TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Cell: The shells retain the size of approximately 200-300 nanometers when the battery cell is charged and the lithium sulfide nanoparticles become sulfur nanoparticles. The nanoparticles have an average size of 200-300 nanometers and the positive electrode comprises above approximately 60 wt.% lithium sulfide nanoparticles. The positive electrode further comprises a conductive foil coated by a polymer matrix, where the nanoparticles are dispersed in the polymer matrix. In the battery cell, the electrolyte comprises an ionic liquid, a lithium salt dissolved in the ionic liquid, and a porous separator, where the ionic liquid is absorbed in the porous separator; and the conductive foil comprises at least one of aluminum, stainless steel, zirconium, niobium or molybdenum.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Nanoparticle: The nanoparticle has a size of approximately 200-300 nanometers. The lithium sulfide nanoparticle core is convertible into a sulfur nanoparticle core having a reduced size, and the nanoparticle retains the size of approximately 200-300 nanometers after the lithium sulfide nanoparticle core is converted into the sulfur nanoparticle core. The nanoparticle is one of a core-shell nanoparticle that forms a positive electrode for a lithium-sulfur cell. Preferred Method: The method further involves synthesizing the lithium sulfide nanoparticles, where the synthesizing involves: dissolving or suspending sulfur particles in an organic solvent to form a solution or suspension; adding a lithium reducing agent to the solution to react with the sulfur particles and form precipitates comprising the lithium sulfide nanoparticles; and separating the lithium sulfide nanoparticles from the solution. The shells comprise carbon shells and forming the shells around the lithium sulfide nanoparticles involves: performing chemical vapor deposition of carbon onto the lithium sulfide nanoparticles based on heating the lithium sulfide nanoparticles in the presence of an oxygen free organic vapor. The formation of the shells around the lithium sulfide nanoparticles involves: adding the lithium sulfide nanoparticles to a solution comprising a polar organic solvent and a polymer; and evaporating the polar organic solvent, leaving behind coated lithium sulfide nanoparticles having polymer shells formed on it. The method further involves: heating the core-shell nanoparticles to convert the polymer shells into carbon shells. The shells comprise titanium disulfide shells and forming the shells around the lithium sulfide nanoparticles involves reacting titanium tetrachloride onto the lithium sulfide nanoparticles. The method further involves: creating a mixture comprising the core-shell nanoparticles, an organic solvent and a polymer binder; and coating an electrical conductor with the mixture to form a positive electrode; and providing a negative electrode; forming a cell of a lithium sulfur battery that comprises the positive electrode, the negative electrode and an electrolyte separating the positive electrode and the negative electrode, where the electrolyte comprises a lithium salt dissolved in an ionic liquid and a porous separator, the ionic liquid being absorbed into the porous separator; and hermetically sealing the cell.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The organic vapor comprises one of methane, ethylene or acetylene. The polar organic solvent comprises toluene.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The polymer comprises polyaniline, and the shells comprise polyaniline shells. EXAMPLE - No suitable example given.