Nitrogen self-doped porous carbon based on sunflower seed hulls as excellent double anodes for potassium/sodium ion batteries

Potassium-ion battery (PIB) and sodium-ion battery (SIB) are the future backups in the field of energy storage technology, and carbonaceous materials are expected to be the prime commercial anode materials for PIBs and SIBs. Hard carbon, a typical amorphous carbon with large surface area, tunable layer spacing and excellent electrical conductivity, has attracted extensive research interest. In this study, a porous hard carbon rich in N with graded porous structure and abundant surface defects was constructed by using K2CO3 impregnated-activated sunflower seed hulls powder. When applied to PIBs and SIBs anodes, the product has high reversible capacities of 619 mAh g−1 and 609 mAh g−1 at 0.2C rate (1C = 279 mAh g−1), and exhibits excellent cycling stability at 1C rate with 80 % capacity retention after 1000 cycles. The superior properties of potassium/sodium storage are attributed to the synergistic effect of the graded pore structure and the surface defects due to self-doped N. It provides an effective strategy for the development of high-performance bifunctional anodes for PIBs and SIBs.