Hierarchical porous nitrogen, oxygen, and phosphorus ternary doped hollow biomass carbon spheres for high-speed and long-life potassium storage

Abstract

Limited lithium resources have promoted the exploration of new battery technologies. Among them, potassium-ion batteries are considered as promising alternatives. At present, commercial graphite and other carbon-based materials have shown good prospects as anodes for potassium-ion batteries. However, the volume expansion and structural collapse caused by periodic K+ insertion/extraction have severely restricted further development and application of potassium-ion batteries. A hollow biomass carbon ball (NOP-PB) ternarily doped with N, O, and P was synthesized and used as the negative electrode of a potassium-ion battery. X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and transmission electron microscopy confirmed that the hollow biomass carbon spheres were successfully doped with N, O, and P. Further analysis proved that N, O, and P ternary doping expands the interlayer distance of the graphite surface and introduces more defect sites. DFT calculations simultaneously proved that the K adsorption energy of the doped structure is greatly improved. The solid hollow hierarchical porous structure buffers the volume expansion of the potassium insertion process, maintains the original structure after a long cycle and promotes the transfer of potassium ions and electrons. Therefore, the NOP-PB negative electrode shows extremely enhanced electrochemical performance, including high specific capacity, excellent long-term stability, and good rate stability.