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.