Golden Bristlegrass-Like Hierarchical Graphene Nanofibers Entangled with N-Doped CNTs Containing CoSe₂ Nanocrystals at Each Node as Anodes for High-Rate Sodium-Ion Batteries

Golden bristlegrass-like unique nanostructures comprising reduced graphene oxide (rGO) matrixed nanofibers entangled with bamboo-like N-doped carbon nanotubes (CNTs) containing CoSe₂ nanocrystals at each node (denoted as N-CNT/rGO/CoSe₂ NF) are designed as anodes for high-rate sodium-ion batteries (SIBs). Bamboo-like N-doped CNTs (N-CNTs) are successfully generated on the rGO matrixed nanofiber surface, between rGO sheets and mesopores, and interconnected chemically with homogeneously distributed rGO sheets. The defects in the N-CNTs formed by a simple etching process allow the complete phase conversion of Co into CoSe₂ through the efficient penetration of H₂Se gas inside the CNT walls. The N-CNTs bridge the vertical defects for electron transfer in the rGO sheet layers and increase the distance between the rGO sheets during cycles. The discharge capacity of N-CNT/rGO/CoSe₂ NF after the 10 000th cycle at an extremely high current density of 10 A g⁻¹ is 264 mA h g⁻¹, and the capacity retention measured at the 100th cycle is 89%. N-CNT/rGO/CoSe₂ NF has final discharge capacities of 395, 363, 328, 304, 283, 263, 246, 223, 197, 171, and 151 mA h g⁻¹ at current densities of 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 A g⁻¹, respectively.