The Electronic Stucture And Diffusion Activation Energy Of Dopant LiFePO₄:First-principles Study

Energy and environment have become both important problems for human society survival and development. In recent years, with the rapid development of electronic and information technologies, the new power supply with high energy density, high power density, and high security are becoming increasingly important. Having high energy density, high working voltage, long cycle life, low self-discharge rate, no pollution and high security, Lithium ion batteries is widely used in portable mobile electronic products, automotive and aerospace and other fields. Based on the first principles calculation, we study physical properties of the doping LiFePO4materials. We hope it can provide guidance and help in the modification and design of LiFePO4materials.(1) We introduced the research status of lithium ion batteries in short, and the calculated method based on density functional theory. Moreover, a brief introduction of VASP software is also given.(2) First-principles method was used to study the structure and performance of Li0.875M0.125FeP04(M=Na, Mg). Calculated results show that the band gaps and lithium ion diffusion activation energies of Li0.875M0.125FePO4(M=Na, Mg) are smaller than those of undoping LiFePO4. Mg dopant is better than Na dopant in improving the conductivity of Li0.875M0.125FePO4.(3) First-principles method was used to study the electronic structures and lithium ion diffusion activation energies for LiFe0.875M0.125PO4(M=V, Cr, Mn, and Cu) materials. Calculated results indicate that the band gaps of LiFe0.875M0.125PO4(M=V, Cr, Mn, and Cu) are smaller than those of undoping LiFePO4From the density of state and lithium ion diffusion activation energy, it is found that Cr dopant is best for enhancing the conductivity of LiFePO4.(4) The electronic structures and lithium ion diffusion activated energies for LiFeo.75Cr0.25PO4with both different Cr doping sites were calculated. It has been found that the band gaps of LiFe0.75Cr0.25PO4(1&2sites,2&3sites, and2&4sites) are smaller than those of undoping LiFePO4Moreover, it is observed that different doping sites can impact the conductivity of LiFe0.75Cr0.25PO4, and LiFe0.75Cr0.25PO4(2&4site) is best for improving the conductivity of LiFePO4.(5) The electronic structures and lithium ion diffusion activated energies for LiFePO4-0.125with one different oxygen vacancy were calculated. It has been found that the band gaps of LiFePO3.875(1to6sites) are smaller than those of undoping LiFePO4. Moreover, it is observed that different oxygen vacancy site can impact the conductivity of LiFePO3.875and LiFePO3.875(3oxygen vacancy site) is best for improving the conductivity of LiFePO4.