Activating Aromatic Rings as Na-Ion Storage Sites to Achieve High Capacity

Abstract

Similar to graphite and graphene, aromatic rings are ultra-stable configurations with highly delocalized sp²-hybridized electrons, which are the basic units for most organic electrode materials. However, the aromatic rings in organic electrode materials are inaccessible for sodium ions storage. We design a wavy-layered 3D structure of metal-organic compound zinc perylenetetracarboxylates (Zn-PTCDA) with stretched space between adjacent perylene planes, which enables aromatic rings activated as Na⁺-storage sites. Such Zn-PTCDA delivers a high specific capacity of 357 mAh g^-1 at a current density of 50 mAg^-1 within the potential range of 0.01-2 V versus Na/Na⁺, corresponding to an eight-electrontransfer process. Experiments and calculations reveal that both the carboxylate groups (C=O) and aromatic rings (C=C) are involved in the sodium insertion processes. We believe that the present strategy can open up a new avenue to develop a big family of 3D open framework structured organic materials for application in high-capacity Na-ion batteries.