Inhibition of Aluminum Corrosion with the Addition of the Tris(pentafluoroethyl)trifluorophosphate Anion to a Sulfonylamide-Based Ionic Liquid for Sodium-Ion Batteries

Ionic liquids (ILs) based on sulfonylamide-type anions have gained widespread utility as electrolytes for secondary batteries. Although sulfonylamide-based IL electrolytes are known to form a stable passivation layer that prevents Al corrosion, the Al electrode in the Na[FSA]-[C₂C₁im][FSA] ([FSA] = bis(fluorosulfonyl)amide and [C₂C₁im] = 1-ethyl-3-methylimidazolium) IL, is found to be afflicted by pitting corrosion at potentials above 4 V vs Na⁺/Na during electrochemical measurement at 90 °C. Therefore, this study investigates the suppressive effect of [FAP]⁻ (FAP = tris(pentafluoroethyl)trifluorophosphate) on the Al corrosion behavior of the IL electrolyte. Here, the inhibited corrosion of the Al electrode is confirmed through a series of cyclic voltammetry measurements, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Charge-discharge tests performed using a Na₃V₂(PO₄)₂F₃ positive electrode demonstrates that the addition of [FAP]⁻ into the IL enhances cycling performance at the intermediate temperature of 90 °C

Electrochemical reduction of cationic Li+@C60to neutral Li+@C60˙−: isolation and characterisation of endohedral [60]fulleride

Lithium-encapsulated [60]fullerene Li@C60, namely, lithium-ion-encapsulated [60]fullerene radical anion Li+@C60˙−, was synthesised by electrochemical reduction of lithium-ion-encapsulated [60]fullerene trifluoromethanesulfonylimide salt [Li+@C60](TFSI−). The product was fully characterised by UV-vis-NIR absorption and ESR spectroscopy as well as single-crystal X-ray analysis for the co-crystal with nickel octaethylporphyrin. In solution Li@C60 exists as a monomer form dominantly, while in the crystal state it forms a dimer (Li@C60–Li@C60) through coupling of the C60 radical anion cage. These structural features were supported by DFT calculations at the M06-2X/6-31G(d) level of theory

Kinetic Study of the Diels–Alder Reaction of Li⁺@C₆₀ with Cyclohexadiene: Greatly Increased Reaction Rate by Encapsulated Li⁺

We studied the kinetics of the Diels–Alder reaction of Li⁺-encapsulated [60]­fullerene with 1,3-cyclohexadiene and characterized the obtained product, [Li⁺@C₆₀(C₆H₈)]­(PF₆^–). Compared with empty C₆₀, Li⁺@C₆₀ reacted 2400-fold faster at 303 K, a rate enhancement that corresponds to lowering the activation energy by 24.2 kJ mol^–1. The enhanced Diels–Alder reaction rate was well explained by DFT calculation at the M06-2X/6-31G­(d) level of theory considering the reactant complex with dispersion corrections. The calculated activation energies for empty C₆₀ and Li⁺@C₆₀ (65.2 and 43.6 kJ mol^–1, respectively) agreed fairly well with the experimentally obtained values (67.4 and 44.0 kJ mol^–1, respectively). According to the calculation, the lowering of the transition state energy by Li⁺ encapsulation was associated with stabilization of the reactant complex (by 14.1 kJ mol^–1) and the [4 + 2] product (by 5.9 kJ mol^–1) through favorable frontier molecular orbital interactions. The encapsulated Li⁺ ion catalyzed the Diels–Alder reaction by lowering the LUMO of Li⁺@C₆₀. This is the first detailed report on the kinetics of a Diels–Alder reaction catalyzed by an encapsulated Lewis acid catalyst rather than one coordinated to a heteroatom in the dienophile