Asymmetric fluorinated polyimide separators with gradient pore structure for lithium metal batteries

To achieve high performance and stability in next-generation lithium metal batteries (LMBs), it is essential to address the low porosity and poor electrolyte wettability of conventional separators. To address the limitations of conventional polyolefin separators, this study aims to develop a fluorinated polyimide (fPI)-based separator featuring an asymmetric porous structure. Herein, poly(amic acid) is synthesized, and an asymmetric porous structure is formed through a phase inversion process, followed by an imidization to prepare an asymmetric fluorinated polyimide separator (A-fPI) with gradient pore structure for LMBs. The A-fPI not only exhibits exceptional thermal stability, maintaining its film form without shrinkage or deformation even at temperatures of 300 ℃, but also uses its asymmetric porous structure to provide a high electrolyte storage capacity and ensure uniform lithium-ion distribution, enabling facilitated lithium-ion transport. The key innovation lies in combining high thermal stability with enhanced ionic conductivity and dendrite suppression through a gradient pore distribution. LMBs assembled with A-fPI show high specific capacity, excellent rate performance, and long cycle stability, demonstrating its potential as a high-performance and safe separator.