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

In this work, 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 opposite is true for the Mn concentration. The co-precipitation synthesis parameters were optimized, with two different annealing protocols for the final products and the effect of chelating agent concentration during synthesis examined. The gradient materials provided superior capacity and rate capability than their respective non-gradient materials, at normal operating potentials and temperatures, e.g. 30^◦C up to 4.3 V vs. Li. The reasons for the improved discharge capacity of the gradient materials were explored through impedance spectroscopy and post-mortem characterization. The gradient structure evolution was examined via TEM and electron diffraction measurements of particle cross-sections. Prolonged cycling, even at elevated temperatures, did not change the initial concentration profiles determined by the synthesis. Additionally, long-term 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.