On Aliovalent Substitution on the Li Site in LiMPO 4 : an X‐ray Diffraction Study of the Systems LiMPO 4 –M 1.5 PO 4 (= Li x M 1.5– x /2 PO 4 ; M = Ni, Co, Fe, Mn)

In this paper we report on the possibility of Li substitution by M 2+ to various high degrees in LiMPO 4 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 II PO 4 and M II 1.5 PO 4 (= M II 3 (PO 4 ) 2 ) to form compounds of composition Li x M II 1.5– x /2 PO 4 (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 LiCoPO 4 and LiFePO 4 (up to compositions of approx. (Li 0.8 Co 0.1 )CoPO 4 and approx. (Li 0.9 Fe 0.05 )FeO 4 . In addition, the nearly stoichiometric monoclinically distorted olivine‐type compounds with compositions (Li 0.42–0.47 Co 0.29–0.265 )CoPO 4 and (Li 0.14–0.16 Fe 0.43–0.42 )FePO 4 could be identified and are described in this article.