The structure and charging and discharging mechanism of LiCoPO4

    The polyanion-type positive electrode material LiCoPO4 is an ordered olitide-type structure, belonging to the orthomorphic system, and the spatial group is Pmnb. The cell parameters are as follows: A =0.5922nm, B =1.0202nm, c=0.4699nm.In the crystal, O atom is packed in hexagonal density,P atom occupies tetrahedral void, while Li atom and Co atom occupy octahedral void.The octahedral CoO6 with common edges is connected to a chain structure by a PO4 tetrahedron along the C axis. Because the co-O-P bond stabilized the three-position frame structure of LiCoPO4, the material structure rearrangement was very small when Li+ exited in it, so the structure maintained good stability during the process of Li+ exited.

    LiCoPO4 has a complex reaction mechanism.N.n.bramnik et al. found that there were two platforms on the constant-current charging curve of LiCoPO4 and two pairs of REDOX peaks on the differential capacity curve of the first charge and discharge, which confirmed the two-step mechanism of Li+ release in LiCoPO4.The mechanism of Li+ ejection obtained by Wang Shaoliang et al is equation (1), (2) :

    Different from the two-step reaction mechanism of LiCoPO4, many researchers have proposed the one-step reaction mechanism.A.Eftekhari materials synthesized by solid phase method have typical charging-discharge curves, and there is a pair of obvious REDOX peaks on the cyclic volt-ampere curve, indicating that it is a one-step emergence mechanism.K.M.V.V.M. S. Atya et al. also proved the conclusion by using solid phase synthesis materials.The charging and discharging mechanism of LiCoPO4 remains to be further studied.