| AVS 66th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Wednesday Sessions |
| Session EM+2D+AS+MI+MN+NS+TF-WeM |
| Session: | Nanostructures and Nanocharacterization of Electronic and Photonic Devices |
| Presenter: | Mitchell Walker, The Ohio State University |
| Authors: | M. Walker, The Ohio State University N. Pronin, The Ohio State University A. Jarry, University of Maryland, College Park J. Ballard, University of Maryland, College Park G.W. Rubloff, University of Maryland, College Park L.J. Brillson, The Ohio State University |
| Correspondent: | Click to Email |
Vanadium pentoxide (V2O5) has attracted considerable interest for its potential use as a cathode for solid state lithium ion batteries. While researchers have studied the V2O5 lithiation charge/discharge cycle for over two decades, we are only now able to measure directly its electronic band structure from the surface to the thin film bulk and its changes with Li intercalation on a near-nanometer scale. We used depth-resolved cathodoluminescence spectroscopy (DRCLS) to monitor the changes in electronic structure from the free surface to the thin film bulk several hundred nm below. DRCLS measures optical transitions at 1.8-2, 3.1-3.2, 3.6-3.7, 4.0-4.1, and 4.6-4.7 eV between multiple conduction bands to the pristine (α) V2O5 valence band maximum in excellent agreement with V3dt2g conduction band densities of states (DOS) predicted by density functional theory (DFT).1 Triplet conduction band states at 1.8, 1.9, and 2 eV correspond to predicted V 3dxy–Oc 2px/2py hybridized states resulting from strong deviations of the unit cell VO6 octahedra from cubic coordination correspond to optical absorption edges along the 3 crystallographic axes. With excitation depth increasing from < 10 to 125 nm calibrated by Monte Carlo simulations, the relative amplitudes and energies of these states change, signifying gradual changes in octahedral distortion. The band structure changes significantly with Li intercalation into LixV2O5 for x = 0, 1, and 2. Lithiation gradually removes the hybridized band and introduces a 2.4-2.7 eV V3d t2g band extending 50 nm (x=1) or 25 nm (x=2) into the surface. Higher (4.0 and 4.4 eV) features possibly related to a secondary phase dominate the spectra deep inside all V2O5 films near the battery electrode. Delithiation reintroduces the 1.8-2 eV split-off band although significantly narrowed by octahedral distortions. Overall, DRCLS shows that the lithiation cycle alters the V2O5 band structure on a scale of 10-100’s of nm with lithiation. The direct measure of V2O5’s electronic band structure as a function of lithiation level provided by DRCLS can help guide future battery engineering work as more efficient lithium ion batteries are developed. In particular, these unique electrode measurements may reveal in what ways lithiation changes V2O5 irreversibly, as well as reveal methods to extend solid state battery life. MW and LJB acknowledge support from NSF grant DMR-18-00130. AJ and GR acknowledge Nanostructures for Electrical Energy Storage (NEES), a Department of Energy Office of Science Frontier Research Center.
1. V. Eyert and K.-H. Höck, “Electronic structure of V2O5: Role of octahedral deformation,” Phys. Rev. B 57, 12727 (1998).