Oligomer-suspended SiO(2)-polyethylene glycol nanoparticles are studied as porous media electrolytes. At SiO(2) volume fractions, phi, bracketing a critical value phi(y) approximate to 0.29, the suspensions jam and their mechanical modulus increase by more than seven orders. For phi > phi(y), the mean pore diameter is close to the anion size, yet the ionic conductivity remains surprisingly high and can be understood, at all phi, using a simple effective medium model proposed by Maxwell. SiO(2)-polyethylene glycol hybrid electrolytes are also reported to manifest attractive electrochemical stability windows (0.3-6.3 V) and to reach a steady-state interfacial impedance when in contact with metallic lithium.