Lithium cobalt phosphate

The working voltage of lithium cobalt phosphate material can reach 4.8v and the capacity can reach 170mAh/g. It has the same crystal structure as lithium iron phosphate, both of which are ordered peridotite structure and belong to orthogonal crystal system, the space group is Pmnb, and the crystal cell parameters are a=0.5922nm, b=1.0202nm and c=0.4699nm. In the crystal, O atoms are hexagonal dense, P atoms occupy tetrahedral gaps, and Li and Co atoms occupy octahedral gaps. CoO6, an octahedron with common edge, is linked to PO4 tetrahedron in the direction of C axis to form a chain. Because the co-o-p bond stabilizes the crystal structure, the crystal rearrangement is very small and the crystal structure is very stable in the process of charging and discharging, which also guarantees the good cycling performance of cobalt phosphate material. Especially in some fields requiring long-term storage, such as distributed energy storage, energy storage batteries need long-term floating charge of small current, which will lead to excessive release of Li+ and damage the structure of positive electrode materials. As for phosphate materials, due to their stable structure, even in the long-term process of small current floating charge, Li+ excessive release, phosphate materials still have good stability and resistance to floating charge. However, the CoO6 octahedron is not directly connected, but is connected by a tetrahedral PO4, so it cannot form a continuous co-o-co structure like lithium cobalt oxide material. Therefore, the conductivity of lithium cobalt phosphate material is very poor, affecting the discharge performance of the material with large current. The discharge mechanism of lithium cobalt phosphate material is relatively complex. According to the research of n.n.ramnik et al., the charging process of lithium cobalt phosphate is mainly divided into two steps:
The synthesis method of lithium cobalt phosphate is similar to that of lithium iron phosphate, including solid phase method, sol-gel method, hydrothermal method, microwave method and spray drying pyrolysis method. The solid phase method is the most simple method, which requires less equipment and is suitable for large-scale industrial production. However, the heat treatment temperature is high, the energy consumption is high, the particle size distribution range of the material is wide, the material batch stability is poor. Sol-gel method can make the raw materials to reach the molecular level of mixing, can effectively reduce the heat treatment temperature and time, the material particle size is small, and the particle size distribution is uniform. However, the raw material cost of sol-gel method is high, and the shrinkage rate of body volume in the heat treatment process is high, so the production efficiency is low. Hydrothermal method is a powerful method to synthesize nanomaterials, which has the advantages of low reaction temperature, low energy consumption, high purity and small particle size. However, hydrothermal method has high requirements on equipment and low production efficiency, so it is not suitable for large-scale industrial production. Spray thermal decomposition method requires relatively simple equipment, can be continuous production, production cost is low. However, due to the low crystallinity of the material, it is necessary to conduct subsequent heat treatment on the material to improve its performance.
Phosphoric acid lithium cobalt materials, not only inherited the lithium iron phosphate material good security, good cycle stability, resistance to the advantages of small current floating voltage, also greatly improved the material working voltage of 4.8 V, the energy density of the material reached 800 wh/kg, electrolyte and ceramic coatings with high voltage diaphragm use, can get a high energy density and high security of lithium ion battery. We believe that with the progress of production technology, it will be widely used in electric vehicles, distributed energy storage and other fields.