Enhanced interfacial lithium storage in nanocomposites of transition metals with LiF and Li2O:: Comparison of DFT calculations and experimental studies

Me/LiX nanocomposites (Me - transition metal and X = F or O) exhibit extra lithium storage, with pseudo-capacitive behavior and high-rate performance. While LiX surface layers or the interfacial core serves as hosts for extra Li, atoms of contacting transition metal serve as electron sinks, depending on Me electronegativity. To verify the mechanism, we have performed comparative DFT-LCAO calculations on the polar Ti vertical bar Li vertical bar Li2O(1 1 1) and non-polar Cu vertical bar Li vertical bar LiF(001) interfaces with extra Li atoms inserted inside both 2D interfaces, gradually changing their concentration. Theoretical calculations confirm validity of this interfacial model for explanation of the extra storage capacity at low potentials. The diffusion barrier for extra Li atom along the Me/LiX interface is markedly smaller than the Li penetration barrier into the bulk. (C) 2007 Elsevier Masson SAS. All rights reserved.