Developing Single-Ion Conductive Polymer Electrolytes for High-Energy-Density Solid State Batteries

Single-ion conductive polymer electrolytes (SICPEs) with a cationic transference number (t(Li+)) close to unity exhibit specific advantages in solid-state batteries (SSBs), including mitigating the ion concentration gradient and derived problems, suppressing the growth of lithium dendrites, and improving the utilization of cathode materials and the rate performance of SSBs. However, the application of SICPEs remains major challenges, i.e., the ionic conductivity is inferior at room temperature. Therefore, the recent accomplishments in improving the ambient ionic conductivity to be compatible SICPEs with a high transference number are discussed in this review. In particular, some strategies of delocalizing charges in polyanions, designing a highly conductive polymer matrix, and utilizing synergistic effects in SICPEs are focused to shed light on the further development of solid polymer electrolytes for SSBs. Finally, multifunctional species of SICPEs are discussed in view of the mechanical contact and/or charge transfer problems at the solid-solid interface in SSBs.