Patent ID: 8409746

Claim:
A battery separator comprising an organic/inorganic composite porous film, which comprises a mixture of: (a) inorganic particles; and (b) a binder polymer coating layer formed partially or totally on surfaces of the inorganic particles, wherein the inorganic particles are interconnected among themselves and are fixed by the binder polymer disposed between the inorganic particles, and the interconnected inorganic particles define uniformly distributed interstitial volumes wherein the interstitial volumes define a pore structure, wherein the inorganic particles have a size of between 0.001 μm and 10 μm, wherein the inorganic particles are present in the mixture of inorganic particles with the binder polymer in an amount of 50-99 wt % based on 100 wt % of the mixture, and wherein the binder polymer has a solubility parameter of between 15 and 45 MPa 1/2 , and wherein the organic/inorganic composite porous film is free-standing and a surface of the organic/inorganic composite porous film is macroscopically smooth.