Intercalation-deposition mechanism induced by aligned carbon fiber toward dendrite-free metallic potassium batteries

Metallic potassium (K) anodes are highly desirable for high energy density batteries. However, challenges lie in uncontrollable dendrite growth and/or inevitable generation of dead K. Here, composite anodes are constructed by covering a layer of aligned carbon fiber on the surface of each metallic K anode (K-ACF). Symmetrical K-ACF//K-ACF cells can work stably without short circuit for over 600 h, which is quite longer than cells using composite anodes with unaligned carbon fiber (K-UCF) and bare metallic K anodes. Comprehensive characterizations reveal a stepwise intercalation-deposition process on the K-ACF anode during the K plating, and the intercalation is proved to be necessary for the uniform K+ flux due to the improved potassiophility of potassiated ACF. Besides, the aligned structure of ACF offers a uniform current density and K+ ion flux on the surface of composite anodes, promoting the stable K stripping/plating. The K-ACF//Prussian blue (PB) cell exhibits a high discharge capacity of 83.6 mAh g−1 (267.4 Wh kg−1 based on the mass of PB) under a charge/discharge rate of 200 mA g−1 with a capacity loss rate of 0.044% per cycle. This work opens up a new avenue toward high energy and dendrite-free potassium batteries.