Effect of Oxidative Synthesis Conditions on the Performance of Single-Crystalline LiMn_2-xM_xO₄ (M = Al, Fe, and Ni) Spinel Cathodes in Lithium-Ion Batteries

LiMn2O4 (LMO) spinel cathode materials attract much interest due to the low price of manganese and high power density for lithium-ion batteries. However, the LMO cathodes suffer from the Mn dissolution problem at particle surfaces, which accelerates capacity fade. Herein, the authors report that the oxidative synthesis condition is a key factor in the cell performance of single-crystalline LiMn2-xMxO4 (0.03 <= x <= 0.1, M = Al, Fe, and Ni) cathode materials prepared at 1000 degrees C. The use of oxygen flow during the spinel-phase formation minimizes the presence of oxygen vacancies generated at 1000 degrees C, thereby yielding a stoichiometrically doped LMO product; otherwise, the spinel cathode prepared in atmospheric air readily loses capacity due to the oxygen vacancies in the structure. As a way of circumventing the use of oxygen flow, a one-pot, two-step heating in air at 1000 degrees C and subsequently at 600 degrees C is used to yield the stoichiometric LMO product. The lithiation heating at 1000-600 degrees C resulted in a significant improvement in the cycling stability of the prepared LMO cathode in graphite-based full cells. This study on oxidative synthesis conditions also confirms the advantage of minimizing the surface area of the cathode particles.