Electrochemical Performance of Overlithiated Li_1+XNi_0.8Co_0.2O₂: Structural and Oxidation State Studies

Pure layered compound of overlithiated Li_1+xNi_0.8Co_0.2O₂ (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 LiNi_0.8Co_0.2O₂ 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 Li_1.05Ni_0.8Co_0.2O₂ compound followed by Li_1.1Ni_0.8Co_0.2O₂ and LiNi_0.8Co_0.2O₂. This implies that the Li⁺ ions can be more easily extracted from Li_1.05Ni_0.8Co_0.2O₂ materials than the other stoichiometries. The XPS results are supported by the electrochemical performance of the samples. Li_1.05Ni_0.8Co_0.2O₂ showed the best results with a specific capacity of 113.29 mAh/g compared to Li_1.1Ni_0.8Co_0.2O₂ with a specific capacity of 112.32 mAh/g and LiNi_0.8Co_0.2O₂ with a specific capacity of 94.71 mAh/g. Li_1.05Ni_0.8Co_0.2O₂ 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 Li_1.1Ni_1/3Co_1/3Mn_1/3O₂

Cathode for Lithium Batteries" Int.J,Electrochem.Sci.,4 (2009) pp. 1770-1778