2014-01

On Aliovalent Substitution on the Li Site in LiMPO₄: an ­X-ray Diffraction Study of the Systems LiMPO₄–M_1.5PO₄ (= Li_xM_1.5–x/2PO₄; M = Ni, Co, Fe, Mn)

Oliver Clemens, Robert Haberkorn, Michael Springborg, Horst Philipp Bec

Z. Anorg. Allg. Chemie 640/1 (2014) 173-183

Article first published online: 15 OCT 2013

DOI: 10.1002/zaac.201300376

Abstract

In this paper we report on the possibility of Li substitution by M²⁺ to various high degrees in LiMPO₄ olivine-type compounds (M = Ni, Co, Fe, Mn), depending on the kind of transition metal M. The experimental studies were carried through by reacting stoichiometric amounts of LiM^IIPO₄ and M^II_1.5PO₄ (= M^II₃(PO₄)₂) to form compounds of composition Li_xM^II_1.5–x/2PO₄ (0 ≤ x ≤ 1). A complete solid solution over the whole range of x was found for M = Ni (together with a second order structural transition from orthorhombic to monoclinic for decreasing x), whereas far smaller degrees of dopability of the Li site were found for LiCoPO₄ and LiFePO₄ (up to compositions of approx. (Li_0.8Co_0.1)CoPO₄ and approx. (Li_0.9Fe_0.05)FeO₄. In addition, the nearly stoichiometric monoclinically distorted olivine-type compounds with compositions (Li_0.42–0.47Co_0.29–0.265)CoPO₄ and (Li_0.14–0.16Fe_0.43–0.42)FePO₄ could be identified and are described in this article.