Developing safe and high energy density batteries is a significant challenge, especially for Li-ion configurations. Using Li-metal as the negative electrode could greatly boost energy density but requires the replacement of liquid electrolytes by solid‑state electrolytes (SSEs) to work properly and safely. Non‑volatile SSEs may prevent dendrite growth related to inhomogeneous Li electrodeposition leading to low-capacity retention and potential short‑circuit. Challenges persist in ensuring close electrode/SSE contact, enhancing ionic conductivities, electrochemical stability at operating temperatures, cycle life and fast charging capabilities. Here, a composite SSE composed of a dispersion of ionic conductive ceramic particles in a polymer electrolyte matrix is studied to leverage different SSE types. Li+ ions dynamics are investigated at 60 °C with Li isotopic tracing after applying an electrical field. High‑resolution solid-state NMR and orthogonal time‑of‑flight secondary ion mass spectrometry are employed for characterizing Li isotopic relative abundance in SSE at global and local levels, respectively. By differentiating Li in the polymer phase from ceramic particles, both techniques reveal that Li+ ions preferentially diffuse through the ceramic dispersion. Surprisingly, electrochemical impedance spectroscopy analysis shows no enhancement in ionic conductivity between polymer and composite electrolytes, highlighting the impact of other parameters such as percolation or polymer/ceramic interface properties.