Boosting the Capacity of Aqueous Li-Ion Capacitors via Pinpoint Surgery in Nanocoral-Like Covalent Organic Frameworks

Aqueous lithium storage devices are promising candidates for next-generation energy storage applications, featuring low-cost, safety, environmental benignness, and grid-scale merits. Developing reliable anode materials with fast Li+ diffusion is paramount to stimulate their development. Herein, the electrochemical performance and mechanism of a redox-active beta-ketoenamine-linked covalent organic framework (COF) (2,6-diaminoanthraquinone and 2,4,6-triformylphloroglucinol COF, DAAQ-TFP-COF) for lithium storage in aqueous electrolyte are explored for the first time. Systematic studies demonstrate that, by the conversion of neutral COF into anionic COF via a pinpoint surgery on the beta-ketoenamine linkage, the resultative COF shows doubled Li+ storage capacity (132 mAh g(-1) at 0.5 A g(-1), 87% of theoretical specific capacity), good rate capability (108 mAh g(-1) at 10 A g(-1)), and excellent cyclability in 1000 cycles. This pinpoint surgery can be promising in extending the electrochemical applications of beta-ketoenamine-linked COFs. The Li+ storage mechanism is investigated by ex situ electron paramagnetic resonance, in situ/ex situ Fourier transform infrared investigations, and density functional theory calculations. As a proof of new concept, a novel aqueous lithium-ion capacitor assembled with DAAQ-TFP-COF anode delivers high specific capacitance of 224 F g(-1) (0.1 A g(-1)), supercapacitor-level power density (approximate to 4000 W kg(-1)), and long cyclability.

Automated summary

This study investigates the electrochemical performance and mechanism of using a covalent organic framework (COF) as a lithium storage material in aqueous electrolyte for the first time. The results show that by modifying the COF structure, higher storage capacity and cycling stability can be achieved. Additionally, a novel aqueous lithium-ion capacitor assembled with the COF as the anode demonstrates high specific capacitance and power density.