An energy storage device, such as a silver oxide battery, can include a silver-containing cathode and an electrolyte having an ionic liquid. An anion of the ionic liquid is selected from the group consisting of: methanesulfonate, methylsulfate, acetate, and fluoroacetate. A cation of the ionic liquid can be selected from the group consisting of: imidazolium, pyridinium, ammonium, piperidinium, pyrrolidinium, sulfonium, and phosphonium. The energy storage device may include a printed or non-printed separator. The printed separator can include a gel including dissolved cellulose powder and the electrolyte. The non-printed separator can include a gel including at least partially dissolved regenerate cellulose and the electrolyte. An energy storage device fabrication process can include applying a plasma treatment to a surface of each of a cathode, anode, separator, and current collectors. The plasma treatment process can improve wettability, adhesion, electron and/or ionic transport across the treated surface.