From P-Type to Bipolar: A Quinone-Core Engineering Strategy in D-A-D Organic Cathodes for Ultra-Stable and High-Energy Organic Lithium-Ion Batteries

In this study, we present a rational donor-acceptor-donor (D-A-D) molecular design strategy to develop high-performance organic cathodes by enhancing the intramolecular charge transfer (ICT) effect. We designed and synthesized two organic molecules: 2,6-bis(10H-phenothiazin-10-yl)benzo[1,2-d:4,5-d’]diimidazole-4,8-dione (PTZBQ), featuring a strong quinone-type acceptor core, and the control compound 2,6-bis(10H-phenothiazin-10-yl)benzo[1,2-d:4,5-d’]diimidazole (PTZTAB), without a quinone core. The strong push-pull electronic structure of PTZBQ not only results in a significantly narrowed bandgap and improved electrode kinetics, but also allows the quinone core to contribute extra n-type capacity, thereby remarkably boosting the electrode's specific capacity and reaction dynamics. Moreover, the extended π-conjugation and D-A-D configuration-induced polarity endow both small molecules with exceptional electrolyte dissolution resistance. Consequently, PTZBQ exhibits bipolar redox activity, delivering a high discharge potential of 3.05 V, a high specific capacity of 163.3 mAh g⁻¹ at 0.1 A g⁻¹, an excellent rate capability (77.6% retention at 5 A g⁻¹), and exceptional long-term cycling stability with 89.4% retention after 5000 cycles at 1 A g⁻¹. DFT calculations and ex situ spectroscopy confirm that the unique D-A-D architecture possesses spatially separated n-type and p-type redox centers, facilitating the redox process. Our findings highlight that quinone-core engineering enhances intramolecular charge transfer and represents a powerful approach for developing high-performance cathode materials.