Solid polymer electrolytes (SPE) possess significant advantages over inorganic solid electrolytes in terms of performance and flexibility, but suffer from low conductivities. To improve their conductivities, ceramic nanoparticle fillers are typically used as additives. However, the conductivity enhancement could arise from both Li⁺ ions and surface-adsorbed moisture/protonic groups on the nanoparticles. Here, to deconvolute these effects, we report the synthesis and performances of polyvinylidene fluoride (PVdF)-based SPEs using a model filler, TiO₂, in as-received and annealed conditions. We find that there could be moderate contribution from non-Li⁺ species, and emphasize the need to anneal the additives prior to their incorporation.