TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The sodium-containing particles have a size of 1 nm to 100 mu and a size distribution of 1-5 orders of magnitude. The polymer film: is a material that is poly(ethylene oxide), poly(acrylonitrile), poly(methyl methacrylate), PVC, poly(vinylidene fluoride), poly(vinylidene fluoride-co-hexafluoropropylene), PTFE, poly(vinyl acetate), poly(vinyl alcohol), poly(styrene), poly(phenylene oxide), poly(ethylene terephthalate), poly(vinyl pyrrolidone), poly(vinyl butyral), polyethylene, polypropylene, poly(imides), poly(urethane), poly(siloxane), their functional derivatives or their binary/ternary blends; and includes a plasticizing material comprising salts, solvents or polymers. The structure further comprises: many polymer film layers each comprising sodium-containing particles. The sodium-containing particles: have a shape of plate or spherical and/or irregular; are coated with a dopant comprising metal ions, organic moieties, inorganic moieties, or hybrid organic/inorganic moieties; and comprise sodium-zirconium-phosphorus-silicon oxide compound (Na3Zr2Psi2O12) (NASICON) and thio-NASICON materials comprising sodium compounds of formula (NaX2(PS4)3)), (Na3PS4) or (Na3(PO4))x(PS4)1-x).X = Ti, Ge, Zr or Sn; andx = greater than 0 to less than 1.Preferred Method: Many polymer film layers form a stack having a top anode layer and a bottom cathode layer, where the percentage of sodium-containing particles in the polymer film layers is graded to increase percentage from the bottom cathode layer to the top anode layer. The polymer film layers are formed from a corresponding many polymer materials. The method further comprises: forming the liquid phase polymer by performing a liquefying process comprising dissolving the polymer in a solvent or melting the polymer; adding a plasticizer to the polymer film; and coating the sodium-containing particles with the dopant. The step of dispersing sodium-containing particles in the liquid polymer comprises dispersing the particles during or after liquefying and is carried by agitation, sonication and/or elevated temperature. The step of forming polymer film: is carried by spin-coating, blade-casting, drop-casting or spray coating; and comprises forming many polymer film layers, where each polymer film layer includes sodium-containing particles. The step of forming polymer film layers includes forming a stack having a top anode layer and a bottom cathode layer.