Towards a green and cost-effective synthesis of polyanionic cathodes: comparative electrochemical behaviour of LiFePO4/C, Li2FeP2O7/C and Li2FeSiO4/C synthesized using methylcellulose matrix

Abstract

The polyanion cathodes for Li-ion batteries, namely LiFePO4, Li2FeP2O7 and Li2FeSiO4, were synthesized by very short high-temperature treatment (approximately several minutes) and subsequent quenching. Methylcellulose—a polymer with thermally driven water solubility—was used as the medium in which the precursor solutions were dispersed prior to high temperature treatment. The methylcellulose pyrolytically decomposes to carbon, thus producing the polyanion material/carbon composites of LiFePO4/C, Li2FeP2O7/C and Li2FeSiO4/C. The obtained powders have reduced crystallinity and significant microstructural characteristics: low crystallite size and notable microstrain. They exhibit stable electrochemical performances in both aqueous and organic electrolyte. The broadening of existing peaks in cyclic voltammetry and/or the emergence of new broad peaks was attributed to the presence of the amorphous phase in the samples. In galvanostatic charge–discharge tests, the materials provided high capacities at low current densities, while the highest rate performance was demonstrated by olivine-phosphate when compared to the other two materials.