New types of semi-interpenetrating polymer gel electrolytes with high conductivity as well as strength for use in rechargeable Lithium polymer batteries are synthesized. Single ion conducting polyelectrolyte gels are made by first synthesizing grafted linear chains of Lithium salt of 2-acrylamido-2-methylpropane sulphonic acid on ethyl cellulose (EC) using free radical initiator azobis (cyclohexanecarbonitrile) in dimethyl acetamide solvent, then copolymerizing methyl methacrylate (MMA) and a crosslinking agent ethyleneglycol dimethacrylate to form semi-interpenetrating network. The effect of concentrations of EC and MMA on electrical conductivity and mechanical strength of gels are determined.