A new direction for the performance improvement of rechargeable lithium/sulfur batteries

Abstract

In this work we introduce a new direction for the performance improvement of rechargeable lithium/sulfur batteries by employing an electrolyte that promotes Li anode passivation in lithium polysulfide solutions. To examine our concept, we assemble and characterize Li/Li 2S 9 liquid cells by using a porous carbon electrode as the current collector and a 0.25 m Li 2S 9 solution as the catholyte. Results show that Li/Li 2S 9 liquid cells are superior to conventional Li/S cells in specific capacity and capacity retention. We also find that use of LiNO 3 as a co-salt in the Li 2S 9 catholyte significantly increases the cell's Coulombic efficiency. More importantly, the cells with LiNO 3 have a ∼2.5 V voltage plateau before the end of charging and demonstrate a steep voltage rise at the end of charging. The former is indicative of the formation of elemental sulfur from soluble lithium polysulfides on the carbon electrode, and the latter provides a distinct signal for full charging. Electrochemical analyses on Li plating and stripping in Li 2S 9 catholyte solutions indicate that LiNO 3 participates in the formation of a highly protective passivation film on the Li metal surface, which effectively prevents the Li anode from chemical reaction with polysulfide anions in the electrolyte and meanwhile prevents polysulfide anions from electrochemical reduction on the Li surface.