Theoretical Studies of Carbonyl-Based Organic Molecules for Energy Storage Applications: The Heteroatom and Substituent Effect

Organic compounds represent an attractive choice for cathode materials in rechargeable lithium batteries. Among all the organic functionalities, carbonyl-based organic molecules (C-bOMs) exhibit rapid and generally chemically reversible electrochemical behavior, and their reduced forms (enolates) can have strong ionic interactions with small radii cations (such as Li+). Furthermore, a wide range of chemical variations/modifications can be performed on C-bOM structures via synthesis. We have systematically investigated how to modify their electrochemical behavior by shifting the formal potential, maximizing the interaction of the various redox forms with lithium ions, and maximizing the number of electrons transferred while minimizing the molecular weight of the compound, thus maximizing their gravimetric energy density. We have performed density-functional calculations to predict the formal potentials of the C-bOMs materials (E = 2.0-4.0 V) and identify the most promising candidates. We have determined how the addition of electron-withdrawing and -donating groups can be used to tune the formal potentials and lithium ion binding energies. Moreover, by using the LUMO energy levels and the aromaticity, which was calculated with nuclear independent chemical shift (NICS), it was possible to study the stability of these systems. Furthermore, we have been able to design and computationally characterize new C-bOMs molecules, which represent new potentially high gravimetric energy density cathode materials for electrical energy storage applications.