Asymmetric bilayer PVDF-SN composite electrolytes with improved interfacial stability for high-performance lithium metal batteries

Succinonitrile (SN)-based plastic crystal electrolytes (PCEs) show great potential for solid-state batteries, but their practical application is limited by poor interfacial stability with lithium metal anodes. To address this critical challenge, an asymmetric bilayer composite electrolyte was designed, which consists of a porous PVDF-SN-LiTFSI-LiDFOB (PSTD) catholyte ensuring fast Li + transport, and a dense PVDF-LLZO-LiTFSI (PLT) anolyte serving as a robust protective layer. Notably, the PLT anolyte acts not only as a physical barrier against Li dendrites but also as a chemical buffer that facilitates the in-situ formation of a robust, tailored SEI from migrant additives, synergistically suppressing harmful side reactions. The resulting bilayer electrolyte exhibits a high ionic conductivity of 3.1 × 10 −4 S cm −1 at 30 °C and a wide electrochemical window of 4.85 V. As a result, the LFP/Li cells demonstrate excellent long-term cycling stability, delivering a high discharge capacity of 144.8 mAh g −1 and a retention rate of 95.9 % after 500 cycles at 1 C and 30 °C.