with solid electrolytes. [ 3 ] Solid electrolytes offer many advantages and could enable the use of new high capacity electrode materials such as sulfur, [ 4 ] manganese, [5][6][7] and vanadate [ 8,9 ] -based cathodes which may not be stable and safe in the current Li-ion battery technology based on liquid electrolytes. [ 10 ] Furthermore, solid electrolytes have the promise to use directly metallic lithium anodes, i.e., preventing dendritic lithium growth, which enables even higher energy densities. From a practical point of view, one may also highlight that solid electrolytes have much-improved thermal operation windows resulting in a higher chemical and thermal stability, benefi ting the long-term operation and safety when compared to their liquid counterparts. This allows for safe packaging of the cell geometries and enables miniaturized cell architectures while simultaneously reducing the battery weight. [ 11,12 ] Among the oxide solid Li-ionic electrolytes, Li 7 La 3 Zr 2 O 12 (LLZO) garnets and their doped variants show one of the highest Li-ion conductivities in the range of ≈10 −4 S cm −1 at room temperature. [ 13 ] LLZO was fi rst synthesized and characterized in 2007 by Murugan et al. [ 14 ] Not until a few years later Geiger et al. [ 15 ] showed that LLZO appears in two different crystal structures, a cubic and a tetragonal one, with the cubic phase showing a Li-ion conductivity two orders of magnitude higher than the tetragonal phase. Using doping strategies, i.e., by introducing Al 3+ , Ga 3+ , Ta 5+ , Nb 5+ , etc., the high conductive cubic phase can be stabilized at room temperature by introducing vacancies into the Li sublattice of the structures. [16][17][18][19] One of the most commonly used dopants is Al 3+ , which stabilizes the cubic phase by substituting for three Li + , thereby creating two Li vacancies and resulting in the stoichiometry of Li 7−3 x Al x La 3 Zr 2 O 12 for the cubic phase.[ 20 ] Despite the promises, all-solid-state Li-ion batteries based on cubic LLZO solid electrolytes have still challenges in realizing high practical performances due to their high electrode-electrolyte interfacial resistances. For the investigations on all-solid-state batteries based on garnet-type cubic LLZO, most of the current research efforts are concentrated on the cathode material, most prominently on LiCoO 2 . [21][22][23][24][25][26][27] Reasonable electrochemical activities are so far only achieved by vacuum deposition of the cathode as thin fi lms, i.e., by pulsed laser deposition (PLD), because of the resulting good electrolyte-electrode contact. [ 25,26 ] Here, the exact chemical composition of the electrolyte-electrode interface also greatly determines the contact properties, the interfacial