N-doped pinecone-based carbon with a hierarchical porous pie-like structure: a long-cycle-life anode material for potassium-ion batteries.

Pinecone-based biomass carbon (PC) is a potential anode material for potassium-ion batteries because it is abundant, cheap, renewable, and easy to obtain. However, because of inferior kinetics and the effects of volume expansion due to the large radius of the K(+) ion, it does not meet commercial performance requirements. In this study, nitrogen-doped PC (NPC) was prepared by carbonization in molten ZnCl(2) with urea as a nitrogen source. A strategy based on synergistic effects between N doping and ZnCl(2) molten salt was used to produce a hierarchically porous pie-like NPC with abundant defects and active sites and an enlarged interlayer distance-properties that enhance K(+) adsorption, promote K(+) intercalation/diffusion, and reduce the effects of volume expansion. This NPC exhibited a high reversible capacity (283 mA h g(-1) at 50 mA g(-1)) and superior rate performance and cyclic stability (110 mA h g(-1) after 1000 cycles at 5 A g(-1)), demonstrating its potential for use in potassium-ion batteries.