Investigation of Crystal Structure-Dependent Capacity in Niobium Pentoxide

Abstract

Nb2O5 has different crystal structures (pseudo hexagonal (TT), orthorhombic (T), tetragonal (M), and monoclinic (H)) depending on its thermal stability. When used as an anode material for lithium ion batteries, it shows different electrochemical characteristics depending on the crystal structure. Most studies have focused on the orthorhombic structure due to an interesting pseudo-capacitance storage mechanism. In this work, we synthesized Nb2O5 of various crystal structures and investigate the electrochemical characteristics of other crystal structures during the battery operation. Structural stability and storage mechanism of each structure were analyzed through electrochemical analysis and XRD analysis before and after the cycle. Among the various structures, the tetragonal structure stands out with the highest capacity (228 mAh/g) at 1 C-rate and good cycling stability (87 %) at 500 cycles than the orthorhombic structure. To overcome the disadvantages of orthorhombic phase (structural instability over cycling), Nb2O5 coated with carbon shell was synthesized. In addition, Nb12O29 with oxygen vacancy was synthesized and characterized, and this study revealed a high capacity and structural stability, which offers a new possibility in niobium-based oxides for an anode material.