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Abstract Lithium-based nonaqueous redox flow batteries (LRFBs) are alternative systems to conventional aqueous redox flow batteries because of their higher operating voltage and theoretical energy density. However, the use of ion-selective membranes limits the large-scale applicability of LRFBs. Here, we report high-voltage membrane-free LRFBs based on an all-organic biphasic system that uses Li metal anode and 2,4,6-tri-(1-cyclohexyloxy-4-imino-2,2,6,6-tetramethylpiperidine)-1,3,5-triazine (Tri-TEMPO), N-propyl phenothiazine (C3-PTZ), and tris(dialkylamino)cyclopropenium (CP) cathodes. Under static conditions, the Li||Tri-TEMPO, Li||C3-PTZ, and Li||CP batteries with 0.5 M redox-active material deliver capacity retentions of 98%, 98%, and 92%, respectively, for 100 cycles over ~55 days at the current density of 1 mA/cm2and a temperature of 27 °C. Moreover, the Li||Tri-TEMPO (0.5 M) flow battery delivers an initial average cell discharge voltage of 3.45 V and an energy density of ~33 Wh/L. This flow battery also demonstrates 81% of capacity for 100 cycles over ~45 days with average Coulombic efficiency of 96% and energy efficiency of 82% at the current density of 1.5 mA/cm2and at a temperature of 27 °C.
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Selective Membrane for Non‐Aqueous Electrochemical Flow Cells
Abstract Non‐aqueous redox flow batteries can support the growing need for grid scale energy storage. Conductive and selective membranes are critical to enabling advanced flow battery technology with higher energy density and lower cost. Herein, a series of crosslinked poly(phenylene oxide)‐based membranes functionalized with phenoxyaniline tri‐sulfonate fixed charges are developed and reported. Increasing the degree of functionalization increased the theoretical ion exchange capacity (IEC) to 2.62 mEq g−1compared with a previously achieved maximum of 2.06 mEq g−1for these materials. Increasing membrane IEC increased conductivity (up to 0.41 mS cm−1) and decreased permeability (<1 × 10−9cm2s−1) based on ex situ measurements. While further improvements are still necessary for economically competitive non‐aqueous flow battery applications, these values are among the highest selectivity reported for cation exchange membranes in non‐aqueous electrolytes. In symmetric non‐aqueous electrochemical flow cell testing, current densities over 2 mA cm−2are achieved, although cell polarization is higher than expected. Long‐term cycling is performed at 1 mA cm−2with average coulombic efficiency over 99% maintained for over 70 cycles. This work reinforces that both ex situ transport properties and electrochemical cell evaluation are necessary when evaluating potential membrane materials, although reporting of both is presently uncommon in the literature.
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- Award ID(s):
- 2342993
- PAR ID:
- 10639984
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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