Electrochemical Performance of Overlithiated Li1+XNi0.8Co0.2O2: Structural and Oxidation State Studies

Pure layered compound of overlithiated Li1+xNi0.8Co0.2O2 (x=1,1.05,1.1) samples were successfully prepared by a combustion method. Structural studies of the XRD results showed that when lithium was doped into the LiNi0.8Co0.2O2 cathode materials, the structural parameters of the materials changed slightly when more lithium is doped, that is the cell parameter decreased. Scanning electron microscopy (SEM) revealed that the morphology of the particle c0.2hanged a little from rounded polyhedral-like particle to sharp edged polyhedral crystals when more lithium is doped. Energy dispersive X-ray spectroscopy (EDX) showed that the stoichiometries of Ni and Co agrees with calculated synthesized values. X-ray photoelectron spectroscopy (XPS) studies showed that the binding energy of Li 1s is decreased for the doped Li1.05Ni0.8Co0.2O2 compound followed by Li1.1Ni0.8Co0.2O2 and LiNi0.8Co0.2O2. This implies that the Li+ ions can be more easily extracted from Li1.05Ni0.8Co0.2O2 materials than the other stoichiometries. The XPS results are supported by the electrochemical performance of the samples. Li1.05Ni0.8Co0.2O2 showed the best results with a specific capacity of 113.29 mAh/g compared to Li1.1Ni0.8Co0.2O2 with a specific capacity of 112.32 mAh/g and LiNi0.8Co0.2O2 with a specific capacity of 94.71 mAh/g. Li1.05Ni0.8Co0.2O2 also showed the best capacity retention of 7.8 % over 10 cycles. Reference [1] R.Santhanam, B.Rambabu, "Improved High Rate Cycling of Li-rich Li1.1Ni1/3Co1/3Mn1/3O2 Cathode for Lithium Batteries" Int.J,Electrochem.Sci.,4 (2009) pp. 1770-1778