Multi-coordination-assisted Li+ transport in an in situ-formed SN/polycarbonate electrolyte for high-voltage and high-safety solid-state lithium metal batteries

Solid polymer electrolytes (SPEs) synthesized via in-situ polymerization exhibit excellent interfacial compatibility; however their inherently low ionic conductivity limits their application in solid-state lithium (Li) metal batteries (LMBs). Herein, we report a type of SPE composed of succinonitrile (SN), LiTFSI, and cross-linked polymer matrix (SNCE). Within the electrolyte, Li + coordinates with ether, carbonyl, and nitrile groups; the strong SN-Li + interactions promote Li + detachment from the polymer matrix, forming continuous Li + conduction pathways. This design imparts both mechanical robustness and superior electrochemical performance to the SPEs. The cross-linked structure restricts the migration of SN, suppressing undesirable side reactions with the Li anode at the initial stage, compensating for the reduction in mechanical strength due to SN addition, and further improving electrochemical stability. The optimized SNCE-2 exhibits an ionic conductivity of 0.16 mS cm −1 at 30 °C, an electrochemical stability window (ESW) up to 5.2 V, and a Li + transference number ( t Li+ ) of 0.44. The in-situ polymerization ensures intimate electrode-electrolyte contact, and the formation of a stable solid-electrolyte interphase (SEI) on the Li anode by SNCE-2 enables Li|SNCE-2|Li symmetric cells to cycle stably for 1000 h at 0.2 mA cm −2 . The superior cycling performance of Li|SNCE-2|NCM622 and Li|SNCE-2|LFMP cells confirms the potential of SNCE-2 for high-voltage LMBs. Furthermore, the Li|SNCE-2|LFP cells demonstrates remarkable cycling durability, maintaining 86.1% of its capacity after 1000 cycles at 0.2C. Moreover, Li|SNCE-2|LFP pouch batteries also exhibit reliable safety performance. Therefore, this work provides a promising strategy for the development of SPEs for next-generation safety solid LMBs.