Challenges regarding thin film deposition of garnet electrolytes for all-solid-state lithium batteries with high energy density

In this work, we studied the deposition of garnet electrolyte thin films in order to realize an all-solid-state battery with high energy density. Therefore, in a first step we investigated the stability of the garnet Li5La3Ta2O12 with the spinel LiCoMnO4 in order to determine the temperature window for a successful thin film deposition on high-voltage spinels. A mixture of both materials showed a thermal stability up to 600 A degrees C, so that all-solid-state batteries could be realized when the electrolyte is applied at a low deposition temperature. The second part of the work was the thin film deposition of Li5La3Ta2O12 by a sputter deposition process. When a stoichiometric Li5La3Ta2O12 sputter target was used, the surface of the target showed a depletion of lithium after several depositions, which leads to decreasing Li content in the thin films. In order to compensate the lithium loss we enriched the target with LiOHa (TM) H2O. Depositions carried out with the lithium rich target showed the garnet structure on glass substrates after deposition at 500 A degrees C. The garnet structure was observed on Au-coated EN 1.4767 substrates already at a substrate temperature of 400 A degrees C, which is 300 K lower than comparable depositions of Li7La3Zr2O12. These results show that the combination of thin garnet-structured electrolytes and high-voltage spinels is possible.