Nanostructured solid electrolytes containing ion-conducting domains and rigid nonconducting domains are obtained by block copolymer self-assembly. Here, we report on the synthesis and characteristics of mixtures of a hybrid diblock copolymer with an organic and inorganic block: poly(ethylene oxide)-b-poly(acryloisobutyl polyhedral oligomeric silsesquioxane) (PEO-POSS) and a lithium salt. In the neat state, PEO-POSS exhibits a classical order-to-disorder transition upon heating. Dilute electrolytes exhibit a dramatic reversal; a disorder-to-order transition upon heating is obtained, indicating that the addition of salt fundamentally changes interactions between the organic and inorganic chains. At higher salt concentrations, the electrolytes primarily form a lamellar phase. Coexisting lamellae and cylinders are found at intermediate salt concentrations and high temperatures. The conductivity and shear modulus of PEO-POSS are significantly higher than that of an all-organic block copolymer electrolyte with similar molecular weight and morphology, demonstrating that organic-inorganic block copolymers provide a promising route for developing the next generation of solid electrolytes for lithium batteries.