Abstract: A bulk ionically conductive polymer gel is prepared by dissolving a salt such as lithium trifluoromethanesulphonate (which would provide lithium ion conductors) in an organic compound such as N-formylpiperidine. The organic compound dissolves the salt at 20.degree. C. but is not a solvent at 20.degree. C. (though it is at 215.degree. C.) for polyethylene terephthalate. The last-named is a crystallizable polymer which is added in a minor amount at a high temperature to the other components and provides the required mechanical rigidity for the product at lower temperatures.