Surface modification of high capacity layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathodes by AlPO4

Layered Li[Li0.2Mn0.54Co0.13Ni0.13]O-2 cathode, which is a solid solution between layered Li[Li1/3Mn2/3]O-2 and Li[Ni1/3Mn1/3Co1/3]O-2, has been surface modified with various amounts (0-4 wt %) of AlPO4 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 degrees C leads to the formation of Li3PO4 on the surface and an incorporation of some Al3+ into the layered oxide lattice. More importantly, surface modification with AlPO4 (< 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 % AlPO4. The results are explained based on the retention of more oxide ion vacancies in the layered lattice after surface modification. (C) 2008 The Electrochemical Society.