A solid-state electrolyte composition for a lithium battery. The composition includes a polymeric matrix material, inorganic nanoparticles dispersed in or chemically bonded with the polymeric matrix material, and a lithium salt. The nanoparticles are formed of a compound including lithium and a different semi-metal element or metal element. Exemplary inorganic nanoparticles include a Li-rich super ionic conductor having a LixMyPzSq structural formula, wherein M refers to the different semi-metal element or a metal element.