KxCy phase induced expanded interlayer in ultra-thin carbon toward full potassium-ion capacitors

Carbonaceous materials have been regarded as highly promising anode candidates for potassium storage with their cost-effectiveness and environmental benignity. However, low specific capacity and difficulty in large-scale synthesis largely hinder their further development. Herein, a thermal-induced potassium-carbon alloy phase (KxCy) with the expanded interlayer spacing strategy is first put forward. Through in situ high-temperature X-ray diffraction, a K2C2 phase is evoked by thermal energy during the in-situ carbonization process of carbon quantum dots intermediate derived from potassium-containing precursors, whereas no lithium or sodium-carbon alloy phase is observed from lithium/sodium-containing precursors. The as-obtained ultra-thin carbon nanosheets achieve adjustable layer spacing, preparation in bulk, delivering reversible potassium storage of 403.4 mAh g(-1) at 100 mA g(-1) and 161.2 mAh g(-1) even at 5.0 A g(-1), which is one of the most impressive K-storage performances reported so far with great potential application. Furthermore, the assembled potassium-ion hybrid capacitor by combining the impressive CFMs-900 anode with the three-dimensional framework-activated carbon delivers a high energy-power density of 251.7 Wh kg(-1) at 250 W kg(-1) with long-term stability. This study opens a scalable avenue to realize the expanded interlayer spacing, which can be extended to other multicarboxyl potassium salts and can provide approach for the design of high-performance carbon anode materials for potassium storage.