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 H2O 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.