During spark plasma sintering (SPS), an electric current is pulsed through a conductive die, such as graphite, to apply thermal energy on powders through Joule heating [56]. Near theoretical sinter-densities can be achieved with significantly shorter holding time for any powder compacts, regardless of the electrical conductivity of the powders [56,57]. In the past years, tremendous efforts have been dedicated to fabricating dense solid electrolytes and solid-state batteries using spark plasma sintering.