Recent Advancements in Single-Ion Polymer Electrolytes for Energy Storage in Lithium Metal Batteries

Polymer electrolytes are expected to play an important role in next-generation lithium metal batteries. In addition to intrinsic enhanced safety, polymer electrolytes can display unique properties such as lithiumion transference number (t+) approaching unity. This new class of materials – namely single-ion polymer electrolytes (SIPE) – may solve the major issue of salt concentration gradients limiting battery lifetime and performance. However, low ionic conductivities remain a practical challenge for SIPEs. This talk will highlight our recent work in the field of SIPEs for lithium metal batteries. New polymer structures were investigated with the final goal to simultaneously obtain high lithium t+, high room temperature ionic conductivity, and good mechanical properties. We focused on poly(LiMTFSI) as a backbone platform and employed RAFT polymerization techniques to prepare well defined block copolymers comprising poly(ethylene oxide) units. Block copolymers showed very high σ as compared to previous examples (≈10-4 S cm-1 at 70 ºC) combined with t+ ≈ 0.91. We have since continued to investigate crosslinking as a further method to incorporate propylene carbonate (PC) into the polymer network and increase the room-temperature ionic conductivity. Such gel-type SIPEs displayed lithium t+ approaching unity and high ionic conductivity (≈10-4 S cm-1 at 25 ºC). As the final goal, the application of these innovative polymers in lithium metal battery was investigated. Block copolymer electrolytes were successfully tested at 70 ºC providing long lifetime up to 300 cycles, and outstanding rate performance (up to 100 mAh g-1 at C/2) whereas lithium metal batteries operating at room temperature demonstrated the potential of gel-type SIPEs for high-performance applications in energy.