Researchers have sulfurized a hybrid polymer network with polyphosphazene and carbon for use as a cathode for Li–S batteries. This hybrid polymer network circumvents the formation of soluble polysulfides and enables a unique, reversible inserting conversion reaction.

In a study published in Nature Sustainability, the team reports that the cathode delivers both high capacity (~900 mAh g⁻¹cathode) and excellent cycling stability in Li–S coin cells, with a pouch cell demonstration of projected energy density of ~300 Wh kg⁻¹ and 84.9% capacity retention after 150 cycles.

The strategy can be extended to other cost-effective, recyclable polymers, advancing sulfur-based batteries towards practical energy storage application.

Assisting SMU mechanical engineer Donghai Wang and his team with designing the cathode were researchers from Pennsylvania State University, Pacific Northwest National Laboratory, Brookhaven National Laboratory, University of Illinois at Chicago and the Argonne National Laboratory.

When lithium ions bind with sulfur atoms at the cathode, they create soluble polysulfide molecules that drift into the electrolyte, causing degradation of the cathode and reducing the battery’s ability to endure multiple charging cycles. This is known as polysulfide dissolution.

Our cathode uses multiple sulfur bonding tethers, atomic adsorption, and fast Li-ion/electron transport at the molecular level. This combination allows for real-time re-bonding and adsorption of any unbound sulfur species, thus effectively eliminating soluble polysulfides and extending the battery’s cycle life.

—Donghai Wang

Resources

• Liao, M., Xu, Y., Rahman, M.M. et al. Hybrid polymer network cathode-enabled soluble-polysulfide-free lithium–sulfur batteries. Nat Sustain (2024). doi: 10.1038/s41893-024-01453-0