Reactivity of Antimony Oxides and MSb2O6 ( M = Cu , Ni , Co ) , Trirutile-type Phases with Metallic Lithium

Abstract

Isostrutural trirutile-type phases were prepared by solid-state synthesis and their electrochemical activity towards lithium was investigated. and showed similar electrochemical behavior, with an uptake of about 18–19 Li per formula unit along the first reduction and only 6–7 Li reversibly removed upon subsequent cycling. This totally differs from the behavior of that was found to react with only about 7 Li during the first reduction, without any capacity recovered on subsequent charge. From X-ray diffraction data, both Cu and Co phases lead to an amorphous composite down to . From high-resolution transmission electron microscopy observations, reduced consists of Co particles dispersed in a matrix. For , our results and observations enlightened a two-step reduction: First, the formation of Cu clusters through an electrochemically-driven exchange reaction leading to , and then reduction of this matrix into Sb domains dispersed in an insulating amorphous Li-rich matrix, preventing any further alloying reaction and any charge reaction. The complete charge irreversibility observed on half-cells confirmed this point, while the Li reduction of emphasized a close similarity with the reactivity of the phases, suggesting a first reduction step of into , assuring conduction and subsequent cycling capacity. Despite the composite nature of the as-formed electrode and the very fine Sb particles, the reversibility of the alloying reaction was not found to be satisfactory for Li-ion cells.