Revealing Temperature‐Driven Interfacial Reactions of Succinonitrile in PEO‒LiTFSI Electrolytes and Suppressing Them via Dual PEDOT‐Based Interfacial Layers

ABSTRACT Achieving a homogeneous ion‐conducting network with sufficient mechanical strength and interfacial stability in Succinonitrile (SN)‐polyethylene oxide (PEO)‐based solid polymer electrolytes remains challenging. In particular, the temperature‐dependent interfacial behavior of SN in PEO‒lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolytes is largely unexplored. Here, we reveal that SN undergoes temperature‐driven interfacial reactions at both lithium metal and cathodes, in addition to reactions involving PEO and LiTFSI. Notably, cathode‐side reactions contribute more to interfacial degradation and capacity fading than the widely studied lithium‐SN interfacial reactions. To address these challenges, a dual‐sided protection strategy using PEDOT‐based interfacial layers is developed. A PEO‒SN‒LiTFSI solid‐polymer electrolyte with high SN content and moderate salt concentration is reinforced with a poly(vinylidene fluoride‐co‐hexafluoropropylene) nanofiber network to maintain mechanical integrity and continuous ion‐conducting pathways. On the anode side, a PEDOT‐based nanofibrous mat coated with a thin gel layer suppresses the transport of reactive electrolyte species toward the lithium interface. On the cathode side, sulfonate‐functionalized PEDOT forms a conformal coating that suppresses interfacial reactions, including those associated with SN. This integrated design enables stable cycling for over 500 cycles and retains >70% capacity at 50°C, demonstrating an effective strategy to suppress temperature‐driven interfacial reactions and achieve stable wide‐temperature (10°C–50°C) solid‐state battery operation.