A Theoretical Study of the Solid Solution Phases of Li<sub>x</sub>FePO<sub>4</sub>

Abstract

For the next generation Li-battery anode materials LiFePO 4 , the forming of the solid solution phase Li x FePO 4 and the related charge/discharge mechanism are the high light topics recently. In the paper, ab-initio calculation was applied to study the formation and electronic structure of the solid solution of Li x FePO4, and a Charge/Discharge model of LiFePO 4 was set up based on the calculation results. Due to the high formation energy, Li x FePO 4 separates into FePO 4 and LiFePO 4 in bulk system under room temperature. The single solid solution phase Li x FePO 4 could exists in the nanoscale particle, and it is due to that the relative larger lattice mismatch energy. The nanoscale particle materials should have a good rating performance due to the forming of Li x FePO 4 in solid solution phase, of which the partially occupied state and the small energy gap between the VBM and the defect state could improve the intrinsic electronic conductivity. In bulk materials, the medium region, which is composed of Li x FePO 4 , is very narrow between the two phases FePO 4 and LiFePO 4 . There is a electron potential well in the region, of which the bottom is at the side of Li x FePO 4 (x<0.5). The number of electron in the well highly affects the lithium insertion and extraction. In order to efficiently transfer the electron between the potential well and the out circuit, an electron conductor network or layer should be coated on the LiFePO 4 particle.