Defect-Driven Configurational Entropy in the High-Entropy Oxide Li_1.5MO_3-δ

Layered lithiated oxides are promising materials for next generation Li-ion battery cathode materials; however, instability during cycling results in poor performance over time compared to the high capacities theoretically possible with these materials. Here we report the characterizations of a Li_1.47Mn_0.57Al_0.13Fe_0.095Co_0.105Ni_0.095O_2.49 high-entropy layered oxide (HELO) with the Li₂MO₃ structure where M = Mn, Al, Fe, Co, and Ni. Using electron microscopy and X-ray spectroscopy, we identify a homogeneous Li₂MO₃ structure stabilized by the entropic contribution of oxygen vacancies. This defect-driven entropy would not be attainable in the LiMO₂ structure sometimes observed in similar materials as a secondary phase owing to the presence of fewer O sites and a 3+ oxidation state for the metal site; instead, a Li_2-γMO_3-δ is produced. Beyond Li₂MO₃, this defect-driven entropy approach to stabilizing novel compositions and phases can be applied to a wide array of future cathode materials including spinel and rock salt structures.