All-solid-state lithium-ion batteries (ASSLIBs) are promising alternatives to conventional organic electrolyte-based batteries due to their higher safety and higher energy densities. Despite advantages, ASSLIBs suffer from issues like high charge transfer resistances due to the brittleness of the inorganic solid electrolyte and chemical instabilities at the lithium/electrolyte interface. Within this work, we investigate composite electrolytes based on garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO), polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl) imide (LiTSFI), prepared via a solvent free cryo-milling approach in contrast to conventional solvent mediated synthesis. Compositions ranging from polymer-rich to garnet-rich systems are investigated via X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy (FT-IR) in order to determine the compatibility of the cryo-milling process towards membrane fabrication along with the possible chemical interactions between the composite membrane components. Electrochemical impedance spectroscopy (EIS) is used to study the role of ceramic to Polymer weight fraction on ionic conductivity. It is shown that the addition of succinonitrile (SCN) to the garnet-rich composite electrolytes can significantly improve the ionic conductivity compared to the SCN free composite electrolytes.