Long Cycle Life for Rechargeable Lithium Battery using Organic Small Molecule Dihydrodibenzo[c,h][2,6]naphthyridine-5,11-dione as a Cathode after Isoindigo Pigment Isomerization

Sustainability and adaptability in structural design of the organic cathodes present promises for applications in alkali metal ion batteries. Nevertheless, a formidable challenge lies in their high solubility in organic electrolytes, particularly for small molecular materials, impeding cycling stability and high capacity. This study focuses on the design and synthesis of organic small molecules, the isomers of (E)-5,5 '-difluoro-[3,3 '-biindolinylidene]-2,2 '-dione (EFID) and 3,9-difluoro-6,12-dihydrodibenzo [c, h][2,6]naphthyridine-5,11-dione (FBND). While EFID, characterized by a less pi-conjugated structure, exhibits subpar cycling stability in lithium-ion batteries (LIBs), intriguingly, another isomer, FBND, demonstrates exceptional capacity and cycling stability in LIBs. FBND delivers a remarkable capacity of 175 mAh g-1 at a current density of 0.05 A g-1 and maintains excellent cycling stability over 2000 cycles, retaining 90% of its initial capacity. Furthermore, an in-depth examination of redox reactions and storage mechanisms of FBND are conducted. The potential of FBND is also explored as an anode in lithium-ion batteries (LIBs) and as a cathode in sodium-ion batteries (SIBs). The FBND framework, featuring extended pi-conjugated molecules with an imide structure compared to EFID, proves to be an excellent material template to develop advanced organic small molecular cathode materials for sustainable batteries. The novel organic cathode, 3,9-difluoro-6,12-dihydrodibenzo [c, h][2,6]naphthyridine-5,11-dione (FBND), is synthesized in success in this paper, which showed enhanced stability with 90% capacity retention over 2000 cycles for energy storage after isomerization of isoindigo pigment (EFID), indicating FBND framework boosts cycling stability. Meanwhile, it showed dual utility in lithium- and sodium-ion batteries. Besides, density functional theory calculations is adopted to confirm mechanism of charge-discharge process.image