Rational Sulfur Cathode Design for Lithium–Sulfur Batteries: Sulfur-Embedded Benzoxazine Polymers

A variety of advanced electrode structures have been developed lately to address the intrinsic drawbacks of lithium–sulfur batteries, such as polysulfide shuttling and low electrical conductivity of elemental sulfur. Nevertheless, it is still desired to find electrode structures that address those issues through an easy synthesis while securing large sulfur contents (i.e., > 70 wt %). Here, we report an orthogonal, "one-pot" synthetic approach to prepare a sulfur-embedded polybenzoxazine (S-BOP) with a high sulfur content of 72 wt %. This sulfur-embedded polymer was achieved via thermal ring-opening polymerization of benzoxazine in the presence of elemental sulfur, and the covalent attachment of sulfur to the polymer was rationally directed through the thiol group of benzoxazine. Also, the resulting S-BOP bears a homogeneous distribution of sulfur due to in situ formation of the polymer backbone. This unique internal structure endows S-BOP with high initial Coulombic efficiency (96.6%) and robust cyclability (92.7% retention after 1000 cycles) when tested as a sulfur cathode.