Rational Molecular Design Strategy of a Carbonyl Cathode for Better Aluminum Organic Batteries

Aluminum batteries with aluminum as the anode and organic materials as the cathode have continuously drawn considerable attention because of their high theoretical energy density, natural abundance, and environmentally benign nature. Herein, we have done an elaborate design work on the basis of π–π conjugated organic molecule PTCDA by a molecular engineering strategy. Introducing a sulfur atom to replace the H atom in the aromatic ring of the PTCDA molecule to form SPTCDA (sulfurized PTCDA) with p−π conjugated system can reduce the energy level of the molecule. In addition, the extension of the conjugated system makes the electrons more delocalized, which is beneficial to the improvement of the conductivity of SPTCDA. Experimental results show that compared with pristine PTCDA, SPTCDA has a more stable structure and better cycle performance, rate capability, and coulombic efficiency, as well as a higher discharge voltage plateau. To further understand the electronic structure, operating voltage, and correct redox mechanism, density functional theory (DFT) calculations were performed for PTCDA and SPTCDA. The diffusion behavior of ions on the electrode surface was also discussed. This work reveals an important molecular structure design strategy for a carbonyl cathode, in order to break the application limitations of this electrode material on aluminum organic batteries.