Mg3(PO4)2-coated Li1.05Ni1/3Mn1/3Co1/3O2 cathode materials were synthesized via co-precipitation method. The morphology, structure, electrochemical performance and thermal stability were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS), charge/discharge cycling and differential scanning calorimeter (DSC). SEM analysis shows that Mg3(PO4)2-coating changes the morphologies of their particles and increases the grains size. XRD and CV results show that Mg3(PO4)2-coating powder is homogeneous and has better layered structure than the bare one. Mg3(PO4)2-coating improved high rate discharge capacity and cycle-life performance. The reason why the cycling performance of Mg3(PO4)2-coated sample at 55 ℃ was better than that of room temperature was the increasing of lithium-ion diffusion rate and charge transfer rate with temperature rising. Mg3(PO4)2-coating improved the cathode thermal stability, and the result was consistent with thermal abuse tests using Li-ion cells: the Mg3(PO4)2 coated Li1.05Ni1/3Mn1/3Co1/3O2 cathode did not exhibit thermal runaway with smoke and explosion, in contrast to the cells containing the bare Li1.05Ni1/3Mn1/3Co1/3O2.
Spinel LiMn2O4 powders were prepared using two-step synthesis method consisting of solid-state reaction method and citrate modified sol-gel method. The effects of the calcination temperature and the Li/Mn ratio of raw materials were studied on the physicochemical and electrochemical properties of the spinel LiMn2O4 powders, such as crystallinity, lattice constant and density. The title compound was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Polycrystalline LiMn2O4 powers calcined at 750 ℃ were found to be composed of very uniformly-sized microcrystal with an average particle size of 300 nm. The improvement in electrochemical properties was mainly attributed to the process of re-grinding by absolute alcohol.
