Justin Whetten1 Jon Weller1 Candace Chan1

1, Arizona State University, Tempe, Arizona, United States

The development of solid Li+ conducting electrolytes for all-solid-state batteries has attracted a great deal of research interest. Polymer-based electrolytes are attractive because they are not brittle and can more easily form interfaces to electrodes compared to inorganic electrolytes, but they also display poor mechanical properties and low ionic conductivities at room temperature. The use of composite polymer electrolytes (CPEs) comprising a polymer electrolyte embedded with ceramic fillers has been an attractive strategy for enhancing the mechanical stability and ionic conductivity of the polymer. The ceramic filler can increase the ionic transport of Li+ in the CPE by several orders of magnitude, for example by decreasing the crystallinity of the conducting polymer and creating space charge regions that can enhance the Li+ diffusion.

Recently, the garnet-type Li+ ion conductor Li7La3Zr2O12 (LLZO) has attracted substantial interest for its potential as ceramic filler in CPEs. Studies from our lab on the use of LLZO nanowires as ceramic fillers in polyacronitrile (PAN)-based polymer electrolytes showed that very small wt% of LLZO was needed to improve the ionic conductivity by 3 orders of magnitude to 1.31 x 10-4 S/cm. It was demonstrated that the preferred Li diffusion pathway was through the interface between the LLZO and polymer, motivating the use of nanostructured LLZO fillers.
Here, LLZO nanoparticles were synthesized using a novel molten salt reaction. This method yields size-homogenous and non-agglomerated nanoparticles, which are ideal for use as ceramic fillers in CPEs. The synthesis and structural characterization of the nanoparticles will be presented. The effect of LLZO wt%, amount of Li salt, and CPE processing conditions on the ionic conductivity of the solid electrolyte composite films will also be discussed.