Graphene-mesoporous silica composite as a rechargeable lithium-sulfur battery cathode material
Even though Li-ion battery is considered as one of the most prospective energy storage technologies, current state of Li ion battery fails to meet the demands in powering advanced electric vehicle because of their relatively low energy and power densities. As a promising next high-performance Li batteries, Li-S battery has been drawn to many people’s attention because of its high theoretical capacity (1675 mA•h/g) of elemental sulfur. However, Li-S battery systems suffer from the insulating nature of elemental sulfur and Li2S, the low retention of sulfur in cathode due to the lithium polysulfide dissolution and thus the passivation of the Li anode. In order to avoid these problems, we synthesized mesoporous graphene-SiO2 (m-GS) composite with the aim of designing a cathode structure with high sulfur retention and consequently high charge/discharge rate capability. A SBA-15-like ordered mesoporous silica structure was introduced onto the surface of functionalized graphene via ternary cooperative assembly among triblock copolymer, silica precursor, and graphene. We expect that the well-defined mesoporous silica structure exhibits high polysulfide retention and allows for fast reaction kinetics of sulfur, the graphene alleviates the insulating nature of silica and sulfur and the synthesis of m-GS is conducted under mild conditions. S@m-GS exhibits a first discharge capacity of 1190 mAh/g and a stable discharge capacity of >560 mAh/g after 40 cycles. We also compared the cell performance of m-GS with pure functionalized graphene and mesoporous silica SBA-15 of similar structures. Pure functionalized graphenen shows the discharge capacity close to that of m-GS, but unstable retention of discharge capacity due to lithium polysulfide dissolution. SBA-15 shows the stable cycling performance but the low discharge capacity of 640mAh/g. Therefore, it can be concluded from these observations that high discharge capacity and stable retention of discharge capacity for m-GS are originated from the combination of graphene with mesoporous silica.