Composition Optimization of Layered Lithium Nickel Manganese Cobalt Oxide Materials Synthesized via Ultrasonic Spray Pyrolysis.

Lithium-rich, layered composites of xLi₂MnO3 ⋅ (1-x)Li(Ni_1/3Mn_1/3Co_1/3)O2were synthesized via spray pyrolysis to identify the chemistry yielding optimal electrochemical performance for materials produced by this method. The x values selected for optimization were x = 0.3, 0.5, 0.7, equivalent to Li_1.14Mn_0.46Ni_0.2Co_0.2O₂, Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ and Li_1.26Mn_0.6Ni_0.07Co_0.07O₂, respectively. The materials were annealed at 850°C or 900°C for 2 hours, and then tested in coin cells. Li_1.2Mn_0.54Ni_0.13Co_0.13O₂annealed at 900°C displayed the best electrochemical performance with excellent capacity retention, displaying a reversible capacity of 236 mAhg^-1after 100 cycles when cycled between 2.0-4.8 V at C/10 rate, where 1C = 280 mAg^-1. The cycling profiles display voltage fade, presumably due to a layered-spinel phase transformation. The synthesis method leads to high purity and excellent uniformity at the nanoscale, and the materials have less voltage fade compared to similar materials produced by co-precipitation. Voltage fade is more pronounced when the upper cut-off voltage is 4.8 V, as opposed to 4.6 V. A decrease in the Li₂MnO₃ content of the material reduces voltage fade, such that x = 0.3 (or Li_1.14Mn_0.46Ni_0.2Co_0.2O₂) shows the best structural stability over cycling. [ABSTRACT FROM AUTHOR]