Polar-group functionalized polyetherimide separator with accelerated li-ion transport for stable lithium metal batteries

Researches on functional separators are crucial for the performance of batteries owing to the inability of commercial polyolefin separators to suppress dendrites growth in lithium metal batteries, resulting in poor performance and safety hazards. Herein, we report a polar-groups of terminal amino and amide functionalized polyetherimide separator (PEI-EDA) with uniformly connected pore structure. The PEI-EDA separator displays excellent thermal stability, electrolyte affinity and ions transport ability with ionic conductivity of 1.96 mS cm⁻¹ and Li⁺ transference number of 0.74. Notably, the lone-pair electrons in nitrogen atoms of the −NH₂ and −CONH− groups have an interaction with Li⁺, and the active hydrogens on them have the electrostatic interaction with PF6⁻, which achieves the desolvation of Li⁺, improves ions transport rate and uniform Li-ion flux, synergistically inducing homogeneous deposition of Li⁺, suppressing the growth of dendritic Li and forming a stable fluorine-rich solid interphase layer and uniform cathode interphase layer. Furthermore, the data from on-line electrochemical mass spectroscopy show that the gas production of battery with PEI-EDA separator is significantly reduced during the cycling process, which effectively improving the battery safety. Uniform and dense Li deposition not only prolongs the cycle-life of Li||Cu and Li||Li cells, but also enhances the rate capability and cycling stability of Li||LiFePO₄ battery even under high cathode loading and extreme temperature conditions. Moreover, the Li||LiFePO₄ pouch battery displays stable cycling performance and benign safety under folding state. This suggests the PEI-EDA separator has a promising application prospect in the next-generation secure dendrite-free metal batteries.