Synthesis of ternary transition metal fluorides Li 3MF 6via a sol-gel route as candidates for cathode materials in lithium-ion batteries

Abstract

A sol-gel route for ternary lithium fluorides of transition metals (M) is presented allowing the synthesis of Li 3MF 6-type and Li 2MF 5-type compounds. It is based on a fluorolytic process using transition metal acetylacetonates as precursors. The domain size of the obtained powders can be controlled by modifying the conditions of synthesis. 6Li and 7Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is used to study local environments of the Li ions in orthorhombic and monoclinic Li 3VF 6 as well as Li 2MnF 5. The number of magnetically inequivalent Li sites found by MAS NMR is in agreement with the respective crystal structure of the compounds studied. Quantum chemical calculations show that all materials have high de-lithiation energies making them suitable candidates to be used as high-voltage battery cathode materials. © 2012 The Royal Society of Chemistry.