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Abstract Aqueous electrolytes are promising in large-scale energy storage applications due to intrinsic low toxicity, non-flammability, high ion conductivity, and low cost. However, pure water’s narrow electrochemical stability window (ESW) limits the energy density of aqueous rechargeable batteries. Water-in-salt electrolytes (WiSE) proposal has expanded the ESW to over 3 V by changing electrolyte solvation structure. The limited solubility and WIS electrolyte crystallization have been persistent concerns for imide-based lithium salts. Asymmetric lithium salts compensate for the above flaws. However, studying the solvation structure of asymmetric salt aqueous electrolytes is rare. Here, we applied small-angle x-ray scattering (SAXS) and Raman spectroscope to reveal the solvation structure of imide-based asymmetric lithium salts. The SAXS spectra show the blue shifts of the lowerqpeak with decreased intensity as the increasing of concentration, indicating a decrease in the average distance between solvated anions. Significantly, an exponential decrease in the d-spacing as a function of concentration was observed. In addition, we also applied the Raman spectroscopy technique to study the evolutions of solvent-separated ion pairs (SSIPs), contacted ion pairs (CIPs), and aggregate ions (AGGs) in the solvation structure of asymmetric salt solutions.
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Designing Alkylammonium Cations for Enhanced Solubility of Anionic Active Materials in Redox Flow Batteries: The Role of Bulk and Chain Length
Abstract Advancing grid‐scale energy storage technologies is crucial for realizing a fully renewable energy landscape, with non‐aqueous redox flow batteries (NRFBs) presenting a promising solution. One of the current challenges in NRFBs stems from the low energy density of redox active materials, primarily due to their limited solubility in non‐aqueous solvents. Herein, this study explores the solubility of vanadium(IV/V) bis‐hydroxyiminodiacetate (VBH) crystals in acetonitrile, aiming to use them as anionic catholytes in NRFBs. We focused on enhancing VBH solubility by modifying the structure of the alkylammonium cation. Employing periodic density functional theory and a solvation model, we calculated the dissolution free energy ), which includes sublimation ( ) and solvation ( ) energies. Our results indicate that neither elongating straight‐chain alkyl groups beyond a tetrabutylammonium baseline nor introducing bulky substituents at the nitrogen center significantly enhances solubility. However, the introduction of carbon spacers combined with terminal bulky substituents markedly improves solubility by favorably altering both and . These findings underline the nuanced impact of cation structure on solubility and suggest a viable approach to optimize VBH‐based anionic catholytes. This advancement promises to enhance NRFB efficiency and sustainability, marking a significant step forward in energy storage technology.
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- Award ID(s):
- 2329652
- PAR ID:
- 10642637
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPhysChem
- Volume:
- 25
- Issue:
- 24
- ISSN:
- 1439-4235
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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