SYNTHESIS AND ELECTROCHEMICAL PERFORMANCE OF NICKEL-RICH LAYERED-STRUCTURE LiNi_0.65Co_0.08Mn_0.27O₂ CATHODE MATERIALS COMPRISING PARTICLES WITH Ni AND Mn FULL CONCENTRATION GRADIENTS

Nickel-rich, layered-structure LiNi_0.65Co_0.08Mn_0.27O₂ cathode materials were synthesized and compared with materials of the same overall composition, but with a concentration gradient throughout the particles: the Ni concentration is higher at the center of the particles and lower at surface, while the Mn concentration is higher at the surface and lower at the center. The synthesis parameters of the co-precipitation method were optimized comparing annealing periods, followed by electrochemical testing. All gradient materials provided superior capacity and rate capability than their respective non-gradient materials, at normal operating potentials and temperatures, e.g. 30 ^oC up to 4.3 V vs. Li. The reasons for the improved discharge capacity of the gradient materials at moderate temperatures and potentials were explored through impedance spectroscopy and post-mortem characterization. The evolution of the gradient structure was examined via TEM and electron diffraction measurements of FIB-produced particle cross-sections. Prolonged cycling, even at elevated temperatures, did not change the initial concentration profiles determined by the synthesis. Finally, long-term, deep cycling experiments of the second-generation material electrodes vs. graphite electrodes in full cells were performed in order to explore the practical advantage of these novel materials (Fig. 1).