| Summary: | There is a growing interest in finding a suitable electrolyte material for the construction of rechargeable Li-ion batteries. Li<sub>2</sub>NiGe<sub>3</sub>O<sub>8</sub> is a material of interest with modest Li-ionic conductivity. The atomistic simulation technique was applied to understand the defect processes and Li-ion diffusion pathways, together with the activation energies and promising dopants on the Li, Ni, and Ge sites. The Li-Ni anti-site defect cluster was found to be the dominant defect in this material, showing the presence of cation mixing, which can influence the properties of this material. Li-ion diffusion pathways were constructed, and it was found that the activation energy for a three-dimensional Li-ion migration pathway is 0.57 eV, which is in good agreement with the values reported in the experiment. The low activation energy indicated that Li-ion conductivity in Li<sub>2</sub>NiGe<sub>3</sub>O<sub>8</sub> is fast. The isovalent doping of Na, Fe and Si on the Li, Ni and Ge sites is energetically favorable. Both Al and Ga are candidate dopants for the formation of Li-interstitials and oxygen vacancies on the Ge site. While Li-interstitials can improve the capacity of batteries, oxygen vacancies can promote Li-ion diffusion.
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