A novel approach to prepare Li-La-Zr-O solid state electrolyte films by suspension plasma spray

Abstract

In this work we investigated a novel approach to prepare Li-La-Zr-O solid-state electrolyte films by the suspension plasma spray process. This process offers several advantages that make it a promising low-cost, rapid and robust production method for garnet-type Li-ion conductors. A cubic garnet-type, Li6.75La3Zr1.75Nb0.25O12, ethanol-based suspension was plasma sprayed on stainless-steel substrates using two torch power levels, 30.9 and 77.1 kW, at different stand-off distances. Solid-state electrolyte films of ~14 μm thickness were deposited in ~0.1 h of spraying. Maximum Li-ion conductivity as high as 7.3·10−6 S cm−1 at 22 °C has been obtained for the samples sprayed at 30.9 kW and stand-off distance of 25 mm. These samples contained a majority of amorphous phase (67.0 wt%), 20.2 wt% of Li6.75La3Zr1.75Nb0.25O12, and the balance of 12.8 wt% of the pyrochlore phase (La2Zr2O7). We associate this result with the relatively high value of Li number density, 2.2·1022 cm−3, and the lowest content of La2Zr2O7. The higher torch power level and/or longer stand-off distance leads to a reduction in Li number density and higher content of La2Zr2O7, likely due to evaporative loss of Li species during the spray process. These factors also translate to a decrease in Li-ion conductivity. The knowledge that has been acquired in this preliminary study provides guidelines for further development and optimization of this rapid deposition technique of garnet-type solid-state electrolyte films.