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

Pourpoint, Frédérique and Hua, Xiao and Middlemiss, Derek S. and Adamson, Paul and Wang, Da and Bruce, Peter G. and Grey, Clare P. (2012) New Insights into the Crystal and Electronic Structures of Li1+xV1–xO2 from Solid State NMR, Pair Distribution Function Analyses, and First Principles Calculations. Chemistry of Materials, 24 (15). pp. 2880-2893. ISSN 0897-4756

Abstract

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 6Li 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.