Presentation Title: Electrochemically induced amorphous-to-rock-salt phase transformation in niobium oxide electrode for Li-ion batteries

Abstract: 

Current strategies for the design and development of new intercalation metal oxide electrode materials typically include (1) traditional ceramic processing by solid-state reactions, (2) hydro(solvo)thermal processing, and (3)ionothermal processing. Nevertheless, most materials made using the aforementioned strategies are prepared chemically before battery testing. Here, we present a new approach to synthesize nanostructured metastable Nb2O5 via electrochemical means. The new RS-Nb2O5 electrode exhibits exceptional electrochemical properties including high Li-ion storage, fast Li⁺ diffusion, and high cycling stability. In this study, we utilize nanoscale amorphous niobium oxide (Nb₂O₅) as an “open framework” and observe that it can be electrochemically driven to form an optimal structure (rock salt) for improved Li-ion battery performance. This is achieved through electrochemically cycling of amorphous nanochanneled niobium oxide with Li ions. Specifically, nanoscale amorphous Nb₂O₅ (a-Nb₂O₅) transforms spontaneously to a rock salt structure (RS-Nb₂O₅) when the electrode is cycled to a potential of 0.5 V vs. Li/Li⁺. We show, for the first time, that the insertion of three lithium into Nb₂O₅ (~ 1.5 electron transfers per Nb) is possible in the new RS-Nb₂O₅ (Li_xNb₂O₅, 0 ≤ x ≤ 3) for Li-ion storage. The RS structure is beneficial from an increased Li⁺ diffusivity and electrical conductivity compared to its amorphous counterpart. Density functional theory (DFT) calculations suggest that a direct octahedral-octahedral (o-o) hop is preferred in the RS structure and 4-Li and 3-Li hops would form statistically ~47% of migration pathways in Li₃Nb₂O₅, which forms a percolating network of low-barrier pathways for fast Li diffusion. Our work has confirmed a hypothesis that that inducing crystallization of amorphous nanomaterials electrochemically is a new synthetic avenue to access rare metal oxide structures of unique properties.

Bio:

Dr. Hui (Claire) Xiong is a Professor in the Micron School of Materials Science and Engineering at Boise State University. Dr. Xiong received her BE degree in Applied Chemistry, MS degree in Solid State Chemistry from East China University of Science and Technology. She received her Ph.D. in Electroanalytical Chemistry from the University of Pittsburgh in 2007. Between 2008 and 2012, she conducted postdoctoral work at Harvard University and Argonne National Laboratory where her research involved electrochemical characterization of micro-fabricated cathode materials for micro-solid oxide fuel cells and the development of novel nanostructured electrode materials for Li-ion and Na-ion batteries. She joined Boise State University in 2012. Dr. Xiong received NSF CAREER Award in 2015, is the Fellow of the Royal Society of Chemistry, the Fellow of the American Ceramic Society, a Scialog Fellow, and the Fellow of the Center for Advanced Energy Studies. Dr Xiong’s research focuses on design and development of nanoarchitectured and defect-driven electrode materials for Li-ion and Na-ion batteries and beyond, ion irradiation effects on electroceramics, mechanistic insights on electrolyte degradation, and in situ and operando characterizations of energy materials.