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With the potential of delivering reversible capacities of up to 300 mAh/g, Li-rich transition-metal oxides hold great promise as cathode materials for future Li-ion batteries. However, a cohesive synthesis-structure-electrochemistry relationship is still lacking for these materials, which impedes progress in the field. This work investigates how and why different synthesis routes, specifically solid-state and modified Pechini sol-gel methods, affect the properties of Li2MnO3, a compositionally simple member of this material system. Through a comprehensive investigation of the synthesis mechanism along with crystallographic, morphological, and electrochemical characterization, the effects of different synthesis routes were found to predominantly influence the degree of stacking faults and particle morphology. That is, the modified Pechini method produced isotropic spherical particles with approximately 57% faulting and the solid-state samples possessed heterogeneous morphology with approximately 43% faulting probability. Inevitably, these differences lead to variations in electrochemical performance. This study accentuates the importance of understanding how synthesis affects the electrochemistry of these materials, which is critical considering the crystallographic and electrochemical complexities of the class of materials more generally. The methodology employed here is extendable to studying synthesis-property relationships of other compositionally complex Li-rich layered oxide systems.

Li- and Mn-rich layered oxides show significant promise as electrode materials for future Li-ion batteries. However, an accurate description of its crystallography remains elusive, with both single-phase solid solution and multiphase structures being proposed for high performing materials such as Li1.2Mn0.54Ni0.13Co0.13O2. Herein, we report the synthesis of single- and multiphase variants of this material through sol-gel and solid-state methods, respectively, and demonstrate that its crystallography is a direct consequence of the synthetic route and not necessarily an inherent property of the composition, as previously argued. This was accomplished via complementary techniques that probe the bulk and local structure followed by in situ methods to map the synthetic progression. As the electrochemical performance and anionic redox behavior are often rationalized on the basis of the presumed crystal structure, clarifying the structural ambiguities is an important step toward harnessing its potential as an electrode material.

Li- and Mn-rich layered oxides are promising positive electrode materials for future Li-ion batteries. The coexistence of complex crystallographic features like cation-mixing and stacking faults make them highly susceptible to synthesis-induced crystallographic changes. Consequently, this has resulted in significant variations in the reported structure of these materials and exacerbated the difficulty in understanding the crystallography of these materials. Here, the effect of synthesis methods and annealing parameters on the average structure of three Li- and Mn-rich layered oxides—Li₂MnO₃, Li_1.2Mn_0.6Ni_0.2O₂ and Li_1.2Mn_0.54Ni_0.13Co_0.13O₂—have been systematically investigated. Each compound is synthesized through two methods using four annealing protocols and the resultant structural changes are studied, to improve our understanding of the synthesis–structure relationships in these materials. Furthermore, synthesis-specific thermodynamic and kinetic factors governing the equilibrium crystallography of each composition are also explored. Improving our understanding of how the synthesis affects the pristine structure of these materials is an important step in developing these material systems for use as future positive electrode materials.

Despite substantial research interest, the crystallography of the promising Li-ion positive electrode material, Li_1.2Mn_0.6Ni_0.2O₂, remains disputed. The dispute is predicated on the description of the cationic arrangement in the structure, and multiple structure models have been proposed. This study attempts to provide a fresh perspective to this debate through a multi-scalar structural characterisation of Li_1.2Mn_0.6Ni_0.2O₂. Combining Bragg diffraction, transmission electron microscopy and magnetic measurements with reverse Monte Carlo analysis of total scattering data, a quantitative structural description of Li_1.2Mn_0.6Ni_0.2O₂ is developed and the existing single- and multi-phase structural descriptions of this compound have been unified. Furthermore, the merits and drawbacks of each technique is evaluated with respect to the crystallography of Li_1.2Mn_0.6Ni_0.2O₂ to explain the factors that have contributed to the lack of clarity pervading the structural description of this material. It is envisioned that a better understanding of the crystallography of Li_1.2Mn_0.6Ni_0.2O₂ contributes to harnessing the electrochemical potential of this compound.