Reversible electrochemical extrusion of copper by lithium. Role of the initial structure

Abstract

The reversible Li-driven copper extrusion/insertion mechanism into Cu_2.33V₄O₁₁ electrode has been studied and a new ion-exchanged assisted electrochemical process was unravelled. This process, entails during the charging of “Li_x V₄O₁₁ + Cu⁰” composite electrodes vs. Li, the oxidation of Cu metal into copper ions that concomitantly exchanged for lithium ions to produce back Cu_2.33V₄O₁₁. The electrochemical performances of such cells, namely in terms of capacity retention and power rates, are explained on the basis of the electrochemically generated Cu ions that can either being ion-exchanged with Li within the Li-V-O host or released in the solution. When the former does occur we show, owing to excellent kinetic of both, the ion-exchanged reaction between Cu²⁺ and Li⁺ together with a fast charge transfer between Cu⁰ and Cu²⁺, that high rate performances electrodes can be achieved whereas when the latter prevails the cells rapidly fail. It appears then that Cu⁺ ions should be removed. Thus, a new copper vanadate Cu_1.1V₄O₁₁ phase has been isolated by both chemical and electrochemical removal of Cu from the mother Cu_2.33V₄O₁₁ phase, and its electrochemical performance in Li cells studied. The removal of copper was shown to occur in a topotactic manner resulting in a stacking of [V₄O₁₁]_n layers linked by differently coordinated copper ions. This new phase reversibly reacts with 5 Li, leading to a capacity of about 260 mAh/g, through a process involving a reversible displacement reaction entailing to the growth/disappearance of Cu dendrites.