Turning Soluble Polysulfide Intermediates Back into Solid State by a Molecule Binder in Li-S Batteries.

Abstract

The shuttle effect of dissolved polysulfides produced during the operation of lithium-sulfur batteries is the most serious and fundamental problem among many challenges. We propose a strategy <i>via in situ</i> formation of a functionalized molecule with a dual-terminal coupling function to bind the dissolved polysulfide intermediates, thus turning them back into solid-state organopolysulfide complexes by molecule binding, and then the polysulfides can be pinned on the cathode firmly. The dual-terminal coupling functional molecule binder (MB), which is formed <i>in situ</i> by reaction between quinhydrone (QH) and lithium, can not only bind polysulfides by reversible chemical coordination but also promote the conversion of polysulfides during cycling synchronously. In theory, with the dual-terminal coupling function, MB can bind polysulfide intermediates to copolymerize them, forming -[MB-Li₂S_<i>n</i>]- that has faster reaction activity and redox conversion kinetics in comparison with simple Li₂S_<i>n</i>. With the MB, the Li-S battery exhibits a large initial capacity of 1347 mAh g^-1 at 0.1 C. The remaining capacity of 963 mAh g^-1 at 1 C shows no obvious decay for more than 400 cycles, and the retention of the first 300 cycles can reach 96.9%, in particular. This study delivers an alternative approach to resolving the shuttle effect and achieving excellent Li-S battery performance, with the potential significance going way beyond battery systems.