Solid electrolyte, method for preparing same, and all-solid-state battery including same

A solid polymer electrolyte comprising:

• a multifunctional acrylate-based polymer;
• a C1 to C10 polyalkylene oxide;
• a flame-retardant polymer;
• a lithium salt;
• and
• a non-aqueous solvent,
• wherein the non-aqueous solvent is present in a solid state at room temperature,
• wherein the non-aqueous solvent is dimethyl sulfone,
• wherein the multifunctional acrylate-based polymer and the polyalkylene oxide form semi-interpenetrating polymer networks (semi-IPN), and the flame-retardant polymer is present blended with the semi-interpenetrating polymer networks, and
• wherein 50% by weight or more of solids of the solid polymer electrolyte comprises the multifunctional acrylate-based polymer, the C1 to C10 polyalkylene oxide, the flame-retardant polymer, the lithium salt, and the non-aqueous solvent based on a total weight of the solid polymer electrolyte.