NOVELTY - Composition comprises an ethylene oxide (EO)-containing copolymer including a first monomer of EO, and at least one additional monomer comprising an alkylene-oxide that is different from the first monomer of EO, an alkyl glycidyl ether, and/or an allyl glycidyl ether, where the EO-containing copolymer has a weight average molecular weight of less than 200000 g/mole, and the EO-containing copolymer has a molar fraction of the first monomer of ethylene oxide (X(EO)) of 0.8-0.995.    USE - The composition is useful: as a binder material for a battery electrode; in the composite electrode; and for preparing the solid polymer electrolyte, where the composite electrode is useful for preparing a secondary battery (all claimed) including an anhydrous secondary battery and an aqueous battery. The composition is useful in fuel cell, photovoltaic cell, electrochemical devices, and sensor devices.    ADVANTAGE - The composition has enhanced ionic conductivity, and is long-lasting. The composition has strong adhesion to electroactive particles even after undergoing mechanical deformation. The batteries provided by the composition exhibit improved durability and efficiency. The electrodes exhibit an appropriate balance of mechanical properties and electrical properties. The composite electrode is more flexible and can be easily processed into a battery. The composite electrode exhibits high strength. The composite electrode eliminates the need for the relatively stiff packaging.    DETAILED DESCRIPTION - Composition comprises an ethylene oxide (EO)-containing copolymer including a first monomer of EO, and at least one additional monomer comprising an alkylene-oxide that is different from the first monomer of EO, an alkyl glycidyl ether, and/or an allyl glycidyl ether, where the EO-containing copolymer has a weight average molecular weight of less than 200000 g/mole, the EO-containing copolymer has a molar fraction of the first monomer of ethylene oxide (X(EO)) of 0.8-0.995, the EO-containing copolymer has a peak melting temperature (Tp) for a selected X(EO) at 0.8-0.995 degrees C, which is below a maximum value of Tpmax (where Tpmax is maximum peak melting temperature) at the selected X(EO), and the Tpmax is equal to 60-150 (1-X(EO)). INDEPENDENT CLAIMS are included for:    (1) a composite electrode comprising the composition, where the composite electrode includes many electroactive particle, and the EO-containing copolymer is in contact with the electroactive particles;    (2) a solid polymer electrolyte prepared using the composition, where the solid polymer electrolyte includes a metal salt and/or a solvent; and    (3) polymerizing the EO-containing copolymer, comprising contacting the first monomer of EO and at least one additional monomer with an activated alkylaluminum catalyst in the presence of a hydrocarbon diluent at a temperature of at least 5 degrees C less than the melting temperature of the copolymer for reacting the monomers to polymerize the copolymer.