The invention discloses an inorganic / organic
composite membrane which comprises a
porous substrate and a porous insulating layer, wherein the porous insulating layer is attached to the
porous substrate, and at least one surface of the
porous substrate is coated with the porous insulating layer; the porous insulating layer comprises
inorganic particles and a binding agent, wherein the
inorganic particles are composed of n particles with different average particle diameters, n is large than or equal to 2, and the average particle diameters from the first type of
inorganic particles to the nth type of inorganic particles are changed in a gradient manner. The invention further discloses a preparation method of the inorganic / organic
composite membrane. The preparation method comprises the following steps: firstly, dissolving the binding agent into a
solvent to form a
polymer solution, then adding the inorganic particles, mixing to prepare the porous insulating layer, and then
coating at least one surface of the porous substrate with the porous insulating layer. The invention further discloses a
lithium ion secondary battery containing the membrane. The inorganic / organic
composite membrane disclosed by the invention has the advantages of high stacking density, low
thermal shrinkage rate, high puncture strength, simple preparation process and proper cost, and the
lithium ion secondary battery containing the membrane has the advantages of good conservation rate of circulating volume and excellent safety performance and electrochemical performance.