A self-stabilized suspension catholyte to enable long-term stable Li-S flow batteries

Lithium-sulfur suspension flow batteries are a promising technology for large-scale energy storage, but long-term stability of the suspension catholyte is urgently needed for future application of this system. Here a special self-stabilized suspension catholyte is designed and prepared based on a pie-structured sulfur-Ketjenblack@reduced graphene oxide (S-KB@rGO) composite. In the S-KB@rGO suspension, the sulfur nanoparticles are loaded onto the conductive KB by an in situ redox reaction; the special hyperbranched structure of KB enhances the stability of the suspension; rGO sheets which wrap the S-KB particles not only act as a multilayered physical barrier for sulfur immobilization, but also facilitate electron transportation in the whole suspension. Therefore, a suspension catholyte with long-term physical and electrochemical stability is achieved by the synergetic effect of the KB and rGO. Li-S flow cells with this catholyte show excellent cycle stability (more than 1000 cycles with 99% coulombic efficiency) and low self-discharge (1.1% loss per day). Continuous charge/discharge tests in different flow modes are performed and the influence of the flow rate on the flow battery performance is discussed. The smooth operation in long-lasting flow mode further demonstrates the stability of the suspension catholyte.