First-principles study of the chemical bonding and conduction behavior of LiFePO4

- Identified unstable chemical bonding between Fe-O1 and Fe-O2 during delithiation.
- Demonstrated fundamental role of Fe-O3 chemical bonding on conductivity of LiFePO4.
- Hopping process can be described by the calculation of polarization of a charged supercell.

The electronic structure and chemical bonding of LiFePO4 were calculated using maximally-localized Wannier functions within the framework of the first-principles method. Comparison of the shifts in Wannier centers between LiFePO4 and delithiated reference (FePO4)r structures demonstrated the unstable chemical bonding of Fe-O1 and Fe-O2 during delithiation. The contribution of each orbital to the small-polaron polarization field was discussed in detail. The small polaron hopping is accompanied by a very small polarization field with the value of 0.049 C/m2. Results of our calculations showed that the chemical bonding of Fe-O3 has an important function in the low-temperature conductivity of LiFePO4.