Designed Tetranuclear Iron-oxo Clusters with Redox Activity for High-Performance Lithium Storage.

ABSTRACT

Polyoxometalates (POMs) are considered as promising catalysts with unique redox activity at the molecular level for energy storage. However, eco-friendly iron-oxo clusters with special metal coordination structures have rarely been reported for Li-ion storage. Herein, three novel redox-active tetranuclear iron-oxo clusters have been synthesized using the solvothermal method with different ratios of Fe3+ and SO4 2- . Further, they can serve as anode materials for Li-ion batteries. Among them, cluster H6 [Fe4 O2 (H2 O)2 (SO4 )7 ]⋅H2 O, the stable structure extended by SO4 2- with a unique 1D pore, displays a specific discharge capacity of 1784 mAh g-1 at 0.2 C and good cycle performance (at 0.2 C and 4 C). This is the first instance of inorganic iron-oxo clusters being used for Li-ion storage. Our findings present a new molecular model system with a well-defined structure and offer new design concepts for the practical application of studying the multi-electron redox activity of iron-oxo clusters.