Introduction to Lithium Iron Phosphate Battery

In the crystal structure of LiFePO4, oxygen atoms are arranged in a hexagonal close-packed arrangement.PO43-tetrahedra and FeO6 octahedra form the spatial skeleton of the crystal.Li and Fe occupy the octahedral voids while P occupies the tetrahedral voids, of which Fe occupies the octahedral co-corner and Li occupies the octahedral co-edge.The FeO6 octahedra are connected with each other in the bc plane of the crystal.The LiO6 octahedral structures are connected with each other to form a chainlike structure in the b-axis. The FeO6 octahedra are interconnected on the bc face of the crystal, and the LiO6 octahedral structures in the b-axis direction are connected to each other to form a chain structure. 1 FeO6 octahedron is co-prismatic with 2 LiO6 octahedra and 1 PO43-tetrahedron.

Due to the discontinuity of the FeO6 co-prismatic octahedral network, resulting in the inability to form the electronic conductivity; at the same time, the PO43-tetrahedron restricts the volume change of the lattice, which affects the de-embedding of Li+ and electron diffusion, leading to the extremely low electronic conductivity and ion diffusion efficiency of the LiFePO4 cathode material.

The LiFePO4 battery has a high theoretical specific capacity (about 170 mAh/g), and the discharge platform is 3.4 V. Li+ is de-embedded back and forth between the positive and negative electrodes to achieve charging and discharging, and an oxidation reaction occurs during charging, with Li+ migrating out of the positive electrode and embedded in the negative electrode via the electrolyte, and iron changing from Fe2+ to Fe3+, and an oxidation reaction occurring.