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

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. Graphical Abstract