As one class of the most promising organic electrode materials, quinone derivatives have received more and more attentions from energy storage community due to structural diversity and electrochemical reversibility.^[1] However, the limited rate capability arising from their electronically insulating nature remains challenging for the use of quinones in rechargeable batteries.^[2] Molecular structure and conformation can significantly affect the electronic conductivity of organic compounds. In this work, we report two heteroaromatic-fused quinone oligomers with extended cross-conjugation paths but different conformation. Using benzo[1,2-b:4,5-b']dithiophene-4,8-dione (BDTD) as the building block, cross-conjugated PBDTD (poly(benzo[1,2-b:4,5-b']dithiophene-4,8-dione-2,6-diyl)) with a rigid and planar conformation was constructed. To further investigate the influence of conformation on electrochemical property, we introduced C-S-C single bonds between BDTD units to obtain PBDTDS (poly(benzo[1,2-b:4,5-b']dithiophene-4,8-dione-2,6-diyl sulfide)), which show a helical conformation. The electrochemcial properties of PBDTD(S) are evaluated in lithium cells. Both oligomers demonstrate over 200 mAh g^–1 and 2.5 V vs. Li/Li⁺ at C/10. PBDTD(S) also show over 96% of capacity retention after 250 cycles as well as ~100% of Coulombic efficiencies. Finally we found PBDTD possesses superior rate capability over PBDTDS (as shown in Figure 1). In contrast to the helical structure of PBDTDS, the planar conformation of PBDTD provides more efficient electron transport paths in both inter- and intra-molecular directions, leading to the superior rate capability.

Reference

[1] B. Häupler, A. Wild, U. S. Schubert, Adv. Energy Mater. 2015, 5, 1402034.

[2] Y. Liang, Z. Tao, J. Chen, Adv. Energy Mater. 2012, 2, 742.