All-Solid-State Na/S Batteries with a Na3PS4 Electrolyte Operating at Room Temperature

Abstract

Bulk-type all-solid-state Na/S cells, which are expected to have high capacity, be highly safe, and have low material cost, were fabricated using a Na3PS4 glass-ceramic as a solid electrolyte. The sulfur composite electrodes were prepared by mechanical milling of sulfur active material, a conductive additive (acetylene black), and a Na3PS4 glass-ceramic electrolyte. The all-solid-state Na/S cells used the reaction up to the final discharge product of sulfur active material, Na2S, and achieved a high capacity of ∼1100 mAh (g of S)−1 at room temperature. The rate of utilization of sulfur active material was ∼2 times higher than that of high-temperature-operating NAS batteries (commercially available NAS batteries, Na/sintered β″-alumina/S), where Na2Sx melts with bridging sulfurs contribute to redox in the sulfur electrodes. The open circuit potential curve of the discharge process of the Na/S batteries operating at room temperature was similar to that of the NAS batteries operating at high temperatures; X-...