Mesoporous Nb₂O₅ microspheres with filled and yolk-shell structure as anode materials for lithium-ion batteries

Nb₂O₅ materials based on intercalation reactions have been extensively studied as anode materials for lithium-ion batteries. Mesoporous Nb₂O₅ microspheres with narrow size distribution are the ideal structure for achieving a high volumetric capacity. Mesoporous filled- and yolk-shell-structured (reported for the first time) Nb₂O₅ microspheres are synthesized using a highly porous carbon template. The NbSe₃-C composite transforms into yolk-shell-structured Nb₂O₅ microspheres by a one-step oxidation process. The filled microspheres having ultrafine crystallite size and high mesopore volume show better cycling and rate performances than the yolk shell microspheres. The discharge capacity of the filled microspheres at a current density of 1 A g⁻¹ is 124 mA h g⁻¹ in the 5000^th cycle, and the capacity retention in the second cycle is 76%. The discharge capacity of the filled microspheres decreases by approximately 26% from 171 mA h g⁻¹ to 127 mA h g⁻¹ when the current density increases from 0.5 A g⁻¹ to 10 A g⁻¹. Particularly, the volumetric capacity of the filled microspheres at a high current density of 10 A g⁻¹ is 2.3 times higher than that of the yolk-shell-structured microspheres (filled ≈ 11.5 mA h cc⁻¹ vs. yolk ≈4.9 mA h cc⁻¹).