A block copolymer consisting of a polyethylene oxide (PEO) and polystyrene (PSt) was applied to the preparation of a microphase separation of solid polymer electrolyte containing LiClO4 with high ionic conductivity at room temperature (more than 10(-4) S cm(-1)). The polystyrene block provided the mechanical strength and the polyethylene oxide one allowed for fast ion conduction in the polymer electrolyte without any plasticizer. Using this new microphase separation solid polymer electrolyte, a LiCoO2/polymer electrolyte/Li metal cell was constructed and tested. The prepared cell exhibited a discharge capacity of 100 mAh g(-1) at 30 degrees C. (c) 2005 The Electrochemical Society.