(63e) Long Cycle Life Lithium-Sulfur Batteries with Bifunctional Aqueous Binder

The practical applications of high energy lithium-sulfur batteries (LSBs) is hindered due to its fast capacity decay and low active sulfur utilization originating from the dissolution of soluble intermediate lithium sulfur species and large volume change along lithium insertion/extraction process, combining with the poor electrical conductivity of sulfur. To overcome these drawbacks, a sustainable polymer, cellulose nanocrystal (CNC), was used here as a bifunctional binder in sulfur cathodes with conductive carbon as sulfur host material. In the presence of CNC binder, the derived LSB delivered a high reversible capacity of 1044 mAh/g (at 0.1 C), while 769 mAh/g from that with PVDF binder. Most important, LSB with CNC binder demonstrated an extremely outstand durability with 655 mAh/g (at 0.5 C) retained after 500 cycles, while less than 300 mAh/g left after 100 cycles for that with PVDF binder. The extremely outstanding behavior of LSB is associated with the strong chemical affinity and reinforced structure of sulfur cathodes with CNC binder. The experimental results showed that CNC has strong affinity to polysulfides through analogous hydrogen bonds. In addition, CNC has the reinforcement effect on the mechanical strength of sulfur cathodes to accommodate large volume change and maintain high electronic connectivity.