"Wane and wax" strategy: Enhanced evolution kinetics of liquid phase LiS to LiS via mutually embedded CNT sponge/Ni-porous carbon electrocatalysts.

The lithium-sulfur battery (Li-S) has been considered a promising energy storage system, however, in the practical application of Li-S batteries, considerable challenges remain. One challenge is the low kinetics involved in the conversion of LiS to LiS. Here, we reveal that highly dispersed Ni nanoparticles play a unique role in the reduction of LiS. Ni-porous carbon (Ni-PC) decorated in situ on a free-standing carbon nanotube sponge (CNTS/Ni-PC) enriches the current response of liquid phase LiS and LiS around the cathode more than 8.1 and 5.7 times higher than that of the CNTS blank sample, respectively, greatly boosting the kinetics and decreasing the reaction overpotential of LiS reduction (lower Tafel slope and larger current response). Thus, with the same total overpotential, more space is provided for the concentration difference overpotential, allowing the more soluble polysulfide intermediates farther away from the surface of the conductive materials to be reduced based on the "wane and wax" strategy, and significantly improving the sulfur utilization. Consequently, S@CNTS/Ni-PC delivers excellent rate performance (812.4 mAh·g at 2C) and a remarkable areal capacity of 10.1 mAh·cm. This work provides a viable strategy for designing a target catalyst to enhance the conversion kinetics in the LiS reduction process.