Thin film deposition of garnet electrolytes for high energy density all-solid-state lithium batteries

Thin film deposition of garnet electrolytes for high energy density all-solid-state lithium batteriesIn recent years battery research concentrated on reaching batteries with high energy and power density and high safety at the same time. A combination of high-voltage cathode materials and solid electrolytes are one approach to fulfill the requirements of future cell technologies. A promising solid electrolyte is the garnet structured Li7La3Zr2O12 (LLZ) because of its high Li-ion conductivity (around 1 mS cm-1) and high chemical (stable with lithium metal) and electrochemical stability. If the solid electrolyte is applied as a thin film, the energy density of the cell will increase remarkably.Our group already showed the deposition of LLZ thin films with a thickness of around 1.8 µm on steel substrates by sputter deposition [1]. The layers showed an in-plane conductivity of 1.2x10-4 S cm-1 at room temperature, which is comparable to bulk LLZ and is the highest value for garnet-structured thin films so far. However, the required high deposition temperature of 700°C leads to unwanted side reactions with the used substrate. This reaction gives a Li-Al-O interlayer with high ionic resistance which makes it not possible for battery application.For a successful combination of LLZ thin films with high-voltage cathodes a decrease of deposition temperature is mandatory, for example high-voltage spinels react with LLZ at temperatures around 500°C [2]. Sputter deposition is a useful technique for depositing thin films far from thermodynamic equilibrium, e.g. the deposition of the high temperature phase of LiCoO2 cathode at around 500°C shows how powerful the technique can be [3]. As a further advantage, sputter deposition processes are comparably easy up-scalable, which would facilitate industrial application.In this presentation, different approaches for lowering the deposition temperature as well as the influence of deposition parameters and annealing conditions on the composition, microstructure and electrochemical properties of garnet-structured thin films will be discussed. Approaches of combining garnet-structured thin films with high-voltage cathode materials will also be presented