Structure, morphology, and cathode performance of Li1−x[Ni0.5Mn1.5]O4 prepared by coprecipitation with oxalic acid

The cathode materials Li_1−xNi_0.5Mn_1.5]O₄ prepared by coprecipitation from acetate solution by oxalic acid and annealing at 900 °C in air had the preferred disordered Ni and Mn on the 16d octahedral sites of a spinel structure. The coprecipitation method provides better crystallinity than the phase previously obtained by quenching from the melt. Polycrystalline octahedral-shaped particles with smooth surfaces contained trace amounts of a Li_yNi_1−yO impurity that introduced some Mn(III) into the spinel phase. Half-cells cycled at 0.2 C rate between 3.5 and 4.8 V versus Li exhibited a flat voltage V ≈ 4.7 V with a small step at x ≈ 0.5 and a capacity at room temperature of 130 mAh g⁻¹ that showed no fade after 50 cycles. A small capacity fade was initiated with a cut-off voltage ≥4.9 V; a significant capacity loss between 2 and 5 C cycling rates was reversible to 134 mAh g⁻¹ on returning to 0.1 C after 50 cycles at 10 C between 3.5 and 5.0 V.