Tune and Thin Lithium Metal Anode – Toward Functional and Optimized Used with Hybrid Solid-State Halide Electrolyte

In the context of the energy transition, lithium metal is considered as the most promising electrode material for battery anodes due to its high capacity, low density, and thus energy density. However, the amount of lithium used in a battery must be minimized (i.e., the thickness of lithium metal anodes should be reduced) to increase the device energy density and to avoid its over-consumption as lithium metal is also considered as a critical raw material by the European Union. Currently, extrusion followed by lamination is the main process used to produce lithium metal foil of at least a dozen of micrometers thick. To further reduce this thickness, we have chosen to use a vacuum evaporation process (PVD), which allows for thickness control on the order of a few hundred nanometers. Lithium films ranging from 5 to 20 µm can be produced using an argon glovebox connected to a vacuum deposition chamber, thereby preventing contact with air. Through various tests, we report on the main governing deposition parameters (e.g., substrate, evaporation temperature) that significantly influence the final film microstructure, which in turn impact the Coulombic efficiency of the corresponding electrochemical cell. As an example, the Figure (SEM pictures of lithium obtained by PVD with a) low speed deposition rate and b) high speed deposition rate) shows SEM images of lithium film microstructures obtained with different deposition parameter speed but with similar thickness. In this work, we propose to present a study of the influence of the microstructure and thickness of thin lithium films on electrochemical performances in lithium symmetric cells using at first a solid polymer electrolyte made of poly(ethylene oxide), PEO, doped with LiTFSI salt. These performances are compared and assessed using electrochemical impedance spectroscopy, linear galvanodynamic, and lithium plating/stripping routines. In-situ imaging by X-ray tomography and SEM studies of the microstructure of post-mortem electrodeposits complete the study. Finally, to extend these observations to other materials, we compare these results with a promising hybrid solid electrolyte comprising an organic Li3InCl6 phase and a polymer matrix. The effect of the solid electrolyte nature (polymer vs. hybrid) on the Coulombic efficiency permits thus to select the most promising type of thin lithium electrode for each kind of electrolyte. Figure 1