Insight into Highly Graphitic Hollow Spheres for Superior Potassium Ion Batteries

Graphite is an attractive anode material for low-cost potassium-ion batteries (PIBs), which are highly promising in addressing the urgent demand for large-scale energy storage systems. However, the large volume variation of graphite during the potassiation/depotassiation may lead to poor long-term stability, which is unfavorable for commercialization. Herein, highly graphitic hollow spheres (HGHS) are designed by using D-ribose as the carbon source and Fe-based catalysts to address these issues, and the effect of graphitization degree on potassium storage performance is explored, which is rarely reported. Fe-based catalysts can promote graphitization of carbon layer and function as a hard template for manufacturing hollow and spherical architecture. HGHS possess a high porosity, which provides good contact when the liquid electrolyte infiltrates throughout the material. HGHS synthesized with a suitable amount of Fe-based catalysts display highly graphitic hollow carbon spheres and show a superior potassium storage performance (264 mAh g(-1) at 100 mA g(-1)). The hollow carbon sphere structure and highly graphitic carbon layer endows HGHS with outstanding stability, retaining 87% of the capacity after 500 cycles at 200 mA g(-1). This study provides an effective strategy in designing highly graphitic hollow nanostructures for addressing the instability issues of graphite anode in PIBs.