New Insights into the Crystal and Electronic Structures of Li1+xV1-xO2 from Solid State NMR, Pair Distribution Function Analyses, and First Principles Calculations

Pair distribution function (PDF) analyses of synchrotron data obtained for the anode materials Li1+xV1-xO2 (0 <= x <= 0.1) have been performed to characterize the short to medium range structural ordering. The data show clear evidence for the magnetically-induced distortion of the V sublattice to form trimers, the distortion persisting at even the highest excess Li content considered of x = 0.1. At least three distinct local environments were observed for the stoichiometric material LiVO2 in Li-6 nuclear magnetic resonance (NMR) spectroscopy, the environments becoming progressively more disordered as the Li content increases. A two-dimensional Li-Li correlation NMR experiment (POST-C7) was used to identify the resonances corresponding to Li within the same layers. NMR spectra were acquired as a function of the state of charge, a distinct environment for Li in Li2VO2 being observed. The results suggest that disorder within the Li layers (in addition to the presence of Li within the V layers as proposed by Armstrong et al. Nat. Mater. 2011, 10, 223-229) may aid the insertion of Li into the Li1+xV1-xO2 phase. The previously little-studied Li2VO2 phase Was also investigated by hybrid density functional theory (DFT) calculations, providing insights into magnetic interactions, spin lattice coupling, and Li hyperfine parameters.