Theory and experimental study on electrochemical performance of LiFePO4 by Cu and Mg Co-doped based on density functional theory

In order to improve the electrochemical performance of LiFePO 4 (LFP) electrode, Cu and Mg co-doped LFP cathode materials were synthesized via a high-temperature solid-state reaction method. The phase purity and morphology were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM). Based on co-doped cathode material, the coin-type cells was assembled for galvanostatic charge-discharge testing. The combined synergistic effect of co-doping into LFP were investigated through density functional theory(DFT) calculations. The first-principles calculation method was employed to study the thermodynamic stability, electronic structure properties, intercalation voltage, and lithium-ion diffusion characteristics of Cu and Mg-doped LiFePO 4 . The results show that smaller particle sizes and larger specific surface areas for Cu and Mg co-doping. It facilitates the diffusion of LFP on the surface and within the bulk of the cathode material during charge and discharge processes. This leads to reduce polarization and thus improve electrochemical performance. A higher initial discharge specific capacity of 142.4 mAh/g is exhibited compared to the undoped counterpart. The incorporation of Cu and Mg reduces the band gap from 3.66 eV to 0.4 eV. This suggests that the electrical conductivity is improved due to electrons more easily transition from the valence band to the conduction band. After co-doping, the lithium ion diffusion barrier decreases from 1.08 eV to 0.75 eV. It is predicted that lithium ions diffuse in LFP-CM six orders of magnitude faster than in its intrinsic counterpart. Meanwhile, a platform with a high operating voltage of 3.64 V makes a positive contribution to the electrochemical performance.