K _xC _y Phase Induced Expanded Interlayer in Ultra-Thin Carbon Toward Full Potassium-Ion Capacitors

Abstract

Carbonaceous materials have been regarded as highly promising anode candidates for potassium storage with its costeffectiveness and environmental benignity. However, low specific capacity and difficulty in large-scale synthesis largely hinder its further development. Herein, a thermal-induced potassium-carbon alloy phase (K_xC_y) with the expanded interlayer spacing strategy is firstly put forward. Through in situ high-temperature XRD, a K₂C₂ phase is evoked by thermal energy during the in-situ carbonization process of carbon quantum dots (CQDs) 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 and preparation in bulk, delivering a 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 hybrid ion capacitor (PHIC) by combining the impressive CFM-900 anode with 3DFAC delivers a high energy-power density of 251.7 Wh kg^-1 at 250 W kg^-1 with long-term stability. This work opens a scalable avenue to realize the expanded interlayer spacing, which can be extended to other multicarboxyl potassium salts, and provides an enlightening approach for the design of high-performance carbon anode materials for potassium storage.

Keywords: KxCy phase, themal-induced, ultra-thin carbon, expanded interlayer, potassium-ion capacitors