Three‐dimensional hierarchically porous nitrogen‐doped carbon from water hyacinth as selenium host for high‐performance lithium–selenium batteries

Abstract Hierarchically porous nitrogen‐doped carbon (HPNC) with interconnected micro‐, meso‐, and macropores was generated from KOH and urea etching as a carbon scaffold to infuse Se. In this structure, micropores confine Se as single‐chain molecules, preventing the generation of higher‐order polyselenides, the mesopores provide effective pathways for electrolyte diffusion and ion transport and offer sufficient void space to accommodate the volume change of Se upon lithiation/delithiation, and the doped nitrogen improves the electrical conductivity of HPNC and increases the utilization of Se. When applied as a scaffold for Se in a lithium–selenium battery, the Se/HPNC cathode with a large Se content of 67.6 wt% maintains a high discharge capacity of 410 mAh·g −1 at the 500th cycle at 1.0C, and it demonstrates a discharge capacity as high as 371 mAh·g −1 even at a high current density of 5.0C. Moreover, when the current density returns to 0.2C, the discharge capacity recovers to 527 mAh·g −1 with a capacity retention rate of 90.5% for the first 0.2C, indicating the excellent structural stability of HPNC. HPNC has significant potential for application in energy storage systems.