Unveiling the Li/Electrolyte Interface Behavior for Dendrite-Free All-Solid-State Lithium Metal Batteries by Operando Nano-Focus WAXS.

Poly(ethylene oxide) (PEO)-based solid composite electrolytes suffer from poor conductivity and lithium dendrite growth, especially toward the metallic lithium metal anode. In this study, succinonitrile (SN) is incorporated into a PEO composite electrolyte to fabricate an electrode-compatible electrolyte with good electrochemical performance. The SN-doped electrolyte successfully inhibits the lithium dendrite growth and facilitates the SEI layer formation, as determined by the operando nanofocus wide-angle X-ray scattering (nWAXS), meanwhile, stably cycled over 500 h in Li/SN-PEO/Li cell. Apart from the observation of lithium dendrite, the robust SEI layer formation mechanism in the first cycle is investigated in the SN-enhanced composite electrolyte by nWAXS. The inorganic electrochemical reaction products, LiF and LiN, are found to initially deposit on the electrolyte side, progressively extending toward the lithium metal anode. This growth process effectively protected the metallic lithium, inhibited electron transfer, and facilitated Li⁺ transport. The study not only demonstrates a high-performance interfacial-stable lithium metal battery with composite electrolyte but also introduces a novel strategy for real-time visualizing dendrite formation and SEI growth directing at the interface area of electrolyte and metallic lithium.