Siloxane-based polymer electrolytes for solid-state lithium batteries

Solid polymer electrolytes (SPEs) have been considered as an effective approach to eliminate most of the potential safety issues encountered in conventional liquid electrolytes for lithium batteries. Substantial research efforts have been devoted to exploiting better comprehensive performance SPE systems, including poly(ethylene oxide), polycarbonates, polymeric siloxanes (PSs), polyphosphazenes and plastic crystals-based SPEs. Among them, PSs-based SPEs have been increasingly regarded as good candidates for SPEs due to low glass transition temperatures (Tg), excellent thermal and chemical stabilities, and facile chemical modifications. Despite great efforts in this field, however, PSs-based electrolytes still suffer from several challenges and can hardly meet the requirements of practical applications. In addition, to the best of our knowledge, separate and detailed reviews on the progress of PSs-based SPEs, especially in the recent progress after 2009 for lithium batteries are rare. In this review, we comprehensively summarize the progress in PSs for solid state lithium batteries (SLBs), including polysiloxanes, silsesquioxanes and oligosiloxanes based electrolytes from perspectives of the ionic conductivity, electrochemical properties and modification strategies, as well as their potential applications in SLBs. In addition, several possible research directions and strategic designs are also suggested to further improve comprehensive performance of siloxane-based polymer electrolytes. Our review will provide clear guidance in exploring high performance siloxane-based polymer electrolytes for SLBs.