A low redox potential and long life organic anode material for sodium-ion batteries

Sodium-ion batteries (SIBs) with organic electrodes are an emerging research direction due to the sustainability of organic materials based on elements like C, H, O, and sodium ions. Currently, organic electrode materials for SIBs are mainly used as cathodes because of their relatively high redox potentials (>1 V). Organic electrodes with low redox potential that can be used as anode are rare. Herein, a novel organic anode material (tetrasodium 1,4,5,8-naphthalenetetracarboxylate, Na₄TDC) has been developed with low redox potential (<0.7 V) and excellent cyclic stability. Its three-sodium storage mechanism was demonstrated with various in-situ/ex-situ spectroscopy and theoretical calculations, showing a high capacity of 208 mAh/g and an average decay rate of merely 0.022% per cycle. Moreover, the Na₄TDC-hard carbon composite can further acquire improved capacity and cycling stability for 1200 cycles even with a high mass loading of up to 20 mg cm⁻². By pairing with a thick Na₃V₂(PO₄)₃ cathode (20.6 mg cm⁻²), the as-fabricated full cell exhibited high operating voltage (2.8 V), excellent rate performance and cycling stability with a high capacity retention of 88.7% after 200 cycles, well highlighting the Na₄TDC anode material for SIBs.