Disclosed is a carbon felt impregnated with inorganic particles. The impregnated carbon felt can be used together with sulfur in a cathode of a sodium-sulfur (NaS) battery. Also disclosed is a method for producing the impregnated carbon felt. According to exemplary embodiments, the problem of the prior art can be solved in which inorganic particles such as alumina particles are not directly adhered to carbon felts, thus necessitating complicated processes. In addition, a slurry including an inorganic binder and alumina particles can be used to directly coat the alumina particles on the surface of a carbon felt, making the production procedure very simple. Furthermore, the use of the carbon felt surface coated with the alumina particles in a NaS battery increases the wicking of sodium polysulfides, suppresses the accumulation of sulfur as an insulator on the surface of beta-alumina as an electrolyte, and inhibits non-uniform aggregation of sulfur or sodium polysulfides on the carbon felt, so that the concentration polarization of charges can be reduced without a significant increase in the internal resistance of the battery, achieving high utilization efficiency of sulfur as a reactant.

A solid electrolyte film for sulfide-based all-solid-state batteries, and more particularly a composition of a solid electrolyte, a binder, and a solvent used to manufacture a solid electrolyte film for sulfide-based all-solid-state batteries that is thin and has high ion conductivity. In particular, a solid electrolyte film composition for sulfide-based all-solid-state batteries including a solvent having a dielectric constant of x (1.5<x<3.0). The thickness of a solid electrolyte film for sulfide-based all-solid-state batteries manufactured using the solid electrolyte film composition is 60 m or less, and the solid electrolyte film is capable of being stably used for at least 1000 hours or more, and up to 2000 hours, based on the evaluation of Li plating and stripping.