Amorphous Nanoporous Niobium Oxide Electrodes for Lithium-Ion Batteries

Abstract

Lithium-ion batteries (LIB) are the leading technology in energy storage systems, however, they are plagued with several limitations including safety and stability. Metal oxide electrodes could provide a safer battery while maintaining high reversible capacity. When compared to the commonly used graphite, metal oxides provide a chemically inert anode with lithiation voltages well above that of Li plating. In addition, nanostructured metal oxides could enhance the performance of the battery by facilitating fast electron- and ion-transport to the active sites. One remarkable material yet to be fully researched by the battery community is nanostructured niobium oxides (Nb2O5). Recent studies have indicated that the electrochemical properties of crystalline Nb2O5 exhibit high capacitance and high rate capability. For example, orthorhombic niobium oxide (T-Nb2O5) has shown to participate in a two-dimensional Li+ transport within the crystal structure that causes no phase changes during the electrochemical reaction. This behavior causes the oxide to exhibit a high stability and power density. Moreover, nanostructuring of this oxide has proven to further increase the power and stability of the electrode material. We report here the results of our investigation into anodically grown nano-channeled niobium oxide (NCNO) as electrodes for LIBs. Through our conditions, it is possible to obtain a uniform amorphous oxide on the surface of niobium metal with the ability to control pore diameter. In a lithium half-cell, this amorphous material undergoes an irreversible phase transition driven by electrochemically cycling with Li. In addition, long-range order can be observed after discharge via structural characterization. Remarkably, the crystalline NCNO has exhibited dramatic improvements in stability compared to the amorphous oxide. This work aims to gain a fundamental understanding about the structural evolution of the metal oxide and charge transport mechanism.