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With values exceeding 1 mS cm –1, Li 2 Sc 2/3 Cl 4 has the highest conductivity among spinel-type cubic chlorides, but it is not cost-effective due to the high price of Sc. In contrast, another cubic spinel, Li 2 MgCl 4, is cost-effective but has very low conductivity of about 10 –4 mS cm –1 . In this first-principles study, we assessed the potential of Li 2 Mg 1–1.5 x M x Cl 4 (0 0.125 until the highest conductivity of 1.36 mS cm –1 (6.69 mS cm –1 ) is reached for Li 2 Sc 2/3 Cl 4 (Li 2 Y 2/3 Cl 4 ) at x = 2/3. As x increases, the proportion of Li (Mg and Sc/Y) ions at the 16d site increases (decreases), which causes the diffusing Li + ions to encounter Li + ions rather than the Mg 2+ or Sc 3+ /Y 3+ ions, thereby reducing the strong cation–cation repulsion and activating the 16d → 48f → 16c jump that is important for improving conductivity. Compared with Sc, Y is considerably cheaper and has a greater conductivity-enhancing effect. This suggests that substituting an appropriate amount of Y for Mg in Li 2 MgCl 4 can realize cubic spinel solid electrolytes that have both high conductivity and low cost.
Jeon et al. (Mon,) studied this question.