Electrochemical Lithium Insertion in Zn₃P₂ Zinc Phosphide

Abstract

Zn3P2 zinc phosphide was synthesized as powders by three different preparation routes: ball-milling, ball-milling followed by annealing, and ceramics at high temperature. Depending on the synthetic route, various powder morphologies (size and crystallinities) were obtained. The electrochemical reactivity toward lithium of these various Zn3P2 powders is shown to be unique despite some quantitative performance differences. The insertion mechanism is shown to involve two distinct but parallel reversible pathways for a large number of inserted lithiums (up to nine): one implies exclusively phosphide phases: Zn3P2, LiZnP, Li4ZnP2, and Li3P. The second one involves only Li−Zn alloys: Zn, LiZn4, and LiZn. Among these various phases two of them are described for the first time: Li4ZnP2 and LiZn4. Both crystal structures have been solved and refined by Rietveld analysis of X-ray diffraction patterns on powders to RB = 3.46 (RF = 2.73, Rp = 5.71, Rwp = 7.33) for Li4ZnP2 and to RB = 6.70 (RF = 5.23, Rp = 6.94, Rwp = 9.19) for LiZn4 powders, respectively.