Ternary Transition Metal Sulfide as High Real Energy Cathode for Lithium-Sulfur Pouch Cell Under Lean Electrolyte Conditions.

Abstract

Fabrication of a highly porous sulfur host and using excess electrolyte is a common strategy to enhance sulfur utilization. However, flooded electrolyte limits the practical energy density of Li-S pouch cells. In this study, a novel Fe0.34 Co0.33 Ni0.33 S2 (FCN) is proposed as host for sulfur to realize Ah-level Li-S full cells demonstrating excellent electrochemical performances under 2 µLmg-1 lean electrolyte conditions. Moreover, Kelvin probe force microscopy shows that the FCN surface contains positive charge with a potential of ≈70 mV, improving the binding of polysulfides through Lewis acid base interaction. In particular, the FCN@S possesses inherent electrochemical activity of simultaneous anionic and cationic redox for lithium storage in the voltage window of 1.8-2.1 V, which additionally contributes to the specific capacity. Due to the low carbon content (≈10wt%), the sulfur loading is as high as ≈6mg cm-2 , approaching an outstanding energy density of 394.9 and 267.2Wh kg-1 at the current density of 1.5 and 4mA cm-2 , respectively. Moreover, after 60 cycles at 1.5mA cm-2 , the pouch cell still retains an energy of 300.2Wh kg-1 . This study represents a milestone in the practical applications of high-energy Li-S batteries.