In situ engineered organic–inorganic bilayer solid electrolyte interphase enabling lithium metal batteries over 15,000-hour lifespan

Despite significant advancements in constructing LiF-rich solid electrolyte interphases (SEIs) for high-performance lithium (Li) metal batteries, reconciling high ionic conductivity, mechanical resilience, and long-term interfacial stability persists as a critical challenge. Current approaches often fail to ensure seamless integration with the Li anode or else compromise electrolyte stability. Here, we present a dynamic in situ self-reinforcing SEI architecture achieved via selective fluorination using 1-fluorooctane, which spontaneously constructs a hybrid organic–inorganic bilayer structure during cycling. The flexible outer organic layer enhances electrolyte compatibility, while the LiF-rich inner layer ensures robust mechanical strength and promotes uniform Li-ion flux, effectively inhibiting Li dendrite growth. With these synergistic effects, the bilayer SEI provides an ultra-stable interphase with homogeneous Li deposition, yielding record-long lifespans exceeding 15,000 hours at 1 mA cm –2 and nearly 15,000 hours at 2–5 mA cm –2 in symmetric Li cells, far surpassing prior reported LiF-based Li anodes. LiFePO 4 ||Li pouch cells (with a high mass loading of 7.8 mg cm –2 and 50 μm thin Li foil) retain 80% capacity over 250 cycles at 0.5 C, demonstrating exceptional stability and practical application potential. The proposed in situ fabricated LiF-rich organic–inorganic bilayer SEI offers new perspectives to guide the practical application of high-performance Li metal batteries. • 1-fluorooctane preferentially reacts with Li to form a dense, LiF-rich inner layer, ensuring both mechanical robustness and homogeneous Li-ion transport. • The 1-fluorooctane contributes to a stable organic outer layer, endowing flexibility to accommodate volume changes. • Residual 1-fluorooctane in the electrolyte spontaneously participates in self-healing processes at solid electrolyte interphase fracture sites, maintaining its prolonged structural integrity. • This unique additive enables a Li metal anode to achieve >15,000 hours of stability at 1 to 5 mA cm –2 in symmetric cells and 80% capacity retention after 250 cycles in practical pouch cells.