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

Abstract

Research on functional separators is 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 polar groups of terminal amino and amide functionalized polyetherimide separators [ethylenediamine grafting polyetherimide (PEI-EDA)] with uniformly connected pore structures. The PEI-EDA separator displays excellent thermal stability, electrolyte affinity and ion transport ability with an ionic conductivity of 1.96 mS·cm^-1 and a Li⁺ transference number of 0.74. Notably, the lone-pair electrons in nitrogen atoms of the −NH₂ and −CONH− groups have interaction with Li⁺, and the active hydrogens on them have the electrostatic interaction with PF₆^-, which achieves the desolvation of Li⁺, and improves ion transport rate and uniform lithium-ion flux, synergistically inducing homogeneous deposition of Li⁺, suppressing the growth of dendritic lithium and forming a stable fluorine-rich solid interphase layer and uniform cathode interphase layer. Furthermore, the data from online electrochemical mass spectroscopy (OLEMS) show that the gas production of a battery with a PEI-EDA separator is significantly reduced during the cycling process, which effectively improves the battery safety. Uniform and dense lithium 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 batteries even under high cathode loading and extreme temperature conditions. Moreover, the Li||LiFePO₄ pouch battery displays stable cycling performance and benign safety under the folding state. This suggests the PEI-EDA separator has a promising application prospect in the next-generation secure dendrite-free metal batteries.

Keywords

Functionalized polyetherimide separator / polar groups / ion transport ability / lithium metal batteries / dendrite-free

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