602030 polymer battery.Introduction to lithium iron phosphate batteries

　　Lithium iron phosphate battery is a lithium-ion battery that uses lithium iron phosphate (LiFePO4) as the positive electrode material and carbon as the negative electrode material. The rated voltage of the monomer is 3.2V, and the charging cut-off voltage is 3.6V-3.65V.

　　During the charging process, some lithium ions in lithium iron phosphate are removed and transferred to the negative electrode through the electrolyte, which is embedded in the negative electrode carbon material; At the same time, electrons are released from the positive electrode and reach the negative electrode from the external circuit, maintaining the balance of chemical reactions. During the discharge process, lithium ions detach from the negative electrode and reach the positive electrode through the electrolyte. At the same time, the negative electrode releases electrons, which reach the positive electrode from the external circuit and provide energy to the outside world.

　　Lithium iron phosphate batteries have the advantages of high working voltage, high energy density, long cycle life, good safety performance, low self discharge rate, and no memory effect.

　　In the crystal structure of LiFePO4, oxygen atoms are tightly packed in a hexagonal arrangement. The PO43 tetrahedron and FeO6 octahedron form the spatial skeleton of the crystal, with Li and Fe occupying the octahedral voids, while P occupying the tetrahedral voids, where Fe occupies the co angular position of the octahedron and Li occupies the co edge position of the octahedron. The FeO6 octahedra are interconnected on the bc plane of the crystal, while the LiO6 octahedra structure in the b-axis direction is interconnected into a chain like structure. 1 FeO6 octahedron coexists with 2 LiO6 octahedrons and 1 PO43 tetrahedron.

　　Due to the discontinuity of the FeO6 co octahedral network, electronic conductivity cannot be formed; At the same time, the PO43 tetrahedron restricts the volume change of the lattice, affecting the de embedding and electron diffusion of Li+, resulting in extremely low electronic conductivity and ion diffusion efficiency of LiFePO4 cathode material.

　　The theoretical specific capacity of LiFePO4 batteries is relatively high (about 170mAh/g), and the discharge platform is 3.4V. Li+undergoes a charge discharge process by removing and embedding it back and forth between the positive and negative electrodes. During charging, an oxidation reaction occurs, where Li+migrates from the positive electrode and is embedded into the negative electrode through the electrolyte. Iron changes from Fe2+to Fe3+, leading to an oxidation reaction.

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