Synthesis and characterization of Li1.2Ni0.6Co0.2Mn0.2O2+δ as a cathode material for secondary lithium batteries

Layered Li1.2Ni0.6Co0.2Mn0.2O2+δ powder material was synthesized by solid-state reaction, and Li2CO3, NiO, Co3O4 and MnO2 were used as starting materials. XRD studies show that the powder material and also the discharged electrode, even cycled in the range of 4.6-3.0 V (vs. Li+/Li) after 45 cycles, maintained layered structure. Cyclic voltammetry (CV) curves of Li1.2Ni0.6Co0.2Mn0.2O2+δ have only one cathodic peak in the voltage window, 4.3-2.5 V, and also only one major anodic current peak in the voltage window, 5.0-2.5 V, indicating that the phase transformations has been restrained. The X-ray photoelectron spectra (XPS) studies indicate that the oxidation states of Ni and Co are 3+ and 3+, respectively, and the main oxidation state of Mn is 4+. Galvanostatic charge-discharge cycling behavior of Li1.2Ni0.6Co0.2Mn0.2O2+δ shows that the dischargable capacity of the 50th is almost the same as that of the 1st in 4.3-3.0 V (vs. Li+/Li). Whereas, discharged at 120 mA/g, a loss of only 7.2% of capacity was observed after 100 cycles; it exhibits excellent cycleability and good rate capability. DSC shows that the thermal stability of Li1.2Ni0.6Co0.2Mn0.2O2+δ is almost the same as that of LiCoO2.