Electronic Transport Properties in Li_xCr_0.11V₂O_5.16

Abstract

Vanadium pentoxide gels, which have been extensively studied during the past [1], exhibit a layered structure suitable for ionic and molecular intercalation reactions. Many applications have been evidenced according to the electronic or ionic properties of the ion inserted compounds, for instance Li_xV₂O₅ [2]. These compounds are electronic conductors, in which polarons and (intersite) bipolarons are the mobile species. The cycling of the electrochemical system Li/V₂O₅ presents a good reversibility up to 1 mole of lithium, attributed to the topotactic formation of three phases α, ɛ and δ. However, a loss of reversibility beyond x=l is observed; this is due to the γ phase which coexists with the δ phase beyond that x value. The insertion of Cr³⁺ ions in the V₂O₅ gels permits to obtain the oxide Cr_0.11V₂O_5.16, with a structure similar to that of orthorhombic V₂O₅. The formation of (O-Cr-O-Cr-0) short chains linking the V₂O₅ layers enhances electrochemical performances [3] when compared to that of V₂O₅. During electrochemical cycling, only both phases α (x < 0.18) and δ (x > l 0.3) are obtained: the (O-Cr-O-Cr-O) chains strengthen the structure and hinder the apparition of the δ and γ phases [4].