N/O double-doped biomass hard carbon material realizes fast and stable potassium ion storage

In this study, N/O co-doped cage-type biomass carbon (NOBC) was prepared through a simple and facile hydrothermal reaction and two-step carbonization method. As the anode of a potassium ion battery, NOBC displays a superhigh long-cycling performance and a super high rate performance. NOBC-2 provides an excellent reversible capacity of 251.2 mAh g−1 after 1500 cycles at 0.5 A g−1, and an excellent performance of 334.6 mAh g−1 at a high current density of 5 A g−1 (after 2000 cycles). The reversible capacity of 124.19 mAh g−1 can be maintained even after 5000 cycles at 10 A g−1. The excellent performance of NOBC is attributed to the unique hollow cage structure, internal 3D carbon network structure and N/O co-doping. Based on the results of detailed fundamental analysis, the pseudo-capacitance mechanism contributes to the higher K ion storage process in NOBC-2. Density functional theory (DFT) calculations further show that N/O double doping can promote the adsorption of K ions in biomass carbon materials and improve the conductivity of the materials. The simple synthesis route and excellent electrochemical performance provide new insights for the search for novel carbon-based K storage anode materials with high energy and long cycle life.