On the Electrochemical Reactivity Mechanism of CoSb[sub 3] vs. Lithium

The electrochemical reactivity of vs. lithium has been studied. This phase reacts with more than 9.5 lithium in a two-step process, consisting of the uptake of 9 Li at a constant voltage close to 0.6 V, and of about one lithium over the final voltage decay to 0.01 V. Upon recharge, only 8 lithium can be extracted. From in situ X-ray diffraction, microscopy, and magnetic measurements, we provide evidence that the constant voltage process is rooted in the decomposition of leading to the formation of a composite made of Co and nanograins. We also illustrate that the mechanism by which the internal nanostructured electrode, formed during reduction, converts back to is quite unusual. It involves, concomitant with the dealloying reaction, a chemical reaction between Co and Sb nanograins. The extra capacity, measured at low potential, appears to be nested in a decomposition-type reaction catalyzed by the cobalt nanoparticles, in a manner similar to that previously reported for CoO. Although these materials can reversibly uptake about 8 lithium, they are of negligible value, since their capacity rapidly decays with cycling, independent of the electrode processing.