Synthesis and properties of LiMIIPO4 (MII = Mg, Mn0.5Mg0.5, Co0.5Mg0.5) affected by isodivalent doping and Li-sources

Abstract

NH4MIIPO4·H2O (MII = Mg, Mn0.5Mg0.5, Co0.5Mg0.5) were synthesized by direct-precipitating method. The olivine-like LiMIIPO4 were successfully generated through the solid state reaction between the synthesized NH4MIIPO4·H2O precursors and two different Li-sources (Li2CO3 or LiOH·H2O). The NH4MIIPO4·H2O and LiMIIPO4 compounds were confirmed by TG/DTG/DTA, AAS/AES, FTIR and XRD methods. The structural and morphological properties of LiMIIPO4 compounds were studied by XRD and SEM, respectively. The XRD reflection shifts of olivine-like LiMIIPO4 from the Li-source of Li2CO3 revealed changing toward higher diffraction angles than that of LiMIIPO4 from the Li-source of LiOH·H2O. The XRD shifts of LiM0.5Mg0.5PO4 (M = Mn or Co) compounds confirmed the formation of the single phase of isodivalent doping of Mn2+ and Co2+ ions according to the change in the lattice parameters and cell volumes. The morphological investigations of the LiMIIPO4 obtained from Li2CO3 system illustrated the grain-like shape particles having smaller size of about 150–400 nm on account of the sequential transformations of types: deammoniation, dehydration, polycondensation and decarbonization. Conversely, the larger size particles (300–700 nm) of the LiMIIPO4 obtained from LiOH·H2O were observed due to the shorter transformation path through the reactions of types: deammoniation and dehydration without polycondensation and decarbonization.