First Principle Calculation of Li₂Fe_0.5Cr_0.5SiO₄ for Li-Ion Battery Cathode

E-ISSN： 1662-8985|2015|1112|286-289

ISSN： 1022-6680

Source： Advanced Materials Research, Vol.2015, Iss.1112, 2015-08, pp. : 286-289

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Abstract

First principle calculation based on Density Functional Theory and U correction (DFT+U) is used to investigate structural change while losing Li atom, average voltage for couple reaction, phase stability, and electronic structure of Li₂Fe_0.5Cr_0.5SiO₄. In this calculation, generalized gradient approach (GGA) of Perdew-Burke-Ernzerhof (PBE) is used for exchange-correlation functional. The initial structure of Li₂Fe_0.5Cr_0.5SiO₄ is obtained from the pmn₂₁ structure of Li₂FeSiO₄ and then the Fe site is substituted by 50 % of Cr. The results of calculation show that the optimized Li₂Fe_0.5Cr_0.5SiO₄ has a monoclinic structure, which has little different with Li₂FeSiO₄ structure. Although the delithiated system (LiFe_0.5Cr_0.5SiO₄) is taken into consideration, the structural geometry does not change significantly. It is indicated that the presence of Cr does not affect to the property of structural change. From the density of states (DOS) analysis, the presence of Cr causes the width of band gap become decrease. Therefore, the electronic properties change from insulator to semiconductor-like behavior. Average voltage for couple reaction M⁺²/ M⁺³ of Li₂Fe_0.5Cr_0.5SiO₄ is about 3.05 V which is lower than Li₂FeSiO₄. Furthermore, the formation energy for Li₂Fe_0.5Cr_0.5SiO₄ and all delithiation have a relatively positive sign compared with Li₂FeSiO₄ that mean that they have poor phase stability than Li₂FeSiO₄.