Comparison of amorphous, pseudohexagonal and orthorhombic Nb2O5 for high-rate lithium ion insertion

Abstract

Amorphous, pseudohexagonal and orthorhombic Nb₂O₅ nanoparticles were synthesized using a facile and green sol–gel process followed by thermal treatment at 450 °C, 600 °C and 800 °C for 3 h in air, respectively. The resulting materials have been subjected to a detailed experimental study and comparison of their structural, electrical and electrochemical properties. The experiments have demonstrated that the pseudohexagonal Nb₂O₅ (TT-Nb₂O₅) exhibited higher storage capacity, largely due to its high specific surface area and small crystallites, and better cycling performance than both amorphous Nb₂O₅ (a-Nb₂O₅) and orthorhombic Nb₂O₅ (T-Nb₂O₅); such experimental findings were found to be associated with and thus ascribed to the lower charge transfer resistance and higher lithium ion diffusion coefficient of TT-Nb₂O₅ than those of a-Nb₂O₅ and T-Nb₂O₅. This research contributes to a better fundamental understanding of the relationship between the crystal structure and the crystallinity and electrochemical properties, particularly Li-ion storage properties, and leads to a possible new advancement in the research field of lithium ion batteries and pseudocapacitors.