Trends in polymer electrolytes for secondary lithium batteries

The polymer electrolytes are promising materials for the ever-growing need for high energy density power sources for power and traction applications. With an emphasis on lithium batteries, the field of polymer electrolytes has gone through a sort of three stages; dry solid systems, polymer gels, and polymer composites. The ‘polymer gels’ and the ‘polymer composites’, the former incorporating organic solvents, have shown room temperature conductivities as high as 10−3 S cm−1 .The ‘dry solid systems’ presently suffer from poor ionic conductivities (∼10−5 S cm−1 at 20°C), but are safer than the former due to absence of any organic solvent which can cause environmental hazards. In the area of electrode systems, one can notice quite good performances by the organo-sulfur polymers as cathode materials and poly(p-phenylene) as an anode material. Specific energies as high as 180 W h kg−1 have been demonstrated in cells containing these polymers. Examples of various test cells based on the above types of polymer electrolytes incorporating lithium metal, intercalation type electrodes, and polymer electrodes are reviewed.