NOVELTY - The microphase separated polymer electrolyte comprises a first nanostructured domain, nanoparticles, and a second nanostructured domain adjacent to the first nanostructured domain. The first nanostructured domain is ionically conductive, and comprises an ionically-conductive comb polymer, an electrolyte salt, ethylene oxide and metal oxide nanoparticles, where the comb polymer comprises a backbone and pendant groups. The nanoparticles have a size of 2.5-15 nm, comprise a material consisting of metal oxides and/or ceramics, and are distributed randomly throughout the first domain.    USE - The microphase separated polymer electrolyte is useful in a lithium-ion rechargeable battery, which is useful for cellular phones, laptop computers, electrical grid load-leveling devices and electrically-powered vehicles and useful in defense, aerospace, back-up storage and transportation applications.    ADVANTAGE - The microphase separated polymer electrolyte offers high thermal stability, low rates of self-discharge, stable operation over a wide range of environmental conditions, enhanced safety, improved flexibility in battery configuration, minimal environmental impacts, low materials and processing costs, high ionic conductivity and good mechanical properties.    DETAILED DESCRIPTION - The microphase separated polymer electrolyte comprises a first nanostructured domain, nanoparticles, and a second nanostructured domain adjacent to the first nanostructured domain. The first nanostructured domain is ionically conductive, and comprises an ionically-conductive comb polymer, an electrolyte salt, ethylene oxide and metal oxide nanoparticles, where the comb polymer comprises a backbone and pendant groups. The nanoparticles have a size of 2.5-15 nm, comprise a material consisting of metal oxides and/or ceramics, and are distributed randomly throughout the first domain or preferentially along boundaries of the first domain. The second nanostructured domain has a modulus in excess of 1x 105 Pa at 80 degrees C.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a polymer with nanostructured domains.    Microphase-separated polymer (100)    Lamellar nano-domains. (110, 120)