A method is provided for forming a NanoElectroChemical (NEC) cell. The method provides a bottom electrode with a top surface. Nanowire shells are formed. Each nanowire shell has a nanowire and a sleeve, with the nanowire connected to the bottom electrode top surface. A top electrode is formed overlying the nanowire shells. A main cavity is formed between the top electrode and bottom electrodes, partially displaced by a first plurality of nanowire shells. Electrolyte cavities are formed between the sleeves and nanowires by etching the first sacrificial layer. In one aspect, electrolyte cavities are formed between the bottom electrode top surface and a shell coating layer joining the sleeve bottom openings. Then, the main and electrolyte cavities are filled with either a liquid or gas phase electrolyte. In a different aspect, the first sacrificial layer is a solid phase electrolyte that is not etched away.