A Fluorinated‐Polyimide‐Based Composite Nanofibrous Separator with Homogenized Pore Size for Wide‐Temperature Lithium Metal Batteries

Abstract

Lithium (Li) is known for excellent theoretical specific capacity and most negative electrochemical potential, while still restricted by the irregular lithium dendrites and safety risks in practical applications of lithium metal batteries (LMBs) due to thermal runaway. Herein, a fluorinated‐polyimide (F‐PI)‐based composite nanofibrous separator containing poly(vinylidene fluoride) (PVDF) component, which is designed as PVDF/F‐PI, is developed via a facile electrospinning strategy for wide‐temperature LMBs. First, abundant polar trifluoromethyl (–CF3) groups in F‐PI create an electronegative environment to facilitate rapid Li‐ions (Li+) transport. Meanwhile, the PVDF component, acting as both the physical linker between F‐PI nanofibers and the regulator of homogenized pore size, simultaneously improves the mechanical properties and homogenizes the Li+ flux on the electrode surface. Therefore, a steady circulation of 2400 h is achieved for the symmetric cell using PVDF/F‐PI separator, which still displays a stable cycle life with a low voltage polarization of 15 mV in 1000 h even under 60 °C. Therefore, the fluorinated‐PI‐based composite nanofibrous separator with high ionic conductivity and uniform pore structure offers a practical method for design of functionalized separators in wide‐temperature LMB applications.