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J. Electrochem. Sci. Technol > Volume 4(3); 2013 > Article
Journal of Electrochemical Science and Technology 2013;4(3):102-107.
DOI: https://doi.org/10.5229/JECST.2013.4.3.102   
Structural and Electrochemical Properties of Doped LiFe0.48Mn0.48Mg0.04PO4 as Cathode Material for Lithium ion Batteries
Donghyuk Jang, Kowsalya Palanisamy, Yunok Kim, Won-Sub Yoon
Department of Energy Science, Sungkyunkwan University;Department of Energy Science, Sungkyunkwan University;Department of Energy Science, Sungkyunkwan University;Department of Energy Science, Sungkyunkwan University;
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) ${AA}^3$ for pure $LiFe_{0.5}Mn_{0.5}PO_4$ and is decreased to 296.177(1) ${AA}^3$ 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.
Key Words: Lithium ion battery, Olivine structure, $LiFe_{0.48}Mn_{0.48}Mg_{0.04}PO_4$ material, Cation doping, Rietveld Analysis


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