MIL-100(V) and MIL-100(V)/rGO with various valence states of vanadium ions as sulfur cathode hosts for lithium-sulfur batteries

MIL-100(V) is an inorganic-organic hybrid material composed of trimesic acid ligands and vanadium trimer supertetrahedra. MIL-100(V) is expected to be a good host for sulfur impregnation and an excellent sulfur cathode host for Li-S batteries, not only because of its unique mesoporous structure, but also owing to the presence of vanadium ions with various valence states, which can offer different Lewis acid sites and allow for strong interactions with sulfur and lithium polysulfides. In this study, mesoporous MIL-100(V) and MIL-100(V)/reduced graphene oxide (rGO) composites have been applied as novel hosts for Li-S batteries for the first time. When tested as cathodes for Li-S batteries, both S@MIL-100(V) and S@MIL-100(V)/rGO exhibit excellent electrochemical performance. The S@MIL-100(V) cathode has been demonstrated to have a reversible capacity of similar to 550 mAh/g at 0.1 C (1 C = 1,675 mAh/g) after 200 cycles with low capacity fading of 0.17% per cycle. Moreover, S@MIL-100(V)/rGO maintains a capacity of 650 mAh/g at 0.1 C after 75 cycles, whereas at 0.5 C, the capacity is maintained at 500 mAh/g after 200 cycles and 450 mAh/g after 300 cycles. The above results reveal that the use of MIL-100(V) and MIL-100(V)/rGO as hosts for Li-S batteries can effectively enhance the cycling stability and improve the electrochemical performance of Li-S batteries.