Electrochemical reactivity of Li2VOSiO4 toward Li

We report on the chemical/electrochemical reactivity of the insulating layered V-based silicate-phase Li2VOSiO4 toward Li. The silicate phase, made by a ceramic approach and consisting of 5-20 mu m agglomerates, exhibits only a slight reactivity with Li in chemical or electrochemical reactions. By ball milling Li2VOSiO4 in the presence of carbon, we succeeded in preparing composites that reversibly react with 0.7 Li+ per unit formula at an average voltage of 3.6 V vs Li+/Li-0. This electrochemical reactivity was chemically mimicked using NO2BF4 or Br-2 and LiI as oxidizing and reducing agents, respectively. Through a combination of X-rays and HRTEM measurements, we showed that the insertion-deinsertion mechanism is a two-phase process with poor kinetics. The delithiated phase crystallizes in space group P4 (a = 6.206 angstrom, c = 4.5715 angstrom), whereas the precursor lithiated phase crystallizes in P4/ nmm (a = 6.366(9) angstrom, c = 4.456(6) angstrom). Because silicates such as phosphates are cheap and can also be made redox-active by carbon coatings, they should not be overlooked as possible electrode candidates in future research.