Bottom-Up Construction of Fluorene-Based Porous Aromatic Frameworks for Ultrahigh-Capacity and High-Rate Alkali Metal-Ion Batteries

Porous aromatic frameworks (PAFs) have attracted much attention in various fields, yet an understanding of their applications in energy storage systems is in its infancy. Herein, a series of fluorene-based PAFs are synthesized and then used as cation-hosting organic anode materials in rechargeable alkali metal-ion batteries. Experimental characterizations combined with theoretical calculations demonstrate that larger micropore volume, higher specific surface area, and more radicals can favor the redox activity and electrochemical performance of PAFs. As the anode material of lithium-ion batteries, the optimum PAF-202 delivers ultrahigh reversible capacity of 1152 mAh g(-1) at 0.05 A g(-1), impressive cyclability with 95% capacity retentions after 5000 cycles at 20 A g(-1), and extraordinary high-rate capability of 286 mAh g(-1) at 10 A g(-1). Moreover, PAF-202 can also show good sodium/potassium-ion storage properties. This work highlights the importance of building units and linking patterns of PAFs in designing high-performance organic electrode materials for energy storage systems.