Thermal Plasma Synthesis of Li 2 S Nanoparticles for Application in Lithium-Sulfur Batteries

Inductively-coupled thermal plasma processes were used to produce nanosized Li 2 S. Prior to the syntheses, the feasibility of forming Li 2 S was first evaluated using FactSage by considering the phase diagrams of sulfur and different lithium precursors in reducing atmospheres; Li 2 O, LiOH·H 2 O, Li 2 CO 3 and Li 2 SO 4 ·H 2 O all showed promises in producing Li 2 S nanoparticles, as confirmed by experiments. Argon and hydrogen mixtures were used as plasma gases, and a carbothermal reduction was implemented for Li 2 SO 4 ·H 2 O. In addition, carbon-coated Li 2 S nanoparticles were synthesized with downstream injection of methane. Carbon was shown to stabilize Li 2 S upon contact with ambient air. The Li 2 S nanoparticles were electrochemically tested in half-cells using electrolytes containing LiNO 3 or Li 2 S 6 as additives. It was found that adding LiNO 3 to the electrolyte was detrimental to the electrochemical performance of Li 2 S, whereas the combination of Li 2 S 6 and LiNO 3 as additives doubled the charge and discharge capacities of the half-cell over 10 cycles.