Unlocking lithium ion conduction in lithium metal fluorides

Abstract

Here, we demonstrate that quasi-crystalline lithium metal fluoride materials prepared by mechanochemical synthesis exhibit up to 300-fold higher ionic conductivity than their crystalline counterparts, with Li₂TiF₆ being the example in point. By probing the “amorphous” and crystalline forms of these materials at different length scales, we show that the introduction of structural disorder at short to long length scales is crucial for facilitating Li⁺ transport. Moreover, we show that the addition of LiF creates an interaction with Li₂TiF₆ at the local level that readily disrupts the long-range order. The ionic conductivity of the composite material reaches a benchmark value of 2.5 × 10⁻³ mS cm⁻¹, the highest of fluoride materials reported in the literature and on par with LiPON and LiNbO₃. This work delivers insights into structure-conductivity relationships contrasting crystalline and amorphous materials and shows strategies to unlock ion conduction.