Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films
The electrochemical properties of fluoride-coated lithium cobalt oxide [LiCoO2] thin films were characterized. Aluminum fluoride [AlF3] and lanthanum fluoride [LaF3] coating layers were fabricated on a pristine LiCoO2 thin film by using a spin-coating process. The AlF3- and LaF3-coated films exhibited a higher rate capability, cyclic performance, and stability at high temperature than the pristine film. This indicates that the AlF3 and LaF3 layers effectively protected the surface of the pristine LiCoO2 film from the reactive electrolyte.
Surface Modification of High Capacity Layered Li [ Li0.2Mn0.54Ni0.13Co0.13 ] O2 Cathodes by AlPO4
Layered Li[Li 0.2 Mn 0.54 Co 0.13 Ni 0.13 ]O 2 cathode, which is a solid solution between layered Li[Li 1/3 Mn 2/3 ]O 2 and Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 , has been surface modified with various amounts (0-4 wt %) of AlPO 4 and characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical measurements in lithium cells. Annealing the surface-modified samples at 400 and 700°C leads to the formation of Li 3 PO 4 on the surface and an incorporation of some Al 3+ into the layered oxide lattice. More importantly, surface modification with AlPO 4 (<4 wt %) increases the discharge capacity and drastically reduces the irreversible capacity loss in the first cycle compared to the values observed with the pristine (unmodified) sample. For example, the irreversible capacity loss decreases from 75 to 27 mAh/g and the discharge capacity increases from 253 to 279 mAh/g on surface modification with 2 wt % AlPO 4 . The results are explained based on the retention of more oxide ion vacancies in the layered lattice after surface modification.
Electrochemical Properties of LiNi 0.8 Co 0.16 Al 0.04 O 2 and Surface Modification with Co 3 (PO 4 ) 2 as Cathode Materials for Lithium Battery
The electrochemical and thermal stability of were studied before and after coating. Different to conventional coating material such as or AlPO4, the coating layer was not detected clearly by TEM analysis, indicating that the nanoparticles effectively reacted with surface impurities such as . The coated sample showed similar capacity at a low C rate condition. However, the rate capability was significantly improved by the coating effect. It is associated with a decrease of impedance after coating because impedance can act as a major barrier for overall cell performances in high C rate cycling. In the DSC profile of the charged sample, exothermic peaks were shifted to high temperatures and heat generation was reduced after coating, indicating the thermal reaction between electrode and electrolyte was sucessfully suppressed by nanoparticle coating.