A new type of polymer electrolyte based on gradient copolymers is proposed to resolve the problem of low ionic conductivity faced by polymer electrolytes. A series of random, block,, and gradient copolymers of styrene (St) and methyl acrylate (MA) are synthesized by a living radical polymerization method and employed as polymer electrolytes for lithium-ion batteries. The gradient copolymer has gradual change in the monomeric composition along polymer chains. There is no abrupt composition change between the adjacent blocks. This design minimizes possible sharp domain boundaries and generates highly conductive smooth ion pathways. The gradient copolymer gel electrolyte filled with a regular ester electrolyte gives the highest ionic conductivity of 1.20 x 10(-3) S cm(-1) at room temperature, which meets the requirement of practical applications.