Abstract: A solid polymer electrolyte composition is made by hydrolyzing cellulose in a dissolution media to form a first mixture; then combining said first mixture with an antisolvent to form a precipitate; and then (in any order) separating said precipitate from excess antisolvent and excess dissolution media; optionally adjusting or neutralizing the pH of said precipitate; optionally washing said precipitate with water; combining said precipitate with an electrolyte salt and a hydrophilic polymer to form a wet polymer electrolyte composition; and then drying said wet polymer electrolyte composition to produce a solid polymer electrolyte composition. Solid polymer electrolyte compositions produced by the process, along with films formed therefrom and devices containing the same, are also described.