A new review of single-ion conducting polymer electrolytes in the light of ion transport mechanisms

With the depletion of fossil fuels and the demand for high-performance energy storage devices, solid-state lithium metal batteries have received widespread attention due to their high energy density and safety advantages. Among them, the earliest developed organic solid-state polymer electrolyte has a promising future due to its advantages such as good mechanical flexibility, but its poor ion transport performance dramatically limits its performance improvement. Therefore, single-ion conducting polymer electrolytes (SICPEs) with high lithium-ion transport number, capable of improving the concentration polarization and inhibiting the growth of lithium dendrites, have been proposed, which provide a new direction for the further development of high-performance organic polymer electrolytes. In view of this, lithium ions transport mechanisms and design principles in SICPEs are summarized and discussed in this paper. The modification principles currently used can be categorized into the following three types: enhancement of lithium salt anion-polymer interactions, weakening of lithium salt anion-cation interactions, and modulation of lithium ion-polymer interactions. In addition, the advances in single-ion conductors of conventional and novel polymer electrolytes are summarized, and several typical high-performance single-ion conductors are enumerated and analyzed in what way they improve ionic conductivity, lithium ions mobility, and the ability to inhibit lithium dendrites. Finally, the advantages and design methodology of SICPEs are summarized again and the future directions are outlined.