High-resolution 7Li solid-state NMR study of LixV2O5 cathode electrodes for Li-rechargeable batteries

The LixV2O5 cathode of Li-rechargeable battery cells under three different charge states have been studied by high-resolution solid-state Li-7 magic angle spinning (MAS) NMR spectroscopy. In the charged and discharged states, three different Li-7 NMR resonances, corresponding to the Li+ ions in the electrolyte, in the V2O5 cathode, and on the surface of the V2O5 cathode, were identified by their spin-lattice relaxation times in inversion recovery experiments. Only signals of the Li+ ions in the electrolyte were observed in the over charged state. It is shown experimentally that the Li+ ions in the electrolyte experience a dynamics or exchange process in a time scale of milliseconds with those in the V2O5 cathode, in particular for the discharged state, where a severe cross relaxation effect was observed in the inversion recovery for the Li+ ions in the electrolyte. It is concluded that such an exchange is mediated by the Li+ ions on the surface of the V2O5 cathode. Therefore, the surface structure of the V2O5 cathode electrode plays an important role in the reversibility of the Li+ ions in the rechargeable battery.