densities among other known batteries making them highly suitable for application in portable electronics and electric vehicles. [3][4][5][6] The energy density of LIBs can be increased further by using Li metal as anode material as it offers several times higher specific capacity (≈3.8 Ah g −1 ) and the lowest electrochemical potential (−3.04 V vs SHE). However, practical use of Li metal is limited in conventional batteries due to its thermodynamic instability with organic liquid electrolytes, forming dendrites during Li cycling which pose threats of short circuits. Volatility, flammability, and leakage of the liquid electrolytes are additional issues demanding strict attention. [7] Further, the solid electrolyte interphase (SEI) layer formed at the interface cannot withstand mechanical deformation and continuously undergoes formation and dissolution resulting in low Coulombic efficiency (80%-90% for carbonate solvents and 90%-95% for ether solvents) and low cycle life. [8] Most of these issues can be addressed by replacing liquid electrolytes with solid-state electrolytes (SSEs) including organic polymer, or inorganic sulfide or oxide-type. [9][10][11] Among them, oxide SSEs in particular have shown improved electrochemical stability with Li metals. [12] Since the first discovery by Thangadurai et al., [11] garnet-type oxide SSEs (Li 5 La 3 M 2 O 12 (M = Nb, Ta)) have attracted considerable attention due to their highest stability with Li, [12] high Li + transference number (t Li+ ≈ 1), high room temperature ionic conductivities (10 −4 −10 −3 S cm −1 ), and thermal stability at higher temperatures. [12,13] However, with garnet SSEs major challenge lies in realizing intimate Li-SSE contact due to their brittle nature. A poor Li-SSE contact results in high charge-transfer resistance at the interface, which contributes towards high voltage polarizations in the cell. To tackle the issue, various approaches have been adopted such as pressing Li against SSEs at high pressures, [14][15][16] electrolyte surface modifications, [17][18][19] and tuning chemical composition of the SSEs. [20,21] Beside the high interfacial resistance, Li dendrite growth in garnet SSEs is also a cause of concern. In principle garnet SSEs should mechanically block Li dendrites due to their high shear While all-solid-state Li metal batteries based on ceramic solid-electrolytes offer higher energy density and better safety features over their liquid counterparts, critical challenges in their design such as high electrodeelectrolyte interface resistance and formation of Li-dendrites still remain unsolved. To address the issues, an intimate contact between Li and the solid-state electrolyte is necessary. Herein, a flexible and mechanically robust polymer membrane comprising of poly(ethylene oxide), lithium perchlorate, and garnet particles is used as an interlayer between Li metal and garnet ceramic electrolyte. The Li salt enhances the ionic conductivity of the membranes and ensures their flexible nature while garnet particles enhance their mech...