| Summary: | Lithium zinc silicate, Li<sub>2</sub>ZnSiO<sub>4</sub>, is a promising ceramic solid electrolyte material for Li-ion batteries. In this study, atomistic simulation techniques were employed to examine intrinsic defect processes; long range Li-ion migration paths, together with activation energies; and candidate substitutional dopants at the Zn and the Si sites in both monoclinic and orthorhombic Li<sub>2</sub>ZnSiO<sub>4</sub> phases. The Li-Zn anti-site defect is the most energetically favourable defect in both phases, suggesting that a small amount of cation mixing would be observed. The Li Frenkel is the second lowest energy process. Long range Li-ion migration is observed in the <i>ac</i> plane in the monoclinic phase and the <i>bc</i> plane in the orthorhombic phase with activation energies of 0.88 eV and 0.90 eV, respectively, suggesting that Li-ion diffusivities in both phases are moderate. Furthermore, we show that Fe<sup>3+</sup> is a promising dopant to increase Li vacancies required for vacancy-mediated Li-ion migration, and that Al<sup>3+</sup> is the best dopant to introduce additional Li in the lattice required for increasing the capacity of this material. The favourable isovalent dopants are Fe<sup>2+</sup> at the Zn site and Ge<sup>4+</sup> at the Si site.
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