In the crystal structure of LiFePO4, oxygen atoms are arranged in a hexagonal close packing. PO43-tetrahedron and FeO6 octahedron constitute the spatial framework of the crystal. Li and Fe occupy the octahedral voids, while P occupies the tetrahedral voids. Fe occupies the co-angular position of the octahedron and Li occupies the co-sided position of the octahedron. FeO6 octahedrons are connected to each other on the bc plane of the crystal, and LiO6 octahedrons in the b-axis direction are connected to each other to form a chain structure. One FeO6 octahedron is aligned with two LiO6 octahedrons and one PO43-tetrahedron.
Because the FeO6 coedge octahedron network is discontinuous, electronic conductivity cannot be formed; at the same time, PO43-tetrahedron limits the volume change of the crystal lattice, affects the deintercalation and electron diffusion of Li+, and leads to the electronic conductivity and ion diffusion of LiFePO4 cathode material The efficiency is extremely low.
The theoretical specific capacity of LiFePO4 battery is relatively high (about 170mAh/g), and the discharge platform is 3.4V. Li+ is de-intercalated back and forth between the positive and negative poles to realize charging and discharging. Oxidation reaction occurs during charging. Li+ migrates out of the positive electrode and is inserted into the negative electrode through the electrolyte. Iron changes from Fe2+ to Fe3+, and oxidation reaction occurs.