Effect of sodium substitution into LiFePO₄ cathode material: a first principles studies

The demand for Lithium-ion batteries has increased drastically with the introduction of electric vehicles and wide use of portable devices. The scarcity of lithium sources will soon increase the prices of the battery. Sodium has been widely studied as an alternative to lithium as they have almost similar chemical properties. Lithium iron phosphate is a widely used cathode material for rechargeable batteries. In this work, the effect of sodium substitution into LiFePO₄ has been studied. Using computational approaches, the structural and electronic properties of sodium-LiFePO₄ have been calculated by means of density functional theory using GGA-PBE + U method. Upon substitution, the lattice parameter of LiFePO₄ undergoes change, resulting in volume expansion. In ternls of electronic properties, no significant change has been seen as the band gap of sodium-LiFePO₄ is almost the same as pure LiFePO₄ suggesting the electronic conductivity would remain the same. However, there is a significant reduction in ionic conductivity, as the sodium ion requires higher energy to mograte.