Microstructure and temperature dependent lithium ion transport of ceramic-polymer composite electrolyte for solid-state lithium ion batteries based on garnet-type Li7La3Zr2O12
In this paper we present the fabrication of a composite electrolyte for solid state batteries consisting of Al-substituted Li7La3Zr2O12 (LLZO) ceramic particles dispersed in a poly(ethylene oxide) (P(EO)20-LiClO4) matrix. The Al-substituted cubic garnet like LLZO solid-state electrolyte filler is obtained by wet-chemical synthesis followed by a solid state lithiation of the as-prepared amorphous mixed hydroxides. Combining both components LLZO powder can be processed directly into a bifunctional electrolyte-separator membrane eliminating any further ceramic processing steps. Homogeneous composite membranes with different ceramic/polymer composition ratio were obtained by tape casting method with ceramic filling up to 40 vol%. Due to addition of the LLZO ceramic filler the crystallinity of the polymer electrolyte matrix within the composites is greatly reduced, which is proved by differential scanning calorimetry (DSC) measurements. It is further demonstrated that the lithium ion conductivity of the membranes strongly depends on the physical condition of the polymer electrolyte. Composite electrolytes show temperature dependent lithium ion conductivity behaviour similar to polymer electrolyte. Ionic conductivity of the composite ceramic/polymer membranes is analysed by impedance spectroscopy and it falls between 7-10−9 S/cm at 20 °C and 5-10−5 S/cm at 80 °C for a composite with 40 vol% LLZO.