Revisiting polymeric single lithium-ion conductors as an organic route for all-solid-state lithium ion and metal batteries

The current surge in demand for high-performance batteries has inspired the relentless pursuit of advanced battery materials and chemistry. Notably, all-solid-state lithium-ion batteries and lithium metal batteries that have recently come into the spotlight have stimulated our research interest in solid-state electrolytes as a promising alternative to conventional liquid electrolytes. Among the various solid-state electrolytes explored to date, polymeric single lithium-ion conductors (polymeric SLICs) have garnered considerable attention as an organic approach that is different from the widely investigated solid inorganic electrolytes. A salient feature of polymeric SLICs is the predominant contribution of Li+ ions to the ionic conductivity, thus enabling the Li+ ion transference number to reach almost unity. This exceptional single ion transport behavior of polymeric SLICs, in combination with their solid-state nature, flexibility and facile processability, brings remarkable benefits to the battery structure and performance, which lie far beyond those achievable with typical dual-ion conductive electrolytes. In this review, we describe the current status and challenges of polymeric SLICs in terms of chemical/structural design and synthesis strategies. Also, the development direction and future outlook of polymeric SLICs are presented with a focus on their potential for application in the newly emerging Li battery systems.