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

Abstract

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 °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 LiOH∙H2O. Depositions carried out with the lithium rich target showed the garnet structure on glass substrates after deposition at 500 °C. The garnet structure was observed on Au-coated EN 1.4767 substrates already at a substrate temperature of 400 °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.