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

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.