Electrochemical Lithium Insertion in Zn₃P₂ Zinc Phosphide

Zn 3 P 2 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 Zn 3 P 2 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: Zn 3 P 2, LiZnP, Li 4 ZnP 2, and Li 3 P. The second one involves only Li−Zn alloys: Zn, LiZn 4, and LiZn. Among these various phases two of them are described for the first time: Li 4 ZnP 2 and LiZn 4 . Both crystal structures have been solved and refined by Rietveld analysis of X-ray diffraction patterns on powders to R B = 3.46 ( R F = 2.73, R p = 5.71, R wp = 7.33) for Li 4 ZnP 2 and to R B = 6.70 ( R F = 5.23, R p = 6.94, R wp = 9.19) for LiZn 4 powders, respectively.