Nanocomposite materials were obtained from poly(vinylidene fluoride) (PVdF) as matrix polymer and a stable DMF suspension of nanocrystalline cellulose (NCC) as the reinforcing phase. Porous and dense nanocomposite membranes were prepared by non-solvent induced phase separation (NIPS) and film casting methods, respectively. The resulting films were characterized regarding their structuration, i.e., the content of crystalline phases, as well as their transport and thermo-mechanical properties. The presence of the fillers led to a mechanical reinforcement, associated with a lower strain at break. For dense nanocomposites, a thermal stabilization at temperatures higher than the melting temperature was highlighted and ascribed to the formation of a rigid cellulosic network within the matrix. The superior electrochemical performances together with the observed reinforcement effect render these porous nanocomposites membranes as interesting candidates for the replacement of commercial polyolefin-based microporous separators in lithium-ion batteries.