A new promising sol–gel synthesis of phospho-olivines asenvironmentally friendly cathode materials for Li-ion cells

Anewsol–gel synthetic route was developed to prepare single-phase phospho-olivines LiMPO4 (M=Fe or Mn) as environmentallyfriendly, low-cost potential cathodematerials for the next generation of Li-ion secondary batteries. Li2CO3 and M(II) acetate were used as Li and M(II) precursor while tri-ethyl phosphate was chosen as phosphate organic precursor for its high hydrolysis activity, with absolute ethanol as solvent. The sol–gelsynthesis ensures homogeneity of the precursors at the nanometric scale and improved reactivity, allowing to obtain very small agglomerates and crystal grain size. Several carbon sources were used in order to improve the electrochemical performances of the samples, increasing their electronic conductivity and hindering particle agglomeration. The powders were annealed at various temperatures in flowing Ar to avoid M(II) oxidation. The crystal structures of the products were analysed by Rietveld refinement of X-ray powder diffraction (XRD) data while the morphology of the samples was analysed by scanning electron microscopy. Galvanostatic cycling tests of the cathodic materials were made on coin cells with Li metal as anode in order to study the influence of the synthesis and the structural–morphological characteristics on the electrochemical performance of the phosphate/C composite.