From HF Scavenging to Li‐Ion Transport Enhancement: Multifunctional Separator Enabling Stable Li Metal Batteries in Carbonate‐Based Electrolytes

ABSTRACT Lithium metal batteries (LMBs) are emerging as promising next‐generation batteries owing to their high energy density. However, carbonate‐based electrolytes, which are essential for high‐voltage operation, induce severe parasitic reactions at the Li metal anode, generating HF and gaseous byproducts that destabilize the interface and accelerate cell failure. To address this problem, we propose a multifunctional separator (APA‐g‐APT) that incorporates uniformly distributed Si─OR moieties capable of chemically scavenging HF, thereby suppressing parasitic reactions and promoting the formation of stable, inorganic‐rich interphases on both Li anodes and NCM811 cathodes. Upon reaction with HF, in situ conversion of Si─OR into electronegative Si─F species further enhances ionic conductivity and promotes homogeneous Li‐ion transport, which is further validated by computational analyses. Consequently, high‐energy‐density Li/NCM811 full cells with thin Li anodes (< 40 µm) deliver stable cycling and high Coulombic efficiency even under harsh conditions, including carbonate electrolytes containing 1000 ppm H 2 O and elevated temperatures (55°C). Furthermore, by pairing thin Li anodes with high‐loading cathodes (up to 32.5 mg cm − 2 ), APA‐g‐APT cell achieves a gravimetric energy density of up to 402.2 Wh kg −1 . These findings demonstrate that APA‐g‐APT provides a practical approach to addressing the inherent instability of carbonate electrolytes, enabling safe, durable, and high‐energy‐density LMBs.