the present invention is directed toward a laminated electrode and porous separator film combination including a solid electrolyte salt within the porous separator film , the combination comprising layer of powdered cathode material adhering to a surface of a separator film with a solid electrolyte therebetween ; the separator film comprising 50 % to 95 % by weight of electrically non - conductive ceramic fibers having a coating of magnesium oxide on the surface of the fibers in an amount in the range of 5 % to 50 % by weight ; wherein the ceramic fibers comprise al 2 o 3 , alsio 2 , bn , aln , or a mixture of two or more of the foregoing ; and the magnesium oxide coating interconnects the ceramic fibers providing a porous network of magnesium oxide - coated fibers having a porosity of not less than 50 % by volume ; the pores of the network containing a solid electrolyte salt in an amount of up to 95 % by volume based on pore volume of the network .