Conjugation effect of amine molecules in non-aqueous Mg redox flow batteries

Journal Article · Thu Jul 31 00:00:00 EDT 2025 · Chemical Science

DOI:https://doi.org/10.1039/D5SC04532K· OSTI ID:2586877

Qin, Yunan ^[1]; Sethuraman, Vaidyanathan Mathamangalath ^[2]; Choi, Seong-Gyu ^[1]; Gonzalez, Richard ^[1]; Chen, Chengxiang ^[3]; Cheng, Lei ^[2]; Luo, Chao ^[3]; Gao, Tao ^[1]

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1. University of Utah, Salt Lake City, UT (United States)
2. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
3. University of Miami, Coral Gables, FL (United States)

Nonaqueous magnesium redox flow batteries (Mg RFBs) are attractive for low-cost, high-energy-density and long-cycle-life stationary energy storage applications. However, state-of-the-art cathode redox-active molecules suffer from low solubility and low redox potential. Herein, we screened a range of cathode redox-active molecules and identified amine molecules as optimal to couple with the Mg anode. The properties of amine derivatives and their performances were collected to establish the correlation between molecular structures and electrochemical performances. The redox potential and solubility of these amine molecules were influenced by the π-conjugated and non-conjugated structures of amine derivatives. Density functional theory (DFT) simulations and the inverse aromatic fluctuation index (FLU⁻¹) verified that conjugation had an important role in stabilizing the molecule and increasing its redox potential. Notably, tris[4-(diethylamino)phenyl]amine (TDPA) achieved the highest theoretical energy density (∼120 Wh L⁻¹) due to its high solubility (∼0.9 M) and voltage (∼2.5 V vs. Mg/Mg²⁺). We also demonstrated that ether solvents were crucial for stable, high-solubility catholytes, while bulk anions did not affect the redox potential of these p-type molecules. In a Mg-amine RFB configuration, the battery delivered 2.50 V, a specific discharge capacity of 106.5 mAh g⁻¹, an initial coulombic efficiency of 90.74%, and a capacity retention of 93.88% after 150 cycles.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: National Science Foundation; USDOE
• Grant/Contract Number: AC05-00OR22725
• Other Award/Contract Number: 2247407
• OSTI ID: 2586877
• Journal Information: Chemical Science, Journal Name: Chemical Science Journal Issue: 35 Vol. 16; ISSN 2041-6539; ISSN 2041-6520
• Publisher: Royal Society of Chemistry (RSC)
• Country of Publication: United States
• Language: English