Abstract
We investigated the effect of inserting lithium into Ag<sub>2</sub>V<sub>4</sub>O<sub>11</sub> (ε-SVO) on the structure, electronic properties and redox committed by combining <i>in situ</i> XRD measurements, ESR spectroscopy and 4 probes DC conductivity coupled with thermopower measurements. The electrochemical discharge occurs in three consecutive steps above 2 V (vs. Li<sup>+</sup>/Li). The first one, between 0 < x < ~0.7 in Li<sub>x</sub>-SVO, has been ascribed to the V<sup>5+</sup> reduction through a solid solution mechanism. This reduction competes with a Li<sup>+</sup>/Ag<sup>+</sup> displacement reaction which leads to a structural collapse owing to the ionic radii mismatch between the withdrawn Ag<sup>+</sup> and the inserted Li<sup>+</sup>. The silver reduction progresses continuously with two different slopes along two composition–potential plateaus at 2.81 V and 2.55 V. Finally, the reduction continues until we obtain an amorphous structure with V<sup>4+</sup> and a ε of V<sup>3+</sup>. Although, the silver re-enters the structure during the subsequent recharge, the original structure is not recovered. The reduction of silver forming silver metal nano-clusters acts to increase the electronic conductivity from 3.8 × 10<sup>−5</sup> S cm<sup>−1</sup> to 1.4 × 10<sup>−3</sup> S cm<sup>−1</sup>. In complement to this study, we also report on a low temperature hydro-(solvo)-thermal approach using HF<sub>(aq)</sub> as a mineralizer, which enables the synthesis of nano-sized ε-SVO particles that exhibit superior electrochemical performances compared to conventional particles synthesized by solid-state reaction.