Aqueous Synthesis of Li3InCl6-XBrx for Low-Cost Electrolyte Processing

Rare-earth alkali halides of the form Li₃MX₆ are known to have high lithium-ion conductivity, some approaching superionic conductivity (≥1 mS/cm) at room temperature. These solid-state materials are candidates for replacing typical lithium-ion battery liquid electrolytes, which are flammable and pose a combustion risk, and could significantly decrease safety concerns associated with lithium-ion batteries. Li­₃InCl₆ (LIC) is one such solid electrolyte. It has been shown that LIC can be synthesized in an aqueous solution with controlled dehydration. However, high pressure must be maintained on devices made with LIC for them to perform as well as devices with liquid electrolytes. Replacing chlorine with bromine can soften halide sublattice dynamics which may lead to more facile Li transport and more favorable mechanical softness. This project explored Li₃InCl_6-xBr_x synthesis from aqueous solutions and whether these derivatives yield better conductivities. The x=0 and x=0.5 syntheses yielded pure products, according to XRD analysis. If x≥1, the resulting powders contained residual lithium chloride that did not react in synthesis. Additionally, if x≥4, the resulting product required an extra annealing step to produce Li₃InCl_6-xBr_x. In all cases, adding bromine did not increase the room temperature conductivity compared to LIC.