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Ion mobility in electrolytes and electrodes is an important performance parameter in electrochemical devices, particularly in batteries. In this review, the authors concentrate on the charge carrier mobility in crystalline battery materials where the diffusion basically corresponds to hopping processes between lattice sites. However, in spite of the seeming simplicity of the migration process in crystalline materials, the factors governing mobility in these materials are still debated. There are well‐accepted factors contributing to the ion mobility such as the size and the charge of the ions, but they are not sufficient to yield a complete picture of ion mobility. In this review, possible factors influencing ion mobility in crystalline battery materials are critically discussed. To gain insights into these factors, chemical trends in batteries, both as far as the charge carriers as well as the host materials are concerned, are discussed. Furthermore, fundamental questions, for example, about the nature of the migrating charge carriers, are also addressed. [ABSTRACT FROM AUTHOR]

Prussian Whites (PW) have gained attention for their potential application as high energy density cathodes in Na‐ion batteries. However, the rhombohedral phase of this compound still remains elusive. This study addresses the electronic and structural properties of the rhombohedral host material, as well as its ionic conductivity. Using periodic density functional theory calculations, we identified the critical factors that determine the sodium‐ion site preference and their ionic mobility. Specifically, the significant role of octahedral tilting and trigonal distortions of the structure have been highlighted. The study shows that the competition between coordination and bond length governs the Na site preference in the rhombohedral phase upon distortion. The results furthermore suggest that the redox activity is dominated by the transition metals. These findings provide insight into the fundamental mechanisms underlying ionic conductivity in solid hosts and could help enhance ion transport in battery electrodes. [ABSTRACT FROM AUTHOR]