High capacity double-layer surface modified LiLi0.2Mn0.54Ni0.13Co0.13O2 cathode with improved rate capability

Layered LiLi0.2Mn0.54Ni0.13Co0.13O2, which is a solid solution between layered LiLi1/3Mn2/3O2 and LiNi1/3Mn1/3Co1/3O2, has been surface modified by single-layer coating with 2–5 wt.% AlPO4, CoPO4, and Al2O3 and double-layer coating with 2 wt.% AlPO4 or 2 wt.% CoPO4 inner layer and 2–3.5 wt.% Al2O3 outer layer. The samples have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements in lithium cells. The double-layer coated samples are found to exhibit lower irreversible capacity loss (Cirr) and higher discharge capacity values than both the pristine and the single-layer coated samples, which are due to the retention of a higher number of oxide ion vacancies in the layered lattice after the first charge. The double-layer coated composite cathodes exhibit Cirr values as low as 26 mAh g−1 with a high discharge capacity of ∼300 mAh g−1, which is two times higher than that achieved with layered LiCoO2. Moreover, the double-layer coated samples exhibit higher rate capabilities than the pristine and single-layer coated samples, which are attributed to the suppression of undesired SEI layers and the fast charge transfer reaction kinetics as indicated by the EIS data.