title: Studies of lithium ion dynamics in paramagnetic cathode materials using (6)Li 1D selective inversion methods.
abstract: The effectiveness of two different selective inversion methods is investigated to determine timescales of Li ion mobility in paramagnetic Li intercalation materials. The first method is 1D exchange spectroscopy, which employs a 90°-τ(1)-90° sequence for selective inversion of a Li resonance undergoing site exchange. The experiment is most easily applied when the first delay period, τ(1), is set to the frequency difference between two resonances undergoing ion exchange. This enables the determination of ion hopping timescales for single exchange pair systems only. To measure ion dynamics in systems having more than one exchange process, a second selective inversion method was tested on two paramagnetic Li intercalation materials. This second technique, replaces the 90°-τ(1)-90° portion of 1D EXSY with a long, selective shaped pulse (SP). Two paramagnetic solid-state materials, which are both cathode materials for lithion ion batteries, were chosen as model compounds to test the effectiveness of both the selective inversion methods. The first compound, Li(2)VPO(4)F, was chosen as it hosts two Li sites with 1-exchange process. The second model compound is a 3-site, 3-exchange process system, Li(2)VOPO(4). For the 2-site material, Li(2)VPO(4)F, the timescales of the single A-B exchange process were found to be within error of one another regardless of the inversion method. For the 3 Li-site material Li(2)VOPO(4), the three exchange processes, AB, BC, and AC, were found to be on the millisecond timescale as revealed using the SP method. These timescales were determined over a variable temperature range where activation energies extended from 0.6 ± 0.1 eV up to 0.9 ± 0.2 eV.
authors.affiliation: McMaster University, Department of Chemistry and Chemical Biology, 1280 Main St. W. Hamilton, ON, Canada L8S 4M1.
authors.forename: L J M
authors.initials: LJ
authors.lastname: Davis
authors.forename: X J
authors.initials: XJ
authors.lastname: He
authors.forename: A D
authors.initials: AD
authors.lastname: Bain
authors.forename: G R
authors.initials: GR
authors.lastname: Goward
mesh_terms: D011211:Electric Power Supplies; D004566:Electrodes; D004735:Energy Transfer; D007477:Ions; D008094:Lithium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008422:Materials Testing / Q000379:methods*
chemical_list: D007477:Ions; D008094:Lithium