Morphology evolution during delithiation of Li-Pb alloys: Oscillatory electrochemical behavior

We report on a study of morphology evolution following de-lithiation of Li-Pb alloys, produced by the electrochemical lithiation of Pb particulate and sheet electrodes. Electrochemical titration and time of flight measurements were performed in order to determine the intrinsic diffusivity of Li, D^¯_Li, as a function of alloy composition, which ranged from 10−¹²-10−¹⁰ cm²s⁻¹. Morphology evolution was studied under conditions of galvanostatic and potentiostatic dealloying. For the particulate electrodes, we observed dealloyed morphologies corresponding to Kirkendall voids, negative dendrites, void nodules and conventional bicontinuous nanoporous structures. In the case of Pb sheets, similar dealloyed morphologies were obtained under galvanostatic dealloying conditions, however, in the case of potentiostatic dealloying, we did not observe the formation of large volume bicontinuous nanoporous structures. For Pb sheets lithiated to a composition corresponding to the Li₈Pb₃ phase and galvanostatically dealloyed at current densities ∼1 mAcm−², voltage oscillations were observed with periods of 70-90 s and amplitudes ranging from 20-130 mV. Current oscillations were also observed for potentiostatic dealloying at 1 V vs Li⁺/Li. The possible mechanism of these oscillations is discussed and attributed to a salt film precipitation and lift-off process.