is increased, the
polymer microsphere based coating is molten or swelled within a short time, then the apertures of the polyolefin microporous membrane are blocked rapidly, the thermal turn-off effect of the diaphragm is achieved, a lithium ion conveying channel is
cut off, and
short circuit inside the battery is prevented; meanwhile as
ceramic grains inside the inorganic
ceramic-based coating have the high-
temperature resistance property, the polyolefin microporous membrane is effectively prevented from shrinkage, and the situation that positive and negative films directly come into contact to cause
short circuit of the battery.