57Fe Mössbauer study of Li x Fe1-y Co y PO4 (y = 0, 0.1, 0.2) as cathode material for Li-ion batteries

Lithium iron phosphates LiFe_1-y Co _y PO₄ (y = 0, 0.1, 0.2) exposed to a charging process were studied by ⁵⁷Fe Mössbauer spectroscopy taking into account XRD and SEM data. Hyperfine parameters of the spectra were determined above and below the magnetic ordering temperature for all the samples. It was shown that the presence of Co impurity atoms in lithium phosphates gives no effect on the hyperfine interaction of ⁵⁷Fe²⁺ cations. However, Co atoms in the nearest cation environment of Fe atoms lead to a significant change of the hyperfine interactions of ⁵⁷Fe³⁺ cations. The Co impurity atoms distribution over the positions of the iron atoms in the structure is found not to be statistical,but correlated.