High-Mass-Loading Li-S Batteries Catalytically Activated by Cerium Oxide: Performance and Failure Analysis under Lean Electrolyte Conditions

Increasing sulfur mass loading and minimizing electrolyte amount remains a major challenge for the development of high-energy-density Li-S batteries, which needs to be tackled with combined efforts of materials development and mechanistic analysis. This work, following the same team's most recent identification of the potential-limiting step of Li-S batteries under lean electrolyte conditions, seeks to advance the understanding by extending it to a new catalyst and into the high-sulfur-mass-loading region. CeOx nanostructures are integrated into cotton-derived carbon to develop a multifunctional 3D network that can host a large amount of active material, facilitate electron transport, and catalyze the sulfur lithiation reaction. The resulting S/CeOx/C electrode can deliver a stable areal capacity of 9 mAh cm-2 with a high sulfur loading of 14 mg cm-2 at a low electrolyte/sulfur ratio of 5 & mu;L mg-1. This study discovers that Li||S/CeOx/C cells usually fail during charging at high current density, as a consequence of local short circuiting caused by electrochemically deposited Li dendrites penetrating through the separator, a previously overlooked failure pattern distinctive to cells operating under lean electrolyte conditions. This work highlights the importance of developing new material structures and analyzing failure mechanisms in the advancement of Li-S batteries. A 3D sulfur electrode with cotton-derived carbon as the substrate and CeOx as the catalyst is developed to achieve high sulfur mass loading and fast reaction kinetics under lean electrolyte conditions. The resulting Li-S cell is found to fail after 100-200 cycles during charging due to local short circuiting caused by Li dendrites penetrating the separator.image