Layered O2-Li2/3(Ni1/3−xMn2/3−xM2x)O2 (M=Cr, Co, x=0.05) cathode materials for Li-ion rechargeable batteries

Layered O2-phase lithium manganese oxides, Li2/3(Ni1/3−xMn2/3−xM2x)O2 (M=Cr, Co, x=0.05) were prepared by ion exchange of Li for Na in P2-Na2/3(Ni1/3−xMn2/3−xM2x)O2 precursors, which were synthesized by a citric acid-assisted sol-gel method. The as-synthesized compounds were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and galvanostatic tests. The discharge capacity of O2-Li2/3(Ni1/3−xMn2/3−xCo2x)O2 (x=0.05) is around 188 mA h g−1 (vs. Li metal; voltage window 2.5-4.6 V) at a current density of 0.2 mA cm−2.