Isovalent substitution modulates average and short-range structure in disordered rocksalt oxides†

Abstract

Li-excess disordered rocksalt oxides are promising candidate materials for high-energy density Li-ion battery cathodes. Their disordered cation sublattice provides opportunity to design compositions that balance performance and sustainability, especially enabling the use of abundant and inexpensive elements. However, relationships between composition, short-range cation ordering, and their effects on performance are not well-understood. Here, we use a compositional series of the form Li_1.2Mn_0.4Ti_0.4−xZr_xO₂, in which Ti⁴⁺ is gradually replaced with Zr⁴⁺, to study the effect of Zr content on average- and short-range structure using synchrotron X-ray diffraction and pair distribution function analysis. We report the coexistence of multiple modes of short-range order, which have a major impact on battery capacity. However, the effects of Zr on degree of short-range ordering, lattice parameter, and chemical segregation also influence battery capacity, reflecting the complex dependencies of composition on structure across length scales in these disordered materials.