Porous solid polymer electrolytes (SPE) were prepared in the form of thin films by phase inversion by direct immersion in non-solvent acetone or methanol, using a copolymer of polyacrylonitrile and poly (vinyl acetate) in ethylene carbonate/dimethylene carbonate (EC/DMC 1:1 v/v) as plasticizer, which contained different LiClO4 percentages. SEM images revealed pores on a micrometer scale (average diameter around 2 mu m) distributed inside and on the surface of the films. XRD patterns revealed a predominantly amorphous behavior, favorable to the ionic conduction process. Thin films presented low glass transition temperatures (T (g)), between -67 and -58 A degrees C. Thin films showed a thermal stability higher than those obtained for the gels. Thin films (average thickness of 22 mu m) showed ionic conductivity around 10(-10) S cm(-1) and 10(-7) S cm(-1) by immersion in acetone and methanol, respectively. The porous thin films when were swollen in liquid electrolyte, the maximum ionic conductivity value reached was of 2.5 x 10(-4) S cm(-1) with 10 % LiClO4 at 25 A degrees C. The oxidation of the SPE only occurred around 4.5 V for the gel and 4.8 V versus Li/Li+ for the SPE thin film, thus resulting in a wide electrochemical stability. A stable passive layer at the interface between the polymer electrolyte and lithium metal was formed within the first 10 h and maintained during 4 weeks. The cell containing LiCoO2 in thin-film electrolyte presented the one well-known plateaux for the Li-ion intercalation in the 4 V region.