Regulating HOMO energy levels of thiophene-based conjugated polymers to facilitate anion storage for high performance dual-ion batteries

Abstract

Organic dual-ion cathode materials offer great potential for high-energy-density lithium-ion batteries but suffer from fast capacity degradation and cycling instability due to the low utility and reversibility of p-type active sites and inherent solubility. To address these challenges, we present a molecular engineering strategy that modulates the highest occupied molecular orbital (HOMO) energy levels through rational structural design. Three novel thiophene-functionalized pyrene-4,5,9,10-tetrone derivatives—2,7-di(thiophen-3-yl)pyrene-4,5,9,10-tetraone (PTO-3TP), 2,7-di(thiophen-2-yl)pyrene-4,5,9,10-tetraone (PTO-2TP), and 2,7-di([2,2′-bithiophen]-5-yl)pyrene-4,5,9,10-tetraone (PTO-BITP)—are designed by strategically tailoring the junction position and number of thiophene bridging units. This structural optimization significantly elevates the HOMO energy levels and enhances the π-conjugation, thereby synergistically boosting the p-type redox activity. Notably, after electropolymerization, the products exhibit further elevated HOMO levels and reduced energy gaps, enabling superior charge transfer kinetics. Specifically, the electropolymerized PTO-BITP cathode demonstrates exceptional electrochemical performances including a high reversible capacity of 280 mAh g^-1 at 0.2 A g^-1 over 500 cycles, remarkable rate capability (120 mAh g^-1 at 10 A g^-1), and ultrahigh cycling stability (100 mAh g^-1 retained after 5000 cycles at 5 A g^-1). This work unveils the great significance of HOMO energy level manipulation through molecular architecture engineering, offering an efficient strategy to enhance both electropolymerization efficiency and redox kinetics for advanced organic lithium-ion batteries.