Breaking Li + Diffusion Limits in Practical Li–S Batteries via Electrolyte-Dispersible Li + -Reservoir Catalysts

Electrocatalysis is a powerful approach to accelerate sulfur redox kinetics in lithium–sulfur (Li–S) batteries. However, in practical high sulfur loading and thick cathodes, the severe concentration polarization induced by the rapid depletion of local lithium ions (Li+) greatly restricts catalysis and battery performance, representing an engineering challenge in a closed microelectrochemical reactor. Here, an electrolyte-dispersible Li+-reservoir catalyst is proposed to sustain the local Li+ concentration to ensure the continuous electrochemical reaction in the battery with an energy density of over 400 Wh kg–1. Such a catalyst is realized by anchoring single cobalt atoms onto uniformly dispersed carbon quantum dots (Co-CQD). The negatively charged CQD strongly attracts and enriches Li+ around the Co catalytic sites by robust electrostatic interactions, ensuring a continuous Li+ supply during the catalytic reactions. Moreover, Co-CQDs are homogeneously dispersed in the electrolyte and distributed in thick electrodes, promoting bulk-phase Li+ distribution and effectively eliminating concentration polarization. As a result, this strategy lowers the sulfur conversion activation energy in thick cathodes from 1.27 to 0.72 eV and enables the battery to maintain a high reversible capacity of 13.5 mAh cm–2 under a high sulfur loading of 13 mg cm–2, outperforming conventional catalysts under identical conditions. Moreover, an Ah-level pouch cell delivers a high energy density of 513 Wh kg–1, offering a scalable strategy to overcome ion transport bottlenecks in thick cathodes for practical Li–S batteries.