Lithium Dissolution Using Garnet-Type Solid Electrolyte with a Thin Ionic Liquid Interlayer

Abstract

Currently, all-solid-state batteries enjoy widespread attention in research due to their expected high safety, power and energy density. This stems from their promise of being able to utilize lithium metal as the anode material. As of now, competitive batteries using lithium metal do not exist since most solid electrolytes are not chemically compatible in combination with a lithium anode. As garnets based on the Li7La3Zr2O12 system are stable versus lithium, this solid electrolyte can be used as a model system to study lithium metal stripping and plating.(1,2)One of the manifold problems regarding lithium metal anodes is based on the morphological changes occurring when stripping and depositing lithium during cycling of a cell.(1) Current densities above a certain threshold lead to pore formation and subsequent contact loss of lithium from the solid electrolyte, as vacancies are not transported away at a sufficient rate. This issue also leads to dendrite formation when depositing lithium due to current constriction on the remaining contact spots. Hence, this work aims to exploit thin ionic liquid interlayers as a means to compensate or attenuate pore formation at the interface. We observed an improvement in dissolution behavior of the lithium metal anode and additionally were able to identify the transport processes when using ionic liquids in combination with Li6.25Al0.25La3Zr2O12 using electrochemical impedance spectroscopy. We underline our conclusions with microscopic morphological studies using scanning electron microscopy. This work acts as a stepping-stone for the assembly of all-solid-state batteries using lithium metal as the anode in hybrid-cell configurations.(1) Krauskopf, T.; Hartmann, H.; Zeier, W. G.; Janek, J. Toward a Fundamental Understanding of the Lithium Metal Anode in Solid-State Batteries - An Electrochemo-Mechanical Study on the Garnet-Type Solid Electrolyte Li6.25Al0.25La3Zr2O12. ACS Appl. Mater. Interfaces 2019, 11 (15), 14463–14477.(2) Krauskopf, T.; Dippel, R.; Hartmann, H.; Peppler, K.; Mogwitz, B.; Richter, F. H.; Zeier, W. G.; Janek, J. Lithium-Metal Growth Kinetics on LLZO Garnet-Type Solid Electrolytes. Joule 2019, 3 (8), 2030–2049.