Freestanding polyimide fiber network as thermally safer separator for high-performance Li metal batteries

A stable and high-performance polyimide (PI) fiber mat was prepared via a facile two-step procedure, electrospinning deposition followed by an imidization process. The PI fiber separator presents higher thermal stability (>300 degrees C) than the commercial polypropylene (PP) separator (<160 degrees C). In Li/Cu half-cell configuration, PI fiber separator shows long cycle life performance with a coulombic efficiency of 82% at 0.5 mA cm(-2) after 100 cycles and an impedance of 29 Omega. It also showed suppression of sharp Li dendrite growth. While the commercial PP separator delivers a poor coulombic efficiency of 24% after 100 cycles and an impedance of 99 Omega because of the formation of dendritic Li. Moreover, the Li/LiFePO4 full cell with a PI fiber separator exhibits a lower polarization and charge transfer impedance than the commercial PP separator. The PI fibers enhanced the electrochemical cycle performance and stability of the full cells that deliver a charge capacity of 118 mAh g(-1) at a C-rate of 0.5 C with a capacity retention of 86% and a coulombic efficiency of > 99% after 200 cycles. Additionally, the multimode calorimetry (MMC) studies under in-situ mode revealed that the freestanding PI fiber separator presents high thermal stability in Li/LiFePO4 full cells. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

A stable and high-performance polyimide fiber mat was prepared using a simple two-step procedure, which exhibits higher thermal stability and better electrochemical performance compared to commercial polypropylene separators. The polyimide fibers show suppression of Li dendrite growth, lower polarization, and charge transfer impedance, as well as enhanced cycle performance and stability in full cells. This results in a higher charge capacity, capacity retention, and coulombic efficiency after multiple cycles.