Structural and Electrochemical Properties of Doped LiFe0.48Mn0.48Mg0.04PO4 as Cathode Material for Lithium ion Batteries

Abstract

The electrochemical properties of Mg-doped LiFe 0.48 Mn 0.48 Mg 0.04 PO 4 and pure LiFe 0.5 Mn 0.5 PO 4 olivine cathodes are examined and the lattice parameters are refined by Rietveld analysis.The calculated atomic parameters from the refinement show that Mg 2+ doping has a significant effect in the olivine LiFeMnPO 4 structure.The unit cell volume is 297.053(2)Å 3 for pure LiFe 0.5 Mn 0.5 PO 4 and is decreased to 296.177(1) Å 3 for Mg-doped LiFe 0.48 Mn 0.48 Mg 0.04 PO 4 sample.The doping of Mg 2+ cation with atomic radius smaller than Mn 2+ and Fe 2+ ion induces longer Li-O bond length in LiO 6 octahedra of the olivine structure.The larger interstitial sites in LiO 6 octahedra facilitate the lithium ion migration and also enhance the diffusion kinetics of olivine cathode material.The LiFe 0.48 Mn 0.48 Mg 0.04 PO 4 sample with larger Li-O bond length delivers higher discharge capacities and also notably increases the rate capability of the electrode.