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 β-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 β-ketoenamine linkage, the resultative COF shows doubled Li storage capacity (132 mAh g at 0.5 A g , 87% of theoretical specific capacity), good rate capability (108 mAh g at 10 A g ), and excellent cyclability in 1000 cycles. This pinpoint surgery can be promising in extending the electrochemical applications of β-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 (0.1 A g ), supercapacitor-level power density (≈4000 W kg ), and long cyclability.