High Molecular Weight Polyacrylonitrile Precursor for S@pPAN Composite Cathode Materials with High Specific Capacity for Rechargeable Lithium Batteries.

Sulfurized pyrolyzed poly(acrylonitrile) (S@pPAN) demonstrates high sulfur utilization, no polysulfide dissolution, no self-discharge, and extremely stable cycling. Its precursor, PAN, directly determines the performances of cathode materials, including the sulfur content and its utilization for S@pPAN composite materials. Adopting PAN with the molecular weight approaching 550,000 as the precursor, the sulfur content in S@pPAN approaches 55 wt %, and its reversible specific capacity was 901 mAh g at 50 °C with sulfur utilization over 98%. Moreover, it enabled stable cycling and excellent high rate capability with a specific capacity of 645 mAh g at 5 C. These significantly enhanced electrochemical properties are mainly due to the high molecular weight of the PAN precursor, which provides more space to accommodate amorphous sulfur, along with improved interfacial resistance of S@pPAN.