The global requirement for green, sustainable energy relies on advanced energy storage systems, such as rechargeable batteries for electric vehicles, or efficient use of renewable power. Sodium-ion batteries have emerged as a lower cost and safer alternative to their lithium analogues. Additionally, using organic electrode materials could offer lighter weight, tunable molecular design, and renewability compared to traditional inorganic electrode materials. However, these electrodes have lower reduction potentials, which are undesirable in rechargeable batteries.
In their article in Advanced Energy Materials, Mahesh Hariharan, Manikoth Shaijumon, and co-workers from the Indian Institute of Science Education and Research demonstrate their simple and efficient approach for tuning the redox properties of perylene diimides (PDIs) as high-voltage cathodes for organic-based sodium-ion batteries (SIBs).
The researchers synthesized various PDI derivatives with different electron-withdrawing substituents and introduced a systematic twist in the perylene ring of tetrabromo-substituted PDIs. Galvanostatic cycling of the PDIs revealed two well-separated redox peaks and discharge plateaus for near-planar perylene rings, indicating the presence of two redox pairs. However, as the dihedral angle was increased, a single plateau was achieved, indicating a single redox pair. In all derivatives the practical and theoretical capacities were closely matched and had a sodium-ion intake greater than 1.7 per molecule.
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