Substituent‐Stabilized Organic Dianions in the Gas Phase and Their Potential Use as Electrolytes in Lithium‐Ion Batteries

Synergetic ligand and size effects of boron cage based electrolytes in Li-ion batteries

We explore the potential application of boron-based clusters as high-performance electrolytes in lithium-ion batteries using first-principles density functional theory. We use small and halogen-free ligands (such as CN, BO, NH₂, NO₂, and CH₃) to replace H in closo-boron cages with different sizes to investigate the ligand and size effects. According to their geometric and electronic stability, Li⁺ dissociation energy in the lithium salt form, and electrochemical stabilities, we screen nine candidate electrolyte anions potentially overcoming the currently used electrolytes in lithium-ion batteries. We show that, when CH₃ is used as a boron cage ligand, both the highest occupied molecular orbital and the lowest unoccupied molecular orbital levels are high, ensuring their electrochemical stability against the oxidation (or reduction) reaction at the anode (or cathode). Solvent effects are also evaluated and high electrostatic screening was found to be favorable for practical usage.

Rational Design of Stable Dianions and the Concept of Super-Chalcogens

Super-atoms are homo/heteroatomic clusters that mimic the chemistry of atoms in the periodic table. While a considerable amount of research over the past three decades has revealed many super-atoms that mimic group I (alkali metals) and group 17 (halogens) elements, little effort has been made to identify super-atoms that mimic the chemistry of chalcogens, i.e., those belonging to group 16 elements. This is particularly important as super-chalcogens can form the building blocks of new materials, just as super-alkalis and super-halogens form a variety of super-salts with unique properties. Using first-principles calculations and various electron counting rules, some of which have been prevalent in chemistry for a century, we provide a route to the rational design of dianions that are stable in the gas phase. And unlike the group 16 atoms, these super-chalcogens can retain the second electron without spontaneous electron emission or fragmentation. A new class of super-chalcogenides with unique properties could be formed with these super-chalcogens as building blocks.

Rational Design of Stable Dianions by Functionalizing Polycyclic Aromatic Hydrocarbons

Using density functional theory, we have carried out a systematic study of the stability and electronic properties of neutral and multiply charged molecules B_n C_10-n X₈ (n=0, 1, 2; X=H, F, CN). Our main objective is to explore if the replacements of core C atoms and/or H atoms in naphthalene (C₁₀ H₈ ) can enhance the stability of their dianions. Indeed, we find that the dianions of B_n C_10-n (CN)₈ are more stable than their monoanions with energies of 0.61 eV, 0.57 eV, and 1.97 eV for n=0, 1, 2, respectively. In addition, polycyclic aromatic hydrocarbons become stable as dianions only when H atoms are substituted by more electronegative species. Thus, a rational design approach by tailoring composition and ligands can lead to a new class of organic molecules that are capable of carrying multiple charges.