New polymer electrolytes based on acrylonitrile-methyl methacrylate-styrene (AMS) terpolymers were prepared using binary plasticizing solvents consisting of ethylene carbonate (EC)/dimethyl carbonate (DMC) or EC/Y-butylolactone (T-BL). The LiNi0.5Co0.5O2 powders with narrow particle-size distribution and phase-pure particles were also synthesized by a sol-gel method using aspartic acid as a chelating agent. With these solid polymer electrolytes (SPE) and LiNi0.5Co0.5O2 powders, the Li/SPE/LiNi0.5Co0.5O2 cells were assembled and their cycling performance was investigated in terms of mixed solvent electrolytes. The cyclability of Li/SPE/LiNi0.5Co0.5O2 cell was significantly affected by the nature of the solvent. The Li/SPE/LiNi0.5Co0.5O2 cells containing EC/DMC mixture showed better cycling characteristics as compared to those based on EC/Y-BL mixture. These cells had an initial capacity of 156 mAh/g in the voltage range of 3.0-4.2 V, and showed an attractive discharge capacity of 116 mAh/g at 2.0 C rate.