Promoting reaction kinetics of lithium polysulfides by cobalt polyphthalocyanine derived ultrafine Co nanoparticles mono-dispersed on graphene flakes for Li-S batteries

Lithium-sulfur (Li-S) batteries have been considered as the next generation high energy storage devices. However, its commercialization has been hindered by several issues, especially the dissolution and shuttle of the soluble lithium polysulfides (LiPSs) as well as the slow reaction kinetics of LiPSs which may make shuttling effect even worse. Herein, we report a strategy to address this issue by in-situ transformation of Co-N-x coordinations in cobalt polyphthalocyanine (CoPPc) into Co nanoparticles (Co NPs) embedded in carbon matrix and mono-dispersed on graphene flakes. The Co NPs can provide rich binding and catalytic sites, while graphene flakes act as ideally LiPSs transportation and electron conducting platform. With a remarkable enhanced reaction kinetics of LiPSs via these merits, the sulfur host with a sulfur content up to 70 wt% shows a high initial capacity of 1048 mA center dot h/g at 0.2C, good rate capability up to 399 mA center dot h/g at 2C.