Crystal Structure and Li-Ion Transport in Li₂CoPO₄F High-Voltage Cathode Material for Li-Ion Batteries

In this work, we provide a structural and computational investigation of the Li₂CoPO₄F high-voltage cathode material by means of neutron powder diffraction (SG <i>Pnma</i>, <i>a</i> = 10.4528(2) Å, <i>b</i> = 6.38667(10) Å, <i>c</i> = 10.8764(2) Å, <i>R</i>_F = 0.0145), crystal chemistry approaches (Voronoi–Dirichlet partitioning and bond valence sums mapping), and density functional theory. The material reveals low energy barriers (0.12–0.43 eV) of Li hopping and a possible 3D channel system for Li-ion migration. It is found that only one Li per formula unit can be extracted within the potential stability window of the commercially available electrolytes. The interrelation between dimensionality, topology and energetics of Li-ion diffusion and peculiarities of the Li₂CoPO₄F crystal structure are discussed in detail

Crystal Structure and Li-Ion Transport in Li₂CoPO₄F High-Voltage Cathode Material for Li-Ion Batteries

In this work, we provide a structural and computational investigation of the Li₂CoPO₄F high-voltage cathode material by means of neutron powder diffraction (SG <i>Pnma</i>, <i>a</i> = 10.4528(2) Å, <i>b</i> = 6.38667(10) Å, <i>c</i> = 10.8764(2) Å, <i>R</i>_F = 0.0145), crystal chemistry approaches (Voronoi–Dirichlet partitioning and bond valence sums mapping), and density functional theory. The material reveals low energy barriers (0.12–0.43 eV) of Li hopping and a possible 3D channel system for Li-ion migration. It is found that only one Li per formula unit can be extracted within the potential stability window of the commercially available electrolytes. The interrelation between dimensionality, topology and energetics of Li-ion diffusion and peculiarities of the Li₂CoPO₄F crystal structure are discussed in detail

Ionic Conductivity in Ti-Doped KFeO₂: Experiment and Mathematical Modeling

The structure peculiarities of K_0.9Fe_0.9Ti_0.1O₂ that favor the emergence of a superionic state have been studied using neutron powder diffraction data as a function of temperature. The migration paths in the structure of both undoped and doped potassium ferrite were modeled by topological (tiling) and DFT methods. It is shown that heating of the low-temperature phase leads to increase of the ionic conductivity thanks to widening the migration channels and the appearance of thermally induced cation vacancies. The calculated migration barrier is found to not exceed 0.3 eV/ion in all phases, which is consistent with the experimental data. Doping also increases the ionic conductivity, but up to about 10% of Ti only; then the experimental activation energy even increases. The DFT modeling shows that it can be caused by growth of the regions unavailable for the mobile cations; the regions are formed around the dopant atoms

Ionic Conductivity in Ti-Doped KFeO₂: Experiment and Mathematical Modeling

The structure peculiarities of K_0.9Fe_0.9Ti_0.1O₂ that favor the emergence of a superionic state have been studied using neutron powder diffraction data as a function of temperature. The migration paths in the structure of both undoped and doped potassium ferrite were modeled by topological (tiling) and DFT methods. It is shown that heating of the low-temperature phase leads to increase of the ionic conductivity thanks to widening the migration channels and the appearance of thermally induced cation vacancies. The calculated migration barrier is found to not exceed 0.3 eV/ion in all phases, which is consistent with the experimental data. Doping also increases the ionic conductivity, but up to about 10% of Ti only; then the experimental activation energy even increases. The DFT modeling shows that it can be caused by growth of the regions unavailable for the mobile cations; the regions are formed around the dopant atoms