One-Step Synthesis of Carbon Supported Nb2O5 Particles for Electrochemical Capacitor Applications by Oxidation of Layered Nb2C

The crystalline network of orthorhombic niobium oxide (T-Nb₂O₅) offers two-dimensional transport pathways for fast intercalation of lithium ions, leading to its high and rate independent intercalation pseudocapacitance. Unlike many other lithium intercalation metal oxides, T-Nb₂O₅ can be charged in short periods of time, making it suitable as a supercapacitor electrode material. This is due to the fast solid-state diffusion and no structural change of T-Nb₂O₅ upon intercalation of Li ions. For practical applications of Nb₂O₅ and other metal oxides in supercapacitors, thick electrodes with large mass loadings are necessary. This, however, will result in ohmic losses and ion transport limitations due the relatively low electrical conductivity of the oxide and limited ion diffusion through the electrode thickness. To address these limitations, we have successfully prepared the layered Nb₂O₅/carbon hybrid materials through controlled oxidation of layered Nb₂C (also called Nb₂C-MXene). As-prepared Nb₂O₅/C well inherited the two dimensional structure of the precursor with Nb₂O₅ nanocrystals formed between the MXene layers. A detailed study of oxidation temperatures and durations was conducted to achieve nanostructured of T- Nb­­₂O₅ and XRD, SEM and TEM studies show the uniform formation T-phase of Nb₂O₅ on carbon sheets after oxidation at 850℃. The electrochemical characterization of thick electrodes of synthesized material show very promising performance, with specific capacitance of about 350 F/g in 1M LiClO₄ /EC/DMC (1:1 in volume ratio) electrolyte. The performance of developed electrodes is believed to be highly dependent of layered two-dimensional structure of Nb­­₂O₅/carbon hybrid materials.

Acknowledgements: Authors acknowledge Dr. Mengqiang Zhao for his help with TEM studies. Support from DOE via Sandia National Laboratory is appreciated.