Calendering of free-standing electrode for lithium-sulfur batteries with high volumetric energy density

The lithium-sulfur (Li-S) batteries are potential candidates for next-generation power sources with very high-energy-density. The rational integration of three dimensional (3D) carbon skeletons into sulfur cathode is an efficient and effective route to full use of conductive scaffolds with chemical and mechanical stability and ability to accommodate large amount of active materials. Herein, a 3D free-standing electrode composed of nitrogen-doped porous graphene/sulfur composite granular and super-long carbon nanotube (CNT) skeleton is proposed for Li-S batteries with high volumetric energy density. With a facile calendering process, the mechanical properties, bulk conductivity, and the pore distribution of the flexible graphene@S-CNT electrodes were tuned. The high rate capability, long-life stability, and high volumetric energy density of Li-S batteries are highly depended on the nanostructure evolution of composite carbon/sulfur electrode. A high rate capability of 40% retention of discharge capacity of 2.0 C against that at 0.05 C, a high cyclic stability of 0.1%/cycle within 180 cycles, and a high volumetric energy density over 850 Wh L⁻¹ are demonstrated with the pressed graphene@S-CNT electrode. This work unfolded a general strategy to modulate the bulk structure of electrodes, which is an efficient route towards Li-S batteries with high volumetric energy density.