Ab-Initio Design of Novel Cathode Material LiFeP₁₋ₓSiₓO₄ for Rechargeable Li-Ion Batteries

Abstract

In this study, newly designed cathode material LiFeP₁₋ₓSiₓO₄, with silicon mixed in LiFePO₄ is investigated using the density functional theory. Its most optimized structure is the olivine structure of the Pnma space group. Bonding length show the anti-site defect which hinders Li diffusivity is prevented in the LiFeP₁₋ₓSiₓO₄. Lithium migration energy barriers in the (010) path of LiFeP₁₋ₓSiₓO₄ (x = 0, 0.5, and 1) are calculated by using nudged elastic band calculations, and the average values are determined as 0.180, 0.245, and 0.280 eV for LiFePO₄, LiFeP₀․₅Si₀․₅O₄, and LiFeSiO₄, respectively. This signifies that the Li ionic diffusivity is degraded thermodynamically, which is contrary to that indicates by the calculated bonding length, however, the difference is negligibly small. Furthermore, the intercalation voltage increases up to 4.97 V, depending on the Si ratio to P, and is much higher than that of the pristine cathode materials LiFePO₄ (~3.47 V) enabling voltage optimization by Si substitution. The energy density is proportional to the intercalation voltage, hence the energy density is increased, respectively. Finally, the Total density of states show that the electronic conductivity of LiFeP₁₋ₓSiₓO₄ (x = 0–1) is better than that of LiFePO₄.