Characterization of Lithium Aluminum Oxide Solid Electrolyte Thin Films from Aqueous Precursors
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Low-temperature routes to solid electrolytes are important for construction of solid-state batteries, electrochromic devices, electrolyte-gated transistors, high-energy capacitors and sensors. Here we report an environmentally friendly aqueous solution route to amorphous thin films of solid lithium based electrolytes and related multi-layered structures. This route allows production of high quality films at very low temperatures, up to 600 °C lower than traditional melt quenching routes. Pinhole free films of thicknesses ranging from 13-150 nm produced by this route are extremely smooth and fully dense, with temperature dependent conductivities similar to those reported for samples made by energy intensive techniques. Processing conditions were examined by TGA-DSC; film evolution was monitored by FTIR; and, resulting films were characterized using FTIR, XPS, SEM, and XRD. These techniques indicate that water and nitrate removal is complete at low temperatures, and the films remain amorphous to 400 °C. Electrical analysis suggests the presence of ionic double layer capacitor behaviour as observed in similar metal oxide systems. Large magnitudes of ε'app are reported for two separate systems herein, surpassing values reported in the literature for similar materials produced by other synthetic methods. A two-fold increase in the breakdown strength of nanolaminate structures over their single-phase counterparts is also reported. The approach developed demonstrates a simple, inexpensive and environmentally benign deposition route for the fabrication of inorganic solid electrolyte thin-films and related nanolaminates, using LiAlPO, LiAlO, and TiO2:LiAlO as model systems.