A sulfur-linked C3-symmetric conjugated trimeric naphthoquinone-benzopyrazine derivative with high-density C=O/C=N redox-active moieties for high-capacity and stable cathodic lithium storage

Organic cathode materials present a highly viable alternative, offering abundant resources, environmental compatibility, and highly designable molecular structures. However, conventional organic materials suffer from high solubility and low electronic conductivity. To overcome these inherent drawbacks, we propose a structural design strategy based on constructing extended π-conjugated molecular frameworks with high-density electrochemically reversible groups. Inspired by this strategy, we synthesized a novel sulfur-linked C3-symmetric conjugated organic compound, tris-benzothioxanthenedione 2,3-b (denoted as 6S6O), via a facile condensation reaction. The unique structure of 6S6O provides multiple high-density C=O/C=N moieties for reversible lithium storage, excellent solvent tolerance, and high intrinsic conductivity due to electron delocalization. Electrochemical testing demonstrates outstanding performance in a Li//6S6O half-cell, delivering a high reversible capacity of 352 mAh g −1 at 0.1 A g −1 , corresponding to a high energy density of ∼748.6 Wh kg −1 . Importantly, the electrode demonstrates excellent rate capability (retaining 65.3% capacity with a 20-fold current increase) and superior long-term cycling stability, maintaining 77.5% capacity retention over 2409 cycles at 2 A g −1 . Ex situ characterization and DFT calculations confirm a highly reversible, capacitive-controlled Li + storage mechanism involving the C=O and C=N bonds of the quinone/pyrazine units. The results validate the effectiveness of the extended π-conjugated design for developing high-performance organic cathode materials.