Structural properties and application in lithium cells of Li(Ni0.5Co0.5)1−yFeyO2 (0 ≤ y ≤ 0.25) prepared by sol–gel route: Doping optimization

• Fe-doped Li(Ni,Co)O2 layered materials have been prepared by sol–gel route.
• Cationic environment has been studied using spectroscopies.
• The phase diagram vs. Fe content has been determined.
• For Fe ≤ 0.1 cathodes show excellent rate capability and cycle performance.

Layered Li(Co0.5Ni0.5)1−yFeyO2 (0.0 ≤ y ≤ 0.25) oxides were prepared by citric-acid assisted sol–gel method. Elemental and structural properties were investigated by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman scattering (RS) and Mössbauer spectroscopy, and magnetometry. EDX images show a homogeneous distribution of Fe ions. XRD and RS spectroscopy reveal that the materials crystallize as a LiNiO2LiCoO2LiFeO2 solid solution with the typical rhombohedral α-NaFeO2 structure (R  3¯ m S.G.) up to y = 0.2 at which composition a secondary phase was observed. For y > 0.2 the XRD results show the appearance of the α-LiFeO2 phase with the cubic structure (Fm3m S.G.). The degree of cation mixing investigated by XRD analysis and magnetic measurements is z < 0.04, for y < 0.2. Electrochemical tests of Li(Co0.5Ni0.5)1−yFeyO2 (0.0 ≤ y ≤ 0.1) oxides in lithium cells show the influence of iron substitution. The best results have been obtained for the composition y(Fe) = 0.05, where the electrical conductivity is maximum. A specific capacity 32 mAh g−1 is maintained at 8C rate.

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