Bitumen-Derived Onion-Like Soft Carbon as High-Performance Potassium-Ion Battery Anode

Potassium-ion batteries (PIBs) have been regarded as a competitive alternative for lithium-ion batteries, owing to the natural abundance, low cost, and similar rocking-chair working mechanism of potassium element. However, it is challenging to simultaneously prepare suitable potassium ion anode materials of low voltage plateau, high capacity, and long cycle life. In this work, onion-like soft carbon (OLSC) of high heteroatom content is prepared by using solvent-sensitive self-assembly properties of asphaltene molecules. The OLSC electrode exhibits a low voltage plateau because of a high degree of graphitization. Meanwhile, it possesses excellent cycling stability and rate capability due to the high stability of the onion-like structure and fast transport of potassium ions, the latter of which is caused by heteroatom-induced expanded interlayers as found by first-principle calculations. Compared with existing carbon materials, the OLSC synthesized in this study exhibits a high reversible capacity of 466 mAh g^-1 at 20 mA g^-1 , a reversible capacity of 222 mAh g^-1 and capacity retention of 95% after 1600 cycles at 1 A g^-1 . This work connects the nanostructure of carbon materials and electrochemical performance and provides new insights in improving carbon-based anodes for PIBs.