Polymer electrolytes, problems, prospects, and promises

摘要

Ionically conducting polymer electrolytes have generated, in recent years, wide-spread interest as candidate materials for a number of applications including high energy density and power lithium batteries. In the early 70s the first measurements of ionic conductivity in polyethylene oxide (PEO)-salt complexes were carried out. However, Armand was the first one to realize potential of these complexes (polymer-salt complexes) as practical ionically conducting materials for use as electrolytes in lithium batteries. Subsequent research efforts identified the limitations and constraints of the polymer electrolytes. These limitations include poor ionic conductivity at RT (< 10(sup (minus)8) S/cm), low cation transport number (<0.2) etc. Several different approaches have been made to improving the ionic conductivity of the polymer electrolytes while retaining the flexibility, processibility, ease of handling and relatively low impact on the environment that polymers inherently possess. This paper- reviews evolution of polymer electrolytes from conventional PEO-LiX slat complexes to the more conducting polyphosphazene and copolymers, gelled electrolytes etc. We also review the various chemical approaches including modifying PEO to synthesizing complicated polymer architecture. In addition, we discuss effect of various lithium salts on the conductivity of PEO-based polymers. Charge/discharge and cycle life data of polymer cells containing oxide and chalcogenide cathodes and lithium (Li) anode are reviewed. Finally, future research directions to improve the electrolyte properties are discussed.