Isovalent Substitution Modulates Average and Short-Range Structure in Disordered Rocksalt Oxides

Li-excess disordered rocksalt oxides are promising high-energy density Li-ion battery cathode materials. Their disordered cation sublattice provides ample opportunity to design compositions that balance good performance and the use of abundant and inexpensive transition metals. However, the short-range structure of these materials - both in how it forms and how it influences cathode performance - is not well-understood. Here, we use a compositional series of the form Li_1.2Mn_0.4Ti_{(0.4-<i>x</i>)}Zr<i>_x</i>O₂, in which Ti⁴⁺ is gradually replaced with Zr⁴⁺, to study the effect of Zr content on the long- and short-range structure using synchrotron X-ray diffraction, pair distribution function analysis, and X-ray absorption spectroscopy. We report the coexistence of multiple forms of short-range order, which have a major impact on battery capacity. However, the effects of Zr on lattice parameter and chemical segregation also influence battery capacity, reflecting the complex dependencies of composition on structure across length scales in these disordered materials.