Nitrates–melt synthesized LiNi0⋅8Co0⋅2O2 and its performance as cathode in Li-ion cells

Layered LiNi0⋅8Co0⋅2O2 crystallizing in R –3m space group is synthesized by decomposing the constituent metal–nitrate precursors. Oxidizing nature of metal nitrates stabilizes nickel in +3 oxidation state, enabling a high degree of cation ordering in the layered LiNi0⋅8Co0⋅2O2. The powder sample characterized by XRD Rietveld refinement reveals < 2% Li–Ni site exchange in the layers. Scanning electron microscopic studies on the as-synthesized LiNi0⋅8Co0⋅2O2 sample reflect well defined particles of cubic morphology with particle size ranging between 200 and 250 nm. Cyclic voltammograms suggest that LiNi0⋅8Co0⋅2O2 undergoes phase transformation on first charge with resultant phase being completely reversible in subsequent cycles. The first-charge-cycle phase transition is further supported by impedance spectroscopy that shows substantial reduction in resistance during initial de-intercalation. Galvanostatic charge–discharge cycles reflect a firstdischarge capacity of 184 mAh g which is stabilized at 170 mAh g over 50 cycles.