Abstract:
A nanoscale and pure olivine structure LiFePO4 (triphylite) and NaFePO4 (maricite) were synthesized at low temperature (from 300°C) using an organic-inorganic steric entrapment solution, from precursor chemicals of LiNO3, NaNO3, Fe(NO3)3*9H2O and (NH4)2HPO4 stoichiometrically dissolved in distilled water. A long-chain polymer, such as polyvinyl alcohol (-[CH2-CHOH]-n or PVA), having a degree of polymerization corresponding to a molecular weight of 9,000 to 10,000, was used as the organic carrier for the precursors, which served for the physical entrapment of the metal ions in the dried network. Normally, when calcined and crystallized in air, this method leads to the synthesis of compounds where the cations in their highest oxidation state. However, in this study we found a way to make compounds having lower oxidation states (e.g. Fe+2 versus Fe+3), which may have wider applications in the synthesis of other compounds having variable oxidation states, with potential applications in electronic ceramics of complex chemistry. The resulting LiFePO4 or (Li2O*2FeO*P2O5) and NaFePO4 or (Na2O*2FeO*P2O5) powders were characterized by TG/DTA thermal analysis, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) nitrogen absorption and particle size analysis.
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